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+2001-10-26  Geert Bosch <bosch@gnat.com>
+
+	* gnat_rm.texi: Add GNAT Reference Manual.
+
 2001-10-25  Robert Dewar <dewar@gnat.com>
 
 	* sem_ch8.adb (Analyze_Package_Renaming): Skip analysis if Name 
diff --git a/gcc/ada/gnat_rm.texi b/gcc/ada/gnat_rm.texi
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+\input texinfo   @c -*-texinfo-*-
+@input texiplus
+
+@c %**start of header
+
+@c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
+@c                                                                            o
+@c                           GNAT DOCUMENTATION                               o
+@c                                                                            o
+@c                              G N A T _ RM                                  o
+@c                                                                            o
+@c                            $Revision$
+@c                                                                            o
+@c          Copyright (C) 1992-2001 Ada Core Technologies, Inc.               o
+@c                                                                            o
+@c  GNAT is free software;  you can  redistribute it  and/or modify it under  o
+@c  terms of the  GNU General Public License as published  by the Free Soft-  o
+@c  ware  Foundation;  either version 2,  or (at your option) any later ver-  o
+@c  sion.  GNAT is distributed in the hope that it will be useful, but WITH-  o
+@c  OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY  o
+@c  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License  o
+@c  for  more details.  You should have  received  a copy of the GNU General  o
+@c  Public License  distributed with GNAT;  see file COPYING.  If not, write  o
+@c  to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston,  o
+@c  MA 02111-1307, USA.                                                       o
+@c                                                                            o
+@c  GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com).    o
+@c                                                                            o
+@c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
+
+@setfilename gnat_rm.info
+@settitle GNAT Reference Manual
+@setchapternewpage odd
+@syncodeindex fn cp
+
+@titlepage
+
+
+@title GNAT Reference Manual
+@subtitle GNAT, The GNU Ada 95 Compiler
+@subtitle Version 3.15w
+@subtitle Document revision level $Revision$
+@subtitle Date: $Date$
+@author Ada Core Technologies, Inc.
+
+@page
+@vskip 0pt plus 1filll
+
+
+Copyright @copyright{} 1995-2001, Ada Core Technologies
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1
+or any later version published by the Free Software Foundation;
+with the Invariant Sections being ``GNU Free Documentation License'', with the
+Front-Cover Texts being ``GNAT Reference Manual'', and with no Back-Cover Texts.
+A copy of the license is included in the section entitled ``GNU
+Free Documentation License''.
+
+Silicon Graphics and IRIS are registered trademarks
+and IRIX is a trademark of Silicon Graphics, Inc.
+
+IBM PC is a trademark of International
+Business Machines Corporation.
+
+UNIX is a registered trademark of AT&T
+Bell Laboratories. 
+DIGITAL 
+
+VADS is a registered trademark of Rational Software Inc.
+
+The following are trademarks of Digital Equipment Corporation:
+DEC, DEC Ada, DECthreads, Digital, OpenVMS, and VAX.
+
+@end titlepage
+@ifinfo
+@node Top, About This Guide, (dir), (dir)
+@top GNAT Reference Manual
+
+
+GNAT Reference Manual
+
+GNAT, The GNU Ada 95 Compiler
+
+Version 3.14a
+
+Date: $Date$
+
+Ada Core Technologies, Inc.
+
+
+Copyright @copyright{} 1995-2001, Ada Core Technologies
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1
+or any later version published by the Free Software Foundation;
+with the Invariant Sections being "GNU Free Documentation License", with the
+Front-Cover Texts being "GNAT Reference Manual", and with no Back-Cover Texts.
+A copy of the license is included in the section entitled "GNU
+Free Documentation License".
+
+
+Silicon Graphics and IRIS are registered trademarks
+and IRIX is a trademark of Silicon Graphics, Inc.
+
+IBM PC is a trademark of International
+Business Machines Corporation.
+
+UNIX is a registered trademark of AT&T
+Bell Laboratories. 
+DIGITAL 
+
+VADS is a registered trademark of Rational Software Inc.
+
+The following are trademarks of Digital Equipment Corporation:
+DEC, DEC Ada, DECthreads, Digital, OpenVMS, and VAX.
+
+@menu
+* About This Guide::            
+* Implementation Defined Pragmas::  
+* Implementation Defined Attributes::  
+* Implementation Advice::       
+* Implementation Defined Characteristics::  
+* Intrinsic Subprograms::
+* Representation Clauses and Pragmas::
+* Standard Library Routines::   
+* The Implementation of Standard I/O::  
+* The GNAT Library::
+* Interfacing to Other Languages::  
+* Machine Code Insertions::
+* GNAT Implementation of Tasking::
+* Code generation for array aggregates::
+* Specialized Needs Annexes::   
+* Compatibility Guide::
+* GNU Free Documentation License::
+* Index::                       
+
+ --- The Detailed Node Listing ---
+
+About This Guide
+
+* What This Reference Manual Contains::  
+* Related Information::         
+
+The Implementation of Standard I/O
+
+* Standard I/O Packages::       
+* FORM Strings::                
+* Direct_IO::                   
+* Sequential_IO::               
+* Text_IO::                     
+* Wide_Text_IO::                
+* Stream_IO::                   
+* Shared Files::                
+* Open Modes::                  
+* Operations on C Streams::     
+* Interfacing to C Streams::    
+
+The GNAT Library
+
+* Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
+* Ada.Command_Line.Remove (a-colire.ads)::
+* Ada.Direct_IO.C_Streams (a-diocst.ads)::
+* Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
+* Ada.Sequential_IO.C_Streams (a-siocst.ads)::
+* Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
+* Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
+* Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
+* Ada.Text_IO.C_Streams (a-tiocst.ads)::
+* Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
+* GNAT.AWK (g-awk.ads)::
+* GNAT.Bubble_Sort_A (g-busora.ads)::
+* GNAT.Bubble_Sort_G (g-busorg.ads)::
+* GNAT.Calendar (g-calend.ads)::
+* GNAT.Calendar.Time_IO (g-catiio.ads)::
+* GNAT.Case_Util (g-casuti.ads)::
+* GNAT.CGI (g-cgi.ads)::
+* GNAT.CGI.Cookie (g-cgicoo.ads)::
+* GNAT.CGI.Debug (g-cgideb.ads)::
+* GNAT.Command_Line (g-comlin.ads)::
+* GNAT.CRC32 (g-crc32.ads)::
+* GNAT.Current_Exception (g-curexc.ads)::
+* GNAT.Debug_Pools (g-debpoo.ads)::
+* GNAT.Debug_Utilities (g-debuti.ads)::
+* GNAT.Directory_Operations (g-dirope.ads)::
+* GNAT.Dynamic_Tables (g-dyntab.ads)::
+* GNAT.Exception_Traces (g-exctra.ads)::
+* GNAT.Expect (g-expect.ads)::
+* GNAT.Float_Control (g-flocon.ads)::
+* GNAT.Heap_Sort_A (g-hesora.ads)::
+* GNAT.Heap_Sort_G (g-hesorg.ads)::
+* GNAT.HTable (g-htable.ads)::
+* GNAT.IO (g-io.ads)::
+* GNAT.IO_Aux (g-io_aux.ads)::
+* GNAT.Lock_Files (g-locfil.ads)::
+* GNAT.Most_Recent_Exception (g-moreex.ads)::
+* GNAT.OS_Lib (g-os_lib.ads)::
+* GNAT.Regexp (g-regexp.ads)::
+* GNAT.Registry (g-regist.ads)::
+* GNAT.Regpat (g-regpat.ads)::
+* GNAT.Sockets (g-socket.ads)::
+* GNAT.Source_Info (g-souinf.ads)::
+* GNAT.Spell_Checker (g-speche.ads)::
+* GNAT.Spitbol.Patterns (g-spipat.ads)::
+* GNAT.Spitbol (g-spitbo.ads)::
+* GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
+* GNAT.Spitbol.Table_Integer (g-sptain.ads)::
+* GNAT.Spitbol.Table_VString (g-sptavs.ads)::
+* GNAT.Table (g-table.ads)::
+* GNAT.Task_Lock (g-tasloc.ads)::
+* GNAT.Threads (g-thread.ads)::
+* GNAT.Traceback (g-traceb.ads)::
+* GNAT.Traceback.Symbolic (g-trasym.ads)::
+* Interfaces.C.Extensions (i-cexten.ads)::
+* Interfaces.C.Streams (i-cstrea.ads)::
+* Interfaces.CPP (i-cpp.ads)::
+* Interfaces.Os2lib (i-os2lib.ads)::
+* Interfaces.Os2lib.Errors (i-os2err.ads)::
+* Interfaces.Os2lib.Synchronization (i-os2syn.ads)::
+* Interfaces.Os2lib.Threads (i-os2thr.ads)::
+* Interfaces.Packed_Decimal (i-pacdec.ads)::
+* Interfaces.VxWorks (i-vxwork.ads)::
+* System.Address_Image (s-addima.ads)::
+* System.Assertions (s-assert.ads)::
+* System.Partition_Interface (s-parint.ads)::
+* System.Task_Info (s-tasinf.ads)::
+* System.Wch_Cnv (s-wchcnv.ads)::
+* System.Wch_Con (s-wchcon.ads)::
+
+Text_IO
+
+* Text_IO Stream Pointer Positioning::  
+* Text_IO Reading and Writing Non-Regular Files::  
+* Get_Immediate::               
+* Treating Text_IO Files as Streams::
+* Text_IO Extensions::
+* Text_IO Facilities for Unbounded Strings::
+
+Wide_Text_IO
+
+* Wide_Text_IO Stream Pointer Positioning::  
+* Wide_Text_IO Reading and Writing Non-Regular Files::  
+
+Interfacing to Other Languages
+
+* Interfacing to C::
+* Interfacing to C++::          
+* Interfacing to COBOL::        
+* Interfacing to Fortran::      
+* Interfacing to non-GNAT Ada code::
+
+GNAT Implementation of Tasking
+
+* Mapping Ada Tasks onto the Underlying Kernel Threads::
+* Ensuring Compliance with the Real-Time Annex::
+@end menu
+
+@end ifinfo
+
+@node About This Guide
+@unnumbered About This Guide
+
+@noindent
+This manual contains useful information in writing programs using the
+GNAT compiler. It includes information on implementation dependent
+characteristics of GNAT, including all the information required by Annex
+M of the standard.
+
+Ada 95 is designed to be highly portable,and guarantees that, for most
+programs, Ada 95 compilers behave in exactly the same manner on
+different machines. However, since Ada 95 is designed to be used in a
+wide variety of applications, it also contains a number of system
+dependent features to be used in interfacing to the external world. 
+
+@c Maybe put the following in platform-specific section
+@ignore
+@cindex ProDev Ada
+This reference manual discusses how these features are implemented for
+use in ProDev Ada running on the IRIX 5.3 or greater operating systems.
+@end ignore
+
+@cindex Implementation-dependent features
+@cindex Portability
+Note: Any program that makes use of implementation-dependent features
+may be non-portable.  You should follow good programming practice and
+isolate and clearly document any sections of your program that make use
+of these features in a non-portable manner.
+
+@menu
+* What This Reference Manual Contains::  
+* Conventions::
+* Related Information::         
+@end menu
+
+@node What This Reference Manual Contains
+@unnumberedsec What This Reference Manual Contains
+
+This reference manual contains the following chapters:
+
+@itemize @bullet
+@item
+@ref{Implementation Defined Pragmas} lists GNAT implementation-dependent
+pragmas, which can be used to extend and enhance the functionality of the
+compiler.
+
+@item
+@ref{Implementation Defined Attributes} lists GNAT
+implementation-dependent attributes which can be used to extend and
+enhance the functionality of the compiler.
+
+@item
+@ref{Implementation Advice} provides information on generally
+desirable behavior which are not requirements that all compilers must
+follow since it cannot be provided on all systems, or which may be
+undesirable on some systems.
+
+@item
+@ref{Implementation Defined Characteristics} provides a guide to
+minimizing implementation dependent features.
+
+@item
+@ref{Intrinsic Subprograms} describes the intrinsic subprograms
+implemented by GNAT, and how they can be imported into user
+application programs.
+
+@item
+@ref{Representation Clauses and Pragmas} describes in detail the
+way that GNAT represents data, and in particular the exact set
+of representation clauses and pragmas that is accepted.
+
+@item
+@ref{Standard Library Routines} provides a listing of packages and a
+brief description of the functionality that is provided by Ada's
+extensive set of standard library routines as implemented by GNAT.
+
+@item
+@ref{The Implementation of Standard I/O} details how the GNAT
+implementation of the input-output facilities.
+
+@item
+@ref{Interfacing to Other Languages} describes how programs
+written in Ada using GNAT can be interfaced to other programming
+languages.
+
+@item
+@ref{Specialized Needs Annexes} describes the GNAT implementation of all
+of the special needs annexes.
+
+@item
+@ref{Compatibility Guide} includes sections on compatibility of GNAT with
+other Ada 83 and Ada 95 compilation systems, to assist in porting code
+from other environments.
+@end itemize
+
+@cindex Ada 95 ISO/ANSI Standard
+This reference manual assumes that you are familiar with Ada 95
+language, as described in the International Standard
+ANSI/ISO/IEC-8652:1995, Jan 1995.
+
+@node Conventions
+@unnumberedsec Conventions
+@cindex Conventions, typographical
+@cindex Typographical conventions
+
+@noindent
+Following are examples of the typographical and graphic conventions used
+in this guide:
+
+@itemize @bullet
+@item
+@code{Functions}, @code{utility program names}, @code{standard names},
+and @code{classes}.
+
+@item
+@samp{Option flags}
+
+@item
+@file{File Names}, @file{button names}, and @file{field names}.
+
+@item
+@var{Variables}.
+
+@item
+@emph{Emphasis}.
+
+@item
+[optional information or parameters]
+
+@item
+Examples are described by text
+@smallexample
+and then shown this way.
+@end smallexample
+@end itemize
+
+@noindent
+Commands that are entered by the user are preceded in this manual by the
+characters "$ " (dollar sign followed by space). If your system uses this
+sequence as a prompt, then the commands will appear exactly as you see them
+in the manual. If your system uses some other prompt, then the command will
+appear with the $ replaced by whatever prompt character you are using.
+
+@node Related Information
+@unnumberedsec Related Information
+See the following documents for further information on GNAT
+
+@itemize @bullet
+@item
+@cite{GNAT User's Guide}, which provides information on how to use
+the GNAT compiler system.
+
+@item
+@cite{Ada 95 Reference Manual}, which contains all reference
+material for the Ada 95 programming language.
+
+@item
+@cite{Ada 95 Annotated Reference Manual}, which is an annotated version
+of the standard reference manual cited above. The annotations describe
+detailed aspects of the design decision, and in particular contain useful
+sections on Ada 83 compatibility.
+
+@item
+@cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
+which contains specific information on compatibility between GNAT and
+DEC Ada 83 systems.
+
+@item
+@cite{DEC Ada, Language Reference Manual, part number AA-PYZAB-TK} which
+describes in detail the pragmas and attributes provided by the DEC Ada 83
+compiler system.
+
+@end itemize
+
+@node Implementation Defined Pragmas
+@chapter Implementation Defined Pragmas
+
+@noindent
+Ada 95 defines a set of pragmas that can be used to supply additional
+information to the compiler. These language defined pragmas are
+implemented in GNAT and work as described in the Ada 95 Reference
+Manual.
+
+In addition, Ada 95 allows implementations to define additional pragmas
+whose meaning is defined by the implementation. GNAT provides a number
+of these implementation-dependent pragmas which can be used to extend
+and enhance the functionality of the compiler. This section of the GNAT
+Reference Manual describes these additional pragmas.
+
+Note that any program using these pragmas may not be portable to other
+compilers (although GNAT implements this set of pragmas on all
+platforms). Therefore if portability to other compilers is an important
+consideration, the use of these pragmas should be minimized.
+
+@table @code
+
+@findex Abort_Defer
+@cindex Deferring aborts
+@item pragma Abort_Defer
+@noindent
+Syntax:
+
+@smallexample
+pragma Abort_Defer;
+@end smallexample
+
+@noindent
+This pragma must appear at the start of the statement sequence of a
+handled sequence of statements (right after the @code{begin}). It has
+the effect of deferring aborts for the sequence of statements (but not
+for the declarations or handlers, if any, associated with this statement
+sequence).
+
+@item pragma Ada_83
+@findex Ada_83
+@noindent
+Syntax:
+
+@smallexample
+pragma Ada_83;
+@end smallexample
+
+@noindent
+A configuration pragma that establishes Ada 83 mode for the unit to
+which it applies, regardless of the mode set by the command line
+switches. In Ada 83 mode, GNAT attempts to be as compatible with
+the syntax and semantics of Ada 83, as defined in the original Ada
+83 Reference Manual as possible. In particular, the new Ada 95
+keywords are not recognized, optional package bodies are allowed,
+and generics may name types with unknown discriminants without using
+the (<>) notation. In addition, some but not all of the additional
+restrictions of Ada 83 are enforced.
+
+Ada 83 mode is intended for two purposes. Firstly, it allows existing
+legacy Ada 83 code to be compiled and adapted to GNAT with less effort.
+Secondly, it aids in keeping code backwards compatible with Ada 83. 
+However, there is no guarantee that code that is processed correctly
+by GNAT in Ada 83 mode will in fact compile and execute with an Ada
+83 compiler, since GNAT does not enforce all the additional checks
+required by Ada 83.
+
+@findex Ada_95
+@item pragma Ada_95
+@noindent
+Syntax:
+
+@smallexample
+pragma Ada_95;
+@end smallexample
+
+@noindent
+A configuration pragma that establishes Ada 95 mode for the unit to which
+it applies, regardless of the mode set by the command line switches.
+This mode is set automatically for the @code{Ada} and @code{System}
+packages and their children, so you need not specify it in these
+contexts. This pragma is useful when writing a reusable component that
+itself uses Ada 95 features, but which is intended to be usable from
+either Ada 83 or Ada 95 programs.
+
+@findex Annotate
+@item pragma Annotate
+@noindent
+Syntax:
+
+@smallexample
+pragma Annotate (IDENTIFIER @{, ARG@});
+
+ARG ::= NAME | EXPRESSION
+@end smallexample
+
+@noindent
+This pragma is used to annotate programs. @var{identifier} identifies
+the type of annotation. GNAT verifies this is an identifier, but does
+not otherwise analyze it. The @var{arg} argument
+can be either a string literal or an
+expression. String literals are assumed to be of type
+@code{Standard.String}. Names of entities are simply analyzed as entity
+names. All other expressions are analyzed as expressions, and must be
+unambiguous.
+
+The analyzed pragma is retained in the tree, but not otherwise processed
+by any part of the GNAT compiler. This pragma is intended for use by
+external tools, including ASIS.
+
+@findex Assert
+@item pragma Assert
+@noindent
+Syntax:
+
+@smallexample
+pragma Assert (
+  boolean_EXPRESSION
+  [, static_string_EXPRESSION])
+@end smallexample
+
+@noindent
+The effect of this pragma depends on whether the corresponding command
+line switch is set to activate assertions. The pragma expands into code
+equivalent to the following:
+
+@smallexample
+if assertions-enabled then
+   if not boolean_EXPRESSION then
+      System.Assertions.Raise_Assert_Failure
+        (string_EXPRESSION); 
+   end if;
+end if;
+@end smallexample
+
+@noindent
+The string argument, if given, is the message that will be associated
+with the exception occurrence if the exception is raised. If no second
+argument is given, the default message is @samp{@var{file}:@var{nnn}},
+where @var{file} is the name of the source file containing the assert,
+and @var{nnn} is the line number of the assert. A pragma is not a
+statement, so if a statement sequence contains nothing but a pragma
+assert, then a null statement is required in addition, as in:
+
+@smallexample
+...
+if J > 3 then
+   pragma Assert (K > 3, "Bad value for K");
+   null;
+end if;
+@end smallexample
+
+@noindent
+Note that, as with the if statement to which it is equivalent, the
+type of the expression is either Standard.Boolean, or any type derived
+from this standard type.
+
+If assertions are disabled (switch @code{-gnata} not used), then there
+is no effect (and in particular, any side effects from the expression
+are suppressed). More precisely it is not quite true that the pragma
+has no effect, since the expression is analyzed, and may cause types
+to be frozen if they are mentioned here for the first time.
+
+If assertions are enabled, then the given expression is tested, and if
+it is @code{False} then System.Assertions.Raise_Assert_Failure is called
+which results in the raising of Assert_Failure with the given message.
+
+If the boolean expression has side effects, these side effects will turn
+on and off with the setting of the assertions mode, resulting in
+assertions that have an effect on the program. You should generally 
+avoid side effects in the expression arguments of this pragma. However,
+the expressions are analyzed for semantic correctness whether or not
+assertions are enabled, so turning assertions on and off cannot affect
+the legality of a program.
+
+@cindex OpenVMS
+@findex Ast_Entry
+@item pragma Ast_Entry
+@noindent
+Syntax:
+
+@smallexample
+pragma AST_Entry (entry_IDENTIFIER);
+@end smallexample
+
+@noindent
+This pragma is implemented only in the OpenVMS implementation of GNAT. The
+argument is the simple name of a single entry; at most one @code{AST_Entry}
+pragma is allowed for any given entry. This pragma must be used in 
+conjunction with the @code{AST_Entry} attribute, and is only allowed after
+the entry declaration and in the same task type specification or single task
+as the entry to which it applies. This pragma specifies that the given entry
+may be used to handle an OpenVMS asynchronous system trap (@code{AST})
+resulting from an OpenVMS system service call. The pragma does not affect
+normal use of the entry. For further details on this pragma, see the 
+DEC Ada Language Reference Manual, section 9.12a.
+
+@cindex Passing by copy
+@findex C_Pass_By_Copy
+@item pragma C_Pass_By_Copy
+@noindent
+Syntax:
+
+@smallexample
+pragma C_Pass_By_Copy
+  ([Max_Size =>] static_integer_EXPRESSION);
+@end smallexample
+
+@noindent
+Normally the default mechanism for passing C convention records to C
+convention subprograms is to pass them by reference, as suggested by RM
+B.3(69). Use the configuration pragma @code{C_Pass_By_Copy} to change
+this default, by requiring that record formal parameters be passed by
+copy if all of the following conditions are met:
+
+@itemize @bullet
+@item
+The size of the record type does not exceed@*@var{static_integer_expression}.
+@item
+The record type has @code{Convention C}.
+@item
+The formal parameter has this record type, and the subprogram has a
+foreign (non-Ada) convention.
+@end itemize
+
+@noindent
+If these conditions are met the argument is passed by copy, i.e. in a
+manner consistent with what C expects if the corresponding formal in the
+C prototype is a struct (rather than a pointer to a struct).
+
+You can also pass records by copy by specifying the convention
+@code{C_Pass_By_Copy} for the record type, or by using the extended
+@code{Import} and @code{Export} pragmas, which allow specification of
+passing mechanisms on a parameter by parameter basis.
+
+@findex Comment
+@item pragma Comment
+@noindent
+Syntax:
+
+@smallexample
+pragma Comment (static_string_EXPRESSION);
+@end smallexample
+
+@noindent
+This is almost identical in effect to pragma Ident. It allows the
+placement of a comment into the object file and hence into the
+executable file if the operating system permits such usage. The
+difference is that Comment, unlike Ident, has no limit on the
+length of the string argument, and no limitations on placement
+of the pragma (it can be placed anywhere in the main source unit).
+
+@findex Common_Object
+@item pragma Common_Object
+@noindent
+Syntax:
+
+@smallexample
+pragma Common_Object (
+     [Internal =>] LOCAL_NAME,
+  [, [External =>] EXTERNAL_SYMBOL]
+  [, [Size     =>] EXTERNAL_SYMBOL] )
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+@end smallexample
+
+@noindent
+This pragma enables the shared use of variables stored in overlaid
+linker areas corresponding to the use of @code{COMMON}
+in Fortran.  The single
+object @var{local_name} is assigned to the area designated by
+the @var{External} argument.
+You may define a record to correspond to a series
+of fields. The @var{size} argument
+is syntax checked in GNAT, but otherwise ignored.
+
+@code{Common_Object} is not supported on all platforms. If no
+support is available, then the code generator will issue a message
+indicating that the necessary attribute for implementation of this
+pragma is not available.
+
+@findex Complex_Representation
+@item pragma Complex_Representation
+@noindent
+Syntax:
+
+@smallexample
+pragma Complex_Representation
+        ([Entity =>] LOCAL_NAME);
+@end smallexample
+
+@noindent
+The @var{Entity} argument must be the name of a record type which has
+two fields of the same floating-point type. The effect of this pragma is
+to force gcc to use the special internal complex representation form for
+this record, which may be more efficient. Note that this may result in
+the code for this type not conforming to standard ABI (application
+binary interface) requirements for the handling of record types. For
+example, in some environments, there is a requirement for passing
+records by pointer, and the use of this pragma may result in passing
+this type in floating-point registers.
+
+@cindex Alignments of components
+@findex Component_Alignment
+@item pragma Component_Alignment
+@noindent
+Syntax:
+
+@smallexample
+pragma Component_Alignment (
+     [Form =>] ALIGNMENT_CHOICE
+  [, [Name =>] type_LOCAL_NAME]);
+
+ALIGNMENT_CHOICE ::=
+  Component_Size
+| Component_Size_4
+| Storage_Unit
+| Default
+@end smallexample
+
+@noindent
+Specifies the alignment of components in array or record types.
+The meaning of the @var{Form} argument is as follows:
+
+@table @code
+@findex Component_Size
+@item Component_Size
+Aligns scalar components and subcomponents of the array or record type
+on boundaries appropriate to their inherent size (naturally
+aligned). For example, 1-byte components are aligned on byte boundaries,
+2-byte integer components are aligned on 2-byte boundaries, 4-byte
+integer components are aligned on 4-byte boundaries and so on. These
+alignment rules correspond to the normal rules for C compilers on all
+machines except the VAX.
+
+@findex Component_Size_4
+@item Component_Size_4
+Naturally aligns components with a size of four or fewer
+bytes. Components that are larger than 4 bytes are placed on the next
+4-byte boundary.
+
+@findex Storage_Unit
+@item Storage_Unit
+Specifies that array or record components are byte aligned, i.e.
+aligned on boundaries determined by the value of the constant
+@code{System.Storage_Unit}.
+
+@cindex OpenVMS
+@item Default
+Specifies that array or record components are aligned on default
+boundaries, appropriate to the underlying hardware or operating system or
+both. For OpenVMS VAX systems, the @code{Default} choice is the same as
+the @code{Storage_Unit} choice (byte alignment). For all other systems,
+the @code{Default} choice is the same as @code{Component_Size} (natural
+alignment).
+@end table
+
+If the @code{Name} parameter is present, @var{type_local_name} must
+refer to a local record or array type, and the specified alignment
+choice applies to the specified type. The use of
+@code{Component_Alignment} together with a pragma @code{Pack} causes the
+@code{Component_Alignment} pragma to be ignored. The use of
+@code{Component_Alignment} together with a record representation clause
+is only effective for fields not specified by the representation clause.
+
+If the @code{Name} parameter is absent, the pragma can be used as either
+a configuration pragma, in which case it applies to one or more units in
+accordance with the normal rules for configuration pragmas, or it can be
+used within a declarative part, in which case it applies to types that
+are declared within this declarative part, or within any nested scope
+within this declarative part. In either case it specifies the alignment
+to be applied to any record or array type which has otherwise standard
+representation.
+
+If the alignment for a record or array type is not specified (using
+pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
+clause), the GNAT uses the default alignment as described previously.
+  
+@findex CPP_Class
+@cindex Interfacing with C++
+@item pragma CPP_Class
+@noindent
+Syntax:
+
+@smallexample
+pragma CPP_Class ([Entity =>] LOCAL_NAME);
+@end smallexample
+
+@noindent
+The argument denotes an entity in the current declarative region
+that is declared as a tagged or untagged record type. It indicates that
+the type corresponds to an externally declared C++ class type, and is to
+be laid out the same way that C++ would lay out the type.
+
+If (and only if) the type is tagged, at least one component in the
+record must be of type @code{Interfaces.CPP.Vtable_Ptr}, corresponding
+to the C++ Vtable (or Vtables in the case of multiple inheritance) used
+for dispatching.
+
+Types for which @code{CPP_Class} is specified do not have assignment or
+equality operators defined (such operations can be imported or declared
+as subprograms as required). Initialization is allowed only by
+constructor functions (see pragma @code{CPP_Constructor}).
+
+Pragma @code{CPP_Class} is intended primarily for automatic generation
+using an automatic binding generator tool. Ada Core Technologies does
+not currently supply such a
+tool; See @ref{Interfacing to C++} for more details.
+
+@cindex Interfacing with C++
+@findex CPP_Constructor
+@item pragma CPP_Constructor
+@noindent
+Syntax:
+
+@smallexample
+pragma CPP_Constructor ([Entity =>] LOCAL_NAME);
+@end smallexample
+
+@noindent
+This pragma identifies an imported function (imported in the usual way
+with pragma Import) as corresponding to a C++
+constructor. The argument is a name that must have been
+previously mentioned in a pragma
+Import with @var{Convention CPP}, and must be of one of the following
+forms:
+
+@itemize @bullet
+@item
+@code{function @var{Fname} return @var{T}'Class}
+
+@item
+@code{function @var{Fname} (@dots{}) return @var{T}'Class}
+@end itemize
+
+@noindent
+where @var{T} is a tagged type to which the pragma @code{CPP_Class} applies.
+
+The first form is the default constructor, used when an object of type
+@var{T} is created on the Ada side with no explicit constructor. Other
+constructors (including the copy constructor, which is simply a special
+case of the second form in which the one and only argument is of type
+@var{T}), can only appear in two contexts:
+
+@itemize @bullet
+@item
+On the right side of an initialization of an object of type @var{T}.
+@item
+In an extension aggregate for an object of a type derived from @var{T}.
+@end itemize
+
+Although the constructor is described as a function that returns a value
+on the Ada side, it is typically a procedure with an extra implicit
+argument (the object being initialized) at the implementation
+level. GNAT issues the appropriate call, whatever it is, to get the
+object properly initialized.
+
+In the case of derived objects, you may use one of two possible forms
+for declaring and creating an object:
+
+@itemize @bullet
+@item @code{New_Object : Derived_T}
+@item @code{New_Object : Derived_T := (@var{constructor-function-call with} @dots{})}
+@end itemize
+
+In the first case the default constructor is called and extension fields
+if any are initialized according to the default initialization
+expressions in the Ada declaration. In the second case, the given
+constructor is called and the extension aggregate indicates the explicit
+values of the extension fields.
+
+If no constructors are imported, it is impossible to create any objects
+on the Ada side. If no default constructor is imported, only the
+initialization forms using an explicit call to a constructor are
+permitted.
+
+Pragma @code{CPP_Constructor} is intended primarily for automatic generation
+using an automatic binding generator tool. Ada Core Technologies does
+not currently supply such a
+tool; See @ref{Interfacing to C++} for more details.
+
+@cindex Interfacing to C++
+@findex CPP_Virtual
+@item pragma CPP_Virtual
+@noindent
+Syntax:
+
+@smallexample
+pragma CPP_Virtual
+     [Entity     =>] ENTITY,
+  [, [Vtable_Ptr =>] vtable_ENTITY,]
+  [, [Position   =>] static_integer_EXPRESSION])
+@end smallexample
+
+This pragma serves the same function as pragma @code{Import} in that
+case of a virtual function imported from C++. The @var{Entity} argument
+must be a
+primitive subprogram of a tagged type to which pragma @code{CPP_Class}
+applies. The @var{Vtable_Ptr} argument specifies
+the Vtable_Ptr component which contains the
+entry for this virtual function. The @var{Position} argument
+is the sequential number
+counting virtual functions for this Vtable starting at 1.
+
+The @code{Vtable_Ptr} and @code{Position} arguments may be omitted if
+there is one Vtable_Ptr present (single inheritance case) and all
+virtual functions are imported.  In that case the compiler can deduce both
+these values.
+
+No @code{External_Name} or @code{Link_Name} arguments are required for a
+virtual function, since it is always accessed indirectly via the
+appropriate Vtable entry.
+
+Pragma @code{CPP_Virtual} is intended primarily for automatic generation
+using an automatic binding generator tool. Ada Core Technologies does
+not currently supply such a
+tool; See @ref{Interfacing to C++} for more details.
+
+@cindex Interfacing with C++
+@findex CPP_Vtable
+@item pragma CPP_Vtable
+@noindent
+Syntax:
+
+@smallexample
+pragma CPP_Vtable (
+  [Entity      =>] ENTITY,
+  [Vtable_Ptr  =>] vtable_ENTITY,
+  [Entry_Count =>] static_integer_EXPRESSION);
+@end smallexample
+
+@noindent
+Given a record to which the pragma @code{CPP_Class} applies,
+this pragma can be specified for each component of type
+@code{CPP.Interfaces.Vtable_Ptr}.
+@var{Entity} is the tagged type, @var{Vtable_Ptr}
+is the record field of type @code{Vtable_Ptr}, and @var{Entry_Count} is
+the number of virtual functions on the C++ side. Not all of these
+functions need to be imported on the Ada side.
+
+You may omit the @code{CPP_Vtable} pragma if there is only one
+@code{Vtable_Ptr} component in the record and all virtual functions are
+imported on the Ada side (the default value for the entry count in this
+case is simply the total number of virtual functions).
+
+Pragma @code{CPP_Vtable} is intended primarily for automatic generation
+using an automatic binding generator tool. Ada Core Technologies does
+not currently supply such a
+tool; See @ref{Interfacing to C++} for more details.
+
+@findex Debug
+@item pragma Debug
+@noindent
+Syntax:
+
+@smallexample
+pragma Debug (PROCEDURE_CALL_STATEMENT);
+@end smallexample
+
+@noindent
+If assertions are not enabled on the command line, this pragma has no
+effect. If asserts are enabled, the semantics of the pragma is exactly
+equivalent to the procedure call. Pragmas are permitted in sequences of
+declarations, so you can use pragma @code{Debug} to intersperse calls to
+debug procedures in the middle of declarations.
+
+@cindex Elaboration control
+@findex Elaboration_Checks
+@item pragma Elaboration_Checks
+@noindent
+Syntax:
+
+@smallexample
+pragma Elaboration_Checks (RM | Static);
+@end smallexample
+
+@noindent
+This is a configuration pragma that provides control over the
+elaboration model used by the compilation affected by the
+pragma. If the parameter is RM, then the dynamic elaboration
+model described in the Ada Reference Manual is used, as though
+the @code{-gnatE} switch had been specified on the command
+line. If the parameter is Static, then the default GNAT static
+model is used. This configuration pragma overrides the setting
+of the command line. For full details on the elaboration models
+used by the GNAT compiler, see section "Elaboration Order
+Handling in GNAT" in the GNAT Users Guide.
+
+@cindex Elimination of unused subprograms
+@findex Eliminate
+@item pragma Eliminate
+@noindent
+Syntax:
+
+@smallexample
+pragma Eliminate (
+    [Unit_Name =>] IDENTIFIER |
+                   SELECTED_COMPONENT);
+
+pragma Eliminate (
+    [Unit_Name       =>]  IDENTIFIER |
+                          SELECTED_COMPONENT
+    [Entity          =>]  IDENTIFIER |
+                          SELECTED_COMPONENT |
+                          STRING_LITERAL]
+   [,[Parameter_Types =>] PARAMETER_TYPES]
+   [,[Result_Type     =>] result_SUBTYPE_NAME]]);
+
+PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
+SUBTYPE_NAME    ::= STRING_LITERAL
+@end smallexample
+
+@noindent
+This pragma indicates that the given entity is not used outside the
+compilation unit it is defined in. The entity may be either a subprogram 
+or a variable.
+
+If the entity to be eliminated is a library level subprogram, then
+the first form of pragma @code{Eliminate} is used with only a single argument.
+In this form, the @code{Unit_Name} argument specifies the name of the
+library  level unit to be eliminated.
+
+In all other cases, both @code{Unit_Name} and @code{Entity} arguments
+are required. item is an entity of a library package, then the first
+argument specifies the unit name, and the second argument specifies
+the particular entity. If the second argument is in string form, it must
+correspond to the internal manner in which GNAT stores entity names (see
+compilation unit Namet in the compiler sources for details).
+The third and fourth parameters are optionally used to distinguish
+between overloaded subprograms, in a manner similar to that used for 
+the extended @code{Import} and @code{Export} pragmas, except that the
+subtype names are always given as string literals, again corresponding
+to the internal manner in which GNAT stores entity names.
+
+The effect of the pragma is to allow the compiler to eliminate
+the code or data associated with the named entity.  Any reference to 
+an eliminated entity outside the compilation unit it is defined in,
+causes a compile time or link time error.
+
+The intention of pragma Eliminate is to allow a program to be compiled
+in a system independent manner, with unused entities eliminated, without
+the requirement of modifying the source text. Normally the required set
+of Eliminate pragmas is constructed automatically using the gnatelim tool.
+Elimination of unused entities local to a compilation unit is automatic,
+without requiring the use of pragma Eliminate.
+
+Note that the reason this pragma takes string literals where names might
+be expected is that a pragma Eliminate can appear in a context where the
+relevant names are not visible.
+
+@cindex OpenVMS
+@findex Export_Exception
+@item pragma Export_Exception
+@noindent
+Syntax:
+
+@smallexample
+pragma Export_Exception (
+     [Internal =>] LOCAL_NAME,
+  [, [External =>] EXTERNAL_SYMBOL,]
+  [, [Form     =>] Ada | VMS]
+  [, [Code     =>] static_integer_EXPRESSION]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+@end smallexample
+
+@noindent
+This pragma is implemented only in the OpenVMS implementation of GNAT. It
+causes the specified exception to be propagated outside of the Ada program,
+so that it can be handled by programs written in other OpenVMS languages.
+This pragma establishes an external name for an Ada exception and makes the
+name available to the OpenVMS Linker as a global symbol. For further details
+on this pragma, see the
+DEC Ada Language Reference Manual, section 13.9a3.2.
+
+@cindex Argument passing mechanisms
+@findex Export_Function
+@item pragma Export_Function @dots{}
+
+@noindent
+Syntax:
+
+@smallexample
+pragma Export_Function (
+     [Internal         =>] LOCAL_NAME,      
+  [, [External         =>] EXTERNAL_SYMBOL]
+  [, [Parameter_Types  =>] PARAMETER_TYPES]
+  [, [Result_Type      =>] result_SUBTYPE_MARK]
+  [, [Mechanism        =>] MECHANISM]
+  [, [Result_Mechanism =>] MECHANISM_NAME]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+
+PARAMETER_TYPES ::=
+  null
+| SUBTYPE_MARK @{, SUBTYPE_MARK@}
+
+MECHANISM ::=
+  MECHANISM_NAME
+| (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
+
+MECHANISM_ASSOCIATION ::=
+  [formal_parameter_NAME =>] MECHANISM_NAME
+
+MECHANISM_NAME ::=
+  Value
+| Reference
+| Descriptor [([Class =>] CLASS_NAME)]
+
+CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
+@end smallexample
+
+Use this pragma to make a function externally callable and optionally
+provide information on mechanisms to be used for passing parameter and
+result values. We recommend, for the purposes of improving portability,
+this pragma always be used in conjunction with a separate pragma
+@code{Export}, which must precede the pragma @code{Export_Function}.
+GNAT does not require a separate pragma @code{Export}, but if none is
+present, @code{Convention Ada} is assumed, which is usually
+not what is wanted, so it is usually appropriate to use this
+pragma in conjunction with a @code{Export} or @code{Convention}
+pragma that specifies the desired foreign convention.
+Pragma @code{Export_Function}
+(and @code{Export}, if present) must appear in the same declarative
+region as the function to which they apply.
+
+@var{internal_name} must uniquely designate the function to which the
+pragma applies. If more than one function name exists of this name in
+the declarative part you must use the @code{Parameter_Types} and
+@code{Result_Type} parameters is mandatory to achieve the required
+unique designation. @var{subtype_ mark}s in these parameters must
+exactly match the subtypes in the corresponding function specification,
+using positional notation to match parameters with subtype marks.
+@cindex OpenVMS
+@cindex Passing by descriptor
+Passing by descriptor is supported only on the OpenVMS ports of GNAT.
+
+@findex Export_Object
+@item pragma Export_Object @dots{}
+@noindent
+Syntax:
+
+@smallexample
+pragma Export_Object
+      [Internal =>] LOCAL_NAME,
+   [, [External =>] EXTERNAL_SYMBOL]
+   [, [Size     =>] EXTERNAL_SYMBOL]
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+@end smallexample
+
+This pragma designates an object as exported, and apart from the
+extended rules for external symbols, is identical in effect to the use of
+the normal @code{Export} pragma applied to an object. You may use a
+separate Export pragma (and you probably should from the point of view
+of portability), but it is not required.  @var{Size} is syntax checked,
+but otherwise ignored by GNAT.
+
+@findex Export_Procedure
+@item pragma Export_Procedure @dots{}
+@noindent
+Syntax:
+
+@smallexample
+pragma Export_Procedure (
+     [Internal        =>] LOCAL_NAME
+  [, [External        =>] EXTERNAL_SYMBOL]
+  [, [Parameter_Types =>] PARAMETER_TYPES]
+  [, [Mechanism       =>] MECHANISM]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+
+PARAMETER_TYPES ::=
+  null
+| SUBTYPE_MARK @{, SUBTYPE_MARK@}
+
+MECHANISM ::=
+  MECHANISM_NAME
+| (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
+
+MECHANISM_ASSOCIATION ::=
+  [formal_parameter_NAME =>] MECHANISM_NAME
+
+MECHANISM_NAME ::=
+  Value
+| Reference
+| Descriptor [([Class =>] CLASS_NAME)]
+
+CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
+@end smallexample
+
+@noindent
+This pragma is identical to @code{Export_Function} except that it
+applies to a procedure rather than a function and the parameters
+@code{Result_Type} and @code{Result_Mechanism} are not permitted.
+GNAT does not require a separate pragma @code{Export}, but if none is
+present, @code{Convention Ada} is assumed, which is usually
+not what is wanted, so it is usually appropriate to use this
+pragma in conjunction with a @code{Export} or @code{Convention}
+pragma that specifies the desired foreign convention.
+
+@findex Export_Valued_Procedure
+@item pragma Export_Valued_Procedure
+@noindent
+Syntax:
+
+@smallexample
+pragma Export_Valued_Procedure (
+     [Internal        =>] LOCAL_NAME
+  [, [External        =>] EXTERNAL_SYMBOL]
+  [, [Parameter_Types =>] PARAMETER_TYPES]
+  [, [Mechanism       =>] MECHANISM]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+
+PARAMETER_TYPES ::=
+  null
+| SUBTYPE_MARK @{, SUBTYPE_MARK@}
+
+MECHANISM ::=
+  MECHANISM_NAME
+| (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
+
+MECHANISM_ASSOCIATION ::=
+  [formal_parameter_NAME =>] MECHANISM_NAME
+
+MECHANISM_NAME ::=
+  Value
+| Reference
+| Descriptor [([Class =>] CLASS_NAME)]
+
+CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
+@end smallexample
+
+This pragma is identical to @code{Export_Procedure} except that the
+first parameter of @var{local_name}, which must be present, must be of
+mode @code{OUT}, and externally the subprogram is treated as a function
+with this parameter as the result of the function. GNAT provides for
+this capability to allow the use of @code{OUT} and @code{IN OUT}
+parameters in interfacing to external functions (which are not permitted
+in Ada functions).
+GNAT does not require a separate pragma @code{Export}, but if none is
+present, @code{Convention Ada} is assumed, which is almost certainly
+not what is wanted since the whole point of this pragma is to interface
+with foreign language functions, so it is usually appropriate to use this
+pragma in conjunction with a @code{Export} or @code{Convention}
+pragma that specifies the desired foreign convention.
+
+@cindex @code{system}, extending
+@cindex Dec Ada 83
+@findex Extend_System
+@item pragma Extend_System
+@noindent
+Syntax:
+
+@smallexample
+pragma Extend_System ([Name =>] IDENTIFIER);
+@end smallexample
+
+@noindent
+This pragma is used to provide backwards compatibility with other
+implementations that extend the facilities of package @code{System}. In
+GNAT, @code{System} contains only the definitions that are present in
+the Ada 95 RM. However, other implementations, notably the DEC Ada 83
+implementation, provide many extensions to package @code{System}.
+
+For each such implementation accommodated by this pragma, GNAT provides a
+package @code{Aux_@var{xxx}}, e.g. @code{Aux_DEC} for the DEC Ada 83
+implementation, which provides the required additional definitions. You
+can use this package in two ways.  You can @code{with} it in the normal
+way and access entities either by selection or using a @code{use}
+clause. In this case no special processing is required.
+
+However, if existing code contains references such as
+@code{System.@var{xxx}} where @var{xxx} is an entity in the extended
+definitions provided in package @code{System}, you may use this pragma
+to extend visibility in @code{System} in a non-standard way that
+provides greater compatibility with the existing code. Pragma
+@code{Extend_System} is a configuration pragma whose single argument is
+the name of the package containing the extended definition
+(e.g. @code{Aux_DEC} for the DEC Ada case). A unit compiled under
+control of this pragma will be processed using special visibility
+processing that looks in package @code{System.Aux_@var{xxx}} where
+@code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
+package @code{System}, but not found in package @code{System}.
+
+You can use this pragma either to access a predefined @code{System}
+extension supplied with the compiler, for example @code{Aux_DEC} or
+you can construct your own extension unit following the above
+definition. Note that such a package is a child of @code{System}
+and thus is considered part of the implementation. To compile
+it you will have to use the appropriate switch for compiling
+system units. See the GNAT User's Guide for details.
+
+@findex External
+@item pragma External
+@noindent
+Syntax:
+
+@smallexample
+pragma External (
+  [   Convention    =>] convention_IDENTIFIER,
+  [   Entity        =>] local_NAME
+  [, [External_Name =>] static_string_EXPRESSION ]
+  [, [Link_Name     =>] static_string_EXPRESSION ]);
+@end smallexample
+
+@noindent
+This pragma is identical in syntax and semantics to pragma
+@code{Export} as defined in the Ada Reference Manual. It is
+provided for compatibility with some Ada 83 compilers that
+used this pragma for exactly the same purposes as pragma
+@code{Export} before the latter was standardized.
+
+@cindex Dec Ada 83 casing compatibility
+@cindex External Names, casing
+@cindex Casing of External names
+@findex External_Name_Casing
+@item pragma External_Name_Casing
+@noindent
+Syntax:
+
+@smallexample
+pragma External_Name_Casing (
+  Uppercase | Lowercase
+  [, Uppercase | Lowercase | As_Is]);
+@end smallexample
+
+@noindent
+This pragma provides control over the casing of external names associated
+with Import and Export pragmas. There are two cases to consider:
+
+@table @asis
+@item Implicit external names
+Implicit external names are derived from identifiers. The most common case
+arises when a standard Ada 95 Import or Export pragma is used with only two
+arguments, as in:
+
+@smallexample
+   pragma Import (C, C_Routine);
+@end smallexample
+
+@noindent
+Since Ada is a case insensitive language, the spelling of the identifier in
+the Ada source program does not provide any information on the desired
+casing of the external name, and so a convention is needed. In GNAT the
+default treatment is that such names are converted to all lower case
+letters. This corresponds to the normal C style in many environments.
+The first argument of pragma @code{External_Name_Casing} can be used to
+control this treatment. If @code{Uppercase} is specified, then the name
+will be forced to all uppercase letters. If @code{Lowercase} is specified,
+then the normal default of all lower case letters will be used.
+
+This same implicit treatment is also used in the case of extended DEC Ada 83
+compatible Import and Export pragmas where an external name is explicitly
+specified using an identifier rather than a string.
+
+@item Explicit external names
+Explicit external names are given as string literals. The most common case
+arises when a standard Ada 95 Import or Export pragma is used with three
+arguments, as in:
+
+@smallexample
+pragma Import (C, C_Routine, "C_routine");
+@end smallexample
+
+@noindent
+In this case, the string literal normally provides the exact casing required
+for the external name. The second argument of pragma 
+@code{External_Name_Casing} may be used to modify this behavior. 
+If @code{Uppercase} is specified, then the name
+will be forced to all uppercase letters. If @code{Lowercase} is specified,
+then the name will be forced to all lowercase letters. A specification of
+@code{As_Is} provides the normal default behavior in which the casing is
+taken from the string provided.
+@end table
+
+@noindent
+This pragma may appear anywhere that a pragma is valid. in particular, it
+can be used as a configuration pragma in the @code{gnat.adc} file, in which
+case it applies to all subsequent compilations, or it can be used as a program
+unit pragma, in which case it only applies to the current unit, or it can
+be used more locally to control individual Import/Export pragmas.
+
+It is primarily intended for use with @code{OpenVMS} systems, where many
+compilers convert all symbols to upper case by default. For interfacing to
+such compilers (e.g. the DEC C compiler), it may be convenient to use
+the pragma:
+
+@smallexample
+pragma External_Name_Casing (Uppercase, Uppercase);
+@end smallexample
+
+@noindent
+to enforce the upper casing of all external symbols. 
+
+@findex Finalize_Storage_Only
+@item pragma Finalize_Storage_Only
+@noindent
+Syntax:
+
+@smallexample
+pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
+@end smallexample
+
+@noindent
+This pragma allows the compiler not to emit a Finalize call for objects
+defined at the library level. This is mostly useful for types where
+finalization is only used to deal with storage reclamation since in most
+environments it is not necessary to reclaim memory just before terminating
+execution, hence the name.
+
+@cindex OpenVMS
+@findex Float_Representation
+@item pragma Float_Representation
+@noindent
+Syntax:
+
+@smallexample
+pragma Float_Representation (FLOAT_REP);
+
+FLOAT_REP ::= VAX_Float | IEEE_Float
+@end smallexample
+
+@noindent
+This pragma is implemented only in the OpenVMS implementation of GNAT.
+It allows control over the internal representation chosen for the predefined
+floating point types declared in the packages @code{Standard} and
+@code{System}. For further details on this pragma, see the
+DEC Ada Language Reference Manual, section 3.5.7a. Note that to use this
+pragma, the standard runtime libraries must be recompiled. See the
+description of the @code{GNAT LIBRARY} command in the OpenVMS version
+of the GNAT Users Guide for details on the use of this command.
+
+@findex Ident
+@item pragma Ident
+@noindent
+Syntax:
+
+@smallexample
+pragma Ident (static_string_EXPRESSION);
+@end smallexample
+
+@noindent
+This pragma provides a string identification in the generated object file,
+if the system supports the concept of this kind of identification string.
+The maximum permitted length of the string literal is 31 characters.
+This pragma is allowed only in the outermost declarative part or
+declarative items of a compilation unit.
+@cindex OpenVMS
+On OpenVMS systems, the effect of the pragma is identical to the effect of
+the DEC Ada 83 pragma of the same name. 
+
+@cindex OpenVMS
+@findex Import_Exception
+@item pragma Import_Exception
+@noindent
+Syntax:
+
+@smallexample
+pragma Import_Exception (
+     [Internal =>] LOCAL_NAME,
+  [, [External =>] EXTERNAL_SYMBOL,]
+  [, [Form     =>] Ada | VMS]
+  [, [Code     =>] static_integer_EXPRESSION]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+@end smallexample
+
+@noindent
+This pragma is implemented only in the OpenVMS implementation of GNAT.
+It allows OpenVMS conditions (for example, from OpenVMS system services or
+other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
+The pragma specifies that the exception associated with an exception
+declaration in an Ada program be defined externally (in non-Ada code).
+For further details on this pragma, see the
+DEC Ada Language Reference Manual, section 13.9a.3.1.
+
+@findex Import_Function
+@item pragma Import_Function @dots{}
+@noindent
+Syntax:
+
+@smallexample
+pragma Import_Function (
+     [Internal                 =>] LOCAL_NAME,
+  [, [External                 =>] EXTERNAL_SYMBOL]
+  [, [Parameter_Types          =>] PARAMETER_TYPES]
+  [, [Result_Type              =>] SUBTYPE_MARK]
+  [, [Mechanism                =>] MECHANISM]
+  [, [Result_Mechanism         =>] MECHANISM_NAME]
+  [, [First_Optional_Parameter =>] IDENTIFIER]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+
+PARAMETER_TYPES ::=
+  null
+| SUBTYPE_MARK @{, SUBTYPE_MARK@}
+
+MECHANISM ::=
+  MECHANISM_NAME
+| (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
+
+MECHANISM_ASSOCIATION ::=
+  [formal_parameter_NAME =>] MECHANISM_NAME
+
+MECHANISM_NAME ::=
+  Value
+| Reference
+| Descriptor [([Class =>] CLASS_NAME)]
+
+CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
+@end smallexample
+
+This pragma is used in conjunction with a pragma @code{Import} to
+specify additional information for an imported function. The pragma
+@code{Import} (or equivalent pragma @code{Interface}) must precede the
+@code{Import_Function} pragma and both must appear in the same
+declarative part as the function specification.
+
+The @var{Internal_Name} argument must uniquely designate
+the function to which the
+pragma applies. If more than one function name exists of this name in
+the declarative part you must use the @code{Parameter_Types} and
+@var{Result_Type} parameters to achieve the required unique
+designation. Subtype marks in these parameters must exactly match the
+subtypes in the corresponding function specification, using positional
+notation to match parameters with subtype marks.
+
+You may optionally use the @var{Mechanism} and @var{Result_Mechanism}
+parameters to specify passing mechanisms for the
+parameters and result. If you specify a single mechanism name, it
+applies to all parameters.  Otherwise you may specify a mechanism on a
+parameter by parameter basis using either positional or named
+notation. If the mechanism is not specified, the default mechanism
+is used.
+
+@cindex OpenVMS
+@cindex Passing by descriptor
+Passing by descriptor is supported only on the to OpenVMS ports of GNAT.
+
+@code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT.
+It specifies that the designated parameter and all following parameters
+are optional, meaning that they are not passed at the generated code
+level (this is distinct from the notion of optional parameters in Ada
+where the parameters are passed anyway with the designated optional
+parameters). All optional parameters must be of mode @code{IN} and have
+default parameter values that are either known at compile time
+expressions, or uses of the @code{'Null_Parameter} attribute.
+
+@findex Import_Object
+@item pragma Import_Object
+@noindent
+Syntax:
+
+@smallexample
+pragma Import_Object
+     [Internal =>] LOCAL_NAME,
+  [, [External =>] EXTERNAL_SYMBOL],
+  [, [Size     =>] EXTERNAL_SYMBOL])
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+@end smallexample
+
+@noindent
+This pragma designates an object as imported, and apart from the
+extended rules for external symbols, is identical in effect to the use of
+the normal @code{Import} pragma applied to an object.  Unlike the
+subprogram case, you need not use a separate @code{Import} pragma,
+although you may do so (and probably should do so from a portability
+point of view). @var{size} is syntax checked, but otherwise ignored by
+GNAT.
+
+@findex Import_Procedure
+@item pragma Import_Procedure
+@noindent
+Syntax:
+
+@smallexample
+pragma Import_Procedure (
+     [Internal                 =>] LOCAL_NAME,
+  [, [External                 =>] EXTERNAL_SYMBOL]
+  [, [Parameter_Types          =>] PARAMETER_TYPES]
+  [, [Mechanism                =>] MECHANISM]
+  [, [First_Optional_Parameter =>] IDENTIFIER]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+
+PARAMETER_TYPES ::=
+  null
+| SUBTYPE_MARK @{, SUBTYPE_MARK@}
+
+MECHANISM ::=
+  MECHANISM_NAME
+| (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
+
+MECHANISM_ASSOCIATION ::=
+  [formal_parameter_NAME =>] MECHANISM_NAME
+
+MECHANISM_NAME ::=
+  Value
+| Reference
+| Descriptor [([Class =>] CLASS_NAME)]
+
+CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
+@end smallexample
+
+@noindent
+This pragma is identical to @code{Import_Function} except that it
+applies to a procedure rather than a function and the parameters
+@code{Result_Type} and @code{Result_Mechanism} are not permitted.
+
+@findex Import_Valued_Procedure
+@item pragma Import_Valued_Procedure @dots{}
+@noindent
+Syntax:
+
+@smallexample
+pragma Import_Valued_Procedure (
+     [Internal                 =>] LOCAL_NAME,
+  [, [External                 =>] EXTERNAL_SYMBOL]
+  [, [Parameter_Types          =>] PARAMETER_TYPES]
+  [, [Mechanism                =>] MECHANISM]
+  [, [First_Optional_Parameter =>] IDENTIFIER]);
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+
+PARAMETER_TYPES ::=
+  null
+| SUBTYPE_MARK @{, SUBTYPE_MARK@}
+
+MECHANISM ::=
+  MECHANISM_NAME
+| (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
+
+MECHANISM_ASSOCIATION ::=
+  [formal_parameter_NAME =>] MECHANISM_NAME
+
+MECHANISM_NAME ::=
+  Value
+| Reference
+| Descriptor [([Class =>] CLASS_NAME)]
+
+CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
+@end smallexample
+
+@noindent
+This pragma is identical to @code{Import_Procedure} except that the
+first parameter of @var{local_name}, which must be present, must be of
+mode @code{OUT}, and externally the subprogram is treated as a function
+with this parameter as the result of the function. The purpose of this
+capability is to allow the use of @code{OUT} and @code{IN OUT}
+parameters in interfacing to external functions (which are not permitted
+in Ada functions).  You may optionally use the @code{Mechanism}
+parameters to specify passing mechanisms for the parameters.
+If you specify a single mechanism name, it applies to all parameters.
+Otherwise you may specify a mechanism on a parameter by parameter
+basis using either positional or named notation. If the mechanism is not
+specified, the default mechanism is used.
+
+Note that it is important to use this pragma in conjunction with a separate
+pragma Import that specifies the desired convention, since otherwise the
+default convention is Ada, which is almost certainly not what is required.
+
+@findex Initialize_Scalars
+@cindex debugging with Initialize_Scalars
+@item pragma Initialize_Scalars
+@noindent
+Syntax:
+
+@smallexample
+pragma Initialize_Scalars;
+@end smallexample
+
+@noindent
+This pragma is similar to @code{Normalize_Scalars} conceptually but has 
+two important differences. First, there is no requirement for the pragma
+to be used uniformly in all units of a partition, in particular, it is fine
+to use this just for some or all of the application units of a partition,
+without needing to recompile the run-time library.
+
+In the case where some units are compiled with the pragma, and some without,
+then a declaration of a variable where the type is defined in package
+Standard or is locally declared will always be subject to initialization,
+as will any declaration of a scalar variable. For composite variables,
+whether the variable is initialized may also depend on whether the package
+in which the type of the variable is declared is compiled with the pragma.
+
+The other important difference is that there is control over the value used
+for initializing scalar objects. At bind time, you can select whether to
+initialize with invalid values (like Normalize_Scalars), or with high or
+low values, or with a specified bit pattern. See the users guide for binder
+options for specifying these cases.
+
+This means that you can compile a program, and then without having to
+recompile the program, you can run it with different values being used
+for initializing otherwise uninitialized values, to test if your program
+behavior depends on the choice. Of course the behavior should not change,
+and if it does, then most likely you have an erroneous reference to an
+uninitialized value.
+
+Note that pragma @code{Initialize_Scalars} is particularly useful in
+conjunction with the enhanced validity checking that is now provided
+in @code{GNAT}, which checks for invalid values under more conditions.
+Using this feature (see description of the @code{-gnatv} flag in the
+users guide) in conjunction with pragma @code{Initialize_Scalars}
+provides a powerful new tool to assist in the detection of problems
+caused by uninitialized variables.
+
+@findex Inline_Always
+@item pragma Inline_Always
+@noindent
+Syntax:
+
+@smallexample
+pragma Inline_Always (NAME [, NAME]);
+@end smallexample
+
+@noindent
+Similar to pragma  @code{Inline} except that inlining is not subject to
+the use of option @code{-gnatn} for inter-unit inlining.
+
+@findex Inline_Generic
+@item pragma Inline_Generic
+@noindent
+Syntax:
+
+@smallexample
+pragma Inline_Generic (generic_package_NAME)
+@end smallexample
+
+@noindent
+This is implemented for compatibility with DEC Ada 83 and is recognized,
+but otherwise ignored, by GNAT. All generic instantiations are inlined
+by default when using GNAT.
+
+@findex Interface
+@item pragma Interface
+@noindent
+Syntax:
+
+@smallexample
+pragma Interface (
+     [Convention    =>] convention_identifier,
+     [Entity =>] local_name
+  [, [External_Name =>] static_string_expression],
+  [, [Link_Name     =>] static_string_expression]);
+@end smallexample
+
+@noindent
+This pragma is identical in syntax and semantics to
+the standard Ada 95 pragma @code{Import}. It is provided for compatibility
+with Ada 83. The definition is upwards compatible both with pragma
+@code{Interface} as defined in the Ada 83 Reference Manual, and also
+with some extended implementations of this pragma in certain Ada 83
+implementations.
+
+@findex Interface_Name
+@item pragma Interface_Name
+@noindent
+Syntax:
+
+@smallexample
+pragma Interface_Name ( 
+     [Entity        =>] LOCAL_NAME
+  [, [External_Name =>] static_string_EXPRESSION]
+  [, [Link_Name     =>] static_string_EXPRESSION]);
+@end smallexample
+
+@noindent
+This pragma provides an alternative way of specifying the interface name
+for an interfaced subprogram, and is provided for compatibility with Ada
+83 compilers that use the pragma for this purpose. You must provide at
+least one of @var{External_Name} or @var{Link_Name}.
+
+@findex License
+@item pragma License
+@cindex License checking
+@noindent
+Syntax:
+
+@smallexample
+pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
+@end smallexample
+
+@noindent
+This pragma is provided to allow automated checking for appropriate license
+conditions with respect to the standard and modified GPL. A pragma License,
+which is a configuration pragma that typically appears at the start of a
+source file or in a separate @file{gnat.adc} file, specifies the licensing
+conditions of a unit as follows:
+
+@itemize @bullet
+@item Unrestricted
+This is used for a unit that can be freely used with no license restrictions.
+Examples of such units are public domain units, and units from the Ada
+Reference Manual.
+
+@item GPL
+This is used for a unit that is licensed under the unmodified GPL, and which
+therefore cannot be @code{with}'ed by a restricted unit.
+
+@item Modified_GPL
+This is used for a unit licensed under the GNAT modified GPL that includes
+a special exception paragraph that specifically permits the inclusion of
+the unit in programs without requiring the entire program to be released
+under the GPL. This is the license used for the GNAT run-time which ensures
+that the run-time can be used freely in any program without GPL concerns.
+
+@item Restricted
+This is used for a unit that is restricted in that it is not permitted to
+depend on units that are licensed under the GPL. Typical examples are
+proprietary code that is to be released under more restrictive license
+conditions. Note that restricted units are permitted to @code{with} units
+which are licensed under the modified GPL (this is the whole point of the
+modified GPL).
+
+@end itemize
+
+@noindent
+Normally a unit with no @code{License} pragma is considered to have an
+unknown license, and no checking is done. However, standard GNAT headers
+are recognized, and license information is derived from them as follows.
+
+@itemize @bullet
+
+A GNAT license header starts with a line containing 78 hyphens. The following
+comment text is searched for the appearence of any of the following strings.
+
+If the string "GNU General Public License" is found, then the unit is assumed
+to have GPL license, unless the string "As a special exception" follows, in
+which case the license is assumed to be modified GPL.
+
+If one of the strings
+"This specification is adapated from the Ada Semantic Interface" or
+"This specification is derived from the Ada Reference Manual" is found
+then the unit is assumed to be unrestricted.
+@end itemize
+
+@noindent
+These default actions means that a program with a restricted license pragma
+will automatically get warnings if a GPL unit is inappropriately
+@code{with}'ed. For example, the program:
+
+@smallexample
+with Sem_Ch3;
+with GNAT.Sockets;
+procedure Secret_Stuff is
+...
+end Secret_Stuff
+@end smallexample
+
+@noindent
+if compiled with pragma @code{License} (@code{Restricted}) in a
+@file{gnat.adc} file will generate the warning:
+
+@smallexample
+1. with Sem_Ch3;
+        |
+   >>> license of withed unit "Sem_Ch3" is incompatible
+
+2. with GNAT.Sockets;
+3. procedure Secret_Stuff is
+@end smallexample
+@noindent
+Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
+compiler and is licensed under the
+GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT 
+run time, and is therefore licensed under the modified GPL.
+
+@findex Link_With
+@item pragma Link_With
+@noindent
+Syntax:
+
+@smallexample
+pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
+@end smallexample
+
+@noindent
+This pragma is provided for compatibility with certain Ada 83 compilers.
+It has exactly the same effect as pragma @code{Linker_Options} except
+that spaces occurring within one of the string expressions are treated
+as separators. For example, in the following case:
+
+@smallexample
+pragma Link_With ("-labc -ldef");
+@end smallexample
+
+@noindent
+results in passing the strings @code{-labc} and @code{-ldef} as two
+separate arguments to the linker.
+
+@findex Linker_Alias
+@item pragma Linker_Alias
+@noindent
+Syntax:
+
+@smallexample
+pragma Linker_Alias (
+  [Entity =>] LOCAL_NAME
+  [Alias  =>] static_string_EXPRESSION);
+@end smallexample
+
+@noindent
+This pragma establishes a linker alias for the given named entity. For
+further details on the exact effect, consult the GCC manual.
+
+@findex Linker_Section
+@item pragma Linker_Section
+@noindent
+Syntax:
+
+@smallexample
+pragma Linker_Section (
+  [Entity  =>] LOCAL_NAME
+  [Section =>] static_string_EXPRESSION);
+@end smallexample
+
+@noindent
+This pragma specifies the name of the linker section for the given entity.
+For further details on the exact effect, consult the GCC manual.
+
+@findex No_Run_Time
+@item pragma No_Run_Time
+@noindent
+Syntax:
+
+@smallexample
+pragma No_Run_Time;
+@end smallexample
+
+@noindent
+This is a configuration pragma that makes sure the user code does not
+use nor need anything from the GNAT run time. This is mostly useful in
+context where code certification is required. Please consult the High
+Integrity product documentation for additional information.
+
+@findex Normalize_Scalars
+@item pragma Normalize_Scalars
+@noindent
+Syntax:
+
+@smallexample
+pragma Normalize_Scalars;
+@end smallexample
+
+@noindent
+This is a language defined pragma which is fully implemented in GNAT. The
+effect is to cause all scalar objects that are not otherwise initialized
+to be initialized. The initial values are implementation dependent and
+are as follows:
+
+@table @code
+@item Standard.Character
+@noindent
+Objects whose root type is Standard.Character are initialized to
+Character'Last. This will be out of range of the subtype only if
+the subtype range excludes this value.
+
+@item Standard.Wide_Character
+@noindent
+Objects whose root type is Standard.Wide_Character are initialized to
+Wide_Character'Last. This will be out of range of the subtype only if
+the subtype range excludes this value.
+
+@item Integer types
+@noindent
+Objects of an integer type are initialized to base_type'First, where
+base_type is the base type of the object type. This will be out of range
+of the subtype only if the subtype range excludes this value. For example,
+if you declare the subtype:
+
+@smallexample
+subtype Ityp is integer range 1 .. 10;
+@end smallexample
+
+@noindent
+then objects of type x will be initialized to Integer'First, a negative
+number that is certainly outside the range of subtype @code{Ityp}.
+
+@item Real types
+Objects of all real types (fixed and floating) are initialized to
+base_type'First, where base_Type is the base type of the object type.
+This will be out of range of the subtype only if the subtype range
+excludes this value.
+
+@item Modular types
+Objects of a modular type are initialized to typ'Last. This will be out
+of range of the subtype only if the subtype excludes this value.
+
+@item Enumeration types
+Objects of an enumeration type are initialized to all one-bits, i.e. to
+the value 2 ** typ'Size - 1. This will be out of range of the enumeration
+subtype in all cases except where the subtype contains exactly
+2**8, 2**16, or 2**32.
+
+@end table
+
+@cindex OpenVMS
+@findex Long_Float
+@item pragma Long_Float
+@noindent
+Syntax:
+
+@smallexample
+pragma Long_Float (FLOAT_FORMAT);
+
+FLOAT_FORMAT ::= D_Float | G_Float
+@end smallexample
+
+@noindent
+This pragma is implemented only in the OpenVMS implementation of GNAT.
+It allows control over the internal representation chosen for the predefined
+type @code{Long_Float} and for floating point type representations with
+@code{digits} specified in the range 7 .. 15.
+For further details on this pragma, see the
+DEC Ada Language Reference Manual, section 3.5.7b. Note that to use this
+pragma, the standard runtime libraries must be recompiled. See the
+description of the @code{GNAT LIBRARY} command in the OpenVMS version
+of the GNAT Users Guide for details on the use of this command.
+
+@findex Machine_Attribute
+@item pragma Machine_Attribute @dots{}
+@noindent
+Syntax:
+
+@smallexample
+pragma Machine_Attribute (
+  [Attribute_Name =>] string_EXPRESSION,
+  [Entity         =>] LOCAL_NAME);
+@end smallexample
+
+Machine dependent attributes can be specified for types and/or
+declarations. Currently only subprogram entities are supported.  This
+pragma is semantically equivalent to @code{__attribute__((
+@var{string_expression}))} in GNU C, where @code{string_expression}> is
+recognized by the GNU C macros @code{VALID_MACHINE_TYPE_ATTRIBUTE} and
+@code{VALID_MACHINE_DECL_ATTRIBUTE} which are defined in the
+configuration header file @file{tm.h} for each machine.  See the GCC
+manual for further information.
+
+@cindex OpenVMS
+@findex Main_Storage
+@item pragma Main_Storage
+@noindent
+Syntax:
+
+@smallexample
+pragma Main_Storage
+  (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
+
+MAIN_STORAGE_OPTION ::=
+  [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
+| [TOP_GUARD       =>] static_SIMPLE_EXPRESSION
+
+@end smallexample
+
+@noindent
+This pragma is provided for compatibility with OpenVMS Vax Systems. It has
+no effect in GNAT, other than being syntax checked. Note that the pragma
+also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
+
+@findex No_Return
+@item pragma No_Return
+@noindent
+Syntax:
+
+@smallexample
+pragma No_Return (procedure_LOCAL_NAME);
+@end smallexample
+
+@noindent
+@var{procedure_local_NAME} must refer to one or more procedure
+declarations in the current declarative part. A procedure to which this
+pragma is applied may not contain any explicit @code{return} statements,
+and also may not contain any implicit return statements from falling off
+the end of a statement sequence. One use of this pragma is to identify
+procedures whose only purpose is to raise an exception.
+
+Another use of this pragma is to suppress incorrect warnings about
+missing returns in functions, where the last statement of a function
+statement sequence is a call to such a procedure.
+
+@findex Passive
+@item pragma Passive
+@noindent
+Syntax:
+
+@smallexample
+pragma Passive ([Semaphore | No]);
+@end smallexample
+
+@noindent
+Syntax checked, but otherwise ignored by GNAT. This is recognized for
+compatibility with DEC Ada 83 implementations, where it is used within a
+task definition to request that a task be made passive.  If the argument
+@code{Semaphore} is present, or no argument is omitted, then DEC Ada 83
+treats the pragma as an assertion that the containing task is passive
+and that optimization of context switch with this task is permitted and
+desired.  If the argument @code{No} is present, the task must not be
+optimized. GNAT does not attempt to optimize any tasks in this manner
+(since protected objects are available in place of passive tasks).
+
+@findex Polling 
+@item pragma Polling
+@noindent
+Syntax:
+
+@smallexample
+pragma Polling (ON | OFF);
+@end smallexample
+
+@noindent
+This pragma controls the generation of polling code. This is normally off.
+If @code{pragma Polling (ON)} is used then periodic calls are generated to
+the routine Ada.Exceptions.Poll. This routine is a separate unit in the
+runtime library, and can be found in file a-excpol.adb.
+
+Pragma polling can appear as a configuration pragma (for example it can be
+placed in the gnat.adc file) to enable polling globally, or it can be used
+in the statement or declaration sequence to control polling more locally.
+
+A call to the polling routine is generated at the start of every loop and
+at the start of every subprogram call. This guarantees that the Poll
+routine is called frequently, and places an upper bound (determined by
+the complexity of the code) on the period between two Poll calls.
+
+The primary purpose of the polling interface is to enable asynchronous 
+aborts on targets that cannot otherwise support it (for example Windows
+NT), but it may be used for any other purpose requiring periodic polling.
+The standard version is null, and can be replaced by a user program. This
+will require re-compilation of the Ada.Exceptions package that can be found
+in files a-except.ads/adb.
+
+A standard alternative unit (called 4wexcpol.adb in the standard GNAT
+distribution) is used to enable the asynchronous abort capability on
+targets that do not normally support the capability. The version of Poll
+in this file makes a call to the appropriate runtime routine to test for
+an abort condition.
+
+Note that polling can also be enabled by use of the -gnatP switch. See
+the GNAT User's Guide for details.
+
+@findex Propagate_Exceptions
+@cindex Zero Cost Exceptions
+@item pragma Propagate_Exceptions
+@noindent
+Syntax:
+
+@smallexample
+pragma Propagate_Exceptions (subprogram_LOCAL_NAME);
+@end smallexample
+
+@noindent
+This pragma indicates that the given entity, which is the name of an
+imported foreign-language subprogram may receive an Ada exception, 
+and that the exception should be propagated. It is relevant only if
+zero cost exception handling is in use, and is thus never needed if
+the alternative longjmp/setjmp implementation of exceptions is used
+(although it is harmless to use it in such cases).
+
+The implementation of fast exceptions always properly propagates
+exceptions through Ada code, as described in the Ada Reference Manual.
+However, this manual is silent about the propagation of exceptions
+through foreign code. For example, consider the
+situation where @code{P1} calls
+@code{P2}, and @code{P2} calls @code{P3}, where
+@code{P1} and @code{P3} are in Ada, but @code{P2} is in C.
+@code{P3} raises an Ada exception. The question is whether or not
+it will be propagated through @code{P2} and can be handled in 
+@code{P1}.
+
+For the longjmp/setjmp implementation of exceptions, the answer is
+always yes. For some targets on which zero cost exception handling
+is implemented, the answer is also always yes. However, there are
+some targets, notably in the current version all x86 architecture
+targets, in which the answer is that such propagation does not
+happen automatically. If such propagation is required on these
+targets, it is mandatory to use @code{Propagate_Exceptions} to 
+name all foreign language routines through which Ada exceptions
+may be propagated.
+
+@findex Psect_Object
+@item pragma Psect_Object
+@noindent
+Syntax:
+
+@smallexample
+pragma Psect_Object
+     [Internal =>] LOCAL_NAME,
+  [, [External =>] EXTERNAL_SYMBOL]
+  [, [Size     =>] EXTERNAL_SYMBOL]
+
+EXTERNAL_SYMBOL ::=
+  IDENTIFIER
+| static_string_EXPRESSION
+@end smallexample
+
+@noindent
+This pragma is identical in effect to pragma @code{Common_Object}.
+
+@findex Pure_Function
+@item pragma Pure_Function
+@noindent
+Syntax:
+
+@smallexample
+pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
+@end smallexample
+
+This pragma appears in the same declarative part as a function
+declaration (or a set of function declarations if more than one
+overloaded declaration exists, in which case the pragma applies
+to all entities). If specifies that the function @code{Entity} is
+to be considered pure for the purposes of code generation. This means
+that the compiler can assume that there are no side effects, and
+in particular that two calls with identical arguments produce the
+same result. It also means that the function can be used in an
+address clause.
+
+Note that, quite deliberately, there are no static checks to try
+to ensure that this promise is met, so @var{Pure_Function} can be used
+with functions that are conceptually pure, even if they do modify
+global variables. For example, a square root function that is
+instrumented to count the number of times it is called is still
+conceptually pure, and can still be optimized, even though it
+modifies a global variable (the count). Memo functions are another
+example (where a table of previous calls is kept and consulted to
+avoid re-computation).
+
+@findex Pure
+Note: Most functions in a @code{Pure} package are automatically pure, and
+there is no need to use pragma @code{Pure_Function} for such functions. An
+exception is any function that has at least one formal of type
+@code{System.Address} or a type derived from it. Such functions are not
+considered pure by default, since the compiler assumes that the
+@code{Address} parameter may be functioning as a pointer and that the
+referenced data may change even if the address value does not. The use
+of pragma Pure_Function for such a function will override this default
+assumption, and cause the compiler to treat such a function as pure.
+
+Note: If pragma @code{Pure_Function} is applied to a renamed function, it
+applies to the underlying renamed function. This can be used to
+disambiguate cases of overloading where some but not all functions
+in a set of overloaded functions are to be designated as pure.
+
+@findex Ravenscar
+@item pragma Ravenscar
+@noindent
+Syntax:
+
+@smallexample
+pragma Ravenscar
+@end smallexample
+
+@noindent
+A configuration pragma that establishes the following set of restrictions:
+
+@table @code
+@item No_Abort_Statements
+[RM D.7] There are no abort_statements, and there are 
+no calls to Task_Identification.Abort_Task.
+
+@item No_Select_Statements
+There are no select_statements.
+
+@item No_Task_Hierarchy
+[RM D.7] All (non-environment) tasks depend 
+directly on the environment task of the partition.  
+
+@item No_Task_Allocators
+[RM D.7] There are no allocators for task types
+or types containing task subcomponents.
+
+@item No_Dynamic_Priorities
+[RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
+
+@item No_Terminate_Alternatives
+[RM D.7] There are no selective_accepts with terminate_alternatives
+
+@item No_Dynamic_Interrupts
+There are no semantic dependencies on Ada.Interrupts.
+
+@item No_Protected_Type_Allocators
+There are no allocators for protected types or
+types containing protected subcomponents.
+
+@item No_Local_Protected_Objects
+Protected objects and access types that designate 
+such objects shall be declared only at library level.
+
+@item No_Requeue
+Requeue statements are not allowed.
+
+@item No_Calendar
+There are no semantic dependencies on the package Ada.Calendar.
+
+@item No_Relative_Delay
+There are no delay_relative_statements.
+
+@item No_Task_Attributes
+There are no semantic dependencies on the Ada.Task_Attributes package and
+there are no references to the attributes Callable and Terminated [RM 9.9].
+
+@item Static_Storage_Size
+The expression for pragma Storage_Size is static.
+
+@item Boolean_Entry_Barriers
+Entry barrier condition expressions shall be boolean 
+objects which are declared in the protected type 
+which contains the entry.
+
+@item Max_Asynchronous_Select_Nesting = 0
+[RM D.7] Specifies the maximum dynamic nesting level of asynchronous_selects.
+A value of zero prevents the use of any asynchronous_select.
+
+@item Max_Task_Entries = 0
+[RM D.7] Specifies the maximum number of entries
+per task.  The bounds of every entry family
+of a task unit shall be static, or shall be
+defined by a discriminant of a subtype whose
+corresponding bound is static.  A value of zero
+indicates that no rendezvous are possible.  For
+the Ravenscar pragma, the value of Max_Task_Entries is always
+0 (zero).
+
+@item Max_Protected_Entries = 1
+[RM D.7] Specifies the maximum number of entries per 
+protected type.  The bounds of every entry family of 
+a protected unit shall be static, or shall be defined 
+by a discriminant of a subtype whose corresponding 
+bound is static.  For the Ravenscar pragma the value of 
+Max_Protected_Entries is always 1.
+
+@item Max_Select_Alternatives = 0
+[RM D.7] Specifies the maximum number of alternatives in a selective_accept.
+For the Ravenscar pragma the value if always 0.
+
+@item No_Task_Termination
+Tasks which terminate are erroneous.
+
+@item No_Entry_Queue
+No task can be queued on a protected entry. Note that this restrictions is
+checked at run time. The violation of this restriction generates a
+Program_Error exception.
+@end table
+
+@noindent
+This set of restrictions corresponds to the definition of the "Ravenscar
+Profile" for limited tasking, devised and published by the International
+Workshop On Real Time Ada", 1997. 
+
+The above set is a superset of the restrictions provided by pragma
+@code{Restricted_Run_Time}, it includes six additional restrictions
+(@code{Boolean_Entry_Barriers}, @code{No_Select_Statements},
+@code{No_Calendar}, @code{Static_Storage_Size},
+@code{No_Relative_Delay} and @code{No_Task_Termination}). This means
+that pragma Ravenscar, like the pragma Restricted_Run_Time, automatically
+causes the use of a simplified, more efficient version of the tasking
+run-time system.
+
+@findex Restricted_Run_Time
+@item pragma Restricted_Run_Time
+@noindent
+Syntax:
+
+@smallexample
+pragma Restricted_Run_Time
+@end smallexample
+
+@noindent
+A configuration pragma that establishes the following set of restrictions:
+
+@itemize @bullet
+@item No_Abort_Statements
+@item No_Asynchronous_Control
+@item No_Entry_Queue
+@item No_Task_Hierarchy
+@item No_Task_Allocators
+@item No_Dynamic_Priorities
+@item No_Terminate_Alternatives
+@item No_Dynamic_Interrupts
+@item No_Protected_Type_Allocators
+@item No_Local_Protected_Objects
+@item No_Requeue
+@item No_Task_Attributes
+@item Max_Asynchronous_Select_Nesting =  0
+@item Max_Task_Entries =  0
+@item Max_Protected_Entries = 1
+@item Max_Select_Alternatives = 0
+@end itemize
+
+@noindent
+This set of restrictions causes the automatic selection of a simplified
+version of the run time that provides improved performance for the
+limited set of tasking functionality permitted by this set of restrictions.
+
+@findex Share_Generic
+@item pragma Share_Generic
+@noindent
+Syntax:
+
+@smallexample
+pragma Share_Generic (NAME @{, NAME@});
+@end smallexample
+
+@noindent
+This pragma is recognized for compatibility with other Ada compilers
+but is ignored by GNAT. GNAT does not provide the capability for
+sharing of generic code. All generic instantiations result in making
+an inlined copy of the template with appropriate substitutions.
+
+@findex Source_File_Name
+@item pragma Source_File_Name
+@noindent
+Syntax:
+
+@smallexample
+pragma Source_File_Name (
+  [Unit_Name   =>] unit_NAME,
+  Spec_File_Name =>  STRING_LITERAL);
+
+pragma Source_File_Name (
+  [Unit_Name   =>] unit_NAME,
+  Body_File_Name =>  STRING_LITERAL);
+@end smallexample
+
+@noindent
+Use this to override the normal naming convention. It is a configuration
+pragma, and so has the usual applicability of configuration pragmas
+(i.e. it applies to either an entire partition, or to all units in a
+compilation, or to a single unit, depending on how it is used.
+@var{unit_name} is mapped to @var{file_name_literal}. The identifier for
+the second argument is required, and indicates whether this is the file
+name for the spec or for the body.
+
+Another form of the @code{Source_File_Name} pragma allows
+the specification of patterns defining alternative file naming schemes
+to apply to all files. 
+
+@smallexample
+pragma Source_File_Name
+  (Spec_File_Name => STRING_LITERAL
+   [,Casing => CASING_SPEC]
+   [,Dot_Replacement => STRING_LITERAL]);
+
+pragma Source_File_Name
+  (Body_File_Name => STRING_LITERAL
+   [,Casing => CASING_SPEC]
+   [,Dot_Replacement => STRING_LITERAL]);
+
+pragma Source_File_Name
+  (Subunit_File_Name => STRING_LITERAL
+   [,Casing => CASING_SPEC]
+   [,Dot_Replacement => STRING_LITERAL]);
+
+CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
+@end smallexample
+
+@noindent
+The first argument is a pattern that contains a single asterisk indicating
+the point at which the unit name is to be inserted in the pattern string
+to form the file name. The second argument is optional. If present it
+specifies the casing of the unit name in the resulting file name string.
+The default is lower case. Finally the third argument allows for systematic
+replacement of any dots in the unit name by the specified string literal.
+
+For more details on the use of the @code{Source_File_Name} pragma,
+see the sections "Using Other File Names", and "Alternative File
+Naming Schemes" in the GNAT User's Guide.
+
+@findex Source_Reference
+@item pragma Source_Reference
+@noindent
+Syntax:
+
+@smallexample
+pragma Source_Reference (INTEGER_LITERAL,
+                         STRING_LITERAL);
+@end smallexample
+
+@noindent
+This pragma must appear as the first line of a source file.
+@var{integer_literal} is the logical line number of the line following
+the pragma line (for use in error messages and debugging
+information). @var{string_literal} is a static string constant that
+specifies the file name to be used in error messages and debugging
+information. This is most notably used for the output of @code{gnatchop}
+with the @samp{-r} switch, to make sure that the original unchopped
+source file is the one referred to.
+
+The second argument must be a string literal, it cannot be a static
+string expression other than a string literal. This is because its value
+is needed for error messages issued by all phases of the compiler.
+
+@findex Stream_Convert
+@item pragma Stream_Convert
+@noindent
+Syntax:
+
+@smallexample
+pragma Stream_Convert (
+  [Entity =>] type_LOCAL_NAME,
+  [Read   =>] function_NAME,
+  [Write  =>] function NAME);
+@end smallexample
+
+@noindent
+This pragma provides an efficient way of providing stream functions for
+types defined in packages. Not only is it simpler to use than declaring
+the necessary functions with attribute representation clauses, but more
+significantly, it allows the declaration to made in such a way that the
+stream packages are not loaded unless they are needed. The use of
+the Stream_Convert pragma adds no overhead at all, unless the stream
+attributes are actually used on the designated type.
+
+The first argument specifies the type for which stream functions are
+provided. The second parameter provides a function used to read values
+of this type. It must name a function whose argument type may be any
+subtype, and whose returned type must be the type given as the first
+argument to the pragma.
+
+The meaning of the @var{Read}
+parameter is that if a stream attribute directly
+or indirectly specifies reading of the type given as the first parameter,
+then a value of the type given as the argument to the Read function is
+read from the stream, and then the Read function is used to convert this
+to the required target type.
+
+Similarly the @var{Write} parameter specifies how to treat write attributes
+that directly or indirectly apply to the type given as the first parameter.
+It must have an input parameter of the type specified by the first parameter,
+and the return type must be the same as the input type of the Read function.
+The effect is to first call the Write function to convert to the given stream
+type, and then write the result type to the stream.
+
+The Read and Write functions must not be overloaded subprograms. If necessary
+renamings can be supplied to meet this requirement.
+The usage of this attribute is best illustrated by a simple example, taken
+from the GNAT implementation of package Ada.Strings.Unbounded:
+
+@smallexample
+function To_Unbounded (S : String)
+           return Unbounded_String
+  renames To_Unbounded_String;
+
+pragma Stream_Convert
+  (Unbounded_String, To_Unbounded, To_String);
+@end smallexample
+
+@noindent
+The specifications of the referenced functions, as given in the Ada 95
+Reference Manual are:
+
+@smallexample
+function To_Unbounded_String (Source : String)
+  return Unbounded_String;
+
+function To_String (Source : Unbounded_String)
+  return String;
+@end smallexample
+
+@noindent
+The effect is that if the value of an unbounded string is written to a
+stream, then the representation of the item in the stream is in the same
+format used for @code{Standard.String}, and this same representation is
+expected when a value of this type is read from the stream.
+
+@findex Style_Checks
+@item pragma Style_Checks
+@noindent
+Syntax:
+
+@smallexample
+pragma Style_Checks (string_LITERAL | ALL_CHECKS |
+                     On | Off [, LOCAL_NAME]);
+@end smallexample
+
+@noindent
+This pragma is used in conjunction with compiler switches to control the
+built in style checking provided by GNAT. The compiler switches, if set
+provide an initial setting for the switches, and this pragma may be used
+to modify these settings, or the settings may be provided entirely by
+the use of the pragma. This pragma can be used anywhere that a pragma
+is legal, including use as a configuration pragma (including use in
+the @file{gnat.adc} file).
+
+The form with a string literal specifies which style options are to be
+activated. These are additive, so they apply in addition to any previously
+set style check options. The codes for the options are the same as those
+used in the @code{-gnaty} switch on the @code{gcc} or @code{gnatmake}
+line. For example the following two methods can be used to enable
+layout checking:
+
+@smallexample
+pragma Style_Checks ("l");
+gcc -c -gnatyl ...
+@end smallexample
+
+@noindent
+The form ALL_CHECKS activates all standard checks (its use is equivalent
+to the use of the @code{gnaty} switch with no options. See GNAT User's
+Guide for details.
+
+The forms with @code{Off} and @code{On}
+can be used to temporarily disable style checks
+as shown in the following example:
+
+@smallexample
+@iftex
+@leftskip=0cm
+@end iftex
+pragma Style_Checks ("k"); -- requires keywords in lower case
+pragma Style_Checks (Off); -- turn off style checks
+NULL;                      -- this will not generate an error message
+pragma Style_Checks (On);  -- turn style checks back on
+NULL;                      -- this will generate an error message
+@end smallexample
+
+@noindent
+Finally the two argument form is allowed only if the first argument is
+@code{On} or @code{Off}. The effect is to turn of semantic style checks
+for the specified entity, as shown in the following example:
+
+@smallexample
+@iftex
+@leftskip=0cm
+@end iftex
+pragma Style_Checks ("r"); -- require consistency of identifier casing
+Arg : Integer;
+Rf1 : Integer := ARG;      -- incorrect, wrong case
+pragma Style_Checks (Off, Arg);
+Rf2 : Integer := ARG;      -- OK, no error
+@end smallexample
+
+@findex Subtitle
+@item pragma Subtitle
+@noindent
+Syntax:
+
+@smallexample
+pragma Subtitle ([Subtitle =>] STRING_LITERAL);
+@end smallexample
+
+@noindent
+This pragma is recognized for compatibility with other Ada compilers
+but is ignored by GNAT.
+
+@findex Suppress_All
+@item pragma Suppress_All
+@noindent
+Syntax:
+
+@smallexample
+pragma Suppress_All;
+@end smallexample
+
+@noindent
+This pragma can only appear immediately following a compilation
+unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
+which it follows. This pragma is implemented for compatibility with DEC
+Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
+configuration pragma is the preferred usage in GNAT.
+
+@findex Suppress_Initialization
+@cindex Suppressing initialization
+@cindex Initialization, suppression of
+@item pragma Suppress_Initialization
+@noindent
+Syntax:
+
+@smallexample
+pragma Suppress_Initialization ([Entity =>] type_Name);
+@end smallexample
+
+@noindent
+This pragma suppresses any implicit or explicit initialization
+associated with the given type name for all variables of this type.
+
+@findex Task_Info
+@item pragma Task_Info
+@noindent
+Syntax
+
+@smallexample
+pragma Task_Info (EXPRESSION);
+@end smallexample
+
+@noindent
+This pragma appears within a task definition (like pragma
+@code{Priority}) and applies to the task in which it appears. The
+argument must be of type @code{System.Task_Info.Task_Info_Type}.
+The @code{Task_Info} pragma provides system dependent control over
+aspect of tasking implementation, for example, the ability to map
+tasks to specific processors. For details on the facilities available
+for the version of GNAT that you are using, see the documentation
+in the specification of package System.Task_Info in the runtime
+library.
+
+@findex Task_Name
+@item pragma Task_Name
+@noindent
+Syntax
+
+@smallexample
+pragma Task_Name (string_EXPRESSION);
+@end smallexample
+
+@noindent
+This pragma appears within a task definition (like pragma
+@code{Priority}) and applies to the task in which it appears. The
+argument must be of type String, and provides a name to be used for
+the task instance when the task is created. Note that this expression
+is not required to be static, and in particular, it can contain
+references to task discriminants. This facility can be used to
+provide different names for different tasks as they are created,
+as illustrated in the example below.
+
+The task name is recorded internally in the run-time structures
+and is accessible to tools like the debugger. In addition the
+routine @code{Ada.Task_Identification.Image} will return this
+string, with a unique task address appended.
+
+@smallexample
+--  Example of the use of pragma Task_Name
+
+with Ada.Task_Identification;
+use Ada.Task_Identification;
+with Text_IO; use Text_IO;
+procedure t3 is
+
+   type Astring is access String;
+
+   task type Task_Typ (Name : access String) is
+      pragma Task_Name (Name.all);
+   end Task_Typ;
+   
+   task body Task_Typ is
+      Nam : constant String := Image (Current_Task);
+   begin
+      Put_Line ("-->" & Nam (1 .. 14) & "<--");
+   end Task_Typ;
+   
+   type Ptr_Task is access Task_Typ;
+   Task_Var : Ptr_Task;
+
+begin
+   Task_Var :=
+     new Task_Typ (new String'("This is task 1"));
+   Task_Var :=
+     new Task_Typ (new String'("This is task 2"));
+end;
+@end smallexample
+
+@findex Task_Storage
+@item pragma Task_Storage
+Syntax:
+
+@smallexample
+pragma Task_Storage
+  [Task_Type =>] LOCAL_NAME,
+  [Top_Guard =>] static_integer_EXPRESSION);
+@end smallexample
+
+This pragma specifies the length of the guard area for tasks.  The guard
+area is an additional storage area allocated to a task.  A value of zero
+means that either no guard area is created or a minimal guard area is
+created, depending on the target. This pragma can appear anywhere a
+@code{Storage_Size} attribute definition clause is allowed for a task
+type.
+
+@findex Time_Slice
+@item pragma Time_Slice
+@noindent
+Syntax:
+
+@smallexample
+pragma Time_Slice (static_duration_EXPRESSION);
+@end smallexample
+
+@noindent
+For implementations of GNAT on operating systems where it is possible
+to supply a time slice value, this pragma may be used for this purpose.
+It is ignored if it is used in a system that does not allow this control,
+or if it appears in other than the main program unit.
+@cindex OpenVMS
+Note that the effect of this pragma is identical to the effect of the
+DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
+
+@findex Title
+@item pragma Title
+@noindent
+Syntax:
+
+@smallexample
+pragma Title (TITLING_OPTION [, TITLING OPTION]);
+
+TITLING_OPTION ::=
+  [Title    =>] STRING_LITERAL,
+| [Subtitle =>] STRING_LITERAL
+@end smallexample
+
+@noindent
+Syntax checked but otherwise ignored by GNAT. This is a listing control
+pragma used in DEC Ada 83 implementations to provide a title and/or
+subtitle for the program listing. The program listing generated by GNAT
+does not have titles or subtitles.
+
+Unlike other pragmas, the full flexibility of named notation is allowed
+for this pragma, i.e. the parameters may be given in any order if named
+notation is used, and named and positional notation can be mixed
+following the normal rules for procedure calls in Ada.
+
+@cindex Unions in C
+@findex Unchecked_Union
+@item pragma Unchecked_Union
+@noindent
+Syntax:
+
+@smallexample
+pragma Unchecked_Union (first_subtype_LOCAL_NAME)
+@end smallexample
+
+@noindent
+This pragma is used to declare that the specified type should be represented
+in a manner
+equivalent to a C union type, and is intended only for use in
+interfacing with C code that uses union types. In Ada terms, the named
+type must obey the following rules:
+
+@itemize @bullet
+@item
+It is a non-tagged non-limited record type.
+@item
+It has a single discrete discriminant with a default value.
+@item
+The component list consists of a single variant part.
+@item
+Each variant has a component list with a single component.
+@item
+No nested variants are allowed.
+@item
+No component has an explicit default value.
+@item
+No component has a non-static constraint.
+@end itemize
+
+In addition, given a type that meets the above requirements, the
+following restrictions apply to its use throughout the program:
+
+@itemize @bullet
+@item
+The discriminant name can be mentioned only in an aggregate.
+@item
+No subtypes may be created of this type.
+@item
+The type may not be constrained by giving a discriminant value.
+@item
+The type cannot be passed as the actual for a generic formal with a
+discriminant.
+@end itemize
+
+Equality and inequality operations on @code{unchecked_unions} are not
+available, since there is no discriminant to compare and the compiler
+does not even know how many bits to compare. It is implementation
+dependent whether this is detected at compile time as an illegality or
+whether it is undetected and considered to be an erroneous construct. In
+GNAT, a direct comparison is illegal, but GNAT does not attempt to catch
+the composite case (where two composites are compared that contain an
+unchecked union component), so such comparisons are simply considered
+erroneous.
+
+The layout of the resulting type corresponds exactly to a C union, where
+each branch of the union corresponds to a single variant in the Ada
+record. The semantics of the Ada program is not changed in any way by
+the pragma, i.e. provided the above restrictions are followed, and no
+erroneous incorrect references to fields or erroneous comparisons occur,
+the semantics is exactly as described by the Ada reference manual.
+Pragma @code{Suppress (Discriminant_Check)} applies implicitly to the
+type and the default convention is C
+
+@findex Unimplemented_Unit
+@item pragma Unimplemented_Unit
+@noindent
+Syntax:
+
+@smallexample
+pragma Unimplemented_Unit;
+@end smallexample
+
+@noindent
+If this pragma occurs in a unit that is processed by the compiler, GNAT
+aborts with the message @samp{@var{xxx} not implemented}, where
+@var{xxx} is the name of the current compilation unit.  This pragma is
+intended to allow the compiler to handle unimplemented library units in
+a clean manner.
+
+The abort only happens if code is being generated.  Thus you can use
+specs of unimplemented packages in syntax or semantic checking mode.
+
+@findex Unreserve_All_Interrupts
+@item pragma Unreserve_All_Interrupts
+@noindent
+Syntax:
+
+@smallexample
+pragma Unreserve_All_Interrupts;
+@end smallexample
+
+@noindent
+Normally certain interrupts are reserved to the implementation. Any attempt
+to attach an interrupt causes Program_Error to be raised, as described in
+RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
+many systems for an @code{Ctrl-C} interrupt. Normally this interrupt is
+reserved to the implementation, so that @code{Ctrl-C} can be used to
+interrupt execution.
+
+If the pragma Unreserve_All_Interrupts appears anywhere in any unit in
+a program, then all such interrupts are unreserved. This allows the
+program to handle these interrupts, but disables their standard
+functions. For example, if this pragma is used, then pressing
+@code{Ctrl-C} will not automatically interrupt execution. However,
+a program can then handle the @code{SIGINT} interrupt as it chooses.
+
+For a full list of the interrupts handled in a specific implementation,
+see the source code for the specification of Ada.Interrupts.Names in
+file a-intnam.ads. This is a target dependent file that contains the
+list of interrupts recognized for a given target. The documentation in
+this file also specifies what interrupts are affected by the use of
+the Unreserve_All_Interrupts pragma.
+
+@findex Unsuppress
+@item pragma Unsuppress
+@noindent
+Syntax:
+
+@smallexample
+pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
+@end smallexample
+
+@noindent
+This pragma undoes the effect of a previous pragma @code{Suppress}. If
+there is no corresponding pragma @code{Suppress} in effect, it has no
+effect. The range of the effect is the same as for pragma
+@code{Suppress}. The meaning of the arguments is identical to that used
+in pragma @code{Suppress}.
+
+One important application is to ensure that checks are on in cases where
+code depends on the checks for its correct functioning, so that the code
+will compile correctly even if the compiler switches are set to suppress
+checks.
+
+@cindex @code{Size}, VADS compatibility
+@findex Use_VADS_Size
+@item pragma Use_VADS_Size
+@noindent
+Syntax:
+
+@smallexample
+pragma Use_VADS_Size;
+@end smallexample
+
+@noindent
+This is a configuration pragma. In a unit to which it applies, any use
+of the 'Size attribute is automatically interpreted as a use of the
+'VADS_Size attribute. Note that this may result in incorrect semantic
+processing of valid Ada 95 programs. This is intended to aid in the
+handling of legacy code which depends on the interpretation of Size
+as implemented in the VADS compiler. See description of the VADS_Size
+attribute for further details.
+
+@findex Validity_Checks
+@item pragma Validity_Checks
+@noindent
+Syntax:
+
+@smallexample
+pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
+@end smallexample
+
+@noindent
+This pragma is used in conjunction with compiler switches to control the
+built in validity checking provided by GNAT. The compiler switches, if set
+provide an initial setting for the switches, and this pragma may be used
+to modify these settings, or the settings may be provided entirely by
+the use of the pragma. This pragma can be used anywhere that a pragma
+is legal, including use as a configuration pragma (including use in
+the @file{gnat.adc} file).
+
+The form with a string literal specifies which validity options are to be
+activated. The validity checks are first set to include only the default
+reference manual settings, and then a string of letters in the string
+specifies the exact set of options required. The form of this string
+is exactly as described for the @code{-gnatVx} compiler switch (see the
+GNAT users guide for details). For example the following two methods
+can be used to enable validity checking for mode @code{in} and
+@code{in out} subprogram parameters:
+
+@smallexample
+pragma Validity_Checks ("im");
+gcc -c -gnatVim ...
+@end smallexample
+
+@noindent
+The form ALL_CHECKS activates all standard checks (its use is equivalent
+to the use of the @code{gnatva} switch.
+
+The forms with @code{Off} and @code{On}
+can be used to temporarily disable validity checks
+as shown in the following example:
+
+@smallexample
+@iftex
+@leftskip=0cm
+@end iftex
+pragma Validity_Checks ("c"); -- validity checks for copies
+pragma Validity_Checks (Off); -- turn off validity checks
+A := B;                       -- B will not be validity checked
+pragma Validity_Checks (On);  -- turn validity checks back on
+A := C;                       -- C will be validity checked
+@end smallexample
+
+@findex Volatile
+@item pragma Volatile
+@noindent
+Syntax:
+
+@smallexample
+pragma Volatile (local_NAME)
+@end smallexample
+
+@noindent
+This pragma is defined by the Ada 95 Reference Manual, and the GNAT
+implementation is fully conformant with this definition. The reason it
+is mentioned in this section is that a pragma of the same name was supplied
+in some Ada 83 compilers, including DEC Ada 83. The Ada 95 implementation
+of pragma Volatile is upwards compatible with the implementation in
+Dec Ada 83.
+
+@findex Warnings
+@item pragma Warnings
+@noindent
+Syntax:
+
+@smallexample
+pragma Warnings (On | Off [, LOCAL_NAME]);
+@end smallexample
+
+@noindent
+Normally warnings are enabled, with the output being controlled by
+the command line switch. Warnings (@code{Off}) turns off generation of
+warnings until a Warnings (@code{On}) is encountered or the end of the
+current unit. If generation of warnings is turned off using this
+pragma, then no warning messages are output, regardless of the
+setting of the command line switches.
+
+The form with a single argument is a configuration pragma.
+
+If the @var{local_name} parameter is present, warnings are suppressed for
+the specified entity. This suppression is effective from the point where
+it occurs till the end of the extended scope of the variable (similar to
+the scope of @code{Suppress}).
+
+@findex Weak_External
+@item pragma Weak_External
+@noindent
+Syntax:
+
+@smallexample
+pragma Weak_External ([Entity =>] LOCAL_NAME);
+@end smallexample
+
+@noindent
+This pragma specifies that the given entity should be marked as a weak
+external (one that does not have to be resolved) for the linker. For
+further details, consult the GCC manual.
+@end table
+
+@node Implementation Defined Attributes
+@chapter Implementation Defined Attributes
+Ada 95 defines (throughout the Ada 95 reference manual,
+summarized in annex K),
+a set of attributes that provide useful additional functionality in all
+areas of the language. These language defined attributes are implemented
+in GNAT and work as described in the Ada 95 Reference Manual.
+
+In addition, Ada 95 allows implementations to define additional
+attributes whose meaning is defined by the implementation. GNAT provides
+a number of these implementation-dependent attributes which can be used
+to extend and enhance the functionality of the compiler. This section of
+the GNAT reference manual describes these additional attributes.
+
+Note that any program using these attributes may not be portable to
+other compilers (although GNAT implements this set of attributes on all
+platforms). Therefore if portability to other compilers is an important
+consideration, you should minimize the use of these attributes.
+
+@table @code
+@findex Abort_Signal
+@item Abort_Signal
+@noindent
+@code{Standard'Abort_Signal} (@code{Standard} is the only allowed
+prefix) provides the entity for the special exception used to signal
+task abort or asynchronous transfer of control. Normally this attribute
+should only be used in the tasking runtime (it is highly peculiar, and
+completely outside the normal semantics of Ada, for a user program to
+intercept the abort exception).
+
+@cindex Size of @code{Address}
+@findex Address_Size
+@item Address_Size
+@noindent
+@code{Standard'Address_Size} (@code{Standard} is the only allowed
+prefix) is a static constant giving the number of bits in an
+@code{Address}. It is used primarily for constructing the definition of
+@code{Memory_Size} in package @code{Standard}, but may be freely used in user
+programs and has the advantage of being static, while a direct
+reference to System.Address'Size is non-static because Address
+is a private type.
+
+@findex Asm_Input
+@item Asm_Input
+@noindent
+The @code{Asm_Input} attribute denotes a function that takes two
+parameters.  The first is a string, the second is an expression of the
+type designated by the prefix. The first (string) argument is required
+to be a static expression, and is the constraint for the parameter,
+(e.g. what kind of register is required). The second argument is the
+value to be used as the input argument. The possible values for the
+constant are the same as those used in the RTL, and are dependent on
+the configuration file used to built the GCC back end.
+@ref{Machine Code Insertions}
+
+@findex Asm_Output
+@item Asm_Output
+@noindent
+The @code{Asm_Output} attribute denotes a function that takes two
+parameters.  The first is a string, the second is the name of a variable
+of the type designated by the attribute prefix. The first (string)
+argument is required to be a static expression and designates the
+constraint for the parameter (e.g. what kind of register is
+required). The second argument is the variable to be updated with the
+result. The possible values for constraint are the same as those used in
+the RTL, and are dependent on the configuration file used to build the
+GCC back end.  If there are no output operands, then this argument may
+either be omitted, or explicitly given as @code{No_Output_Operands}.
+@ref{Machine Code Insertions}
+
+@cindex OpenVMS
+@findex AST_Entry
+@item AST_Entry
+@noindent
+This attribute is implemented only in OpenVMS versions of GNAT. Applied to
+the name of an entry, it yields a value of the predefined type AST_Handler
+(declared in the predefined package System, as extended by the use of
+pragma Extend_System (Aux_DEC)). This value enables the given entry to
+be called when an AST occurs. For further details, refer to the DEC Ada
+Language Reference Manual, section 9.12a.
+
+@findex Bit
+@item Bit
+@code{@var{obj}'Bit}, where @var{obj} is any object, yields the bit
+offset within the storage unit (byte) that contains the first bit of
+storage allocated for the object. The value of this attribute is of the
+type @code{Universal_Integer}, and is always a non-negative number not
+exceeding the value of @code{System.Storage_Unit}.
+
+For an object that is a variable or a constant allocated in a register,
+the value is zero. (The use of this attribute does not force the
+allocation of a variable to memory).
+
+For an object that is a formal parameter, this attribute applies
+to either the matching actual parameter or to a copy of the
+matching actual parameter.
+
+For an access object the value is zero. Note that
+@code{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
+designated object. Similarly for a record component
+@code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
+@code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
+are subject to index checks.
+
+This attribute is designed to be compatible with the DEC Ada 83 definition
+and implementation of the @code{Bit} attribute.
+
+@findex Bit_Position
+@item Bit_Position
+@noindent
+@code{@var{R.C}'Bit}, where @var{R} is a record object and C is one
+of the fields of the record type, yields the bit
+offset within the record contains the first bit of
+storage allocated for the object. The value of this attribute is of the
+type @code{Universal_Integer}. The value depends only on the field
+@var{C} and is independent of the alignment of
+the containing record @var{R}.
+
+@findex Code_Address
+@cindex Subprogram address
+@cindex Address of subprogram code
+@item Code_Address
+@noindent
+The @code{'Address}
+attribute may be applied to subprograms in Ada 95, but the
+intended effect from the Ada 95 reference manual seems to be to provide
+an address value which can be used to call the subprogram by means of
+an address clause as in the following example:
+
+@smallexample
+procedure K is ...
+
+procedure L;
+for L'Address use K'Address;
+pragma Import (Ada, L);
+@end smallexample
+
+@noindent
+A call to L is then expected to result in a call to K. In Ada 83, where
+there were no access-to-subprogram values, this was a common work around
+for getting the effect of an indirect call.
+GNAT implements the above use of Address and the technique illustrated
+by the example code works correctly.
+
+However, for some purposes, it is useful to have the address of the start
+of the generated code for the subprogram. On some architectures, this is
+not necessarily the same as the Address value described above. For example,
+the Address value may reference a subprogram descriptor rather than the
+subprogram itself.
+
+The @code{'Code_Address} attribute, which can only be applied to 
+subprogram entities, always returns the address of the start of the 
+generated code of the specified subprogram, which may or may not be
+the same value as is returned by the corresponding @code{'Address}
+attribute.
+
+@cindex Big endian
+@cindex Little endian
+@findex Default_Bit_Order
+@item Default_Bit_Order
+@noindent
+@code{Standard'Default_Bit_Order} (@code{Standard} is the only
+permissible prefix), provides the value @code{System.Default_Bit_Order}
+as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
+@code{Low_Order_First}). This is used to construct the definition of
+@code{Default_Bit_Order} in package @code{System}.
+
+@findex Elaborated
+@item Elaborated
+@noindent
+The prefix of the @code{'Elaborated} attribute must be a unit name. The
+value is a Boolean which indicates whether or not the given unit has been
+elaborated. This attribute is primarily intended for internal use by the
+generated code for dynamic elaboration checking, but it can also be used
+in user programs. The value will always be True once elaboration of all
+units has been completed.
+
+@findex Elab_Body
+@item Elab_Body
+@noindent
+This attribute can only be applied to a program unit name. It returns
+the entity for the corresponding elaboration procedure for elaborating
+the body of the referenced unit. This is used in the main generated
+elaboration procedure by the binder and is not normally used in any
+other context.  However, there may be specialized situations in which it
+is useful to be able to call this elaboration procedure from Ada code,
+e.g. if it is necessary to do selective re-elaboration to fix some
+error.
+
+@findex Elab_Spec
+@item Elab_Spec
+@noindent
+This attribute can only be applied to a program unit name. It returns
+the entity for the corresponding elaboration procedure for elaborating
+the specification of the referenced unit. This is used in the main
+generated elaboration procedure by the binder and is not normally used
+in any other context.  However, there may be specialized situations in
+which it is useful to be able to call this elaboration procedure from
+Ada code, e.g. if it is necessary to do selective re-elaboration to fix
+some error.
+
+@cindex Ada 83 attributes
+@findex Emax
+@item Emax
+@noindent
+The @code{Emax} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@cindex Representation of enums
+@findex Enum_Rep
+@item Enum_Rep
+@noindent
+For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
+function with the following specification:
+
+@smallexample
+function @var{S}'Enum_Rep (Arg : @var{S}'Base)
+  return Universal_Integer;
+@end smallexample
+
+@noindent
+It is also allowable to apply Enum_Rep directly to an object of an
+enumeration type or to a non-overloaded enumeration
+literal. In this case @code{@var{S}'Enum_Rep} is equivalent to 
+@code{@var{typ}'Enum_Rep(@var{S})} where @var{typ} is the type of the
+enumeration literal or object.
+
+The function returns the representation value for the given enumeration
+value. This will be equal to value of the @code{Pos} attribute in the
+absence of an enumeration representation clause. This is a static
+attribute (i.e. the result is static if the argument is static).
+
+@var{S}'Enum_Rep can also be used with integer types and objects, in which
+case it simply returns the integer value. The reason for this is to allow
+it to be used for (<>) discrete formal arguments in a generic unit that
+can be instantiated with either enumeration types or integer types. Note
+that if Enum_Rep is used on a modular type whose upper bound exceeds the
+upper bound of the largest signed integer type, and the argument is a
+variable, so that the universal integer calculation is done at run-time,
+then the call to @code{Enum_Rep} may raise @code{Constraint_Error}.
+
+@cindex Ada 83 attributes
+@findex Epsilon
+@item Epsilon
+@noindent
+The @code{Epsilon} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@findex Fixed_Value
+@item Fixed_Value
+@noindent
+For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
+function with the following specification:
+
+@smallexample
+function @var{S}'Fixed_Value (Arg : Universal_Integer)
+  return @var{S};
+@end smallexample
+
+@noindent
+The value returned is the fixed-point value @var{V} such that
+
+@smallexample
+@var{V} = Arg * @var{S}'Small
+@end smallexample
+
+@noindent
+The effect is thus equivalent to first converting the argument to the
+integer type used to represent @var{S}, and then doing an unchecked
+conversion to the fixed-point type. This attribute is primarily intended
+for use in implementation of the input-output functions for fixed-point
+values.
+
+@cindex Discriminants, testing for
+@findex Has_Discriminants
+@item Has_Discriminants
+@noindent
+The prefix of the @code{Has_Discriminants} attribute is a type. The result
+is a Boolean value which is True if the type has discriminants, and False
+otherwise. The intended use of this attribute is in conjunction with generic
+definitions. If the attribute is applied to a generic private type, it
+indicates whether or not the corresponding actual type has discriminants.
+
+@findex Img
+@item Img
+@noindent
+The @code{Img} attribute differs from @code{Image} in that it may be
+applied to objects as well as types, in which case it gives the
+@code{Image} for the subtype of the object. This is convenient for
+debugging:
+
+@smallexample
+Put_Line ("X = " & X'Img);
+@end smallexample
+
+@noindent
+has the same meaning as the more verbose:
+
+@smallexample
+Put_Line ("X = " & @var{type}'Image (X));
+@end smallexample
+
+where @var{type} is the subtype of the object X.
+
+@findex Integer_Value
+@item Integer_Value
+@noindent
+For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
+function with the following specification:
+
+@smallexample
+function @var{S}'Integer_Value (Arg : Universal_Fixed)
+  return @var{S};
+@end smallexample
+
+@noindent
+The value returned is the integer value @var{V}, such that
+
+@smallexample
+Arg = @var{V} * @var{type}'Small
+@end smallexample
+
+@noindent
+The effect is thus equivalent to first doing an unchecked convert from
+the fixed-point type to its corresponding implementation type, and then
+converting the result to the target integer type. This attribute is
+primarily intended for use in implementation of the standard
+input-output functions for fixed-point values.
+
+@cindex Ada 83 attributes
+@findex Large
+@item Large
+@noindent
+The @code{Large} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@findex Machine_Size
+@item Machine_Size
+@noindent
+This attribute is identical to the @code{Object_Size} attribute. It is
+provided for compatibility with the DEC Ada 83 attribute of this name.
+   
+@cindex Ada 83 attributes
+@findex Mantissa
+@item Mantissa
+@noindent
+The @code{Mantissa} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@cindex Interrupt priority, maximum
+@findex Max_Interrupt_Priority
+@item Max_Interrupt_Priority
+@noindent
+@code{Standard'Max_Interrupt_Priority} (@code{Standard} is the only
+permissible prefix), provides the value
+@code{System.Max_Interrupt_Priority} and is intended primarily for
+constructing this definition in package @code{System}.
+
+@cindex Priority, maximum
+@findex Max_Priority
+@item Max_Priority
+@noindent
+@code{Standard'Max_Priority} (@code{Standard} is the only permissible
+prefix) provides the value @code{System.Max_Priority} and is intended
+primarily for constructing this definition in package @code{System}.
+
+@cindex Alignment, maximum
+@findex Maximum_Alignment
+@item Maximum_Alignment
+@noindent
+@code{Standard'Maximum_Alignment} (@code{Standard} is the only
+permissible prefix) provides the maximum useful alignment value for the
+target. This is a static value that can be used to specify the alignment
+for an object, guaranteeing that it is properly aligned in all
+cases. This is useful when an external object is imported and its
+alignment requirements are unknown.
+
+@cindex Return values, passing mechanism
+@cindex Parameters, passing mechanism
+@findex Mechanism_Code
+@item Mechanism_Code
+@noindent
+@code{@var{function}'Mechanism_Code} yields an integer code for the
+mechanism used for the result of function, and
+@code{@var{subprogram}'Mechanism_Code (@var{n})} yields the mechanism
+used for formal parameter number @var{n} (a static integer value with 1
+meaning the first parameter) of @var{subprogram}. The code returned is:
+
+@table @asis
+@item 1
+by copy (value)
+@item 2
+by reference
+@item 3
+by descriptor (default descriptor class)
+@item 4
+by descriptor (UBS: unaligned bit string)
+@item 5
+by descriptor (UBSB: aligned bit string with arbitrary bounds)
+@item 6
+by descriptor (UBA: unaligned bit array)
+@item 7
+by descriptor (S: string, also scalar access type parameter)
+@item 8
+by descriptor (SB: string with arbitrary bounds)
+@item 9
+by descriptor (A: contiguous array)
+@item 10
+by descriptor (NCA: non-contiguous array)
+@end table
+
+@cindex OpenVMS
+Values from 3-10 are only relevant to Digital OpenVMS implementations.
+
+@cindex Zero address, passing
+@findex Null_Parameter
+@item Null_Parameter
+@noindent
+A reference @code{@var{T}'Null_Parameter} denotes an imaginary object of
+type or subtype @var{T} allocated at machine address zero. The attribute
+is allowed only as the default expression of a formal parameter, or as
+an actual expression of a subprogram call. In either case, the
+subprogram must be imported.
+
+The identity of the object is represented by the address zero in the
+argument list, independent of the passing mechanism (explicit or
+default).
+
+This capability is needed to specify that a zero address should be
+passed for a record or other composite object passed by reference.
+There is no way of indicating this without the @code{Null_Parameter}
+attribute.
+
+@cindex Size, used for objects
+@findex Object_Size
+@item Object_Size
+@noindent
+The size of an object is not necessarily the same as the size of the type
+of an object. This is because by default object sizes are increased to be
+a multiple of the alignment of the object. For example, 
+@code{Natural'Size} is
+31, but by default objects of type @code{Natural} will have a size of 32 bits.
+Similarly, a record containing an integer and a character:
+
+@smallexample
+type Rec is record
+   I : Integer;
+   C : Character;
+end record;
+@end smallexample
+
+@noindent
+will have a size of 40 (that is @code{Rec'Size} will be 40. The 
+alignment will be 4, because of the
+integer field, and so the default size of record objects for this type
+will be 64 (8 bytes).
+
+The @code{@var{type}'Object_Size} attribute
+has been added to GNAT to allow the
+default object size of a type to be easily determined. For example,
+@code{Natural'Object_Size} is 32, and
+@code{Rec'Object_Size} (for the record type in the above example) will be
+64. Note also that, unlike the situation with the
+@code{Size} attribute as defined in the Ada RM, the 
+@code{Object_Size} attribute can be specified individually
+for different subtypes. For example:
+
+@smallexample
+type R is new Integer;
+subtype R1 is R range 1 .. 10;
+subtype R2 is R range 1 .. 10;
+for R2'Object_Size use 8;
+@end smallexample
+
+@noindent
+In this example, @code{R'Object_Size} and @code{R1'Object_Size} are both
+32 since the default object size for a subtype is the same as the object size
+for the parent subtype. This means that objects of type @code{R}
+or @code{R1} will
+by default be 32 bits (four bytes). But objects of type
+@code{R2} will be only
+8 bits (one byte), since @code{R2'Object_Size} has been set to 8.
+
+@cindex Parameters, when passed by reference
+@findex Passed_By_Reference
+@item Passed_By_Reference
+@noindent
+@code{@var{type}'Passed_By_Reference} for any subtype @var{type} returns
+a value of type @code{Boolean} value that is @code{True} if the type is
+normally passed by reference and @code{False} if the type is normally
+passed by copy in calls. For scalar types, the result is always @code{False}
+and is static. For non-scalar types, the result is non-static.
+
+@findex Range_Length
+@item Range_Length
+@noindent
+@code{@var{type}'Range_Length} for any discrete type @var{type} yields
+the number of values represented by the subtype (zero for a null
+range). The result is static for static subtypes. @code{Range_Length}
+applied to the index subtype of a one dimensional array always gives the
+same result as @code{Range} applied to the array itself.
+
+@cindex Ada 83 attributes
+@findex Safe_Emax
+@item Safe_Emax
+@noindent
+The @code{Safe_Emax} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@cindex Ada 83 attributes
+@findex Safe_Large
+@item Safe_Large
+@noindent
+The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@cindex Ada 83 attributes
+@findex Safe_Large
+@item Safe_Large
+@noindent
+The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute.
+
+@cindex Ada 83 attributes
+@findex Small
+@item Small
+@noindent
+The @code{Small} attribute is defined in Ada 95 only for fixed-point types.
+GNAT also allows this attribute to be applied to floating-point types
+for compatibility with Ada 83. See
+the Ada 83 reference manual for an exact description of the semantics of
+this attribute when applied to floating-point types.
+
+@findex Storage_Unit
+@item Storage_Unit
+@noindent
+@code{Standard'Storage_Unit} (@code{Standard} is the only permissible
+prefix) provides the value @code{System.Storage_Unit} and is intended
+primarily for constructing this definition in package @code{System}.
+
+@findex Tick
+@item Tick
+@noindent
+@code{Standard'Tick} (@code{Standard} is the only permissible prefix)
+provides the value of @code{System.Tick} and is intended primarily for
+constructing this definition in package @code{System}.
+
+@findex To_Address
+@item To_Address
+@noindent
+The @code{System'To_Address}
+(@code{System} is the only permissible prefix)
+denotes a function identical to 
+@code{System.Storage_Elements.To_Address} except that
+it is a static attribute. This means that if its argument is
+a static expression, then the result of the attribute is a
+static expression. The result is that such an expression can be
+used in contexts (e.g. preelaborable packages) which require a
+static expression and where the function call could not be used
+(since the function call is always non-static, even if its 
+argument is static).
+
+@findex Type_Class
+@item Type_Class
+@noindent
+@code{@var{type}'Type_Class} for any type or subtype @var{type} yields
+the value of the type class for the full type of @var{type}. If
+@var{type} is a generic formal type, the value is the value for the
+corresponding actual subtype.  The value of this attribute is of type
+@code{System.Aux_DEC.Type_Class}, which has the following definition:
+
+@smallexample
+  type Type_Class is
+    (Type_Class_Enumeration,
+     Type_Class_Integer,
+     Type_Class_Fixed_Point,
+     Type_Class_Floating_Point,
+     Type_Class_Array,
+     Type_Class_Record,
+     Type_Class_Access,
+     Type_Class_Task,
+     Type_Class_Address);
+@end smallexample
+
+@noindent
+Protected types yield the value @code{Type_Class_Task}, which thus
+applies to all concurrent types. This attribute is designed to
+be compatible with the DEC Ada 83 attribute of the same name.
+
+@findex UET_Address
+@item UET_Address
+@noindent
+The @code{UET_Address} attribute can only be used for a prefix which
+denotes a library package. It yields the address of the unit exception
+table when zero cost exception handling is used. This attribute is
+intended only for use within the GNAT implementation. See the unit
+@code{Ada.Exceptions} in files @file{a-except.ads,a-except.adb}
+for details on how this attribute is used in the implementation.
+
+@cindex Named numbers, representation of
+@findex Universal_Literal_String
+@item Universal_Literal_String
+@noindent
+The prefix of @code{Universal_Literal_String} must be a named
+number. The static result is the string consisting of the characters of
+the number as defined in the original source. This allows the user
+program to access the actual text of named numbers without intermediate
+conversions and without the need to enclose the strings in quotes (which
+would preclude their use as numbers). This is used internally for the
+construction of values of the floating-point attributes from the file
+@file{ttypef.ads}, but may also be used by user programs.
+
+@cindex @code{Access}, unrestricted
+@findex Unrestricted_Access
+@item Unrestricted_Access
+@noindent
+The @code{Unrestricted_Access} attribute is similar to @code{Access}
+except that all accessibility and aliased view checks are omitted. This
+is a user-beware attribute.  It is similar to
+@code{Address}, for which it is a desirable replacement where the value
+desired is an access type. In other words, its effect is identical to
+first applying the @code{Address} attribute and then doing an unchecked
+conversion to a desired access type. In GNAT, but not necessarily in
+other implementations, the use of static chains for inner level
+subprograms means that @code{Unrestricted_Access} applied to a
+subprogram yields a value that can be called as long as the subprogram
+is in scope (normal Ada 95 accessibility rules restrict this usage).
+
+@cindex @code{Size}, VADS compatibility
+@findex VADS_Size
+@item VADS_Size
+@noindent
+The @code{'VADS_Size} attribute is intended to make it easier to port
+legacy code which relies on the semantics of @code{'Size} as implemented
+by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
+same semantic interpretation. In particular, @code{'VADS_Size} applied
+to a predefined or other primitive type with no Size clause yields the
+Object_Size (for example, @code{Natural'Size} is 32 rather than 31 on
+typical machines). In addition @code{'VADS_Size} applied to an object
+gives the result that would be obtained by applying the attribute to
+the corresponding type.
+
+@cindex @code{Size}, setting for not-first subtype
+@findex Value_Size
+@item Value_Size
+@code{@var{type}'Value_Size} is the number of bits required to represent
+a value of the given subtype. It is the same as @code{@var{type}'Size},
+but, unlike @code{Size}, may be set for non-first subtypes.
+
+@findex Wchar_T_Size
+@item Wchar_T_Size
+@code{Standard'Wchar_T_Size} (@code{Standard} is the only permissible
+prefix) provides the size in bits of the C @code{wchar_t} type 
+primarily for constructing the definition of this type in 
+package @code{Interfaces.C}.
+
+@findex Word_Size
+@item Word_Size
+@code{Standard'Word_Size} (@code{Standard} is the only permissible
+prefix) provides the value @code{System.Word_Size} and is intended
+primarily for constructing this definition in package @code{System}.
+@end table
+@node Implementation Advice
+@chapter Implementation Advice
+The main text of the Ada 95 Reference Manual describes the required
+behavior of all Ada 95 compilers, and the GNAT compiler conforms to
+these requirements.
+
+In addition, there are sections throughout the Ada 95
+reference manual headed
+by the phrase ``implementation advice''. These sections are not normative,
+i.e. they do not specify requirements that all compilers must
+follow. Rather they provide advice on generally desirable behavior. You
+may wonder why they are not requirements. The most typical answer is
+that they describe behavior that seems generally desirable, but cannot
+be provided on all systems, or which may be undesirable on some systems.
+
+As far as practical, GNAT follows the implementation advice sections in
+the Ada 95 Reference Manual. This chapter contains a table giving the
+reference manual section number, paragraph number and several keywords
+for each advice.  Each entry consists of the text of the advice followed
+by the GNAT interpretation of this advice. Most often, this simply says
+``followed'', which means that GNAT follows the advice. However, in a
+number of cases, GNAT deliberately deviates from this advice, in which
+case the text describes what GNAT does and why.
+
+@table @strong
+@cindex Error detection
+@item 1.1.3(20): Error Detection
+@sp 1
+@cartouche
+If an implementation detects the use of an unsupported Specialized Needs
+Annex feature at run time, it should raise @code{Program_Error} if
+feasible.
+@end cartouche
+Not relevant. All specialized needs annex features are either supported,
+or diagnosed at compile time.
+
+@cindex Child Units
+@item 1.1.3(31): Child Units
+@sp 1
+@cartouche
+If an implementation wishes to provide implementation-defined
+extensions to the functionality of a language-defined library unit, it
+should normally do so by adding children to the library unit.
+@end cartouche
+Followed.
+
+@cindex Bounded errors
+@item 1.1.5(12): Bounded Errors
+@sp 1
+@cartouche
+If an implementation detects a bounded error or erroneous
+execution, it should raise @code{Program_Error}.
+@end cartouche
+Followed in all cases in which the implementation detects a bounded
+error or erroneous execution. Not all such situations are detected at
+runtime.
+
+@cindex Pragmas
+@item 2.8(16): Pragmas
+@sp 1
+@cartouche
+Normally, implementation-defined pragmas should have no semantic effect
+for error-free programs; that is, if the implementation-defined pragmas
+are removed from a working program, the program should still be legal,
+and should still have the same semantics.
+@end cartouche
+The following implementation defined pragmas are exceptions to this
+rule:
+
+@table @code
+@item Abort_Defer
+Affects semantics
+@item Ada_83
+Affects legality
+@item Assert
+Affects semantics
+@item CPP_Class
+Affects semantics
+@item CPP_Constructor
+Affects semantics
+@item CPP_Virtual
+Affects semantics
+@item CPP_Vtable
+Affects semantics
+@item Debug
+Affects semantics
+@item Interface_Name
+Affects semantics
+@item Machine_Attribute
+Affects semantics
+@item Unimplemented_Unit
+Affects legality
+@item Unchecked_Union
+Affects semantics
+@end table
+
+In each of the above cases, it is essential to the purpose of the pragma
+that this advice not be followed. For details see the separate section
+on implementation defined pragmas.
+
+@item 2.8(17-19): Pragmas
+@sp 1
+@cartouche
+Normally, an implementation should not define pragmas that can
+make an illegal program legal, except as follows:
+@end cartouche
+@sp 1
+@cartouche
+A pragma used to complete a declaration, such as a pragma @code{Import};
+@end cartouche
+@sp 1
+@cartouche
+A pragma used to configure the environment by adding, removing, or
+replacing @code{library_items}.
+@end cartouche
+See response to paragraph 16 of this same section.
+
+@cindex Character Sets
+@cindex Alternative Character Sets
+@item 3.5.2(5): Alternative Character Sets
+@sp 1
+@cartouche
+If an implementation supports a mode with alternative interpretations
+for @code{Character} and @code{Wide_Character}, the set of graphic
+characters of @code{Character} should nevertheless remain a proper
+subset of the set of graphic characters of @code{Wide_Character}. Any
+character set ``localizations'' should be reflected in the results of
+the subprograms defined in the language-defined package
+@code{Characters.Handling} (see A.3) available in such a mode. In a mode with
+an alternative interpretation of @code{Character}, the implementation should
+also support a corresponding change in what is a legal
+@code{identifier_letter}.
+@end cartouche
+Not all wide character modes follow this advice, in particular the JIS
+and IEC modes reflect standard usage in Japan, and in these encoding,
+the upper half of the Latin-1 set is not part of the wide-character
+subset, since the most significant bit is used for wide character
+encoding. However, this only applies to the external forms. Internally
+there is no such restriction.
+
+@cindex Integer types
+@item 3.5.4(28): Integer Types
+
+@sp 1
+@cartouche
+An implementation should support @code{Long_Integer} in addition to
+@code{Integer} if the target machine supports 32-bit (or longer)
+arithmetic. No other named integer subtypes are recommended for package
+@code{Standard}. Instead, appropriate named integer subtypes should be
+provided in the library package @code{Interfaces} (see B.2).
+@end cartouche
+@code{Long_Integer} is supported. Other standard integer types are supported
+so this advice is not fully followed. These types
+are supported for convenient interface to C, and so that all hardware
+types of the machine are easily available.
+@item 3.5.4(29): Integer Types
+
+@sp 1
+@cartouche
+An implementation for a two's complement machine should support
+modular types with a binary modulus up to @code{System.Max_Int*2+2}. An
+implementation should support a non-binary modules up to @code{Integer'Last}.
+@end cartouche
+Followed.
+
+@cindex Enumeration values
+@item 3.5.5(8): Enumeration Values
+@sp 1
+@cartouche
+For the evaluation of a call on @code{@var{S}'Pos} for an enumeration
+subtype, if the value of the operand does not correspond to the internal
+code for any enumeration literal of its type (perhaps due to an
+un-initialized variable), then the implementation should raise
+@code{Program_Error}. This is particularly important for enumeration
+types with noncontiguous internal codes specified by an
+enumeration_representation_clause.
+@end cartouche
+Followed.
+
+@cindex Float types
+@item 3.5.7(17): Float Types
+@sp 1
+@cartouche
+An implementation should support @code{Long_Float} in addition to
+@code{Float} if the target machine supports 11 or more digits of
+precision. No other named floating point subtypes are recommended for
+package @code{Standard}. Instead, appropriate named floating point subtypes
+should be provided in the library package @code{Interfaces} (see B.2).
+@end cartouche
+@code{Short_Float} and @code{Long_Long_Float} are also provided. The
+former provides improved compatibility with other implementations
+supporting this type. The latter corresponds to the highest precision
+floating-point type supported by the hardware. On most machines, this
+will be the same as @code{Long_Float}, but on some machines, it will
+correspond to the IEEE extended form. The notable case is all ia32
+(x86) implementations, where @code{Long_Long_Float} corresponds to
+the 80-bit extended precision format supported in hardware on this
+processor. Note that the 128-bit format on SPARC is not supported,
+since this is a software rather than a hardware format.
+
+@cindex Multidimensional arrays
+@cindex Arrays, multidimensional
+@item 3.6.2(11): Multidimensional Arrays
+@sp 1
+@cartouche
+An implementation should normally represent multidimensional arrays in
+row-major order, consistent with the notation used for multidimensional
+array aggregates (see 4.3.3). However, if a pragma @code{Convention}
+(@code{Fortran}, ...) applies to a multidimensional array type, then
+column-major order should be used instead (see B.5, ``Interfacing with
+Fortran'').
+@end cartouche
+Followed.
+
+@findex Duration'Small
+@item 9.6(30-31): Duration'Small
+@sp 1
+@cartouche
+Whenever possible in an implementation, the value of @code{Duration'Small}
+should be no greater than 100 microseconds.
+@end cartouche
+Followed. (@code{Duration'Small} = 10**(-9)).
+
+@sp 1
+@cartouche
+The time base for @code{delay_relative_statements} should be monotonic;
+it need not be the same time base as used for @code{Calendar.Clock}.
+@end cartouche
+Followed.
+
+@item 10.2.1(12): Consistent Representation
+@sp 1
+@cartouche
+In an implementation, a type declared in a pre-elaborated package should
+have the same representation in every elaboration of a given version of
+the package, whether the elaborations occur in distinct executions of
+the same program, or in executions of distinct programs or partitions
+that include the given version.
+@end cartouche
+Followed, except in the case of tagged types. Tagged types involve
+implicit pointers to a local copy of a dispatch table, and these pointers
+have representations which thus depend on a particular elaboration of the
+package. It is not easy to see how it would be possible to follow this
+advice without severely impacting efficiency of execution.
+
+@cindex Exception information
+@item 11.4.1(19): Exception Information
+@sp 1
+@cartouche
+@code{Exception_Message} by default and @code{Exception_Information}
+should produce information useful for
+debugging. @code{Exception_Message} should be short, about one
+line. @code{Exception_Information} can be long. @code{Exception_Message}
+should not include the
+@code{Exception_Name}. @code{Exception_Information} should include both
+the @code{Exception_Name} and the @code{Exception_Message}.
+@end cartouche
+Followed. For each exception that doesn't have a specified
+@code{Exception_Message}, the compiler generates one containing the location
+of the raise statement. This location has the form "file:line", where
+file is the short file name (without path information) and line is the line
+number in the file. Note that in the case of the Zero Cost Exception
+mechanism, these messages become redundant with the Exception_Information that
+contains a full backtrace of the calling sequence, so they are disabled.
+To disable explicitly the generation of the source location message, use the
+Pragma @code{Discard_Names}.
+
+@cindex Suppression of checks
+@cindex Checks, suppression of
+@item 11.5(28): Suppression of Checks
+@sp 1
+@cartouche
+The implementation should minimize the code executed for checks that
+have been suppressed.
+@end cartouche
+Followed.
+
+@cindex Representation clauses
+@item 13.1 (21-24): Representation Clauses
+@sp 1
+@cartouche
+The recommended level of support for all representation items is
+qualified as follows:
+@end cartouche
+@sp 1
+@cartouche
+An implementation need not support representation items containing
+non-static expressions, except that an implementation should support a
+representation item for a given entity if each non-static expression in
+the representation item is a name that statically denotes a constant
+declared before the entity.
+@end cartouche
+Followed. GNAT does not support non-static expressions in representation
+clauses unless they are constants declared before the entity. For
+example:
+
+@smallexample
+X : typ;
+for X'Address use To_address (16#2000#); 
+@end smallexample
+
+@noindent
+will be rejected, since the To_Address expression is non-static. Instead
+write: 
+
+@smallexample
+X_Address : constant Address : = 
+To_Address    ((16#2000#); 
+X : typ;
+for X'Address use X_Address;
+@end smallexample
+
+@sp 1
+@cartouche
+An implementation need not support a specification for the @code{Size}
+for a given composite subtype, nor the size or storage place for an
+object (including a component) of a given composite subtype, unless the
+constraints on the subtype and its composite subcomponents (if any) are
+all static constraints.
+@end cartouche
+Followed. Size Clauses are not permitted on non-static components, as
+described above.
+
+@sp 1
+@cartouche
+An aliased component, or a component whose type is by-reference, should
+always be allocated at an addressable location.
+@end cartouche
+Followed.
+
+@cindex Packed types
+@item 13.2(6-8): Packed Types
+@sp 1
+@cartouche
+If a type is packed, then the implementation should try to minimize
+storage allocated to objects of the type, possibly at the expense of
+speed of accessing components, subject to reasonable complexity in
+addressing calculations.
+@end cartouche
+@sp 1
+@cartouche
+The recommended level of support pragma @code{Pack} is:
+
+For a packed record type, the components should be packed as tightly as
+possible subject to the Sizes of the component subtypes, and subject to
+any @code{record_representation_clause} that applies to the type; the
+implementation may, but need not, reorder components or cross aligned
+word boundaries to improve the packing. A component whose @code{Size} is
+greater than the word size may be allocated an integral number of words.
+@end cartouche
+Followed. Tight packing of arrays is supported for all component sizes
+up to 64-bits.
+
+@sp 1
+@cartouche
+An implementation should support Address clauses for imported
+subprograms.
+@end cartouche
+Followed.
+@cindex @code{Address} clauses
+@item 13.3(14-19): Address Clauses
+
+@sp 1
+@cartouche
+For an array @var{X}, @code{@var{X}'Address} should point at the first
+component of the array, and not at the array bounds.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+The recommended level of support for the @code{Address} attribute is:
+
+@code{@var{X}'Address} should produce a useful result if @var{X} is an
+object that is aliased or of a by-reference type, or is an entity whose
+@code{Address} has been specified.
+@end cartouche
+Followed.  A valid address will be produced even if none of those
+conditions have been met.  If necessary, the object is forced into
+memory to ensure the address is valid.
+
+@sp 1
+@cartouche
+An implementation should support @code{Address} clauses for imported
+subprograms.
+@end cartouche
+Followed.
+            
+@sp 1
+@cartouche
+Objects (including subcomponents) that are aliased or of a by-reference
+type should be allocated on storage element boundaries.
+@end cartouche
+Followed.
+          
+@sp 1
+@cartouche
+If the @code{Address} of an object is specified, or it is imported or exported,
+then the implementation should not perform optimizations based on
+assumptions of no aliases.
+@end cartouche
+Followed.
+
+@cindex @code{Alignment} clauses
+@item 13.3(29-35): Alignment Clauses
+@sp 1
+@cartouche
+The recommended level of support for the @code{Alignment} attribute for
+subtypes is:
+
+An implementation should support specified Alignments that are factors
+and multiples of the number of storage elements per word, subject to the
+following:
+@end cartouche
+Followed.
+          
+@sp 1
+@cartouche
+An implementation need not support specified @code{Alignment}s for
+combinations of @code{Size}s and @code{Alignment}s that cannot be easily
+loaded and stored by available machine instructions.
+@end cartouche
+Followed.
+            
+@sp 1
+@cartouche
+An implementation need not support specified @code{Alignment}s that are
+greater than the maximum @code{Alignment} the implementation ever returns by
+default.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+The recommended level of support for the @code{Alignment} attribute for
+objects is:
+
+Same as above, for subtypes, but in addition:
+@end cartouche
+Followed.
+           
+@sp 1
+@cartouche
+For stand-alone library-level objects of statically constrained
+subtypes, the implementation should support all @code{Alignment}s
+supported by the target linker. For example, page alignment is likely to
+be supported for such objects, but not for subtypes.
+@end cartouche
+Followed.
+
+@cindex @code{Size} clauses
+@item 13.3(42-43): Size Clauses
+@sp 1
+@cartouche
+The recommended level of support for the @code{Size} attribute of
+objects is:
+
+A @code{Size} clause should be supported for an object if the specified
+@code{Size} is at least as large as its subtype's @code{Size}, and
+corresponds to a size in storage elements that is a multiple of the
+object's @code{Alignment} (if the @code{Alignment} is nonzero).
+@end cartouche
+Followed.
+
+@item 13.3(50-56): Size Clauses
+@sp 1
+@cartouche
+If the @code{Size} of a subtype is specified, and allows for efficient
+independent addressability (see 9.10) on the target architecture, then
+the @code{Size} of the following objects of the subtype should equal the
+@code{Size} of the subtype:
+
+Aliased objects (including components).
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+@code{Size} clause on a composite subtype should not affect the
+internal layout of components.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+The recommended level of support for the @code{Size} attribute of subtypes is:
+@end cartouche
+@sp 1
+@cartouche
+The @code{Size} (if not specified) of a static discrete or fixed point
+subtype should be the number of bits needed to represent each value
+belonging to the subtype using an unbiased representation, leaving space
+for a sign bit only if the subtype contains negative values. If such a
+subtype is a first subtype, then an implementation should support a
+specified @code{Size} for it that reflects this representation.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+For a subtype implemented with levels of indirection, the @code{Size}
+should include the size of the pointers, but not the size of what they
+point at.
+@end cartouche
+Followed.
+
+@cindex @code{Component_Size} clauses
+@item 13.3(71-73): Component Size Clauses
+@sp 1
+@cartouche
+The recommended level of support for the @code{Component_Size}
+attribute is:
+@end cartouche
+@sp 1
+@cartouche
+An implementation need not support specified @code{Component_Sizes} that are
+less than the @code{Size} of the component subtype.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An implementation should support specified @code{Component_Size}s that
+are factors and multiples of the word size. For such
+@code{Component_Size}s, the array should contain no gaps between
+components. For other @code{Component_Size}s (if supported), the array
+should contain no gaps between components when packing is also
+specified; the implementation should forbid this combination in cases
+where it cannot support a no-gaps representation.
+@end cartouche
+Followed.
+
+@cindex Enumeration representation clauses
+@cindex Representation clauses, enumeration
+@item 13.4(9-10): Enumeration Representation Clauses
+@sp 1
+@cartouche
+The recommended level of support for enumeration representation clauses
+is:
+
+An implementation need not support enumeration representation clauses
+for boolean types, but should at minimum support the internal codes in
+the range @code{System.Min_Int.System.Max_Int}.
+@end cartouche
+Followed.
+
+@cindex Record representation clauses
+@cindex Representation clauses, records
+@item 13.5.1(17-22): Record Representation Clauses
+@sp 1
+@cartouche
+The recommended level of support for
+@*@code{record_representation_clauses} is:
+
+An implementation should support storage places that can be extracted
+with a load, mask, shift sequence of machine code, and set with a load,
+shift, mask, store sequence, given the available machine instructions
+and run-time model.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+A storage place should be supported if its size is equal to the
+@code{Size} of the component subtype, and it starts and ends on a
+boundary that obeys the @code{Alignment} of the component subtype.
+@end cartouche
+Followed.
+           
+@sp 1
+@cartouche
+If the default bit ordering applies to the declaration of a given type,
+then for a component whose subtype's @code{Size} is less than the word
+size, any storage place that does not cross an aligned word boundary
+should be supported.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An implementation may reserve a storage place for the tag field of a
+tagged type, and disallow other components from overlapping that place.
+@end cartouche
+Followed. The storage place for the tag field is the beginning of the tagged
+record, and its size is Address'Size. GNAT will reject an explicit component
+clause for the tag field.
+
+@sp 1
+@cartouche
+An implementation need not support a @code{component_clause} for a
+component of an extension part if the storage place is not after the
+storage places of all components of the parent type, whether or not
+those storage places had been specified.
+@end cartouche
+Followed. The above advice on record representation clauses is followed,
+and all mentioned features are implemented.
+
+@cindex Storage place attributes
+@item 13.5.2(5): Storage Place Attributes
+@sp 1
+@cartouche
+If a component is represented using some form of pointer (such as an
+offset) to the actual data of the component, and this data is contiguous
+with the rest of the object, then the storage place attributes should
+reflect the place of the actual data, not the pointer. If a component is
+allocated discontinuously from the rest of the object, then a warning
+should be generated upon reference to one of its storage place
+attributes.
+@end cartouche
+Followed. There are no such components in GNAT.
+
+@cindex Bit ordering
+@item 13.5.3(7-8): Bit Ordering
+@sp 1
+@cartouche
+The recommended level of support for the non-default bit ordering is:
+@end cartouche
+@sp 1
+@cartouche
+If @code{Word_Size} = @code{Storage_Unit}, then the implementation
+should support the non-default bit ordering in addition to the default
+bit ordering.
+@end cartouche
+Followed. Word size does not equal storage size in this implementation.
+Thus non-default bit ordering is not supported.
+
+@cindex @code{Address}, as private type
+@item 13.7(37): Address as Private
+@sp 1
+@cartouche
+@code{Address} should be of a private type.
+@end cartouche
+Followed.
+
+@cindex Operations, on @code{Address}
+@cindex @code{Address}, operations of
+@item 13.7.1(16): Address Operations
+@sp 1
+@cartouche
+Operations in @code{System} and its children should reflect the target
+environment semantics as closely as is reasonable. For example, on most
+machines, it makes sense for address arithmetic to ``wrap around.''
+Operations that do not make sense should raise @code{Program_Error}.
+@end cartouche
+Followed. Address arithmetic is modular arithmetic that wraps around. No
+operation raises @code{Program_Error}, since all operations make sense.
+
+@cindex Unchecked conversion
+@item 13.9(14-17): Unchecked Conversion
+@sp 1
+@cartouche
+The @code{Size} of an array object should not include its bounds; hence,
+the bounds should not be part of the converted data.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+The implementation should not generate unnecessary run-time checks to
+ensure that the representation of @var{S} is a representation of the
+target type. It should take advantage of the permission to return by
+reference when possible. Restrictions on unchecked conversions should be
+avoided unless required by the target environment.
+@end cartouche
+Followed. There are no restrictions on unchecked conversion. A warning is
+generated if the source and target types do not have the same size since
+the semantics in this case may be target dependent.
+
+@sp 1
+@cartouche
+The recommended level of support for unchecked conversions is:
+@end cartouche
+@sp 1
+@cartouche
+Unchecked conversions should be supported and should be reversible in
+the cases where this clause defines the result. To enable meaningful use
+of unchecked conversion, a contiguous representation should be used for
+elementary subtypes, for statically constrained array subtypes whose
+component subtype is one of the subtypes described in this paragraph,
+and for record subtypes without discriminants whose component subtypes
+are described in this paragraph.
+@end cartouche
+Followed. 
+
+@cindex Heap usage, implicit
+@item 13.11(23-25): Implicit Heap Usage
+@sp 1
+@cartouche
+An implementation should document any cases in which it dynamically
+allocates heap storage for a purpose other than the evaluation of an
+allocator.
+@end cartouche
+Followed, the only other points at which heap storage is dynamically
+allocated are as follows:
+
+@itemize @bullet
+@item
+At initial elaboration time, to allocate dynamically sized global
+objects.
+
+@item
+To allocate space for a task when a task is created.
+
+@item
+To extend the secondary stack dynamically when needed. The secondary
+stack is used for returning variable length results.
+@end itemize
+
+@sp 1
+@cartouche
+A default (implementation-provided) storage pool for an access-to-
+constant type should not have overhead to support de-allocation of
+individual objects.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+A storage pool for an anonymous access type should be created at the
+point of an allocator for the type, and be reclaimed when the designated
+object becomes inaccessible.
+@end cartouche
+Followed. 
+
+@cindex Unchecked deallocation
+@item 13.11.2(17): Unchecked De-allocation
+@sp 1
+@cartouche
+For a standard storage pool, @code{Free} should actually reclaim the
+storage.
+@end cartouche
+Followed. 
+
+@cindex Stream oriented attributes
+@item 13.13.2(17): Stream Oriented Attributes
+@sp 1
+@cartouche
+If a stream element is the same size as a storage element, then the
+normal in-memory representation should be used by @code{Read} and
+@code{Write} for scalar objects. Otherwise, @code{Read} and @code{Write}
+should use the smallest number of stream elements needed to represent
+all values in the base range of the scalar type.
+@end cartouche
+Followed. In particular, the interpretation chosen is that of AI-195,
+which specifies that the size to be used is that of the first subtype.
+
+@item A.1(52): Implementation Advice
+@sp 1
+@cartouche
+If an implementation provides additional named predefined integer types,
+then the names should end with @samp{Integer} as in
+@samp{Long_Integer}. If an implementation provides additional named
+predefined floating point types, then the names should end with
+@samp{Float} as in @samp{Long_Float}.
+@end cartouche
+Followed. 
+
+@findex Ada.Characters.Handling
+@item A.3.2(49): @code{Ada.Characters.Handling}
+@sp 1
+@cartouche
+If an implementation provides a localized definition of @code{Character}
+or @code{Wide_Character}, then the effects of the subprograms in
+@code{Characters.Handling} should reflect the localizations. See also
+3.5.2.
+@end cartouche
+Followed. GNAT provides no such localized definitions. 
+
+@cindex Bounded-length strings
+@item A.4.4(106): Bounded-Length String Handling
+@sp 1
+@cartouche
+Bounded string objects should not be implemented by implicit pointers
+and dynamic allocation.
+@end cartouche
+Followed. No implicit pointers or dynamic allocation are used. 
+
+@cindex Random number generation
+@item A.5.2(46-47): Random Number Generation
+@sp 1
+@cartouche
+Any storage associated with an object of type @code{Generator} should be
+reclaimed on exit from the scope of the object.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+If the generator period is sufficiently long in relation to the number
+of distinct initiator values, then each possible value of
+@code{Initiator} passed to @code{Reset} should initiate a sequence of
+random numbers that does not, in a practical sense, overlap the sequence
+initiated by any other value. If this is not possible, then the mapping
+between initiator values and generator states should be a rapidly
+varying function of the initiator value.
+@end cartouche
+Followed. The generator period is sufficiently long for the first
+condition here to hold true. 
+
+@findex Get_Immediate
+@item A.10.7(23): @code{Get_Immediate}
+@sp 1
+@cartouche
+The @code{Get_Immediate} procedures should be implemented with
+unbuffered input. For a device such as a keyboard, input should be
+@dfn{available} if a key has already been typed, whereas for a disk
+file, input should always be available except at end of file. For a file
+associated with a keyboard-like device, any line-editing features of the
+underlying operating system should be disabled during the execution of
+@code{Get_Immediate}.
+@end cartouche
+Followed.
+
+@findex Export
+@item B.1(39-41): Pragma @code{Export}
+@sp 1
+@cartouche
+If an implementation supports pragma @code{Export} to a given language,
+then it should also allow the main subprogram to be written in that
+language. It should support some mechanism for invoking the elaboration
+of the Ada library units included in the system, and for invoking the
+finalization of the environment task. On typical systems, the
+recommended mechanism is to provide two subprograms whose link names are
+@code{adainit} and @code{adafinal}. @code{adainit} should contain the
+elaboration code for library units. @code{adafinal} should contain the
+finalization code. These subprograms should have no effect the second
+and subsequent time they are called.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+Automatic elaboration of pre-elaborated packages should be
+provided when pragma Export is supported.
+@end cartouche
+Followed when the main program is in Ada. If the main program is in a
+foreign language, then
+@code{adainit} must be called to elaborate pre-elaborated
+packages.
+
+@sp 1
+@cartouche
+For each supported convention @var{L} other than @code{Intrinsic}, an
+implementation should support @code{Import} and @code{Export} pragmas
+for objects of @var{L}-compatible types and for subprograms, and pragma
+@code{Convention} for @var{L}-eligible types and for subprograms,
+presuming the other language has corresponding features. Pragma
+@code{Convention} need not be supported for scalar types.
+@end cartouche
+Followed. 
+
+@cindex Package @code{Interfaces}
+@findex Interfaces
+@item B.2(12-13): Package @code{Interfaces}
+@sp 1
+@cartouche
+For each implementation-defined convention identifier, there should be a
+child package of package Interfaces with the corresponding name. This
+package should contain any declarations that would be useful for
+interfacing to the language (implementation) represented by the
+convention. Any declarations useful for interfacing to any language on
+the given hardware architecture should be provided directly in
+@code{Interfaces}.
+@end cartouche
+Followed. An additional package not defined
+in the Ada 95 Reference Manual is @code{Interfaces.CPP}, used
+for interfacing to C++.
+
+@sp 1
+@cartouche
+An implementation supporting an interface to C, COBOL, or Fortran should
+provide the corresponding package or packages described in the following
+clauses.
+@end cartouche
+Followed. GNAT provides all the packages described in this section. 
+
+@cindex C, interfacing with
+@item B.3(63-71): Interfacing with C
+@sp 1
+@cartouche
+An implementation should support the following interface correspondences
+between Ada and C.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An Ada procedure corresponds to a void-returning C function.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada function corresponds to a non-void C function.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada @code{in} scalar parameter is passed as a scalar argument to a C
+function.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada @code{in} parameter of an access-to-object type with designated
+type @var{T} is passed as a @code{@var{t}*} argument to a C function,
+where @var{t} is the C type corresponding to the Ada type @var{T}.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada access @var{T} parameter, or an Ada @code{out} or @code{in out}
+parameter of an elementary type @var{T}, is passed as a @code{@var{t}*}
+argument to a C function, where @var{t} is the C type corresponding to
+the Ada type @var{T}. In the case of an elementary @code{out} or
+@code{in out} parameter, a pointer to a temporary copy is used to
+preserve by-copy semantics.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada parameter of a record type @var{T}, of any mode, is passed as a
+@code{@var{t}*} argument to a C function, where @var{t} is the C
+structure corresponding to the Ada type @var{T}.
+@end cartouche
+Followed. This convention may be overridden by the use of the C_Pass_By_Copy
+pragma, or Convention, or by explicitly specifying the mechanism for a given
+call using an extended import or export pragma.
+
+@sp 1
+@cartouche
+An Ada parameter of an array type with component type @var{T}, of any
+mode, is passed as a @code{@var{t}*} argument to a C function, where
+@var{t} is the C type corresponding to the Ada type @var{T}.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada parameter of an access-to-subprogram type is passed as a pointer
+to a C function whose prototype corresponds to the designated
+subprogram's specification.
+@end cartouche
+Followed. 
+
+@cindex COBOL, interfacing with
+@item B.4(95-98): Interfacing with COBOL
+@sp 1
+@cartouche
+An Ada implementation should support the following interface
+correspondences between Ada and COBOL.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An Ada access @var{T} parameter is passed as a ``BY REFERENCE'' data item of
+the COBOL type corresponding to @var{T}.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+An Ada in scalar parameter is passed as a ``BY CONTENT'' data item of
+the corresponding COBOL type.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+Any other Ada parameter is passed as a ``BY REFERENCE'' data item of the
+COBOL type corresponding to the Ada parameter type; for scalars, a local
+copy is used if necessary to ensure by-copy semantics.
+@end cartouche
+Followed. 
+
+@cindex Fortran, interfacing with
+@item B.5(22-26): Interfacing with Fortran
+@sp 1
+@cartouche
+An Ada implementation should support the following interface
+correspondences between Ada and Fortran:
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An Ada procedure corresponds to a Fortran subroutine.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An Ada function corresponds to a Fortran function.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An Ada parameter of an elementary, array, or record type @var{T} is
+passed as a @var{T} argument to a Fortran procedure, where @var{T} is
+the Fortran type corresponding to the Ada type @var{T}, and where the
+INTENT attribute of the corresponding dummy argument matches the Ada
+formal parameter mode; the Fortran implementation's parameter passing
+conventions are used. For elementary types, a local copy is used if
+necessary to ensure by-copy semantics.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+An Ada parameter of an access-to-subprogram type is passed as a
+reference to a Fortran procedure whose interface corresponds to the
+designated subprogram's specification.
+@end cartouche
+Followed.
+
+@cindex Machine operations
+@item C.1(3-5): Access to Machine Operations
+@sp 1
+@cartouche
+The machine code or intrinsic support should allow access to all
+operations normally available to assembly language programmers for the
+target environment, including privileged instructions, if any.
+@end cartouche
+Followed.
+
+@sp 1
+@cartouche
+The interfacing pragmas (see Annex B) should support interface to
+assembler; the default assembler should be associated with the
+convention identifier @code{Assembler}.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+If an entity is exported to assembly language, then the implementation
+should allocate it at an addressable location, and should ensure that it
+is retained by the linking process, even if not otherwise referenced
+from the Ada code. The implementation should assume that any call to a
+machine code or assembler subprogram is allowed to read or update every
+object that is specified as exported.
+@end cartouche
+Followed. 
+
+@item C.1(10-16): Access to Machine Operations
+@sp 1
+@cartouche
+The implementation should ensure that little or no overhead is
+associated with calling intrinsic and machine-code subprograms.
+@end cartouche
+Followed for both intrinsics and machine-code subprograms.
+
+@sp 1
+@cartouche
+It is recommended that intrinsic subprograms be provided for convenient
+access to any machine operations that provide special capabilities or
+efficiency and that are not otherwise available through the language
+constructs.
+@end cartouche
+Followed. A full set of machine operation intrinsic subprograms is provided.
+
+@sp 1
+@cartouche
+Atomic read-modify-write operations -- e.g., test and set, compare and
+swap, decrement and test, enqueue/dequeue.
+@end cartouche
+Followed on any target supporting such operations.
+
+@sp 1
+@cartouche
+Standard numeric functions -- e.g., sin, log.
+@end cartouche
+Followed on any target supporting such operations.
+
+@sp 1
+@cartouche
+String manipulation operations -- e.g., translate and test.
+@end cartouche
+Followed on any target supporting such operations.
+
+@sp 1
+@cartouche
+Vector operations -- e.g., compare vector against thresholds.
+@end cartouche
+Followed on any target supporting such operations.
+
+@sp 1
+@cartouche
+Direct operations on I/O ports.
+@end cartouche
+Followed on any target supporting such operations.
+
+@cindex Interrupt support
+@item C.3(28): Interrupt Support
+@sp 1
+@cartouche
+If the @code{Ceiling_Locking} policy is not in effect, the
+implementation should provide means for the application to specify which
+interrupts are to be blocked during protected actions, if the underlying
+system allows for a finer-grain control of interrupt blocking.
+@end cartouche
+Followed. The underlying system does not allow for finer-grain control
+of interrupt blocking.
+
+@cindex Protected procedure handlers
+@item C.3.1(20-21): Protected Procedure Handlers
+@sp 1
+@cartouche
+Whenever possible, the implementation should allow interrupt handlers to
+be called directly by the hardware.
+@end cartouche
+@c SGI info:
+@ignore
+This is never possible under IRIX, so this is followed by default. 
+@end ignore
+Followed on any target where the underlying operating system permits
+such direct calls.
+
+@sp 1
+@cartouche
+Whenever practical, violations of any
+implementation-defined restrictions should be detected before run time.
+@end cartouche
+Followed. Compile time warnings are given when possible. 
+
+@cindex Package @code{Interrupts}
+@findex Interrupts
+@item C.3.2(25): Package @code{Interrupts}
+
+@sp 1
+@cartouche
+If implementation-defined forms of interrupt handler procedures are
+supported, such as protected procedures with parameters, then for each
+such form of a handler, a type analogous to @code{Parameterless_Handler}
+should be specified in a child package of @code{Interrupts}, with the
+same operations as in the predefined package Interrupts.
+@end cartouche
+Followed. 
+
+@cindex Pre-elaboration requirements
+@item C.4(14): Pre-elaboration Requirements
+@sp 1
+@cartouche
+It is recommended that pre-elaborated packages be implemented in such a
+way that there should be little or no code executed at run time for the
+elaboration of entities not already covered by the Implementation
+Requirements.
+@end cartouche
+Followed. Executable code is generated in some cases, e.g. loops
+to initialize large arrays.
+
+@item C.5(8): Pragma @code{Discard_Names}
+
+@sp 1
+@cartouche
+If the pragma applies to an entity, then the implementation should
+reduce the amount of storage used for storing names associated with that
+entity.
+@end cartouche
+Followed.
+
+@cindex Package @code{Task_Attributes}
+@findex Task_Attributes
+@item C.7.2(30): The Package Task_Attributes
+@sp 1
+@cartouche
+Some implementations are targeted to domains in which memory use at run
+time must be completely deterministic. For such implementations, it is
+recommended that the storage for task attributes will be pre-allocated
+statically and not from the heap. This can be accomplished by either
+placing restrictions on the number and the size of the task's
+attributes, or by using the pre-allocated storage for the first @var{N}
+attribute objects, and the heap for the others. In the latter case,
+@var{N} should be documented.
+@end cartouche
+Not followed. This implementation is not targeted to such a domain. 
+
+@cindex Locking Policies
+@item D.3(17): Locking Policies
+
+@sp 1
+@cartouche
+The implementation should use names that end with @samp{_Locking} for
+locking policies defined by the implementation.
+@end cartouche
+Followed. A single implementation-defined locking policy is defined,
+whose name (@code{Inheritance_Locking}) follows this suggestion.
+
+@cindex Entry queuing policies
+@item D.4(16): Entry Queuing Policies
+@sp 1
+@cartouche
+Names that end with @samp{_Queuing} should be used
+for all implementation-defined queuing policies.
+@end cartouche
+Followed. No such implementation-defined queueing policies exist. 
+
+@cindex Preemptive abort
+@item D.6(9-10): Preemptive Abort
+@sp 1
+@cartouche
+Even though the @code{abort_statement} is included in the list of
+potentially blocking operations (see 9.5.1), it is recommended that this
+statement be implemented in a way that never requires the task executing
+the @code{abort_statement} to block.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+On a multi-processor, the delay associated with aborting a task on
+another processor should be bounded; the implementation should use
+periodic polling, if necessary, to achieve this.
+@end cartouche
+Followed. 
+
+@cindex Tasking restrictions
+@item D.7(21): Tasking Restrictions
+@sp 1
+@cartouche
+When feasible, the implementation should take advantage of the specified
+restrictions to produce a more efficient implementation.
+@end cartouche
+GNAT currently takes advantage of these restrictions by providing an optimized
+run time when the Ravenscar profile and the GNAT restricted run time set
+of restrictions are specified. See pragma @code{Ravenscar} and pragma
+@code{Restricted_Run_Time} for more details.
+
+@cindex Time, monotonic
+@item D.8(47-49): Monotonic Time
+@sp 1
+@cartouche
+When appropriate, implementations should provide configuration
+mechanisms to change the value of @code{Tick}.
+@end cartouche
+Such configuration mechanisms are not appropriate to this implementation
+and are thus not supported.
+
+@sp 1
+@cartouche
+It is recommended that @code{Calendar.Clock} and @code{Real_Time.Clock}
+be implemented as transformations of the same time base.
+@end cartouche
+Followed. 
+
+@sp 1
+@cartouche
+It is recommended that the @dfn{best} time base which exists in
+the underlying system be available to the application through
+@code{Clock}. @dfn{Best} may mean highest accuracy or largest range.
+@end cartouche
+Followed. 
+
+@cindex Partition communication subsystem
+@cindex PCS
+@item E.5(28-29): Partition Communication Subsystem
+@sp 1
+@cartouche
+Whenever possible, the PCS on the called partition should allow for
+multiple tasks to call the RPC-receiver with different messages and
+should allow them to block until the corresponding subprogram body
+returns.
+@end cartouche
+Followed by GLADE, a separately supplied PCS that can be used with
+GNAT. For information on GLADE, contact Ada Core Technologies.
+
+@sp 1
+@cartouche
+The @code{Write} operation on a stream of type @code{Params_Stream_Type}
+should raise @code{Storage_Error} if it runs out of space trying to
+write the @code{Item} into the stream.
+@end cartouche
+Followed by GLADE, a separately supplied PCS that can be used with
+GNAT. For information on GLADE, contact Ada Core Technologies.
+
+@cindex COBOL support
+@item F(7): COBOL Support
+@sp 1
+@cartouche
+If COBOL (respectively, C) is widely supported in the target
+environment, implementations supporting the Information Systems Annex
+should provide the child package @code{Interfaces.COBOL} (respectively,
+@code{Interfaces.C}) specified in Annex B and should support a
+@code{convention_identifier} of COBOL (respectively, C) in the interfacing
+pragmas (see Annex B), thus allowing Ada programs to interface with
+programs written in that language.
+@end cartouche
+Followed. 
+
+@cindex Decimal radix support
+@item F.1(2): Decimal Radix Support
+@sp 1
+@cartouche
+Packed decimal should be used as the internal representation for objects
+of subtype @var{S} when @var{S}'Machine_Radix = 10.
+@end cartouche
+Not followed. GNAT ignores @var{S}'Machine_Radix and always uses binary
+representations.
+
+@cindex Numerics
+@item G: Numerics
+@sp 2
+@cartouche
+If Fortran (respectively, C) is widely supported in the target
+environment, implementations supporting the Numerics Annex
+should provide the child package @code{Interfaces.Fortran} (respectively,
+@code{Interfaces.C}) specified in Annex B and should support a
+@code{convention_identifier} of Fortran (respectively, C) in the interfacing
+pragmas (see Annex B), thus allowing Ada programs to interface with
+programs written in that language.
+@end cartouche
+Followed.
+
+@cindex Complex types
+@item G.1.1(56-58): Complex Types
+@sp 2
+@cartouche
+Because the usual mathematical meaning of multiplication of a complex
+operand and a real operand is that of the scaling of both components of
+the former by the latter, an implementation should not perform this
+operation by first promoting the real operand to complex type and then
+performing a full complex multiplication. In systems that, in the
+future, support an Ada binding to IEC 559:1989, the latter technique
+will not generate the required result when one of the components of the
+complex operand is infinite. (Explicit multiplication of the infinite
+component by the zero component obtained during promotion yields a NaN
+that propagates into the final result.) Analogous advice applies in the
+case of multiplication of a complex operand and a pure-imaginary
+operand, and in the case of division of a complex operand by a real or
+pure-imaginary operand.
+@end cartouche
+Not followed. 
+
+@sp 1
+@cartouche
+Similarly, because the usual mathematical meaning of addition of a
+complex operand and a real operand is that the imaginary operand remains
+unchanged, an implementation should not perform this operation by first
+promoting the real operand to complex type and then performing a full
+complex addition. In implementations in which the @code{Signed_Zeros}
+attribute of the component type is @code{True} (and which therefore
+conform to IEC 559:1989 in regard to the handling of the sign of zero in
+predefined arithmetic operations), the latter technique will not
+generate the required result when the imaginary component of the complex
+operand is a negatively signed zero. (Explicit addition of the negative
+zero to the zero obtained during promotion yields a positive zero.)
+Analogous advice applies in the case of addition of a complex operand
+and a pure-imaginary operand, and in the case of subtraction of a
+complex operand and a real or pure-imaginary operand.
+@end cartouche
+Not followed. 
+
+@sp 1
+@cartouche
+Implementations in which @code{Real'Signed_Zeros} is @code{True} should
+attempt to provide a rational treatment of the signs of zero results and
+result components. As one example, the result of the @code{Argument}
+function should have the sign of the imaginary component of the
+parameter @code{X} when the point represented by that parameter lies on
+the positive real axis; as another, the sign of the imaginary component
+of the @code{Compose_From_Polar} function should be the same as
+(respectively, the opposite of) that of the @code{Argument} parameter when that
+parameter has a value of zero and the @code{Modulus} parameter has a
+nonnegative (respectively, negative) value.
+@end cartouche
+Followed. 
+
+@cindex Complex elementary functions
+@item G.1.2(49): Complex Elementary Functions
+@sp 1
+@cartouche
+Implementations in which @code{Complex_Types.Real'Signed_Zeros} is
+@code{True} should attempt to provide a rational treatment of the signs
+of zero results and result components. For example, many of the complex
+elementary functions have components that are odd functions of one of
+the parameter components; in these cases, the result component should
+have the sign of the parameter component at the origin. Other complex
+elementary functions have zero components whose sign is opposite that of
+a parameter component at the origin, or is always positive or always
+negative.
+@end cartouche
+Followed. 
+
+@cindex Accuracy requirements
+@item G.2.4(19): Accuracy Requirements
+@sp 1
+@cartouche
+The versions of the forward trigonometric functions without a
+@code{Cycle} parameter should not be implemented by calling the
+corresponding version with a @code{Cycle} parameter of
+@code{2.0*Numerics.Pi}, since this will not provide the required
+accuracy in some portions of the domain. For the same reason, the
+version of @code{Log} without a @code{Base} parameter should not be
+implemented by calling the corresponding version with a @code{Base}
+parameter of @code{Numerics.e}.
+@end cartouche
+Followed. 
+
+@cindex Complex arithmetic accuracy
+@cindex Accuracy, complex arithmetic
+@item G.2.6(15): Complex Arithmetic Accuracy
+
+@sp 1
+@cartouche
+The version of the @code{Compose_From_Polar} function without a
+@code{Cycle} parameter should not be implemented by calling the
+corresponding version with a @code{Cycle} parameter of
+@code{2.0*Numerics.Pi}, since this will not provide the required
+accuracy in some portions of the domain.
+@end cartouche
+Followed.
+
+@end table
+@node Implementation Defined Characteristics
+@chapter Implementation Defined Characteristics
+In addition to the implementation dependent pragmas and attributes, and
+the implementation advice, there are a number of other features of Ada
+95 that are potentially implementation dependent. These are mentioned
+throughout the Ada 95 Reference Manual, and are summarized in annex M.
+
+A requirement for conforming Ada compilers is that they provide
+documentation describing how the implementation deals with each of these
+issues. In this chapter, you will find each point in annex M listed
+followed by a description in italic font of how GNAT
+@c SGI info:
+@ignore
+in the ProDev Ada
+implementation on IRIX 5.3 operating system or greater 
+@end ignore
+handles the implementation dependence.
+
+You can use this chapter as a guide to minimizing implementation
+dependent features in your programs if portability to other compilers
+and other operating systems is an important consideration.  The numbers
+in each section below correspond to the paragraph number in the Ada 95
+Reference Manual.
+
+@sp 1
+@cartouche
+@noindent
+@strong{2}.  Whether or not each recommendation given in Implementation
+Advice is followed. See 1.1.2(37).
+@end cartouche
+@noindent
+@xref{Implementation Advice}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{3}.  Capacity limitations of the implementation. See 1.1.3(3).
+@end cartouche
+@noindent
+The complexity of programs that can be processed is limited only by the
+total amount of available virtual memory, and disk space for the
+generated object files.
+
+@sp 1
+@cartouche
+@noindent
+@strong{4}.  Variations from the standard that are impractical to avoid
+given the implementation's execution environment. See 1.1.3(6).
+@end cartouche
+@noindent
+There are no variations from the standard.
+
+@sp 1
+@cartouche
+@noindent
+@strong{5}.  Which @code{code_statement}s cause external
+interactions. See 1.1.3(10).
+@end cartouche
+@noindent
+Any @code{code_statement} can potentially cause external interactions.
+
+@sp 1
+@cartouche
+@noindent
+@strong{6}.  The coded representation for the text of an Ada
+program. See 2.1(4).
+@end cartouche
+@noindent
+See separate section on source representation.
+
+@sp 1
+@cartouche
+@noindent
+@strong{7}.  The control functions allowed in comments. See 2.1(14).
+@end cartouche
+@noindent
+See separate section on source representation.
+
+@sp 1
+@cartouche
+@noindent
+@strong{8}.  The representation for an end of line. See 2.2(2).
+@end cartouche
+@noindent
+See separate section on source representation.
+
+@sp 1
+@cartouche
+@noindent
+@strong{9}.  Maximum supported line length and lexical element
+length. See 2.2(15).
+@end cartouche
+@noindent
+The maximum line length is 255 characters an the maximum length of a
+lexical element is also 255 characters.
+
+@sp 1
+@cartouche
+@noindent
+@strong{10}.  Implementation defined pragmas. See 2.8(14).
+@end cartouche
+@noindent
+
+@xref{Implementation Defined Pragmas}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{11}.  Effect of pragma @code{Optimize}. See 2.8(27).
+@end cartouche
+@noindent
+Pragma @code{Optimize}, if given with a @code{Time} or @code{Space}
+parameter, checks that the optimization flag is set, and aborts if it is
+not.
+
+@sp 1
+@cartouche
+@noindent
+@strong{12}.  The sequence of characters of the value returned by
+@code{@var{S}'Image} when some of the graphic characters of
+@code{@var{S}'Wide_Image} are not defined in @code{Character}. See
+3.5(37).
+@end cartouche
+@noindent
+The sequence of characters is as defined by the wide character encoding
+method used for the source. See section on source representation for
+further details.
+
+@sp 1
+@cartouche
+@noindent
+@strong{13}.  The predefined integer types declared in
+@code{Standard}. See 3.5.4(25).
+@end cartouche
+@noindent
+@table @code
+@item Short_Short_Integer
+8 bit signed
+@item Short_Integer
+(Short) 16 bit signed
+@item Integer
+32 bit signed
+@item Long_Integer
+64 bit signed (Alpha OpenVMS only)
+32 bit signed (all other targets)
+@item Long_Long_Integer
+64 bit signed
+@end table
+
+@sp 1
+@cartouche
+@noindent
+@strong{14}.  Any nonstandard integer types and the operators defined
+for them. See 3.5.4(26).
+@end cartouche
+@noindent
+There are no nonstandard integer types. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{15}.  Any nonstandard real types and the operators defined for
+them. See 3.5.6(8).
+@end cartouche
+@noindent
+There are no nonstandard real types. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{16}.  What combinations of requested decimal precision and range
+are supported for floating point types. See 3.5.7(7).
+@end cartouche
+@noindent
+The precision and range is as defined by the IEEE standard. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{17}.  The predefined floating point types declared in
+@code{Standard}. See 3.5.7(16).
+@end cartouche
+@noindent
+@table @code
+@item Short_Float 
+32 bit IEEE short
+@item Float 
+(Short) 32 bit IEEE short 
+@item Long_Float 
+64 bit IEEE long 
+@item Long_Long_Float 
+64 bit IEEE long (80 bit IEEE long on x86 processors)
+@end table
+
+@sp 1
+@cartouche
+@noindent
+@strong{18}.  The small of an ordinary fixed point type. See 3.5.9(8).
+@end cartouche
+@noindent
+@code{Fine_Delta} is 2**(-63) 
+
+@sp 1
+@cartouche
+@noindent
+@strong{19}.  What combinations of small, range, and digits are
+supported for fixed point types. See 3.5.9(10).
+@end cartouche
+@noindent
+Any combinations are permitted that do not result in a small less than
+@code{Fine_Delta} and do not result in a mantissa larger than 63 bits.
+If the mantissa is larger than 53 bits on machines where Long_Long_Float
+is 64 bits (true of all architectures except ia32), then the output from
+Text_IO is accurate to only 53 bits, rather than the full mantissa. This
+is because floating-point conversions are used to convert fixed point.
+
+@sp 1
+@cartouche
+@noindent
+@strong{20}.  The result of @code{Tags.Expanded_Name} for types declared
+within an unnamed @code{block_statement}. See 3.9(10).
+@end cartouche
+@noindent
+Block numbers of the form @code{B@var{nnn}}, where @var{nnn} is a
+decimal integer are allocated.
+
+@sp 1
+@cartouche
+@noindent
+@strong{21}.  Implementation-defined attributes. See 4.1.4(12).
+@end cartouche
+@noindent
+@xref{Implementation Defined Attributes}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{22}.  Any implementation-defined time types. See 9.6(6).
+@end cartouche
+@noindent
+There are no implementation-defined time types. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{23}.  The time base associated with relative delays.
+@end cartouche
+@noindent
+See 9.6(20). The time base used is that provided by the C library
+function @code{gettimeofday}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{24}.  The time base of the type @code{Calendar.Time}. See
+9.6(23).
+@end cartouche
+@noindent
+The time base used is that provided by the C library function
+@code{gettimeofday}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{25}.  The time zone used for package @code{Calendar}
+operations. See 9.6(24).
+@end cartouche
+@noindent
+The time zone used by package @code{Calendar} is the current system time zone
+setting for local time, as accessed by the C library function
+@code{localtime}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{26}.  Any limit on @code{delay_until_statements} of
+@code{select_statements}. See 9.6(29).
+@end cartouche
+@noindent
+There are no such limits. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{27}.  Whether or not two non overlapping parts of a composite
+object are independently addressable, in the case where packing, record
+layout, or @code{Component_Size} is specified for the object. See
+9.10(1).
+@end cartouche
+@noindent
+Separate components are independently addressable if they do not share
+overlapping storage units.
+
+@sp 1
+@cartouche
+@noindent
+@strong{28}.  The representation for a compilation. See 10.1(2).
+@end cartouche
+@noindent
+A compilation is represented by a sequence of files presented to the
+compiler in a single invocation of the @file{gcc} command.
+
+@sp 1
+@cartouche
+@noindent
+@strong{29}.  Any restrictions on compilations that contain multiple
+compilation_units. See 10.1(4).
+@end cartouche
+@noindent
+No single file can contain more than one compilation unit, but any
+sequence of files can be presented to the compiler as a single
+compilation.
+
+@sp 1
+@cartouche
+@noindent
+@strong{30}.  The mechanisms for creating an environment and for adding
+and replacing compilation units. See 10.1.4(3).
+@end cartouche
+@noindent
+See separate section on compilation model. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{31}.  The manner of explicitly assigning library units to a
+partition. See 10.2(2).
+@end cartouche
+@noindent
+If a unit contains an Ada main program, then the Ada units for the partition
+are determined by recursive application of the rules in the Ada Reference
+Manual section 10.2(2-6). In other words, the Ada units will be those that
+are needed by the main program, and then this definition of need is applied
+recursively to those units, and the partition contains the transitive
+closure determined by this relationship. In short, all the necessary units
+are included, with no need to explicitly specify the list. If additional
+units are required, e.g. by foreign language units, then all units must be
+mentioned in the context clause of one of the needed Ada units.
+
+If the partition contains no main program, or if the main program is in
+a language other than Ada, then GNAT 
+provides the binder options -z and -n respectively, and in this case a
+list of units can be explicitly supplied to the binder for inclusion in
+the partition (all units needed by these units will also be included
+automatically). For full details on the use of these options, refer to
+the User Guide sections on Binding and Linking.
+
+@sp 1
+@cartouche
+@noindent
+@strong{32}.  The implementation-defined means, if any, of specifying
+which compilation units are needed by a given compilation unit. See
+10.2(2).
+@end cartouche
+@noindent
+The units needed by a given compilation unit are as defined in
+the Ada Reference Manual section 10.2(2-6). There are no 
+implementation-defined pragmas or other implementation-defined
+means for specifying needed units.
+
+@sp 1
+@cartouche
+@noindent
+@strong{33}.  The manner of designating the main subprogram of a
+partition. See 10.2(7).
+@end cartouche
+@noindent
+The main program is designated by providing the name of the
+corresponding ali file as the input parameter to the binder.
+
+@sp 1
+@cartouche
+@noindent
+@strong{34}.  The order of elaboration of @code{library_items}. See
+10.2(18).
+@end cartouche
+@noindent
+The first constraint on ordering is that it meets the requirements of
+chapter 10 of the Ada 95 Reference Manual. This still leaves some
+implementation dependent choices, which are resolved by first
+elaborating bodies as early as possible (i.e. in preference to specs
+where there is a choice), and second by evaluating the immediate with
+clauses of a unit to determine the probably best choice, and
+third by elaborating in alphabetical order of unit names
+where a choice still remains.
+
+@sp 1
+@cartouche
+@noindent
+@strong{35}.  Parameter passing and function return for the main
+subprogram. See 10.2(21).
+@end cartouche
+@noindent
+The main program has no parameters. It may be a procedure, or a function
+returning an integer type. In the latter case, the returned integer
+value is the return code of the program.
+
+@sp 1
+@cartouche
+@noindent
+@strong{36}.  The mechanisms for building and running partitions. See
+10.2(24).
+@end cartouche
+@noindent
+GNAT itself supports programs with only a single partition. The GNATDIST
+tool provided with the GLADE package (which also includes an implementation
+of the PCS) provides a completely flexible method for building and running
+programs consisting of multiple partitions. See the separate GLADE manual
+for details.
+
+@sp 1
+@cartouche
+@noindent
+@strong{37}.  The details of program execution, including program
+termination. See 10.2(25).
+@end cartouche
+@noindent
+See separate section on compilation model.
+
+@sp 1
+@cartouche
+@noindent
+@strong{38}.  The semantics of any non-active partitions supported by the
+implementation. See 10.2(28).
+@end cartouche
+@noindent
+Passive partitions are supported on targets where shared memory is
+provided by the operating system. See the GLADE reference manual for
+further details.
+
+@sp 1
+@cartouche
+@noindent
+@strong{39}.  The information returned by @code{Exception_Message}. See
+11.4.1(10).
+@end cartouche
+@noindent
+Exception message returns the null string unless a specific message has
+been passed by the program.
+
+@sp 1
+@cartouche
+@noindent
+@strong{40}.  The result of @code{Exceptions.Exception_Name} for types
+declared within an unnamed @code{block_statement}. See 11.4.1(12).
+@end cartouche
+@noindent
+Blocks have implementation defined names of the form @code{B@var{nnn}}
+where @var{nnn} is an integer.
+
+@sp 1
+@cartouche
+@noindent
+@strong{41}.  The information returned by
+@code{Exception_Information}. See 11.4.1(13).
+@end cartouche
+@noindent
+@code{Exception_Information} contains the expanded name of the exception
+in upper case, and no other information.
+
+@sp 1
+@cartouche
+@noindent
+@strong{42}.  Implementation-defined check names. See 11.5(27).
+@end cartouche
+@noindent
+No implementation-defined check names are supported. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{43}.  The interpretation of each aspect of representation. See
+13.1(20).
+@end cartouche
+@noindent
+See separate section on data representations.
+
+@sp 1
+@cartouche
+@noindent
+@strong{44}.  Any restrictions placed upon representation items. See
+13.1(20).
+@end cartouche
+@noindent
+See separate section on data representations.
+
+@sp 1
+@cartouche
+@noindent
+@strong{45}.  The meaning of @code{Size} for indefinite subtypes. See
+13.3(48).
+@end cartouche
+@noindent
+Size for an indefinite subtype is the maximum possible size, except that
+for the case of a subprogram parameter, the size of the parameter object
+is the actual size.
+
+@sp 1
+@cartouche
+@noindent
+@strong{46}.  The default external representation for a type tag. See
+13.3(75).
+@end cartouche
+@noindent
+The default external representation for a type tag is the fully expanded
+name of the type in upper case letters.
+
+@sp 1
+@cartouche
+@noindent
+@strong{47}.  What determines whether a compilation unit is the same in
+two different partitions. See 13.3(76).
+@end cartouche
+@noindent
+A compilation unit is the same in two different partitions if and only
+if it derives from the same source file.
+
+@sp 1
+@cartouche
+@noindent
+@strong{48}.  Implementation-defined components. See 13.5.1(15).
+@end cartouche
+@noindent
+The only implementation defined component is the tag for a tagged type,
+which contains a pointer to the dispatching table.
+
+@sp 1
+@cartouche
+@noindent
+@strong{49}.  If @code{Word_Size} = @code{Storage_Unit}, the default bit
+ordering. See 13.5.3(5).
+@end cartouche
+@noindent
+@code{Word_Size} (32) is not the same as @code{Storage_Unit} (8) for this
+implementation, so no non-default bit ordering is supported. The default
+bit ordering corresponds to the natural endianness of the target architecture.
+
+@sp 1
+@cartouche
+@noindent
+@strong{50}.  The contents of the visible part of package @code{System}
+and its language-defined children. See 13.7(2).
+@end cartouche
+@noindent
+See the definition of these packages in files @file{system.ads} and
+@file{s-stoele.ads}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{51}.  The contents of the visible part of package
+@code{System.Machine_Code}, and the meaning of
+@code{code_statements}. See 13.8(7).
+@end cartouche
+@noindent
+See the definition and documentation in file @file{s-maccod.ads}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{52}.  The effect of unchecked conversion. See 13.9(11).
+@end cartouche
+@noindent
+Unchecked conversion between types of the same size
+and results in an uninterpreted transmission of the bits from one type
+to the other. If the types are of unequal sizes, then in the case of
+discrete types, a shorter source is first zero or sign extended as
+necessary, and a shorter target is simply truncated on the left.
+For all non-discrete types, the source is first copied if necessary
+to ensure that the alignment requirements of the target are met, then
+a pointer is constructed to the source value, and the result is obtained
+by dereferencing this pointer after converting it to be a pointer to the
+target type.
+
+@sp 1
+@cartouche
+@noindent
+@strong{53}.  The manner of choosing a storage pool for an access type
+when @code{Storage_Pool} is not specified for the type. See 13.11(17).
+@end cartouche
+@noindent
+There are 3 different standard pools used by the compiler when
+@code{Storage_Pool} is not specified depending whether the type is local
+to a subprogram or defined at the library level and whether
+@code{Storage_Size}is specified or not. See documentation in the runtime
+library units @code{System.Pool_Global}, @code{System.Pool_Size} and
+@code{System.Pool_Local} in files @file{s-poosiz.ads},
+@file{s-pooglo.ads} and @file{s-pooloc.ads} for full details on the
+default pools used.
+
+@sp 1
+@cartouche
+@noindent
+@strong{54}.  Whether or not the implementation provides user-accessible
+names for the standard pool type(s). See 13.11(17).
+@end cartouche
+@noindent
+
+See documentation in the sources of the run time mentioned in paragraph
+@strong{53} . All these pools are accessible by means of @code{with}'ing
+these units.
+
+@sp 1
+@cartouche
+@noindent
+@strong{55}.  The meaning of @code{Storage_Size}. See 13.11(18).
+@end cartouche
+@noindent
+@code{Storage_Size} is measured in storage units, and refers to the
+total space available for an access type collection, or to the primary
+stack space for a task.
+
+@sp 1
+@cartouche
+@noindent
+@strong{56}.  Implementation-defined aspects of storage pools. See
+13.11(22).
+@end cartouche
+@noindent
+See documentation in the sources of the run time mentioned in paragraph
+@strong{53} for details on GNAT-defined aspects of storage pools.
+
+@sp 1
+@cartouche
+@noindent
+@strong{57}.  The set of restrictions allowed in a pragma
+@code{Restrictions}. See 13.12(7).
+@end cartouche
+@noindent
+All RM defined Restriction identifiers are implemented. The following
+additional restriction identifiers are provided. There are two separate
+lists of implementation dependent restriction identifiers. The first
+set requires consistency throughout a partition (in other words, if the
+restriction identifier is used for any compilation unit in the partition,
+then all compilation units in the partition must obey the restriction.
+
+@table @code
+
+@item Boolean_Entry_Barriers
+@findex Boolean_Entry_Barriers
+This restriction ensures at compile time that barriers in entry declarations
+for protected types are restricted to references to simple boolean variables
+defined in the private part of the protected type. No other form of entry
+barriers is permitted. This is one of the restrictions of the Ravenscar
+profile for limited tasking (see also pragma Ravenscar).
+
+@item Max_Entry_Queue_Depth => Expr
+@findex Max_Entry_Queue_Depth
+This restriction is a declaration that any protected entry compiled in
+the scope of the restriction has at most the specified number of
+tasks waiting on the entry
+at any one time, and so no queue is required. This restriction is not
+checked at compile time. A program execution is erroneous if an attempt
+is made to queue more than the specified number of tasks on such an entry.
+
+@item No_Calendar
+@findex No_Calendar
+This restriction ensures at compile time that there is no implicit or
+explicit dependence on the package @code{Ada.Calendar}.
+
+@item No_Dynamic_Interrupts
+@findex No_Dynamic_Interrupts
+This restriction ensures at compile time that there is no attempt to
+dynamically associate interrupts. Only static association is allowed.
+
+@item No_Enumeration_Maps
+@findex No_Enumeration_Maps
+This restriction ensures at compile time that no operations requiring
+enumeration maps are used (that is Image and Value attributes applied
+to enumeration types).
+
+@item No_Entry_Calls_In_Elaboration_Code
+@findex No_Entry_Calls_In_Elaboration_Code
+This restriction ensures at compile time that no task or protected entry
+calls are made during elaboration code. As a result of the use of this
+restriction, the compiler can assume that no code past an accept statement
+in a task can be executed at elaboration time.
+
+@item No_Exception_Handlers
+@findex No_Exception_Handlers
+This restriction ensures at compile time that there are no explicit
+exception handlers.
+
+@item No_Implicit_Conditionals
+@findex No_Implicit_Conditionals
+This restriction ensures that the generated code does not contain any
+implicit conditionals, either by modifying the generated code where possible,
+or by rejecting any construct that would otherwise generate an implicit
+conditional. The details and use of this restriction are described in
+more detail in the High Integrity product documentation.
+
+@item No_Implicit_Loops
+@findex No_Implicit_Loops
+This restriction ensures that the generated code does not contain any
+implicit @code{for} loops, either by modifying
+the generated code where possible,
+or by rejecting any construct that would otherwise generate an implicit
+@code{for} loop. The details and use of this restriction are described in
+more detail in the GNORT Reference Manual.
+
+@item No_Local_Protected_Objects
+@findex No_Local_Protected_Objects
+This restriction ensures at compile time that protected objects are
+only declared at the library level.
+
+@item No_Protected_Type_Allocators
+@findex No_Protected_Type_Allocators
+This restriction ensures at compile time that there are no allocator
+expressions that attempt to allocate protected objects.
+
+@item No_Select_Statements
+@findex No_Select_Statements
+This restriction ensures at compile time no select statements of any kind
+are permitted, that is the keyword @code{select} may not appear. 
+This is one of the restrictions of the Ravenscar
+profile for limited tasking (see also pragma Ravenscar).
+
+@item No_Standard_Storage_Pools
+@findex No_Standard_Storage_Pools
+This restriction ensures at compile time that no access types
+use the standard default storage pool. Any access type declared must
+have an explicit Storage_Pool attribute defined specifying a
+user-defined storage pool.
+
+@item No_Streams
+@findex No_Streams
+This restriction ensures at compile time that there are no implicit or
+explicit dependencies on the package @code{Ada.Streams}.
+
+@item No_Task_Attributes
+@findex No_Task_Attributes
+This restriction ensures at compile time that there are no implicit or
+explicit dependencies on the package @code{Ada.Task_Attributes}.
+
+@item No_Task_Termination
+@findex No_Task_Termination
+This restriction ensures at compile time that no terminate alternatives
+appear in any task body.
+
+@item No_Wide_Characters
+@findex No_Wide_Characters
+This restriction ensures at compile time that no uses of the types
+@code{Wide_Character} or @code{Wide_String}
+appear, and that no wide character literals
+appear in the program (that is literals representing characters not in
+type @code{Character}.
+
+@item Static_Priorities
+@findex Static_Priorities
+This restriction ensures at compile time that all priority expressions
+are static, and that there are no dependencies on the package
+@code{Ada.Dynamic_Priorities}.
+
+@item Static_Storage_Size
+@findex Static_Storage_Size
+This restriction ensures at compile time that any expression appearing
+in a Storage_Size pragma or attribute definition clause is static.
+
+@end table
+
+@noindent
+The second set of implementation dependent restriction identifiers
+does not require partition-wide consistency.
+The restriction may be enforced for a single
+compilation unit without any effect on any of the
+other compilation units in the partition.
+
+@table @code
+
+@item No_Elaboration_Code
+@findex No_Elaboration_Code
+This restriction ensures at compile time that no elaboration code is
+generated. Note that this is not the same condition as is enforced
+by pragma Preelaborate. There are cases in which pragma Preelaborate
+still permits code to be generated (e.g. code to initialize a large
+array to all zeroes), and there are cases of units which do not meet
+the requirements for pragma Preelaborate, but for which no elaboration
+code is generated. Generally, it is the case that preelaborable units
+will meet the restrictions, with the exception of large aggregates
+initialized with an others_clause, and exception declarations (which
+generate calls to a run-time registry procedure). Note that this restriction
+is enforced on a unit by unit basis, it need not be obeyed consistently
+throughout a partition.
+
+@item No_Entry_Queue
+@findex No_Entry_Queue
+This restriction is a declaration that any protected entry compiled in
+the scope of the restriction has at most one task waiting on the entry
+at any one time, and so no queue is required. This restriction is not
+checked at compile time. A program execution is erroneous if an attempt
+is made to queue a second task on such an entry.
+
+@item No_Implementation_Attributes
+@findex No_Implementation_Attributes
+This restriction checks at compile time that no GNAT-defined attributes
+are present. With this restriction, the only attributes that can be used
+are those defined in the Ada 95 Reference Manual.
+
+@item No_Implementation_Pragmas
+@findex No_Implementation_Pragmas
+This restriction checks at compile time that no GNAT-defined pragmas
+are present. With this restriction, the only pragmas that can be used
+are those defined in the Ada 95 Reference Manual.
+
+@item No_Implementation_Restrictions
+@findex No_Implementation_Restrictions
+This restriction checks at compile time that no GNAT-defined restriction
+identifiers (other than @code{No_Implementation_Restrictions} itself)
+are present. With this restriction, the only other restriction identifiers
+that can be used are those defined in the Ada 95 Reference Manual.
+
+@end table
+
+@sp 1
+@cartouche
+@noindent
+@strong{58}.  The consequences of violating limitations on
+@code{Restrictions} pragmas. See 13.12(9).
+@end cartouche
+@noindent
+Restrictions that can be checked at compile time result in illegalities
+if violated. Currently there are no other consequences of violating
+restrictions.
+
+@sp 1
+@cartouche
+@noindent
+@strong{59}.  The representation used by the @code{Read} and
+@code{Write} attributes of elementary types in terms of stream
+elements. See 13.13.2(9).
+@end cartouche
+@noindent
+The representation is the in-memory representation of the base type of
+the type, using the number of bits corresponding to the
+@code{@var{type}'Size} value, and the natural ordering of the machine.
+
+@sp 1
+@cartouche
+@noindent
+@strong{60}.  The names and characteristics of the numeric subtypes
+declared in the visible part of package @code{Standard}. See A.1(3).
+@end cartouche
+@noindent
+See items describing the integer and floating-point types supported.
+
+@sp 1
+@cartouche
+@noindent
+@strong{61}.  The accuracy actually achieved by the elementary
+functions. See A.5.1(1).
+@end cartouche
+@noindent
+The elementary functions correspond to the functions available in the C
+library. Only fast math mode is implemented.
+
+@sp 1
+@cartouche
+@noindent
+@strong{62}.  The sign of a zero result from some of the operators or
+functions in @code{Numerics.Generic_Elementary_Functions}, when
+@code{Float_Type'Signed_Zeros} is @code{True}. See A.5.1(46).
+@end cartouche
+@noindent
+The sign of zeroes follows the requirements of the IEEE 754 standard on
+floating-point.
+
+@sp 1
+@cartouche
+@noindent
+@strong{63}.  The value of
+@code{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27).
+@end cartouche
+@noindent
+Maximum image width is 649, see library file @file{a-numran.ads}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{64}.  The value of
+@code{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27).
+@end cartouche
+@noindent
+Maximum image width is 80, see library file @file{a-nudira.ads}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{65}.  The algorithms for random number generation. See
+A.5.2(32).
+@end cartouche
+@noindent
+The algorithm is documented in the source files @file{a-numran.ads} and
+@file{a-numran.adb}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{66}.  The string representation of a random number generator's
+state. See A.5.2(38).
+@end cartouche
+@noindent
+See the documentation contained in the file @file{a-numran.adb}. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{67}.  The minimum time interval between calls to the
+time-dependent Reset procedure that are guaranteed to initiate different
+random number sequences. See A.5.2(45).
+@end cartouche
+@noindent
+The minimum period between reset calls to guarantee distinct series of
+random numbers is one microsecond.
+
+@sp 1
+@cartouche
+@noindent
+@strong{68}.  The values of the @code{Model_Mantissa},
+@code{Model_Emin}, @code{Model_Epsilon}, @code{Model},
+@code{Safe_First}, and @code{Safe_Last} attributes, if the Numerics
+Annex is not supported. See A.5.3(72).
+@end cartouche
+@noindent
+See the source file @file{ttypef.ads} for the values of all numeric
+attributes.
+
+@sp 1
+@cartouche
+@noindent
+@strong{69}.  Any implementation-defined characteristics of the
+input-output packages. See A.7(14).
+@end cartouche
+@noindent
+There are no special implementation defined characteristics for these
+packages.
+
+@sp 1
+@cartouche
+@noindent
+@strong{70}.  The value of @code{Buffer_Size} in @code{Storage_IO}. See
+A.9(10).
+@end cartouche
+@noindent
+All type representations are contiguous, and the @code{Buffer_Size} is
+the value of @code{@var{type}'Size} rounded up to the next storage unit
+boundary.
+
+@sp 1
+@cartouche
+@noindent
+@strong{71}.  External files for standard input, standard output, and
+standard error See A.10(5).
+@end cartouche
+@noindent
+These files are mapped onto the files provided by the C streams
+libraries. See source file @file{i-cstrea.ads} for further details.
+
+@sp 1
+@cartouche
+@noindent
+@strong{72}.  The accuracy of the value produced by @code{Put}. See
+A.10.9(36).
+@end cartouche
+@noindent
+If more digits are requested in the output than are represented by the
+precision of the value, zeroes are output in the corresponding least
+significant digit positions.
+
+@sp 1
+@cartouche
+@noindent
+@strong{73}.  The meaning of @code{Argument_Count}, @code{Argument}, and
+@code{Command_Name}. See A.15(1).
+@end cartouche
+@noindent
+These are mapped onto the @code{argv} and @code{argc} parameters of the
+main program in the natural manner.
+
+@sp 1
+@cartouche
+@noindent
+@strong{74}.  Implementation-defined convention names. See B.1(11).
+@end cartouche
+@noindent
+The following convention names are supported
+
+@table @code
+@item  Ada
+Ada
+@item Asm 
+Assembly language 
+@item Assembler 
+Assembly language 
+@item C
+C
+@item C_Pass_By_Copy
+Treated like C, except for record types
+@item COBOL 
+COBOL 
+@item CPP 
+C++ 
+@item Default
+Treated the same as C
+@item DLL
+DLL (used for Windows implementations only) is handled like the Stdcall
+convention. This convention is used to access variables and functions
+(with Stdcall convention) in a DLL.
+@item Win32
+Win32 (used for Windows implementations only) is handled like the Stdcall
+convention. This convention is used to access variables and functions
+(with Stdcall convention) in a DLL.
+@item External
+Treated the same as C
+@item Fortran 
+Fortran 
+@item Intrinsic 
+For support of pragma @code{Import} with convention Intrinsic, see
+separate section on Intrinsic Subprograms.
+@item Stdcall 
+Stdcall (used for Windows implementations only). This convention correspond
+to the WINAPI (previously called Pascal convention) C/C++ convention under
+Windows. A function with this convention clean the stack before exit.
+@item Stubbed
+Stubbed is a special convention used to indicate that the body of the
+subprogram will be entirely ignored. Any call to the subprogram
+is converted into a raise of the @code{Program_Error} exception. If a
+pragma @code{Import} specifies convention @code{stubbed} then no body need
+be present at all. This convention is useful during development for the
+inclusion of subprograms whose body has not yet been written.
+
+@end table
+@noindent
+In addition, all otherwise unrecognized convention names are also
+treated as being synonymous with convention C. In all implementations
+except for VMS, use of such other names results in a warning. In VMS
+implementations, these names are accepted silently.
+
+@sp 1
+@cartouche
+@noindent
+@strong{75}.  The meaning of link names. See B.1(36).
+@end cartouche
+@noindent
+Link names are the actual names used by the linker.
+
+@sp 1
+@cartouche
+@noindent
+@strong{76}.  The manner of choosing link names when neither the link
+name nor the address of an imported or exported entity is specified. See
+B.1(36).
+@end cartouche
+@noindent
+The default linker name is that which would be assigned by the relevant
+external language, interpreting the Ada name as being in all lower case
+letters.
+
+@sp 1
+@cartouche
+@noindent
+@strong{77}.  The effect of pragma @code{Linker_Options}. See B.1(37).
+@end cartouche
+@noindent
+The string passed to @code{Linker_Options} is presented uninterpreted as
+an argument to the link command, unless it contains Ascii.NUL characters.
+NUL characters if they appear act as argument separators, so for example
+
+@smallexample
+pragma Linker_Options ("-labc" & ASCII.Nul & "-ldef");
+@end smallexample
+
+@noindent
+causes two separate arguments "-labc" and "-ldef" to be passed to the
+linker with a guarantee that the order is preserved (no such guarantee
+exists for the use of separate Linker_Options pragmas).
+
+In addition, GNAT allow multiple arguments to @code{Linker_Options}
+with exactly the same meaning, so the above pragma could also be
+written as:
+
+@smallexample
+pragma Linker_Options ("-labc", "-ldef");
+@end smallexample
+
+@noindent
+The above multiple argument form is a GNAT extension.
+
+@sp 1
+@cartouche
+@noindent
+@strong{78}.  The contents of the visible part of package
+@code{Interfaces} and its language-defined descendants. See B.2(1).
+@end cartouche
+@noindent
+See files with prefix @file{i-} in the distributed library.
+
+@sp 1
+@cartouche
+@noindent
+@strong{79}.  Implementation-defined children of package
+@code{Interfaces}. The contents of the visible part of package
+@code{Interfaces}. See B.2(11).
+@end cartouche
+@noindent
+See files with prefix @file{i-} in the distributed library.
+
+@sp 1
+@cartouche
+@noindent
+@strong{80}.  The types @code{Floating}, @code{Long_Floating},
+@code{Binary}, @code{Long_Binary}, @code{Decimal_ Element}, and
+@code{COBOL_Character}; and the initialization of the variables
+@code{Ada_To_COBOL} and @code{COBOL_To_Ada}, in
+@code{Interfaces.COBOL}. See B.4(50).
+@end cartouche
+@noindent
+@table @code
+@item Floating
+Float
+@item Long_Floating 
+(Floating) Long_Float 
+@item Binary 
+Integer 
+@item Long_Binary 
+Long_Long_Integer 
+@item Decimal_Element 
+Character 
+@item COBOL_Character 
+Character 
+@end table
+
+For initialization, see the file @file{i-cobol.ads} in the distributed library.
+
+@sp 1
+@cartouche
+@noindent
+@strong{81}.  Support for access to machine instructions. See C.1(1).
+@end cartouche
+@noindent
+See documentation in file @file{s-maccod.ads} in the distributed library.
+
+@sp 1
+@cartouche
+@noindent
+@strong{82}.  Implementation-defined aspects of access to machine
+operations. See C.1(9).
+@end cartouche
+@noindent
+See documentation in file @file{s-maccod.ads} in the distributed library.
+
+@sp 1
+@cartouche
+@noindent
+@strong{83}.  Implementation-defined aspects of interrupts. See C.3(2).
+@end cartouche
+@noindent
+Interrupts are mapped to signals or conditions as appropriate. See
+definition of unit
+@code{Ada.Interrupt_Names} in source file @file{a-intnam.ads} for details
+on the interrupts supported on a particular target.
+
+@sp 1
+@cartouche
+@noindent
+@strong{84}.  Implementation-defined aspects of pre-elaboration. See
+C.4(13).
+@end cartouche
+@noindent
+GNAT does not permit a partition to be restarted without reloading,
+except under control of the debugger.
+
+@sp 1
+@cartouche
+@noindent
+@strong{85}.  The semantics of pragma @code{Discard_Names}. See C.5(7).
+@end cartouche
+@noindent
+Pragma @code{Discard_Names} causes names of enumeration literals to
+be suppressed. In the presence of this pragma, the Image attribute 
+provides the image of the Pos of the literal, and Value accepts
+Pos values.
+
+@sp 1
+@cartouche
+@noindent
+@strong{86}.  The result of the @code{Task_Identification.Image}
+attribute. See C.7.1(7).
+@end cartouche
+@noindent
+The result of this attribute is an 8-digit hexadecimal string
+representing the virtual address of the task control block.
+
+@sp 1
+@cartouche
+@noindent
+@strong{87}.  The value of @code{Current_Task} when in a protected entry
+or interrupt handler. See C.7.1(17).
+@end cartouche
+@noindent
+Protected entries or interrupt handlers can be executed by any
+convenient thread, so the value of @code{Current_Task} is undefined.
+
+@sp 1
+@cartouche
+@noindent
+@strong{88}.  The effect of calling @code{Current_Task} from an entry
+body or interrupt handler. See C.7.1(19).
+@end cartouche
+@noindent
+The effect of calling @code{Current_Task} from an entry body or
+interrupt handler is to return the identification of the task currently
+executing the code.
+
+@sp 1
+@cartouche
+@noindent
+@strong{89}.  Implementation-defined aspects of
+@code{Task_Attributes}. See C.7.2(19).
+@end cartouche
+@noindent
+There are no implementation-defined aspects of @code{Task_Attributes}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{90}.  Values of all @code{Metrics}. See D(2).
+@end cartouche
+@noindent
+The metrics information for GNAT depends on the performance of the
+underlying operating system. The sources of the run-time for tasking
+implementation, together with the output from @code{-gnatG} can be
+used to determine the exact sequence of operating systems calls made
+to implement various tasking constructs. Together with appropriate
+information on the performance of the underlying operating system,
+on the exact target in use, this information can be used to determine
+the required metrics.
+
+@sp 1
+@cartouche
+@noindent
+@strong{91}.  The declarations of @code{Any_Priority} and
+@code{Priority}. See D.1(11).
+@end cartouche
+@noindent
+See declarations in file @file{system.ads}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{92}.  Implementation-defined execution resources. See D.1(15).
+@end cartouche
+@noindent
+There are no implementation-defined execution resources.
+
+@sp 1
+@cartouche
+@noindent
+@strong{93}.  Whether, on a multiprocessor, a task that is waiting for
+access to a protected object keeps its processor busy. See D.2.1(3).
+@end cartouche
+@noindent
+On a multi-processor, a task that is waiting for access to a protected
+object does not keep its processor busy.
+
+@sp 1
+@cartouche
+@noindent
+@strong{94}.  The affect of implementation defined execution resources
+on task dispatching. See D.2.1(9).
+@end cartouche
+@noindent
+@c SGI info
+@ignore
+Tasks map to IRIX threads, and the dispatching policy is as defined by
+the IRIX implementation of threads.
+@end ignore
+Tasks map to threads in the threads package used by GNAT. Where possible
+and appropriate, these threads correspond to native threads of the
+underlying operating system.
+
+@sp 1
+@cartouche
+@noindent
+@strong{95}.  Implementation-defined @code{policy_identifiers} allowed
+in a pragma @code{Task_Dispatching_Policy}. See D.2.2(3).
+@end cartouche
+@noindent
+There are no implementation-defined policy-identifiers allowed in this
+pragma.
+
+@sp 1
+@cartouche
+@noindent
+@strong{96}.  Implementation-defined aspects of priority inversion. See
+D.2.2(16).
+@end cartouche
+@noindent
+Execution of a task cannot be preempted by the implementation processing
+of delay expirations for lower priority tasks.
+
+@sp 1
+@cartouche
+@noindent
+@strong{97}.  Implementation defined task dispatching. See D.2.2(18).
+@end cartouche
+@noindent
+@c SGI info:
+@ignore
+Tasks map to IRIX threads, and the dispatching policy is as defied by
+the IRIX implementation of threads.
+@end ignore
+The policy is the same as that of the underlying threads implementation.
+
+@sp 1
+@cartouche
+@noindent
+@strong{98}.  Implementation-defined @code{policy_identifiers} allowed
+in a pragma @code{Locking_Policy}. See D.3(4).
+@end cartouche
+@noindent
+The only implementation defined policy permitted in GNAT is
+@code{Inheritance_Locking}. On targets that support this policy, locking
+is implemented by inheritance, i.e. the task owning the lock operates
+at a priority equal to the highest priority of any task currently
+requesting the lock.
+
+@sp 1
+@cartouche
+@noindent
+@strong{99}.  Default ceiling priorities. See D.3(10).
+@end cartouche
+@noindent
+The ceiling priority of protected objects of the type
+@code{System.Interrupt_Priority'Last} as described in the Ada 95
+Reference Manual D.3(10),
+
+@sp 1
+@cartouche
+@noindent
+@strong{100}.  The ceiling of any protected object used internally by
+the implementation. See D.3(16).
+@end cartouche
+@noindent
+The ceiling priority of internal protected objects is
+@code{System.Priority'Last}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{101}.  Implementation-defined queuing policies. See D.4(1).
+@end cartouche
+@noindent
+There are no implementation-defined queueing policies. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{102}.  On a multiprocessor, any conditions that cause the
+completion of an aborted construct to be delayed later than what is
+specified for a single processor. See D.6(3).
+@end cartouche
+@noindent
+The semantics for abort on a multi-processor is the same as on a single
+processor, there are no further delays.
+
+@sp 1
+@cartouche
+@noindent
+@strong{103}.  Any operations that implicitly require heap storage
+allocation. See D.7(8).
+@end cartouche
+@noindent
+The only operation that implicitly requires heap storage allocation is
+task creation.
+
+@sp 1
+@cartouche
+@noindent
+@strong{104}.  Implementation-defined aspects of pragma
+@code{Restrictions}. See D.7(20).
+@end cartouche
+@noindent
+There are no such implementation-defined aspects. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{105}.  Implementation-defined aspects of package
+@code{Real_Time}. See D.8(17).
+@end cartouche
+@noindent
+There are no implementation defined aspects of package @code{Real_Time}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{106}.  Implementation-defined aspects of
+@code{delay_statements}. See D.9(8).
+@end cartouche
+@noindent
+Any difference greater than one microsecond will cause the task to be
+delayed (see D.9(7)).
+
+@sp 1
+@cartouche
+@noindent
+@strong{107}.  The upper bound on the duration of interrupt blocking
+caused by the implementation. See D.12(5).
+@end cartouche
+@noindent
+The upper bound is determined by the underlying operating system. In
+no cases is it more than 10 milliseconds.
+
+@sp 1
+@cartouche
+@noindent
+@strong{108}.  The means for creating and executing distributed
+programs. See E(5).
+@end cartouche
+@noindent
+The GLADE package provides a utility GNATDIST for creating and executing
+distributed programs. See the GLADE reference manual for further details.
+
+@sp 1
+@cartouche
+@noindent
+@strong{109}.  Any events that can result in a partition becoming
+inaccessible. See E.1(7).
+@end cartouche
+@noindent
+See the GLADE reference manual for full details on such events.
+
+@sp 1
+@cartouche
+@noindent
+@strong{110}.  The scheduling policies, treatment of priorities, and
+management of shared resources between partitions in certain cases. See
+E.1(11).
+@end cartouche
+@noindent
+See the GLADE reference manual for full details on these aspects of
+multi-partition execution.
+
+@sp 1
+@cartouche
+@noindent
+@strong{111}.  Events that cause the version of a compilation unit to
+change. See E.3(5).
+@end cartouche
+@noindent
+Editing the source file of a compilation unit, or the source files of
+any units on which it is dependent in a significant way cause the version
+to change. No other actions cause the version number to change. All changes
+are significant except those which affect only layout, capitalization or
+comments.
+
+@sp 1
+@cartouche
+@noindent
+@strong{112}.  Whether the execution of the remote subprogram is
+immediately aborted as a result of cancellation. See E.4(13).
+@end cartouche
+@noindent
+See the GLADE reference manual for details on the effect of abort in
+a distributed application.
+
+@sp 1
+@cartouche
+@noindent
+@strong{113}.  Implementation-defined aspects of the PCS. See E.5(25).
+@end cartouche
+@noindent
+See the GLADE reference manual for a full description of all implementation
+defined aspects of the PCS.
+
+@sp 1
+@cartouche
+@noindent
+@strong{114}.  Implementation-defined interfaces in the PCS. See
+E.5(26).
+@end cartouche
+@noindent
+See the GLADE reference manual for a full description of all
+implementation defined interfaces.
+
+@sp 1
+@cartouche
+@noindent
+@strong{115}.  The values of named numbers in the package
+@code{Decimal}. See F.2(7).
+@end cartouche
+@noindent
+@table @code
+@item Max_Scale
++18
+@item Min_Scale
+-18
+@item Min_Delta
+1.0E-18
+@item Max_Delta
+1.0E+18
+@item Max_Decimal_Digits
+18
+@end table
+
+@sp 1
+@cartouche
+@noindent
+@strong{116}.  The value of @code{Max_Picture_Length} in the package
+@code{Text_IO.Editing}. See F.3.3(16).
+@end cartouche
+@noindent
+64
+
+@sp 1
+@cartouche
+@noindent
+@strong{117}.  The value of @code{Max_Picture_Length} in the package
+@code{Wide_Text_IO.Editing}. See F.3.4(5).
+@end cartouche
+@noindent
+64
+
+@sp 1
+@cartouche
+@noindent
+@strong{118}.  The accuracy actually achieved by the complex elementary
+functions and by other complex arithmetic operations. See G.1(1).
+@end cartouche
+@noindent
+Standard library functions are used for the complex arithmetic
+operations. Only fast math mode is currently supported.
+
+@sp 1
+@cartouche
+@noindent
+@strong{119}.  The sign of a zero result (or a component thereof) from
+any operator or function in @code{Numerics.Generic_Complex_Types}, when
+@code{Real'Signed_Zeros} is True. See G.1.1(53).
+@end cartouche
+@noindent
+The signs of zero values are as recommended by the relevant
+implementation advice.
+
+@sp 1
+@cartouche
+@noindent
+@strong{120}.  The sign of a zero result (or a component thereof) from
+any operator or function in
+@code{Numerics.Generic_Complex_Elementary_Functions}, when
+@code{Real'Signed_Zeros} is @code{True}. See G.1.2(45).
+@end cartouche
+@noindent
+The signs of zero values are as recommended by the relevant
+implementation advice.
+
+@sp 1
+@cartouche
+@noindent
+@strong{121}.  Whether the strict mode or the relaxed mode is the
+default. See G.2(2).
+@end cartouche
+@noindent
+The strict mode is the default. There is no separate relaxed mode. GNAT
+provides a highly efficient implementation of strict mode.
+
+@sp 1
+@cartouche
+@noindent
+@strong{122}.  The result interval in certain cases of fixed-to-float
+conversion. See G.2.1(10).
+@end cartouche
+@noindent
+For cases where the result interval is implementation dependent, the
+accuracy is that provided by performing all operations in 64-bit IEEE
+floating-point format.
+
+@sp 1
+@cartouche
+@noindent
+@strong{123}.  The result of a floating point arithmetic operation in
+overflow situations, when the @code{Machine_Overflows} attribute of the
+result type is @code{False}. See G.2.1(13).
+@end cartouche
+@noindent
+Infinite and Nan values are produced as dictated by the IEEE
+floating-point standard.
+
+@sp 1
+@cartouche
+@noindent
+@strong{124}.  The result interval for division (or exponentiation by a
+negative exponent), when the floating point hardware implements division
+as multiplication by a reciprocal. See G.2.1(16).
+@end cartouche
+@noindent
+Not relevant, division is IEEE exact. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{125}.  The definition of close result set, which determines the
+accuracy of certain fixed point multiplications and divisions. See
+G.2.3(5).
+@end cartouche
+@noindent
+Operations in the close result set are performed using IEEE long format
+floating-point arithmetic. The input operands are converted to
+floating-point, the operation is done in floating-point, and the result
+is converted to the target type.
+
+@sp 1
+@cartouche
+@noindent
+@strong{126}.  Conditions on a @code{universal_real} operand of a fixed
+point multiplication or division for which the result shall be in the
+perfect result set. See G.2.3(22).
+@end cartouche
+@noindent
+The result is only defined to be in the perfect result set if the result
+can be computed by a single scaling operation involving a scale factor
+representable in 64-bits.
+
+@sp 1
+@cartouche
+@noindent
+@strong{127}.  The result of a fixed point arithmetic operation in
+overflow situations, when the @code{Machine_Overflows} attribute of the
+result type is @code{False}. See G.2.3(27).
+@end cartouche
+@noindent
+Not relevant, @code{Machine_Overflows} is @code{True} for fixed-point
+types.
+
+@sp 1
+@cartouche
+@noindent
+@strong{128}.  The result of an elementary function reference in
+overflow situations, when the @code{Machine_Overflows} attribute of the
+result type is @code{False}. See G.2.4(4).
+@end cartouche
+@noindent
+IEEE infinite and Nan values are produced as appropriate.
+
+@sp 1
+@cartouche
+@noindent
+@strong{129}.  The value of the angle threshold, within which certain
+elementary functions, complex arithmetic operations, and complex
+elementary functions yield results conforming to a maximum relative
+error bound. See G.2.4(10).
+@end cartouche
+@noindent
+Information on this subject is not yet available.
+
+@sp 1
+@cartouche
+@noindent
+@strong{130}.  The accuracy of certain elementary functions for
+parameters beyond the angle threshold. See G.2.4(10).
+@end cartouche
+@noindent
+Information on this subject is not yet available.
+
+@sp 1
+@cartouche
+@noindent
+@strong{131}.  The result of a complex arithmetic operation or complex
+elementary function reference in overflow situations, when the
+@code{Machine_Overflows} attribute of the corresponding real type is
+@code{False}. See G.2.6(5).
+@end cartouche
+@noindent
+IEEE infinite and Nan values are produced as appropriate. 
+
+@sp 1
+@cartouche
+@noindent
+@strong{132}.  The accuracy of certain complex arithmetic operations and
+certain complex elementary functions for parameters (or components
+thereof) beyond the angle threshold. See G.2.6(8).
+@end cartouche
+@noindent
+Information on those subjects is not yet available.
+
+@sp 1
+@cartouche
+@noindent
+@strong{133}.  Information regarding bounded errors and erroneous
+execution. See H.2(1).
+@end cartouche
+@noindent
+Information on this subject is not yet available.
+
+@sp 1
+@cartouche
+@noindent
+@strong{134}.  Implementation-defined aspects of pragma
+@code{Inspection_Point}. See H.3.2(8).
+@end cartouche
+@noindent
+Pragma @code{Inspection_Point} ensures that the variable is live and can
+be examined by the debugger at the inspection point.
+
+@sp 1
+@cartouche
+@noindent
+@strong{135}.  Implementation-defined aspects of pragma
+@code{Restrictions}. See H.4(25).
+@end cartouche
+@noindent
+There are no implementation-defined aspects of pragma @code{Restrictions}. The
+use of pragma @code{Restrictions [No_Exceptions]} has no effect on the
+generated code. Checks must suppressed by use of pragma @code{Suppress}.
+
+@sp 1
+@cartouche
+@noindent
+@strong{136}.  Any restrictions on pragma @code{Restrictions}. See
+H.4(27).
+@end cartouche
+@noindent
+There are no restrictions on pragma @code{Restrictions}.
+
+@node Intrinsic Subprograms
+@chapter Intrinsic Subprograms
+@cindex Intrinsic Subprograms
+
+@menu
+* Intrinsic Operators::
+* Enclosing_Entity::
+* Exception_Information::
+* Exception_Message::
+* Exception_Name::
+* File::
+* Line::
+* Rotate_Left::
+* Rotate_Right::
+* Shift_Left::
+* Shift_Right::
+* Shift_Right_Arithmetic::
+* Source_Location::
+@end menu
+
+GNAT allows a user application program to write the declaration:
+
+@smallexample
+   pragma Import (Intrinsic, name);
+@end smallexample
+
+@noindent
+providing that the name corresponds to one of the implemented intrinsic
+subprograms in GNAT, and that the parameter profile of the referenced
+subprogram meets the requirements. This chapter describes the set of
+implemented intrinsic subprograms, and the requirements on parameter profiles.
+Note that no body is supplied; as with other uses of pragma Import, the
+body is supplied elsewhere (in this case by the compiler itself). Note
+that any use of this feature is potentially non-portable, since the
+Ada standard does not require Ada compilers to implement this feature.
+
+@node Intrinsic Operators
+@section Intrinsic Operators
+@cindex Intrinsic operator
+
+@noindent
+All predefined operators can be used in @code{pragma Import (Intrinsic,..)}
+declarations. In the binary operator case, the operands must have the same
+size. The operand or operands must also be appropriate for
+the operator. For example, for addition, the operands must 
+both be floating-point or both be fixed-point. You can use an intrinsic
+operator declaration as in the following example:
+
+@smallexample
+   type Int1 is new Integer;
+   type Int2 is new Integer;
+
+   function "+" (X1 : Int1; X2 : Int2) return Int1;
+   function "+" (X1 : Int1; X2 : Int2) return Int2;
+   pragma Import (Intrinsic, "+");
+@end smallexample
+
+@noindent
+This declaration would permit "mixed mode" arithmetic on items
+of the differing types Int1 and Int2.
+
+@node Enclosing_Entity
+@section Enclosing_Entity
+@cindex Enclosing_Entity
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Source_Info}. The only useful use of the
+intrinsic import in this case is the one in this unit, so an
+application program should simply call the function
+@code{GNAT.Source_Info.Enclosing_Entity} to obtain the name of
+the current subprogram, package, task, entry, or protected subprogram.
+
+@node Exception_Information
+@section Exception_Information
+@cindex Exception_Information'
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Current_Exception}. The only useful
+use of the intrinsic import in this case is the one in this unit,
+so an application program should simply call the function
+@code{GNAT.Current_Exception.Exception_Information} to obtain
+the exception information associated with the current exception.
+
+@node Exception_Message
+@section Exception_Message
+@cindex Exception_Message
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Current_Exception}. The only useful
+use of the intrinsic import in this case is the one in this unit,
+so an application program should simply call the function
+@code{GNAT.Current_Exception.Exception_Message} to obtain
+the message associated with the current exception.
+
+@node Exception_Name
+@section Exception_Name
+@cindex Exception_Name
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Current_Exception}. The only useful
+use of the intrinsic import in this case is the one in this unit,
+so an application program should simply call the function
+@code{GNAT.Current_Exception.Exception_Name} to obtain
+the name of the current exception.
+
+@node File
+@section File
+@cindex File
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Source_Info}. The only useful use of the
+intrinsic import in this case is the one in this unit, so an
+application program should simply call the function
+@code{GNAT.Source_Info.File} to obtain the name of the current
+file.
+
+@node Line
+@section Line
+@cindex Line
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Source_Info}. The only useful use of the
+intrinsic import in this case is the one in this unit, so an
+application program should simply call the function
+@code{GNAT.Source_Info.Line} to obtain the number of the current
+source line.
+
+@node Rotate_Left
+@section Rotate_Left
+@cindex Rotate_Left
+@noindent
+In standard Ada 95, the @code{Rotate_Left} function is available only
+for the predefined modular types in package @code{Interfaces}. However, in
+GNAT it is possible to define a Rotate_Left function for a user
+defined modular type or any signed integer type as in this example:
+
+@smallexample
+   function Shift_Left
+     (Value  : My_Modular_Type;
+      Amount : Natural)
+      return   My_Modular_Type;
+@end smallexample
+
+@noindent
+The requirements are that the profile be exactly as in the example
+above. The only modifications allowed are in the formal parameter
+names, and in the type of @code{Value} and the return type, which
+must be the same, and must be either a signed integer type, or
+a modular integer type with a binary modulus, and the size must
+be 8. 16, 32 or 64 bits.
+
+@node Rotate_Right
+@section Rotate_Right
+@cindex Rotate_Right
+@noindent
+A @code{Rotate_Right} function can be defined for any user defined
+binary modular integer type, or signed integer type, as described
+above for @code{Rotate_Left}.
+
+@node Shift_Left
+@section Shift_Left
+@cindex Shift_Left
+@noindent
+A @code{Shift_Left} function can be defined for any user defined
+binary modular integer type, or signed integer type, as described
+above for @code{Rotate_Left}.
+
+@node Shift_Right
+@section Shift_Right
+@cindex Shift_Right
+@noindent
+A @code{Shift_Right} function can be defined for any user defined
+binary modular integer type, or signed integer type, as described
+above for @code{Rotate_Left}.
+
+@node Shift_Right_Arithmetic
+@section Shift_Right_Arithmetic
+@cindex Shift_Right_Arithmetic
+@noindent
+A @code{Shift_Right_Arithmetic} function can be defined for any user
+defined binary modular integer type, or signed integer type, as described
+above for @code{Rotate_Left}.
+
+@node Source_Location
+@section Source_Location
+@cindex Source_Location
+@noindent
+This intrinsic subprogram is used in the implementation of the
+library routine @code{GNAT.Source_Info}. The only useful use of the
+intrinsic import in this case is the one in this unit, so an
+application program should simply call the function
+@code{GNAT.Source_Info.Source_Location} to obtain the current
+source file location.
+
+@node Representation Clauses and Pragmas
+@chapter Representation Clauses and Pragmas
+@cindex Representation Clauses
+
+@menu
+* Alignment Clauses::
+* Size Clauses::
+* Storage_Size Clauses::
+* Size of Variant Record Objects::
+* Biased Representation ::
+* Value_Size and Object_Size Clauses::
+* Component_Size Clauses::
+* Bit_Order Clauses::
+* Effect of Bit_Order on Byte Ordering::
+* Pragma Pack for Arrays::
+* Pragma Pack for Records::
+* Record Representation Clauses::
+* Enumeration Clauses::
+* Address Clauses::
+* Effect of Convention on Representation::
+* Determining the Representations chosen by GNAT::
+@end menu
+
+@noindent
+@cindex Representation Clause
+@cindex Representation Pragma
+@cindex Pragma, representation
+This section describes the representation clauses accepted by GNAT, and
+their effect on the representation of corresponding data objects.
+
+GNAT fully implements Annex C (Systems Programming). This means that all
+the implementation advice sections in chapter 13 are fully implemented.
+However, these sections only require a minimal level of support for
+representation clauses. GNAT provides much more extensive capabilities,
+and this section describes the additional capabilities provided.
+
+@node Alignment Clauses
+@section Alignment Clauses
+@cindex Alignment Clause
+
+@noindent
+GNAT requires that all alignment clauses specify a power of 2, and all
+default alignments are always a power of 2. The default alignment
+values are as follows:
+
+@itemize @bullet
+@item Primitive Types
+For primitive types, the alignment is the maximum of the actual size of
+objects of the type, and the maximum alignment supported by the target.
+For example, for type Long_Float, the object size is 8 bytes, and the
+default alignment will be 8 on any target that supports alignments
+this large, but on some targets, the maximum alignment may be smaller
+than 8, in which case objects of type Long_Float will be maximally
+aligned.
+
+@item Arrays
+For arrays, the alignment is equal to the alignment of the component type
+for the normal case where no packing or component size is given. If the
+array is packed, and the packing is effective (see separate section on
+packed arrays), then the alignment will be one for long packed arrays,
+or arrays whose length is not known at compile time. For short packed
+arrays, which are handled internally as modular types, the alignment
+will be as described for primitive types, e.g. a packed array of length
+31 bits will have an object size of four bytes, and an alignment of 4.
+
+@item Records
+For the normal non-packed case, the alignment of a record is equal to
+the maximum alignment of any of its components. For tagged records, this
+includes the implicit access type used for the tag. If a pragma Pack is
+used and all fields are packable (see separate section on pragma Pack),
+then the resulting alignment is 1.
+
+@end itemize
+
+@noindent
+An alignment clause may
+always specify a larger alignment than the default value, up to some
+maximum value dependent on the target (obtainable by using the
+attribute reference System'Maximum_Alignment). The only case in which
+it is permissible to specify a smaller alignment than the default value
+is in the case of a record for which a record representation clause is
+given. In this case, packable fields for which a component clause is
+given still result in a default alignment corresponding to the original
+type, but this may be overridden, since these components in fact only
+require an alignment of one byte. For example, given
+
+@smallexample
+  type v is record
+     a : integer;
+  end record;
+
+  for v use record
+     a at 0  range 0 .. 31;
+  end record;
+
+  for v'alignment use 1;
+@end smallexample
+
+@noindent
+@cindex Alignment, default
+The default alignment for the type @code{v} is 4, as a result of the
+integer field in the record, but since this field is placed with a
+component clause, it is permissible, as shown, to override the default
+alignment of the record to a smaller value.
+
+@node Size Clauses
+@section Size Clauses
+@cindex Size Clause
+
+@noindent
+The default size of types is as specified in the reference manual. For
+objects, GNAT will generally increase the type size so that the object
+size is a multiple of storage units, and also a multiple of the
+alignment. For example
+
+@smallexample
+   type Smallint is range 1 .. 6;
+
+   type Rec is record
+      y1 : integer;
+      y2 : boolean;
+   end record;
+@end smallexample
+
+@noindent
+In this example, @code{Smallint}
+has a size of 3, as specified by the RM rules,
+but objects of this type will have a size of 8, 
+since objects by default occupy an integral number
+of storage units. On some targets, notably older
+versions of the Digital Alpha, the size of stand
+alone objects of this type may be 32, reflecting
+the inability of the hardware to do byte load/stores.
+
+Similarly, the size of type @code{Rec} is 40 bits, but
+the alignment is 4, so objects of this type will have
+their size increased to 64 bits so that it is a multiple
+of the alignment. The reason for this decision, which is
+in accordance with the specific note in RM 13.3(43):
+
+@smallexample
+A Size clause should be supported for an object if the specified
+Size is at least as large as its subtype's Size, and corresponds
+to a size in storage elements that is a multiple of the object's
+Alignment (if the Alignment is nonzero).
+@end smallexample
+
+@noindent
+An explicit size clause may be used to override the default size by
+increasing it. For example, if we have:
+
+@smallexample
+   type My_Boolean is new Boolean;
+   for My_Boolean'Size use 32;
+@end smallexample
+
+@noindent
+then objects of this type will always be 32 bits long. In the case of
+discrete types, the size can be increased up to 64 bits, with the effect
+that the entire specified field is used to hold the value, sign- or
+zero-extended as appropriate. If more than 64 bits is specified, then
+padding space is allocated after the value, and a warning is issued that
+there are unused bits.
+
+Similarly the size of records and arrays may be increased, and the effect
+is to add padding bits after the value. This also causes a warning message
+to be generated.
+
+The largest Size value permitted in GNAT is 2**32-1. Since this is a
+Size in bits, this corresponds to an object of size 256 megabytes (minus
+one). This limitation is true on all targets. The reason for this
+limitation is that it improves the quality of the code in many cases
+if it is known that a Size value can be accommodated in an object of
+type Integer.
+
+@node Storage_Size Clauses
+@section Storage_Size Clauses
+@cindex Storage_Size Clause
+
+@noindent
+For tasks, the @code{Storage_Size} clause specifies the amount of space
+to be allocated for the task stack. This cannot be extended, and if the
+stack is exhausted, then @code{Storage_Error} will be raised if stack
+checking is enabled. If the default size of 20K bytes is insufficient,  
+then you need to use a @code{Storage_Size} attribute definition clause,
+or a @code{Storage_Size} pragma in the task definition to set the
+appropriate required size. A useful technique is to include in every
+task definition a pragma of the form:
+
+@smallexample
+   pragma Storage_Size (Default_Stack_Size);
+@end smallexample
+
+@noindent
+Then Default_Stack_Size can be defined in a global package, and modified
+as required. Any tasks requiring different task stack sizes from the
+default can have an appropriate alternative reference in the pragma.
+
+For access types, the @code{Storage_Size} clause specifies the maximum
+space available for allocation of objects of the type. If this space is
+exceeded then @code{Storage_Error} will be raised by an allocation attempt.
+In the case where the access type is declared local to a subprogram, the
+use of a @code{Storage_Size} clause triggers automatic use of a special
+predefined storage pool (@code{System.Pool_Size}) that ensures that all
+space for the pool is automatically reclaimed on exit from the scope in
+which the type is declared.
+
+A special case recognized by the compiler is the specification of a
+@code{Storage_Size} of zero for an access type. This means that no
+items can be allocated from the pool, and this is recognized at compile
+time, and all the overhead normally associated with maintaining a fixed
+size storage pool is eliminated. Consider the following example:
+
+@smallexample
+   procedure p is
+      type R is array (Natural) of Character;
+      type P is access all R;
+      for P'Storage_Size use 0;
+      --  Above access type intended only for interfacing purposes
+   
+      y : P;
+   
+      procedure g (m : P);
+      pragma Import (C, g);
+   
+      --  ...
+   
+   begin
+      --  ...
+      y := new R;
+   end;
+@end smallexample
+
+@noindent
+As indicated in this example, these dummy storage pools are often useful in
+connection with interfacing where no object will ever be allocated. If you
+compile the above example, you get the warning:
+
+@smallexample
+   p.adb:16:09: warning: allocation from empty storage pool
+   p.adb:16:09: warning: Storage_Error will be raised at run time
+@end smallexample
+
+@noindent
+Of course in practice, there will not be any explicit allocators in the
+case of such an access declaration.
+
+@node Size of Variant Record Objects
+@section Size of Variant Record Objects
+@cindex Size, variant record objects
+@cindex Variant record objects, size
+
+@noindent
+An issue arises in the case of variant record objects of whether Size gives
+information about a particular variant, or the maximum size required
+for any variant. Consider the following program
+
+@smallexample
+with Text_IO; use Text_IO;
+procedure q is
+   type R1 (A : Boolean := False) is record
+     case A is
+       when True  => X : Character;
+       when False => null;
+     end case;
+   end record;
+   
+   V1 : R1 (False);
+   V2 : R1;
+
+begin
+   Put_Line (Integer'Image (V1'Size));
+   Put_Line (Integer'Image (V2'Size));
+end q;
+@end smallexample
+
+@noindent
+Here we are dealing with a variant record, where the True variant
+requires 16 bits, and the False variant requires 8 bits.
+In the above example, both V1 and V2 contain the False variant,
+which is only 8 bits long. However, the result of running the
+program is:
+
+@smallexample
+8
+16
+@end smallexample
+
+@noindent
+The reason for the difference here is that the discriminant value of
+V1 is fixed, and will always be False. It is not possible to assign
+a True variant value to V1, therefore 8 bits is sufficient. On the
+other hand, in the case of V2, the initial discriminant value is
+False (from the default), but it is possible to assign a True
+variant value to V2, therefore 16 bits must be allocated for V2
+in the general case, even fewer bits may be needed at any particular
+point during the program execution.
+
+As can be seen from the output of this program, the @code{'Size}
+attribute applied to such an object in GNAT gives the actual allocated
+size of the variable, which is the largest size of any of the variants.
+The Ada Reference Manual is not completely clear on what choice should
+be made here, but the GNAT behavior seems most consistent with the
+language in the RM.
+
+In some cases, it may be desirable to obtain the size of the current
+variant, rather than the size of the largest variant. This can be
+achieved in GNAT by making use of the fact that in the case of a
+subprogram parameter, GNAT does indeed return the size of the current
+variant (because a subprogram has no way of knowing how much space
+is actually allocated for the actual).
+
+Consider the following modified version of the above program:
+
+@smallexample
+with Text_IO; use Text_IO;
+procedure q is
+   type R1 (A : Boolean := False) is record
+     case A is
+       when True  => X : Character;
+       when False => null;
+     end case;
+   end record;
+   
+   V2 : R1;
+
+   function Size (V : R1) return Integer is
+   begin
+      return V'Size;
+   end Size;
+
+begin
+   Put_Line (Integer'Image (V2'Size));
+   Put_Line (Integer'IMage (Size (V2)));
+   V2 := (True, 'x');
+   Put_Line (Integer'Image (V2'Size));
+   Put_Line (Integer'IMage (Size (V2)));
+end q;
+@end smallexample
+
+@noindent
+The output from this program is
+
+@smallexample
+16
+8
+16
+16
+@end smallexample
+
+@noindent
+Here we see that while the @code{'Size} attribute always returns
+the maximum size, regardless of the current variant value, the
+@code{Size} function does indeed return the size of the current
+variant value.
+
+@node Biased Representation
+@section Biased Representation
+@cindex Size for biased representation
+@cindex Biased representation
+
+@noindent
+In the case of scalars with a range starting at other than zero, it is
+possible in some cases to specify a size smaller than the default minimum
+value, and in such cases, @code{GNAT} uses an unsigned biased representation,
+in which zero is used to represent the lower bound, and successive values
+represent successive values of the type.
+
+For example, suppose we have the declaration:
+
+@smallexample
+   type Small is range -7 .. -4;
+   for Small'Size use 2;
+@end smallexample
+
+@noindent
+Although the default size of type @code{Small} is 4, the @code{Size}
+clause is accepted by GNAT and results in the following representation
+scheme:
+
+@smallexample
+  -7 is represented as 2#00#
+  -6 is represented as 2#01#
+  -5 is represented as 2#10#
+  -4 is represented as 2#11#
+@end smallexample
+
+@noindent
+Biased representation is only used if the specified @code{Size} clause
+cannot be accepted in any other manner. These reduced sizes that force
+biased representation can be used for all discrete types except for 
+enumeration types for which a representation clause is given.
+
+@node Value_Size and Object_Size Clauses
+@section Value_Size and Object_Size Clauses
+@findex Value_Size
+@findex Object_Size
+@cindex Size, of objects
+
+@noindent
+In Ada 95, the @code{Size} of a discrete type is the minimum number of bits
+required to hold values of the type. Although this interpretation was
+allowed in Ada 83, it was not required, and this requirement in practice
+can cause some significant difficulties. For example, in most Ada 83
+compilers, @code{Natural'Size} was 32. However, in Ada-95,
+@code{Natural'Size} is
+typically 31. This means that code may change in behavior when moving
+from Ada 83 to Ada 95. For example, consider:
+
+@smallexample
+   type Rec is record;
+      A : Natural;
+      B : Natural;
+   end record;
+
+   for Rec use record
+      for A use at 0  range 0 .. Natural'Size - 1;
+      for B use at 0  range Natural'Size .. 2 * Natural'Size - 1;
+   end record;
+@end smallexample
+
+@noindent
+In the above code, since the typical size of @code{Natural} objects
+is 32 bits and @code{Natural'Size} is 31, the above code can cause
+unexpected inefficient packing in Ada 95, and in general there are
+surprising cases where the fact that the object size can exceed the
+size of the type causes surprises.
+
+To help get around this problem GNAT provides two implementation
+dependent attributes @code{Value_Size} and @code{Object_Size}. When 
+applied to a type, these attributes yield the size of the type
+(corresponding to the RM defined size attribute), and the size of
+objects of the type respectively.
+
+The @code{Object_Size} is used for determining the default size of
+objects and components. This size value can be referred to using the
+@code{Object_Size} attribute. The phrase "is used" here means that it is
+the basis of the determination of the size. The backend is free to
+pad this up if necessary for efficiency, e.g. an 8-bit stand-alone
+character might be stored in 32 bits on a machine with no efficient
+byte access instructions such as the Alpha.
+
+The default rules for the value of @code{Object_Size} for fixed-point and
+discrete types are as follows:
+
+@itemize @bullet
+@item
+The @code{Object_Size} for base subtypes reflect the natural hardware
+size in bits (run the utility gnatpsta to find those values for numeric types). 
+Enumeration types and fixed-point base subtypes have 8. 16. 32 or 64
+bits for this size, depending on the range of values to be stored.
+
+@item
+The @code{Object_Size} of a subtype is the same as the
+@code{Object_Size} of
+the type from which it is obtained.
+
+@item
+The @code{Object_Size} of a derived base type is copied from the parent
+base type, and the @code{Object_Size} of a derived first subtype is copied
+from the parent first subtype.
+@end itemize
+
+@noindent
+The @code{Value_Size} attribute
+is the number of bits required to store a value
+of the type. This size can be referred to using the @code{Value_Size}
+attribute. This value is used to determine how tightly to pack
+records or arrays with components of this type, and also affects
+the semantics of unchecked conversion (unchecked conversions where
+the @code{Value_Size} values differ generate a warning, and are potentially
+target dependent).
+
+The default rules for the value of @code{Value_Size} are as follows:
+
+@itemize @bullet
+@item
+The @code{Value_Size} for a base subtype is the minimum number of bits
+required to store all values of the type (including the sign bit
+only if negative values are possible).
+
+@item
+If a subtype statically matches the first subtype of a given type, then it has
+by default the same @code{Value_Size} as the first subtype. This is a
+consequence of RM 13.1(14) ("if two subtypes statically match,
+then their subtype-specific aspects are the same".)
+
+@item
+All other subtypes have a @code{Value_Size} corresponding to the minimum
+number of bits required to store all values of the subtype. For
+dynamic bounds, it is assumed that the value can range down or up
+to the corresponding bound of the ancestor
+@end itemize
+
+@noindent
+The RM defined attribute @code{Size} corresponds to the
+@code{Value_Size} attribute.
+
+The @code{Size} attribute may be defined for a first-named subtype. This sets
+the @code{Value_Size} of
+the first-named subtype to the given value, and the
+@code{Object_Size} of this first-named subtype to the given value padded up
+to an appropriate boundary. It is a consequence of the default rules
+above that this @code{Object_Size} will apply to all further subtypes. On the
+other hand, @code{Value_Size} is affected only for the first subtype, any
+dynamic subtypes obtained from it directly, and any statically matching
+subtypes. The @code{Value_Size} of any other static subtypes is not affected.
+
+@code{Value_Size} and
+@code{Object_Size} may be explicitly set for any subtype using
+an attribute definition clause. Note that the use of these attributes
+can cause the RM 13.1(14) rule to be violated. If two access types
+reference aliased objects whose subtypes have differing @code{Object_Size}
+values as a result of explicit attribute definition clauses, then it
+is erroneous to convert from one access subtype to the other.
+
+At the implementation level, Esize stores the Object_SIze and the
+RM_Size field stores the @code{Value_Size} (and hence the value of the
+@code{Size} attribute,
+which, as noted above, is equivalent to @code{Value_Size}).
+
+To get a feel for the difference, consider the following examples (note
+that in each case the base is short_short_integer with a size of 8):
+
+@smallexample
+                                       Object_Size     Value_Size
+
+type x1 is range 0..5;                      8               3
+
+type x2 is range 0..5;
+for x2'size use 12;                        12              12
+
+subtype x3 is x2 range 0 .. 3;             12               2
+
+subtype x4 is x2'base range 0 .. 10;        8               4
+
+subtype x5 is x2 range 0 .. dynamic;       12              (7)
+
+subtype x6 is x2'base range 0 .. dynamic;   8              (7)
+
+@end smallexample
+
+@noindent
+Note: the entries marked (7) are not actually specified by the Ada 95 RM,
+but it seems in the spirit of the RM rules to allocate the minimum number
+of bits known to be large enough to hold the given range of values.
+
+So far, so good, but GNAT has to obey the RM rules, so the question is
+under what conditions must the RM @code{Size} be used.
+The following is a list
+of the occasions on which the RM @code{Size} must be used:
+
+@itemize @bullet
+@item
+Component size for packed arrays or records
+
+@item
+Value of the attribute @code{Size} for a type
+
+@item
+Warning about sizes not matching for unchecked conversion
+@end itemize
+
+@noindent
+For types other than discrete and fixed-point types, the @code{Object_Size}
+and Value_Size are the same (and equivalent to the RM attribute @code{Size}).
+Only @code{Size} may be specified for such types.
+
+@node Component_Size Clauses
+@section Component_Size Clauses
+@cindex Component_Size Clause
+
+@noindent
+Normally, the value specified in a component clause must be consistent
+with the subtype of the array component with regard to size and alignment.
+In other words, the value specified must be at least equal to the size
+of this subtype, and must be a multiple of the alignment value.
+
+In addition, component size clauses are allowed which cause the array
+to be packed, by specifying a smaller value. The cases in which this
+is allowed are for component size values in the range 1-63. The value
+specified must not be smaller than the Size of the subtype. GNAT will
+accurately honor all packing requests in this range. For example, if
+we have:
+
+@smallexample
+type r is array (1 .. 8) of Natural;
+for r'Size use 31;
+@end smallexample
+
+@noindent
+then the resulting array has a length of 31 bytes (248 bits = 8 * 31).
+Of course access to the components of such an array is considerably
+less efficient than if the natural component size of 32 is used.
+
+@node Bit_Order Clauses
+@section Bit_Order Clauses
+@cindex Bit_Order Clause
+@cindex bit ordering
+@cindex ordering, of bits
+
+@noindent
+For record subtypes, GNAT permits the specification of the @code{Bit_Order}
+attribute. The specification may either correspond to the default bit
+order for the target, in which case the specification has no effect and
+places no additional restrictions, or it may be for the non-standard
+setting (that is the opposite of the default).
+
+In the case where the non-standard value is specified, the effect is
+to renumber bits within each byte, but the ordering of bytes is not
+affected. There are certain
+restrictions placed on component clauses as follows:
+
+@itemize @bullet
+
+@item Components fitting within a single storage unit.
+@noindent
+These are unrestricted, and the effect is merely to renumber bits. For
+example if we are on a little-endian machine with @code{Low_Order_First}
+being the default, then the following two declarations have exactly
+the same effect:
+
+@smallexample
+   type R1 is record
+      A : Boolean;
+      B : Integer range 1 .. 120;
+   end record;
+
+   for R1 use record
+      A at 0 range 0 .. 0;
+      B at 0 range 1 .. 7;
+   end record;
+
+   type R2 is record
+      A : Boolean;
+      B : Integer range 1 .. 120;
+   end record;
+
+   for R2'Bit_Order use High_Order_First;
+
+   for R2 use record
+      A at 0 range 7 .. 7;
+      B at 0 range 0 .. 6;
+   end record;
+@end smallexample
+
+@noindent
+The useful application here is to write the second declaration with the
+@code{Bit_Order} attribute definition clause, and know that it will be treated
+the same, regardless of whether the target is little-endian or big-endian.
+
+@item Components occupying an integral number of bytes.
+@noindent
+These are components that exactly fit in two or more bytes. Such component
+declarations are allowed, but have no effect, since it is important to realize
+that the @code{Bit_Order} specification does not affect the ordering of bytes.
+In particular, the following attempt at getting an endian-independent integer
+does not work:
+
+@smallexample
+   type R2 is record
+      A : Integer;
+   end record;
+
+   for R2'Bit_Order use High_Order_First;
+
+   for R2 use record
+      A at 0 range 0 .. 31;
+   end record;
+@end smallexample
+
+@noindent
+This declaration will result in a little-endian integer on a
+little-endian machine, and a big-endian integer on a big-endian machine.
+If byte flipping is required for interoperability between big- and
+little-endian machines, this must be explicitly programmed. This capability
+is not provided by @code{Bit_Order}.
+
+@item Components that are positioned across byte boundaries
+@noindent
+but do not occupy an integral number of bytes. Given that bytes are not
+reordered, such fields would occupy a non-contiguous sequence of bits
+in memory, requiring non-trivial code to reassemble. They are for this
+reason not permitted, and any component clause specifying such a layout
+will be flagged as illegal by GNAT.
+
+@end itemize
+
+@noindent
+Since the misconception that Bit_Order automatically deals with all
+endian-related incompatibilities is a common one, the specification of
+a component field that is an integral number of bytes will always
+generate a warning This warning may be suppressed using
+@code{pragma Suppress} if desired. The following section contains additional
+details regarding the issue of byte ordering.
+
+@node Effect of Bit_Order on Byte Ordering
+@section Effect of Bit_Order on Byte Ordering
+@cindex byte ordering
+@cindex ordering, of bytes
+
+@noindent
+In this section we will review the effec of the @code{Bit_Order} attribute
+definition clause on byte ordering. Briefly, it has no effect at all, but
+a detailed example will be helpful. Before giving this
+example, let us review the precise
+definition of the effect of defining @code{Bit_Order}. The effect of a
+non-standard bit order is described in section 15.5.3 of the Ada
+Reference Manual:
+
+@smallexample
+2   A bit ordering is a method of interpreting the meaning of
+the storage place attributes.
+@end smallexample
+
+@noindent
+To understand the precise definition of storage place attributes in
+this context, we visit section 13.5.1 of the manual:
+
+@smallexample
+13   A record_representation_clause (without the mod_clause)
+specifies the layout. The storage place attributes (see 13.5.2)
+are taken from the values of the position, first_bit, and last_bit
+expressions after normalizing those values so that first_bit is
+less than Storage_Unit.
+@end smallexample
+
+@noindent
+The critical point here is that storage places are taken from
+the values after normalization, not before. So the @code{Bit_Order}
+interpretation applies to normalized values. The interpretation
+is described in the later part of the 15.5.3 paragraph:
+
+@smallexample
+2   A bit ordering is a method of interpreting the meaning of
+the storage place attributes.  High_Order_First (known in the
+vernacular as "big endian") means that the first bit of a
+storage element (bit 0) is the most significant bit (interpreting
+the sequence of bits that represent a component as an unsigned
+integer value). Low_Order_First (known in the vernacular as
+"little endian") means the opposite: the first bit is the
+least significant.
+@end smallexample
+
+@noindent
+Note that the numbering is with respect to the bits of a storage
+unit. In other words, the specification affects only the numbering
+of bits within a single storage unit.
+
+We can make the effect clearer by giving an example.
+
+Suppose that we have an external device which presents two bytes, the first
+byte presented, which is the first (low addressed byte) of the two byte
+record is called Master, and the second byte is called Slave.
+
+The left most (most significant bit is called Control for each byte, and
+the remaing 7 bits are called V1, V2 .. V7, where V7 is the right most
+(least significant bit).
+
+On a big-endian machine, we can write the following representation clause
+
+@smallexample
+   type Data is record
+      Master_Control : Bit;
+      Master_V1      : Bit;
+      Master_V2      : Bit;
+      Master_V3      : Bit;
+      Master_V4      : Bit;
+      Master_V5      : Bit;
+      Master_V6      : Bit;
+      Master_V7      : Bit;
+      Slave_Control  : Bit;
+      Slave_V1       : Bit;
+      Slave_V2       : Bit;
+      Slave_V3       : Bit;
+      Slave_V4       : Bit;
+      Slave_V5       : Bit;
+      Slave_V6       : Bit;
+      Slave_V7       : Bit;
+   end record;
+
+   for Data use record
+      Master_Control at 0 range 0 .. 0;
+      Master_V1      at 0 range 1 .. 1;
+      Master_V2      at 0 range 2 .. 2;
+      Master_V3      at 0 range 3 .. 3;
+      Master_V4      at 0 range 4 .. 4;
+      Master_V5      at 0 range 5 .. 5;
+      Master_V6      at 0 range 6 .. 6;
+      Master_V7      at 0 range 7 .. 7;
+      Slave_Control  at 1 range 0 .. 0;
+      Slave_V1       at 1 range 1 .. 1;
+      Slave_V2       at 1 range 2 .. 2;
+      Slave_V3       at 1 range 3 .. 3;
+      Slave_V4       at 1 range 4 .. 4;
+      Slave_V5       at 1 range 5 .. 5;
+      Slave_V6       at 1 range 6 .. 6;
+      Slave_V7       at 1 range 7 .. 7;
+   end record;
+@end smallexample
+
+@noindent
+Now if we move this to a little endian machine, then the bit ordering within
+the byte is backwards, so we have to rewrite the record rep clause as:
+
+@smallexample
+   for Data use record
+      Master_Control at 0 range 7 .. 7;
+      Master_V1      at 0 range 6 .. 6;
+      Master_V2      at 0 range 5 .. 5;
+      Master_V3      at 0 range 4 .. 4;
+      Master_V4      at 0 range 3 .. 3;
+      Master_V5      at 0 range 2 .. 2;
+      Master_V6      at 0 range 1 .. 1;
+      Master_V7      at 0 range 0 .. 0;
+      Slave_Control  at 1 range 7 .. 7;
+      Slave_V1       at 1 range 6 .. 6;
+      Slave_V2       at 1 range 5 .. 5;
+      Slave_V3       at 1 range 4 .. 4;
+      Slave_V4       at 1 range 3 .. 3;
+      Slave_V5       at 1 range 2 .. 2;
+      Slave_V6       at 1 range 1 .. 1;
+      Slave_V7       at 1 range 0 .. 0;
+   end record;
+@end smallexample
+
+It is a nuisance to have to rewrite the clause, especially if
+the code has to be maintained on both machines. However,
+this is a case that we can handle with the
+@code{Bit_Order} attribute if it is implemented.
+Note that the implementation is not required on byte addressed
+machines, but it is indeed implemented in @code{GNAT}.
+This means that we can simply use the
+first record clause, together with the declaration
+
+@smallexample
+   for Data'Bit_Order use High_Order_First;
+@end smallexample
+
+@noindent
+and the effect is what is desired, namely the layout is exactly the same,
+independent of whether the code is compiled on a big-endial or little-endian
+machine.
+
+The important point to understand is that byte ordering is not affected.
+A @code{Bit_Order} attribute definition never affects which byte a field
+ends up in, only where it ends up in that byte.
+To make this clear, let us rewrite the record rep clause of the previous
+example as:
+
+@smallexample
+   for Data'Bit_Order use High_Order_First;
+   for Data use record
+      Master_Control at 0 range  0 ..  0;
+      Master_V1      at 0 range  1 ..  1;
+      Master_V2      at 0 range  2 ..  2;
+      Master_V3      at 0 range  3 ..  3;
+      Master_V4      at 0 range  4 ..  4;
+      Master_V5      at 0 range  5 ..  5;
+      Master_V6      at 0 range  6 ..  6;
+      Master_V7      at 0 range  7 ..  7;
+      Slave_Control  at 0 range  8 ..  8;
+      Slave_V1       at 0 range  9 ..  9;
+      Slave_V2       at 0 range 10 .. 10;
+      Slave_V3       at 0 range 11 .. 11;
+      Slave_V4       at 0 range 12 .. 12;
+      Slave_V5       at 0 range 13 .. 13;
+      Slave_V6       at 0 range 14 .. 14;
+      Slave_V7       at 0 range 15 .. 15;
+   end record;
+@end smallexample
+
+@noindent
+This is exactly equivalent to saying (a repeat of the first example):
+
+@smallexample
+   for Data'Bit_Order use High_Order_First;
+   for Data use record
+      Master_Control at 0 range 0 .. 0;
+      Master_V1      at 0 range 1 .. 1;
+      Master_V2      at 0 range 2 .. 2;
+      Master_V3      at 0 range 3 .. 3;
+      Master_V4      at 0 range 4 .. 4;
+      Master_V5      at 0 range 5 .. 5;
+      Master_V6      at 0 range 6 .. 6;
+      Master_V7      at 0 range 7 .. 7;
+      Slave_Control  at 1 range 0 .. 0;
+      Slave_V1       at 1 range 1 .. 1;
+      Slave_V2       at 1 range 2 .. 2;
+      Slave_V3       at 1 range 3 .. 3;
+      Slave_V4       at 1 range 4 .. 4;
+      Slave_V5       at 1 range 5 .. 5;
+      Slave_V6       at 1 range 6 .. 6;
+      Slave_V7       at 1 range 7 .. 7;
+   end record;
+@end smallexample
+
+@noindent
+Why are they equivalent? Well take a specific field, the @code{Slave_V2}
+field. The storage place attributes are obtained by normalizing the
+values given so that the @code{First_Bit} value is less than 8. After
+nromalizing the values (0,10,10) we get (1,2,2) which is exactly what
+we specified in the other case.
+
+Now one might expect that the @code{Bit_Order} attribute might affect
+bit numbering within the entire record component (two bytes in this
+case, thus affecting which byte fields end up in), but that is not
+the way this feature is defined, it only affects numbering of bits,
+not which byte they end up in.
+
+Consequently it never makes sense to specify a starting bit number
+greater than 7 (for a byte addressable field) if an attribute
+definition for @code{Bit_Order} has been given, and indeed it
+may be actively confusing to specify such a value, so the compiler
+generates a warning for such usage.
+
+If you do need to control byte ordering then appropriate conditional
+values must be used. If in our example, the slave byte came first on
+some machines we might write:
+
+@smallexample
+   Master_Byte_First constant Boolean := ...;
+
+   Master_Byte : constant Natural :=
+                   1 - Boolean'Pos (Master_Byte_First);
+   Slave_Byte  : constant Natural :=
+                   Boolean'Pos (Master_Byte_First);
+
+   for Data'Bit_Order use High_Order_First;
+   for Data use record
+      Master_Control at Master_Byte range 0 .. 0;
+      Master_V1      at Master_Byte range 1 .. 1;
+      Master_V2      at Master_Byte range 2 .. 2;
+      Master_V3      at Master_Byte range 3 .. 3;
+      Master_V4      at Master_Byte range 4 .. 4;
+      Master_V5      at Master_Byte range 5 .. 5;
+      Master_V6      at Master_Byte range 6 .. 6;
+      Master_V7      at Master_Byte range 7 .. 7;
+      Slave_Control  at Slave_Byte  range 0 .. 0;
+      Slave_V1       at Slave_Byte  range 1 .. 1;
+      Slave_V2       at Slave_Byte  range 2 .. 2;
+      Slave_V3       at Slave_Byte  range 3 .. 3;
+      Slave_V4       at Slave_Byte  range 4 .. 4;
+      Slave_V5       at Slave_Byte  range 5 .. 5;
+      Slave_V6       at Slave_Byte  range 6 .. 6;
+      Slave_V7       at Slave_Byte  range 7 .. 7;
+   end record;
+@end smallexample
+
+@noindent
+Now to switch between machines, all that is necessary is
+to set the boolean constant @code{Master_Byte_First} in
+an appropriate manner.
+
+@node Pragma Pack for Arrays
+@section Pragma Pack for Arrays
+@cindex Pragma Pack (for arrays)
+
+@noindent
+Pragma Pack applied to an array has no effect unless the component type
+is packable. For a component type to be packable, it must be one of the
+following cases:
+
+@itemize @bullet
+@item
+Any scalar type
+@item
+Any fixed-point type
+@item
+Any type whose size is specified with a size clause
+@item
+Any packed array type with a static size
+@end itemize
+
+@noindent
+For all these cases, if the component subtype size is in the range
+1- 63, then the effect of the pragma Pack is exactly as though a
+component size were specified giving the component subtype size.
+For example if we have:
+
+@smallexample
+   type r is range 0 .. 17;
+ 
+   type ar is array (1 .. 8) of r;
+   pragma Pack (ar);
+@end smallexample
+
+@noindent
+Then the component size of @code{ar} will be set to 5 (i.e. to @code{r'size},
+and the size of the array @code{ar} will be exactly 40 bits.
+
+Note that in some cases this rather fierce approach to packing can produce
+unexpected effects. For example, in Ada 95, type Natural typically has a
+size of 31, meaning that if you pack an array of Natural, you get 31-bit
+close packing, which saves a few bits, but results in far less efficient
+access. Since many other Ada compilers will ignore such a packing request,
+GNAT will generate a warning on some uses of pragma Pack that it guesses
+might not be what is intended. You can easily remove this warning by
+using an explicit Component_Size setting instead, which never generates
+a warning, since the intention of the programmer is clear in this case.
+
+GNAT treats packed arrays in one of two ways. If the size of the array is
+known at compile time and is less than 64 bits, then internally the array
+is represented as a single modular type, of exactly the appropriate number
+of bits. If the length is greater than 63 bits, or is not known at compile
+time, then the packed array is represented as an array of bytes, and the
+length is always a multiple of 8 bits.
+
+@node Pragma Pack for Records
+@section Pragma Pack for Records
+@cindex Pragma Pack (for records)
+
+@noindent
+Pragma Pack applied to a record will pack the components to reduce wasted
+space from alignment gaps and by reducing the amount of space taken by
+components. We distinguish between package components and non-packable
+components. Components of the following types are considered packable:
+
+@itemize @bullet
+@item
+All scalar types are packable.
+
+@item
+All fixed-point types are represented internally as integers, and
+are packable.
+
+@item
+Small packed arrays, whose size does not exceed 64 bits, and where the
+size is statically known at compile time, are represented internally
+as modular integers, and so they are also packable.
+
+@end itemize
+
+@noindent
+All packable components occupy the exact number of bits corresponding to
+their @code{Size} value, and are packed with no padding bits, i.e. they
+can start on an arbitrary bit boundary.
+
+All other types are non-packable, they occupy an integral number of
+storage units, and 
+are placed at a boundary corresponding to their alignment requirements.
+
+For example, consider the record
+
+@smallexample
+   type Rb1 is array (1 .. 13) of Boolean;
+   pragma Pack (rb1);
+
+   type Rb2 is array (1 .. 65) of Boolean;
+   pragma Pack (rb2);
+
+   type x2 is record
+      l1 : Boolean;
+      l2 : Duration;
+      l3 : Float;
+      l4 : Boolean;
+      l5 : Rb1;
+      l6 : Rb2;
+   end record;
+   pragma Pack (x2);
+@end smallexample
+
+@noindent
+The representation for the record x2 is as follows:
+
+@smallexample
+for x2'Size use 224;
+for x2 use record
+   l1 at  0 range  0 ..  0;
+   l2 at  0 range  1 .. 64;
+   l3 at 12 range  0 .. 31;
+   l4 at 16 range  0 ..  0;
+   l5 at 16 range  1 .. 13;
+   l6 at 18 range  0 .. 71;
+end record;
+@end smallexample
+
+@noindent
+Studying this example, we see that the packable fields @code{l1}
+and @code{l2} are
+of length equal to their sizes, and placed at specific bit boundaries (and
+not byte boundaries) to
+eliminate padding. But @code{l3} is of a non-packable float type, so
+it is on the next appropriate alignment boundary. 
+
+The next two fields are fully packable, so @code{l4} and @code{l5} are
+minimally packed with no gaps. However, type @code{Rb2} is a packed
+array that is longer than 64 bits, so it is itself non-packable. Thus
+the @code{l6} field is aligned to the next byte boundary, and takes an
+integral number of bytes, i.e. 72 bits.
+
+@node Record Representation Clauses
+@section Record Representation Clauses
+@cindex Record Representation Clause
+
+@noindent
+Record representation clauses may be given for all record types, including
+types obtained by record extension. Component clauses are allowed for any
+static component. The restrictions on component clauses depend on the type
+of the component.
+
+@cindex Component Clause
+For all components of an elementary type, the only restriction on component
+clauses is that the size must be at least the 'Size value of the type
+(actually the Value_Size). There are no restrictions due to alignment,
+and such components may freely cross storage boundaries.
+
+Packed arrays with a size up to and including 64-bits are represented
+internally using a modular type with the appropriate number of bits, and
+thus the same lack of restriction applies. For example, if you declare:
+
+@smallexample
+   type R is array (1 .. 49) of Boolean;
+   pragma Pack (R);
+   for R'Size use 49;
+@end smallexample
+
+@noindent
+then a component clause for a component of type R may start on any
+specified bit boundary, and may specify a value of 49 bits or greater.
+
+For non-primitive types, including packed arrays with a size greater than
+64-bits, component clauses must respect the alignment requirement of the
+type, in particular, always starting on a byte boundary, and the length
+must be a multiple of the storage unit.
+
+The tag field of a tagged type always occupies an address sized field at
+the start of the record. No component clause may attempt to overlay this
+tag.
+
+In the case of a record extension T1, of a type T, no component clause applied
+to the type T1 can specify a storage location that would overlap the first
+T'Size bytes of the record.
+
+@node Enumeration Clauses
+@section Enumeration Clauses
+
+The only restriction on enumeration clauses is that the range of values
+must be representable. For the signed case, if one or more of the
+representation values are negative, all values must be in the range:
+
+@smallexample
+   System.Min_Int .. System.Max_Int
+@end smallexample
+
+@noindent
+For the unsigned case, where all values are non negative, the values must
+be in the range:
+
+@smallexample
+   0 .. System.Max_Binary_Modulus;
+@end smallexample
+
+@noindent
+A "confirming" representation clause is one in which the values range
+from 0 in sequence, i.e. a clause that confirms the default representation
+for an enumeration type.
+Such a confirming representation
+is permitted by these rules, and is specially recognized by the compiler so
+that no extra overhead results from the use of such a clause.
+
+If an array has an index type which is an enumeration type to which an
+enumeration clause has been applied, then the array is stored in a compact
+manner. Consider the declarations:
+
+@smallexample
+   type r is (A, B, C);
+   for r use (A => 1, B => 5, C => 10);
+   type t is array (r) of Character;
+@end smallexample
+
+@noindent
+The array type t corresponds to a vector with exactly three elements and
+has a default size equal to @code{3*Character'Size}. This ensures efficient
+use of space, but means that accesses to elements of the array will incur
+the overhead of converting representation values to the corresponding
+positional values, (i.e. the value delivered by the  @code{Pos} attribute).
+
+@node Address Clauses
+@section Address Clauses
+@cindex Address Clause
+
+The reference manual allows a general restriction on representation clauses,
+as found in RM 13.1(22):
+
+@smallexample
+   An implementation need not support representation
+   items containing nonstatic expressions, except that
+   an implementation should support a representation item
+   for a given entity if each nonstatic expression in the
+   representation item is a name that statically denotes
+   a constant declared before the entity.
+@end smallexample
+
+@noindent
+In practice this is applicable only to address clauses, since this is the
+only case in which a non-static expression is permitted by the syntax. As
+the AARM notes in sections 13.1 (22.a-22.h):
+
+@smallexample
+  22.a   Reason: This is to avoid the following sort
+         of thing:
+
+  22.b        X : Integer := F(...);
+              Y : Address := G(...);
+              for X'Address use Y;
+
+  22.c   In the above, we have to evaluate the
+         initialization expression for X before we
+         know where to put the result. This seems
+         like an unreasonable implementation burden.
+
+  22.d   The above code should instead be written
+         like this:
+
+  22.e        Y : constant Address := G(...);
+              X : Integer := F(...);
+              for X'Address use Y;
+
+  22.f   This allows the expression ``Y'' to be safely
+         evaluated before X is created.
+
+  22.g   The constant could be a formal parameter of mode in.
+
+  22.h   An implementation can support other nonstatic
+         expressions if it wants to. Expressions of type
+         Address are hardly ever static, but their value
+         might be known at compile time anyway in many
+         cases.
+@end smallexample
+
+@noindent
+GNAT does indeed permit many additional cases of non-static expressions. In
+particular, if the type involved is elementary there are no restrictions
+(since in this case, holding a temporary copy of the initialization value,
+if one is present, is inexpensive). In addition, if there is no implicit or
+explicit initialization, then there are no restrictions. GNAT will reject
+only the case where all three of these conditions hold:
+
+@itemize @bullet
+
+@item
+The type of the item is non-elementary (e.g. a record or array).
+
+@item
+There is explicit or implicit initialization required for the object.
+
+@item
+The address value is non-static. Here GNAT is more permissive than the
+RM, and allows the address value to be the address of a previously declared
+stand-alone variable, as long as it does not itself have an address clause.
+
+@smallexample
+           Anchor : Some_Initialized_Type;
+           Overlay : Some_Initialized_Type;
+           for Overlay'Address use Anchor'Address;
+@end smallexample
+
+However, the prefix of the address clause cannot be an array component, or
+a component of a discriminated record.
+
+@end itemize
+
+@noindent
+As noted above in section 22.h, address values are typically non-static. In
+particular the To_Address function, even if applied to a literal value, is
+a non-static function call. To avoid this minor annoyance, GNAT provides
+the implementation defined attribute 'To_Address. The following two 
+expressions have identical values:
+
+@findex Attribute
+@findex To_Address
+@smallexample
+   To_Address (16#1234_0000#)
+   System'To_Address (16#1234_0000#);
+@end smallexample
+
+@noindent
+except that the second form is considered to be a static expression, and
+thus when used as an address clause value is always permitted.
+
+@noindent
+Additionally, GNAT treats as static an address clause that is an
+unchecked_conversion of a static integer value. This simplifies the porting
+of legacy code, and provides a portable equivalent to the GNAT attribute
+To_Address.
+
+@findex Export
+An address clause cannot be given for an exported object. More
+understandably the real restriction is that objects with an address
+clause cannot be exported. This is because such variables are not
+defined by the Ada program, so there is no external object so export.
+
+@findex Import
+It is permissible to give an address clause and a pragma Import for the
+same object. In this case, the variable is not really defined by the
+Ada program, so there is no external symbol to be linked. The link name
+and the external name are ignored in this case. The reason that we allow this
+combination is that it provides a useful idiom to avoid unwanted
+initializations on objects with address clauses.
+
+When an address clause is given for an object that has implicit or
+explicit initialization, then by default initialization takes place. This
+means that the effect of the object declaration is to overwrite the
+memory at the specified address. This is almost always not what the
+programmer wants, so GNAT will output a warning:
+
+@smallexample
+  with System;
+  package G is
+     type R is record
+        M : Integer := 0;
+     end record;
+  
+     Ext : R;
+     for Ext'Address use System'To_Address (16#1234_1234#);
+         |
+  >>> warning: implicit initialization of "Ext" may
+      modify overlaid storage
+  >>> warning: use pragma Import for "Ext" to suppress
+      initialization (RM B(24))
+  
+  end G;
+@end smallexample
+
+@noindent
+As indicated by the warning message, the solution is to use a (dummy) pragma
+Import to suppress this initialization. The pragma tell the compiler that the
+object is declared and initialized elsewhere. The following package compiles
+without warnings (and the initialization is suppressed):
+
+@smallexample
+   with System;
+   package G is
+      type R is record
+         M : Integer := 0;
+      end record;
+   
+      Ext : R;
+      for Ext'Address use System'To_Address (16#1234_1234#);
+      pragma Import (Ada, Ext);
+   end G;
+@end smallexample
+
+@node Effect of Convention on Representation
+@section Effect of Convention on Representation
+@cindex Convention, effect on representation
+
+@noindent
+Normally the specification of a foreign language convention for a type or
+an object has no effect on the chosen representation. In particular, the
+representation chosen for data in GNAT generally meets the standard system
+conventions, and for example records are laid out in a manner that is
+consistent with C. This means that specifying convention C (for example)
+has no effect.
+
+There are three exceptions to this general rule:
+
+@itemize @bullet
+
+@item Convention Fortran and array subtypes
+If pragma Convention Fortran is specified for an array subtype, then in
+accordance with the implementation advice in section 3.6.2(11) of the
+Ada Reference Manual, the array will be stored in a Fortran-compatible
+column-major manner, instead of the normal default row-major order.
+
+@item Convention C and enumeration types
+GNAT normally stores enumeration types in 8, 16, or 32 bits as required
+to accommodate all values of the type. For example, for the enumeration
+type declared by:
+
+@smallexample
+   type Color is (Red, Green, Blue);
+@end smallexample
+
+@noindent
+8 bits is sufficient to store all values of the type, so by default, objects
+of type @code{Color} will be represented using 8 bits. However, normal C
+convention is to use 32-bits for all enum values in C, since enum values
+are essentially of type int. If pragma Convention C is specified for an
+Ada enumeration type, then the size is modified as necessary (usually to
+32 bits) to be consistent with the C convention for enum values.
+
+@item Convention C/Fortran and Boolean types
+In C, the usual convention for boolean values, that is values used for
+conditions, is that zero represents false, and nonzero values represent
+true. In Ada, the normal convention is that two specific values, typically
+0/1, are used to represent false/true respectively.
+
+Fortran has a similar convention for @code{LOGICAL} values (any nonzero
+value represents true).
+
+To accommodate the Fortran and C conventions, if a pragma Convention specifies
+C or Fortran convention for a derived Boolean, as in the following example:
+
+@smallexample
+   type C_Switch is new Boolean;
+   pragma Convention (C, C_Switch);
+@end smallexample
+
+@noindent
+then the GNAT generated code will treat any nonzero value as true. For truth
+values generated by GNAT, the conventional value 1 will be used for True, but
+when one of these values is read, any nonzero value is treated as True.
+
+@end itemize
+
+@node Determining the Representations chosen by GNAT
+@section Determining the Representations chosen by GNAT
+@cindex Representation, determination of
+@cindex -gnatR switch
+
+@noindent
+Although the descriptions in this section are intended to be complete, it is
+often easier to simply experiment to see what GNAT accepts and what the
+effect is on the layout of types and objects.
+
+As required by the Ada RM, if a representation clause is not accepted, then
+it must be rejected as illegal by the compiler. However, when a representation
+clause or pragma is accepted, there can still be questions of what the
+compiler actually does. For example, if a partial record representation
+clause specifies the location of some components and not others, then where
+are the non-specified components placed? Or if pragma pack is used on a
+record, then exactly where are the resulting fields placed? The section
+on pragma Pack in this chapter can be used to answer the second question,
+but it is often easier to just see what the compiler does.
+
+For this purpose, GNAT provides the option @code{-gnatR}. If you compile
+with this option, then the compiler will output information on the actual
+representations chosen, in a format similar to source representation
+clauses. For example, if we compile the package:
+
+@smallexample
+package q is
+   type r (x : boolean) is tagged record
+      case x is
+         when True => S : String (1 .. 100);
+         when False => null;
+      end case;
+   end record;
+
+   type r2 is new r (false) with record
+      y2 : integer;
+   end record;
+
+   for r2 use record
+      y2 at 16 range 0 .. 31;
+   end record;
+
+   type x is record
+      y : character;
+   end record;
+
+   type x1 is array (1 .. 10) of x;
+   for x1'component_size use 11;
+
+   type ia is access integer;
+
+   type Rb1 is array (1 .. 13) of Boolean;
+   pragma Pack (rb1);
+
+   type Rb2 is array (1 .. 65) of Boolean;
+   pragma Pack (rb2);
+
+   type x2 is record
+      l1 : Boolean;
+      l2 : Duration;
+      l3 : Float;
+      l4 : Boolean;
+      l5 : Rb1;
+      l6 : Rb2;
+   end record;
+   pragma Pack (x2);
+end q;
+@end smallexample
+
+@noindent
+using the switch @code{-gnatR} we obtain the following output:
+
+@smallexample
+Representation information for unit q
+-------------------------------------
+
+for r'Size use ??;
+for r'Alignment use 4;
+for r use record
+   x    at 4 range  0 ..  7;
+   _tag at 0 range  0 .. 31;
+   s    at 5 range  0 .. 799;
+end record;
+
+for r2'Size use 160;
+for r2'Alignment use 4;
+for r2 use record
+   x       at  4 range  0 ..  7;
+   _tag    at  0 range  0 .. 31;
+   _parent at  0 range  0 .. 63;
+   y2      at 16 range  0 .. 31;
+end record;
+
+for x'Size use 8;
+for x'Alignment use 1;
+for x use record
+   y at 0 range  0 ..  7;
+end record;
+
+for x1'Size use 112;
+for x1'Alignment use 1;
+for x1'Component_Size use 11;
+
+for rb1'Size use 13;
+for rb1'Alignment use 2;
+for rb1'Component_Size use 1;
+
+for rb2'Size use 72;
+for rb2'Alignment use 1;
+for rb2'Component_Size use 1;
+
+for x2'Size use 224;
+for x2'Alignment use 4;
+for x2 use record
+   l1 at  0 range  0 ..  0;
+   l2 at  0 range  1 .. 64;
+   l3 at 12 range  0 .. 31;
+   l4 at 16 range  0 ..  0;
+   l5 at 16 range  1 .. 13;
+   l6 at 18 range  0 .. 71;
+end record;
+@end smallexample
+
+@noindent
+The Size values are actually the Object_Size, i.e. the default size that
+will be allocated for objects of the type.
+The ?? size for type r indicates that we have a variant record, and the
+actual size of objects will depend on the discriminant value.
+
+The Alignment values show the actual alignment chosen by the compiler
+for each record or array type.
+
+The record representation clause for type r shows where all fields
+are placed, including the compiler generated tag field (whose location
+cannot be controlled by the programmer).
+
+The record representation clause for the type extension r2 shows all the
+fields present, including the parent field, which is a copy of the fields
+of the parent type of r2, i.e. r1.
+
+The component size and size clauses for types rb1 and rb2 show
+the exact effect of pragma Pack on these arrays, and the record
+representation clause for type x2 shows how pragma Pack affects
+this record type.
+
+In some cases, it may be useful to cut and paste the representation clauses
+generated by the compiler into the original source to fix and guarantee
+the actual representation to be used.
+
+@node Standard Library Routines
+@chapter Standard Library Routines
+
+@noindent
+The Ada 95 Reference Manual contains in Annex A a full description of an
+extensive set of standard library routines that can be used in any Ada
+program, and which must be provided by all Ada compilers. They are
+analogous to the standard C library used by C programs.
+
+GNAT implements all of the facilities described in annex A, and for most
+purposes the description in the Ada 95
+reference manual, or appropriate Ada
+text book, will be sufficient for making use of these facilities.
+
+In the case of the input-output facilities, @xref{The Implementation of
+Standard I/O}, gives details on exactly how GNAT interfaces to the
+file system. For the remaining packages, the Ada 95 reference manual
+should be sufficient. The following is a list of the packages included,
+together with a brief description of the functionality that is provided.
+
+For completeness, references are included to other predefined library
+routines defined in other sections of the Ada 95 reference manual (these are
+cross-indexed from annex A).
+
+@table @code
+@item Ada (A.2)
+This is a parent package for all the standard library packages. It is
+usually included implicitly in your program, and itself contains no
+useful data or routines.
+
+@item Ada.Calendar (9.6)
+@code{Calendar} provides time of day access, and routines for
+manipulating times and durations.
+
+@item Ada.Characters (A.3.1)
+This is a dummy parent package that contains no useful entities
+
+@item Ada.Characters.Handling (A.3.2)
+This package provides some basic character handling capabilities,
+including classification functions for classes of characters (e.g. test
+for letters, or digits).
+
+@item Ada.Characters.Latin_1 (A.3.3)
+This package includes a complete set of definitions of the characters
+that appear in type CHARACTER. It is useful for writing programs that
+will run in international environments. For example, if you want an
+upper case E with an acute accent in a string, it is often better to use
+the definition of @code{UC_E_Acute} in this package. Then your program
+will print in an understandable manner even if your environment does not
+support these extended characters.
+
+@item Ada.Command_Line (A.15)
+This package provides access to the command line parameters and the name
+of the current program (analogous to the use of argc and argv in C), and
+also allows the exit status for the program to be set in a
+system-independent manner.
+
+@item Ada.Decimal (F.2)
+This package provides constants describing the range of decimal numbers
+implemented, and also a decimal divide routine (analogous to the COBOL
+verb DIVIDE .. GIVING .. REMAINDER ..)
+
+@item Ada.Direct_IO (A.8.4)
+This package provides input-output using a model of a set of records of
+fixed-length, containing an arbitrary definite Ada type, indexed by an
+integer record number.
+
+@item Ada.Dynamic_Priorities (D.5)
+This package allows the priorities of a task to be adjusted dynamically
+as the task is running.
+
+@item Ada.Exceptions (11.4.1)
+This package provides additional information on exceptions, and also
+contains facilities for treating exceptions as data objects, and raising
+exceptions with associated messages.
+
+@item Ada.Finalization (7.6)
+This package contains the declarations and subprograms to support the
+use of controlled types, providing for automatic initialization and
+finalization (analogous to the constructors and destructors of C++)
+
+@item Ada.Interrupts (C.3.2)
+This package provides facilities for interfacing to interrupts, which
+includes the set of signals or conditions that can be raised and
+recognized as interrupts.
+
+@item Ada.Interrupts.Names (C.3.2)
+This package provides the set of interrupt names (actually signal
+or condition names) that can be handled by GNAT.
+
+@item Ada.IO_Exceptions (A.13)
+This package defines the set of exceptions that can be raised by use of
+the standard IO packages.
+
+@item Ada.Numerics
+This package contains some standard constants and exceptions used
+throughout the numerics packages. Note that the constants pi and e are
+defined here, and it is better to use these definitions than rolling
+your own.
+
+@item Ada.Numerics.Complex_Elementary_Functions
+Provides the implementation of standard elementary functions (such as
+log and trigonometric functions) operating on complex numbers using the
+standard @code{Float} and the @code{Complex} and @code{Imaginary} types
+created by the package @code{Numerics.Complex_Types}.
+
+@item Ada.Numerics.Complex_Types
+This is a predefined instantiation of
+@code{Numerics.Generic_Complex_Types} using @code{Standard.Float} to
+build the type @code{Complex} and @code{Imaginary}.
+
+@item Ada.Numerics.Discrete_Random
+This package provides a random number generator suitable for generating
+random integer values from a specified range.
+
+@item Ada.Numerics.Float_Random
+This package provides a random number generator suitable for generating
+uniformly distributed floating point values.
+
+@item Ada.Numerics.Generic_Complex_Elementary_Functions
+This is a generic version of the package that provides the
+implementation of standard elementary functions (such as log an
+trigonometric functions) for an arbitrary complex type.
+
+The following predefined instantiations of this package exist
+
+@table @code
+@item Short_Float
+@code{Ada.Numerics.Short_Complex_Elementary_Functions}
+@item Float
+@code{Ada.Numerics.Complex_Elementary_Functions}
+@item Long_Float
+@code{Ada.Numerics.
+ Long_Complex_Elementary_Functions}
+@end table
+
+@item Ada.Numerics.Generic_Complex_Types
+This is a generic package that allows the creation of complex types,
+with associated complex arithmetic operations.
+
+The following predefined instantiations of this package exist
+@table @code
+@item Short_Float
+@code{Ada.Numerics.Short_Complex_Complex_Types}
+@item Float
+@code{Ada.Numerics.Complex_Complex_Types}
+@item Long_Float
+@code{Ada.Numerics.Long_Complex_Complex_Types}
+@end table
+
+@item Ada.Numerics.Generic_Elementary_Functions
+This is a generic package that provides the implementation of standard
+elementary functions (such as log an trigonometric functions) for an
+arbitrary float type.
+
+The following predefined instantiations of this package exist
+
+@table @code
+@item Short_Float
+@code{Ada.Numerics.Short_Elementary_Functions}
+@item Float
+@code{Ada.Numerics.Elementary_Functions}
+@item Long_Float
+@code{Ada.Numerics.Long_Elementary_Functions}
+@end table
+
+@item Ada.Real_Time (D.8)
+This package provides facilities similar to those of @code{Calendar}, but
+operating with a finer clock suitable for real time control.
+
+@item Ada.Sequential_IO (A.8.1)
+This package provides input-output facilities for sequential files,
+which can contain a sequence of values of a single type, which can be
+any Ada type, including indefinite (unconstrained) types.
+
+@item Ada.Storage_IO (A.9)
+This package provides a facility for mapping arbitrary Ada types to and
+from a storage buffer. It is primarily intended for the creation of new
+IO packages.
+
+@item Ada.Streams (13.13.1)
+This is a generic package that provides the basic support for the
+concept of streams as used by the stream attributes (@code{Input},
+@code{Output}, @code{Read} and @code{Write}).
+
+@item Ada.Streams.Stream_IO (A.12.1)
+This package is a specialization of the type @code{Streams} defined in
+package @code{Streams} together with a set of operations providing
+Stream_IO capability. The Stream_IO model permits both random and
+sequential access to a file which can contain an arbitrary set of values
+of one or more Ada types.
+
+@item Ada.Strings (A.4.1)
+This package provides some basic constants used by the string handling
+packages.
+
+@item Ada.Strings.Bounded (A.4.4)
+This package provides facilities for handling variable length
+strings. The bounded model requires a maximum length. It is thus
+somewhat more limited than the unbounded model, but avoids the use of
+dynamic allocation or finalization.
+
+@item Ada.Strings.Fixed (A.4.3)
+This package provides facilities for handling fixed length strings.
+
+@item Ada.Strings.Maps (A.4.2)
+This package provides facilities for handling character mappings and
+arbitrarily defined subsets of characters. For instance it is useful in
+defining specialized translation tables.
+
+@item Ada.Strings.Maps.Constants (A.4.6)
+This package provides a standard set of predefined mappings and
+predefined character sets. For example, the standard upper to lower case
+conversion table is found in this package. Note that upper to lower case
+conversion is non-trivial if you want to take the entire set of
+characters, including extended characters like E with an acute accent,
+into account. You should use the mappings in this package (rather than
+adding 32 yourself) to do case mappings.
+
+@item Ada.Strings.Unbounded (A.4.5)
+This package provides facilities for handling variable length
+strings. The unbounded model allows arbitrary length strings, but
+requires the use of dynamic allocation and finalization.
+
+@item Ada.Strings.Wide_Bounded (A.4.7)
+@itemx Ada.Strings.Wide_Fixed (A.4.7)
+@itemx Ada.Strings.Wide_Maps (A.4.7)
+@itemx Ada.Strings.Wide_Maps.Constants (A.4.7)
+@itemx Ada.Strings.Wide_Unbounded (A.4.7)
+These package provide analogous capabilities to the corresponding
+packages without @samp{Wide_} in the name, but operate with the types
+@code{Wide_String} and @code{Wide_Character} instead of @code{String}
+and @code{Character}.
+
+@item Ada.Synchronous_Task_Control (D.10)
+This package provides some standard facilities for controlling task
+communication in a synchronous manner.
+
+@item Ada.Tags
+This package contains definitions for manipulation of the tags of tagged
+values.
+
+@item Ada.Task_Attributes
+This package provides the capability of associating arbitrary
+task-specific data with separate tasks.
+
+@item Ada.Text_IO
+This package provides basic text input-output capabilities for
+character, string and numeric data. The subpackages of this
+package are listed next.
+
+@item Ada.Text_IO.Decimal_IO
+Provides input-output facilities for decimal fixed-point types
+
+@item Ada.Text_IO.Enumeration_IO 
+Provides input-output facilities for enumeration types.
+
+@item Ada.Text_IO.Fixed_IO
+Provides input-output facilities for ordinary fixed-point types.
+
+@item Ada.Text_IO.Float_IO
+Provides input-output facilities for float types. The following
+predefined instantiations of this generic package are available:
+
+@table @code
+@item Short_Float
+@code{Short_Float_Text_IO}
+@item Float
+@code{Float_Text_IO}
+@item Long_Float
+@code{Long_Float_Text_IO}
+@end table
+
+@item Ada.Text_IO.Integer_IO
+Provides input-output facilities for integer types. The following
+predefined instantiations of this generic package are available:
+
+@table @code
+@item Short_Short_Integer
+@code{Ada.Short_Short_Integer_Text_IO}
+@item Short_Integer
+@code{Ada.Short_Integer_Text_IO}
+@item Integer
+@code{Ada.Integer_Text_IO}
+@item Long_Integer
+@code{Ada.Long_Integer_Text_IO}
+@item Long_Long_Integer
+@code{Ada.Long_Long_Integer_Text_IO}
+@end table
+
+@item Ada.Text_IO.Modular_IO
+Provides input-output facilities for modular (unsigned) types
+
+@item Ada.Text_IO.Complex_IO (G.1.3)
+This package provides basic text input-output capabilities for complex
+data.
+
+@item Ada.Text_IO.Editing (F.3.3)
+This package contains routines for edited output, analogous to the use
+of pictures in COBOL. The picture formats used by this package are a
+close copy of the facility in COBOL.
+
+@item Ada.Text_IO.Text_Streams (A.12.2)
+This package provides a facility that allows Text_IO files to be treated
+as streams, so that the stream attributes can be used for writing
+arbitrary data, including binary data, to Text_IO files.
+
+@item Ada.Unchecked_Conversion (13.9)
+This generic package allows arbitrary conversion from one type to
+another of the same size, providing for breaking the type safety in
+special circumstances.
+
+If the types have the same Size (more accurately the same Value_Size),
+then the effect is simply to transfer the bits from the source to the
+target type without any modification. This usage is well defined, and
+for simple types whose representation is typically the same across
+all implementations, gives a portable method of performing such
+conversions.
+
+If the types do not have the same size, then the result is implementation
+defined, and thus may be non-portable. The following describes how GNAT
+handles such unchecked conversion cases.
+
+If the types are of different sizes, and are both discrete types, then
+the effect is of a normal type conversion without any constraint checking.
+In particular if the result type has a larger size, the result will be
+zero or sign extended. If the result type has a smaller size, the result
+will be truncated by ignoring high order bits.
+
+If the types are of different sizes, and are not both discrete types,
+then the conversion works as though pointers were created to the source
+and target, and the pointer value is converted. The effect is that bits
+are copied from successive low order storage units and bits of the source
+up to the length of the target type.
+
+A warning is issued if the lengths differ, since the effect in this
+case is implementation dependent, and the above behavior may not match
+that of some other compiler.
+
+A pointer to one type may be converted to a pointer to another type using
+unchecked conversion. The only case in which the effect is undefined is
+when one or both pointers are pointers to unconstrained array types. In
+this case, the bounds information may get incorrectly transferred, and in
+particular, GNAT uses double size pointers for such types, and it is
+meaningless to convert between such pointer types. GNAT will issue a
+warning if the alignment of the target designated type is more strict
+than the alignment of the source designated type (since the result may
+be unaligned in this case).
+
+A pointer other than a pointer to an unconstrained array type may be
+converted to and from System.Address. Such usage is common in Ada 83
+programs, but note that Ada.Address_To_Access_Conversions is the
+preferred method of performing such conversions in Ada 95. Neither
+unchecked conversion nor Ada.Address_To_Access_Conversions should be
+used in conjunction with pointers to unconstrained objects, since
+the bounds information cannot be handled correctly in this case.
+
+@item Ada.Unchecked_Deallocation (13.11.2)
+This generic package allows explicit freeing of storage previously
+allocated by use of an allocator.
+
+@item Ada.Wide_Text_IO (A.11)
+This package is similar to @code{Ada.Text_IO}, except that the external
+file supports wide character representations, and the internal types are
+@code{Wide_Character} and @code{Wide_String} instead of @code{Character}
+and @code{String}. It contains generic subpackages listed next.
+
+@item Ada.Wide_Text_IO.Decimal_IO
+Provides input-output facilities for decimal fixed-point types
+
+@item Ada.Wide_Text_IO.Enumeration_IO
+Provides input-output facilities for enumeration types.
+
+@item Ada.Wide_Text_IO.Fixed_IO
+Provides input-output facilities for ordinary fixed-point types.
+
+@item Ada.Wide_Text_IO.Float_IO
+Provides input-output facilities for float types. The following
+predefined instantiations of this generic package are available:
+
+@table @code
+@item Short_Float
+@code{Short_Float_Wide_Text_IO}
+@item Float
+@code{Float_Wide_Text_IO}
+@item Long_Float
+@code{Long_Float_Wide_Text_IO}
+@end table
+
+@item Ada.Wide_Text_IO.Integer_IO
+Provides input-output facilities for integer types. The following
+predefined instantiations of this generic package are available:
+
+@table @code
+@item Short_Short_Integer
+@code{Ada.Short_Short_Integer_Wide_Text_IO}
+@item Short_Integer
+@code{Ada.Short_Integer_Wide_Text_IO}
+@item Integer
+@code{Ada.Integer_Wide_Text_IO}
+@item Long_Integer
+@code{Ada.Long_Integer_Wide_Text_IO}
+@item Long_Long_Integer
+@code{Ada.Long_Long_Integer_Wide_Text_IO}
+@end table
+
+@item Ada.Wide_Text_IO.Modular_IO
+Provides input-output facilities for modular (unsigned) types
+
+@item Ada.Wide_Text_IO.Complex_IO (G.1.3)
+This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
+external file supports wide character representations.
+
+@item Ada.Wide_Text_IO.Editing (F.3.4)
+This package is similar to @code{Ada.Text_IO.Editing}, except that the
+types are @code{Wide_Character} and @code{Wide_String} instead of
+@code{Character} and @code{String}.
+
+@item Ada.Wide_Text_IO.Streams (A.12.3)
+This package is similar to @code{Ada.Text_IO.Streams}, except that the
+types are @code{Wide_Character} and @code{Wide_String} instead of
+@code{Character} and @code{String}.
+@end table
+@node The Implementation of Standard I/O
+@chapter The Implementation of Standard I/O
+
+@noindent
+GNAT implements all the required input-output facilities described in
+A.6 through A.14. These sections of the Ada 95 reference manual describe the
+required behavior of these packages from the Ada point of view, and if
+you are writing a portable Ada program that does not need to know the
+exact manner in which Ada maps to the outside world when it comes to
+reading or writing external files, then you do not need to read this
+chapter. As long as your files are all regular files (not pipes or
+devices), and as long as you write and read the files only from Ada, the
+description in the Ada 95 reference manual is sufficient.
+
+However, if you want to do input-output to pipes or other devices, such
+as the keyboard or screen, or if the files you are dealing with are
+either generated by some other language, or to be read by some other
+language, then you need to know more about the details of how the GNAT
+implementation of these input-output facilities behaves.
+
+In this chapter we give a detailed description of exactly how GNAT
+interfaces to the file system. As always, the sources of the system are
+available to you for answering questions at an even more detailed level,
+but for most purposes the information in this chapter will suffice.
+
+Another reason that you may need to know more about how input-output is
+implemented arises when you have a program written in mixed languages
+where, for example, files are shared between the C and Ada sections of
+the same program. GNAT provides some additional facilities, in the form
+of additional child library packages, that facilitate this sharing, and
+these additional facilities are also described in this chapter.
+
+@menu
+* Standard I/O Packages::       
+* FORM Strings::                
+* Direct_IO::                   
+* Sequential_IO::               
+* Text_IO::                     
+* Wide_Text_IO::                
+* Stream_IO::                   
+* Shared Files::                
+* Open Modes::                  
+* Operations on C Streams::     
+* Interfacing to C Streams::    
+@end menu
+
+@node Standard I/O Packages
+@section Standard I/O Packages
+
+@noindent
+The Standard I/O packages described in Annex A for
+
+@itemize @bullet
+@item
+Ada.Text_IO
+@item
+Ada.Text_IO.Complex_IO
+@item
+Ada.Text_IO.Text_Streams,
+@item
+Ada.Wide_Text_IO
+@item
+Ada.Wide_Text_IO.Complex_IO,
+@item
+Ada.Wide_Text_IO.Text_Streams
+@item
+Ada.Stream_IO
+@item
+Ada.Sequential_IO
+@item
+Ada.Direct_IO
+@end itemize
+
+@noindent
+are implemented using the C
+library streams facility; where
+
+@itemize @bullet
+@item
+All files are opened using @code{fopen}.
+@item
+All input/output operations use @code{fread}/@code{fwrite}.
+@end itemize
+
+There is no internal buffering of any kind at the Ada library level. The
+only buffering is that provided at the system level in the
+implementation of the C library routines that support streams. This
+facilitates shared use of these streams by mixed language programs.
+
+@node FORM Strings
+@section FORM Strings
+
+@noindent
+The format of a FORM string in GNAT is:
+
+@smallexample
+"keyword=value,keyword=value,...,keyword=value"
+@end smallexample
+
+@noindent
+where letters may be in upper or lower case, and there are no spaces
+between values. The order of the entries is not important. Currently
+there are two keywords defined.
+
+@smallexample
+SHARED=[YES|NO]
+WCEM=[n|h|u|s\e]
+@end smallexample
+
+The use of these parameters is described later in this section.
+
+@node Direct_IO
+@section Direct_IO
+
+@noindent
+Direct_IO can only be instantiated for definite types. This is a
+restriction of the Ada language, which means that the records are fixed
+length (the length being determined by @code{@var{type}'Size}, rounded
+up to the next storage unit boundary if necessary).
+
+The records of a Direct_IO file are simply written to the file in index
+sequence, with the first record starting at offset zero, and subsequent
+records following. There is no control information of any kind. For
+example, if 32-bit integers are being written, each record takes
+4-bytes, so the record at index @var{K} starts at offset (@var{K} -
+1)*4.
+
+There is no limit on the size of Direct_IO files, they are expanded as
+necessary to accommodate whatever records are written to the file.
+
+@node Sequential_IO
+@section Sequential_IO
+
+@noindent
+Sequential_IO may be instantiated with either a definite (constrained)
+or indefinite (unconstrained) type.
+
+For the definite type case, the elements written to the file are simply
+the memory images of the data values with no control information of any
+kind. The resulting file should be read using the same type, no validity
+checking is performed on input.
+
+For the indefinite type case, the elements written consist of two
+parts. First is the size of the data item, written as the memory image
+of a @code{Interfaces.C.size_t} value, followed by the memory image of
+the data value. The resulting file can only be read using the same
+(unconstrained) type. Normal assignment checks are performed on these
+read operations, and if these checks fail, @code{Data_Error} is
+raised. In particular, in the array case, the lengths must match, and in
+the variant record case, if the variable for a particular read operation
+is constrained, the discriminants must match.
+
+Note that it is not possible to use Sequential_IO to write variable
+length array items, and then read the data back into different length
+arrays. For example, the following will raise @code{Data_Error}:
+
+@smallexample
+ package IO is new Sequential_IO (String);
+ F : IO.File_Type;
+ S : String (1..4);
+ ...
+ IO.Create (F)
+ IO.Write (F, "hello!")
+ IO.Reset (F, Mode=>In_File);
+ IO.Read (F, S);
+ Put_Line (S);
+
+@end smallexample
+
+On some Ada implementations, this will print @samp{hell}, but the program is
+clearly incorrect, since there is only one element in the file, and that
+element is the string @samp{hello!}.
+
+In Ada 95, this kind of behavior can be legitimately achieved using
+Stream_IO, and this is the preferred mechanism. In particular, the above
+program fragment rewritten to use Stream_IO will work correctly.
+
+@node Text_IO
+@section Text_IO
+
+@noindent
+Text_IO files consist of a stream of characters containing the following
+special control characters:
+
+@smallexample
+LF (line feed, 16#0A#) Line Mark
+FF (form feed, 16#0C#) Page Mark
+@end smallexample
+
+A canonical Text_IO file is defined as one in which the following
+conditions are met:
+
+@itemize @bullet
+@item
+The character @code{LF} is used only as a line mark, i.e. to mark the end
+of the line.
+
+@item
+The character @code{FF} is used only as a page mark, i.e. to mark the
+end of a page and consequently can appear only immediately following a
+@code{LF} (line mark) character.
+
+@item
+The file ends with either @code{LF} (line mark) or @code{LF}-@code{FF}
+(line mark, page mark). In the former case, the page mark is implicitly
+assumed to be present.
+@end itemize
+
+A file written using Text_IO will be in canonical form provided that no
+explicit @code{LF} or @code{FF} characters are written using @code{Put}
+or @code{Put_Line}. There will be no @code{FF} character at the end of
+the file unless an explicit @code{New_Page} operation was performed
+before closing the file.
+
+A canonical Text_IO file that is a regular file, i.e. not a device or a
+pipe, can be read using any of the routines in Text_IO. The
+semantics in this case will be exactly as defined in the Ada 95 reference
+manual and all the routines in Text_IO are fully implemented.
+
+A text file that does not meet the requirements for a canonical Text_IO
+file has one of the following:
+
+@itemize @bullet
+@item
+The file contains @code{FF} characters not immediately following a
+@code{LF} character.
+
+@item
+The file contains @code{LF} or @code{FF} characters written by
+@code{Put} or @code{Put_Line}, which are not logically considered to be
+line marks or page marks.
+
+@item
+The file ends in a character other than @code{LF} or @code{FF},
+i.e. there is no explicit line mark or page mark at the end of the file.
+@end itemize
+
+Text_IO can be used to read such non-standard text files but subprograms
+to do with line or page numbers do not have defined meanings. In
+particular, a @code{FF} character that does not follow a @code{LF}
+character may or may not be treated as a page mark from the point of
+view of page and line numbering. Every @code{LF} character is considered
+to end a line, and there is an implied @code{LF} character at the end of
+the file.
+
+@menu
+* Text_IO Stream Pointer Positioning::  
+* Text_IO Reading and Writing Non-Regular Files::  
+* Get_Immediate::               
+* Treating Text_IO Files as Streams::
+* Text_IO Extensions::
+* Text_IO Facilities for Unbounded Strings::
+@end menu
+@node Text_IO Stream Pointer Positioning
+
+@subsection Stream Pointer Positioning
+
+@noindent
+@code{Ada.Text_IO} has a definition of current position for a file that
+is being read. No internal buffering occurs in Text_IO, and usually the
+physical position in the stream used to implement the file corresponds
+to this logical position defined by Text_IO. There are two exceptions:
+
+@itemize @bullet
+@item
+After a call to @code{End_Of_Page} that returns @code{True}, the stream
+is positioned past the @code{LF} (line mark) that precedes the page
+mark. Text_IO maintains an internal flag so that subsequent read
+operations properly handle the logical position which is unchanged by
+the @code{End_Of_Page} call.
+
+@item
+After a call to @code{End_Of_File} that returns @code{True}, if the
+Text_IO file was positioned before the line mark at the end of file
+before the call, then the logical position is unchanged, but the stream
+is physically positioned right at the end of file (past the line mark,
+and past a possible page mark following the line mark. Again Text_IO
+maintains internal flags so that subsequent read operations properly
+handle the logical position.
+@end itemize
+
+These discrepancies have no effect on the observable behavior of
+Text_IO, but if a single Ada stream is shared between a C program and
+Ada program, or shared (using @samp{shared=yes} in the form string)
+between two Ada files, then the difference may be observable in some
+situations.
+
+@node Text_IO Reading and Writing Non-Regular Files
+@subsection Reading and Writing Non-Regular Files
+
+@noindent
+A non-regular file is a device (such as a keyboard), or a pipe. Text_IO
+can be used for reading and writing. Writing is not affected and the
+sequence of characters output is identical to the normal file case, but
+for reading, the behavior of Text_IO is modified to avoid undesirable
+look-ahead as follows:
+
+An input file that is not a regular file is considered to have no page
+marks. Any @code{Ascii.FF} characters (the character normally used for a
+page mark) appearing in the file are considered to be data
+characters. In particular:
+
+@itemize @bullet
+@item
+@code{Get_Line} and @code{Skip_Line} do not test for a page mark
+following a line mark. If a page mark appears, it will be treated as a
+data character.
+
+@item
+This avoids the need to wait for an extra character to be typed or
+entered from the pipe to complete one of these operations.
+
+@item
+@code{End_Of_Page} always returns @code{False}
+
+@item
+@code{End_Of_File} will return @code{False} if there is a page mark at
+the end of the file.
+@end itemize
+
+Output to non-regular files is the same as for regular files. Page marks
+may be written to non-regular files using @code{New_Page}, but as noted
+above they will not be treated as page marks on input if the output is
+piped to another Ada program.
+
+Another important discrepancy when reading non-regular files is that the end
+of file indication is not "sticky". If an end of file is entered, e.g. by
+pressing the @code{EOT} key,
+then end of file
+is signalled once (i.e. the test @code{End_Of_File}
+will yield @code{True}, or a read will
+raise @code{End_Error}), but then reading can resume
+to read data past that end of
+file indication, until another end of file indication is entered.
+
+@node Get_Immediate
+@subsection Get_Immediate
+@cindex Get_Immediate
+
+@noindent
+Get_Immediate returns the next character (including control characters)
+from the input file. In particular, Get_Immediate will return LF or FF
+characters used as line marks or page marks. Such operations leave the
+file positioned past the control character, and it is thus not treated
+as having its normal function. This means that page, line and column
+counts after this kind of Get_Immediate call are set as though the mark
+did not occur. In the case where a Get_Immediate leaves the file
+positioned between the line mark and page mark (which is not normally
+possible), it is undefined whether the FF character will be treated as a
+page mark.
+
+@node Treating Text_IO Files as Streams
+@subsection Treating Text_IO Files as Streams
+@cindex Stream files
+
+@noindent
+The package @code{Text_IO.Streams} allows a Text_IO file to be treated
+as a stream. Data written to a Text_IO file in this stream mode is
+binary data. If this binary data contains bytes 16#0A# (@code{LF}) or
+16#0C# (@code{FF}), the resulting file may have non-standard
+format. Similarly if read operations are used to read from a Text_IO
+file treated as a stream, then @code{LF} and @code{FF} characters may be
+skipped and the effect is similar to that described above for
+@code{Get_Immediate}.
+
+@node Text_IO Extensions
+@subsection Text_IO Extensions
+@cindex Text_IO extensions
+
+@noindent
+A package GNAT.IO_Aux in the GNAT library provides some useful extensions
+to the standard @code{Text_IO} package:
+
+@itemize @bullet
+@item function File_Exists (Name : String) return Boolean;
+Determines if a file of the given name exists and can be successfully
+opened (without actually performing the open operation).
+
+@item function Get_Line return String;
+Reads a string from the standard input file. The value returned is exactly
+the length of the line that was read.
+
+@item function Get_Line (File : Ada.Text_IO.File_Type) return String;
+Similar, except that the parameter File specifies the file from which
+the string is to be read.
+
+@end itemize
+
+@node Text_IO Facilities for Unbounded Strings
+@subsection Text_IO Facilities for Unbounded Strings
+@cindex Text_IO for unbounded strings
+@cindex Unbounded_String, Text_IO operations
+
+@noindent
+The package @code{Ada.Strings.Unbounded.Text_IO}
+in library files @code{a-suteio.ads/adb} contains some GNAT-specific
+subprograms useful for Text_IO operations on unbounded strings:
+
+@itemize @bullet
+
+@item function Get_Line (File : File_Type) return Unbounded_String;
+Reads a line from the specified file
+and returns the result as an unbounded string.
+
+@item procedure Put (File : File_Type; U : Unbounded_String);
+Writes the value of the given unbounded string to the specified file
+Similar to the effect of
+@code{Put (To_String (U))} except that an extra copy is avoided.
+
+@item procedure Put_Line (File : File_Type; U : Unbounded_String);
+Writes the value of the given unbounded string to the specified file,
+followed by a @code{New_Line}.
+Similar to the effect of @code{Put_Line (To_String (U))} except
+that an extra copy is avoided.
+@end itemize
+
+@noindent
+In the above procedures, @code{File} is of type @code{Ada.Text_IO.File_Type}
+and is optional. If the parameter is omitted, then the standard input or
+output file is referenced as appropriate.
+
+The package @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library
+files @code{a-swuwti.ads/adb} provides similar extended @code{Wide_Text_IO}
+functionality for unbounded wide strings.
+
+@node Wide_Text_IO
+@section Wide_Text_IO
+
+@noindent
+@code{Wide_Text_IO} is similar in most respects to Text_IO, except that
+both input and output files may contain special sequences that represent
+wide character values. The encoding scheme for a given file may be
+specified using a FORM parameter:
+
+@smallexample
+WCEM=@var{x}
+@end smallexample
+
+@noindent
+as part of the FORM string (WCEM = wide character encoding method),
+where @var{x} is one of the following characters
+
+@table @samp
+@item h
+Hex ESC encoding
+@item u
+Upper half encoding
+@item s
+Shift-JIS encoding
+@item e
+EUC Encoding
+@item 8
+UTF-8 encoding
+@item b
+Brackets encoding
+@end table
+
+The encoding methods match those that
+can be used in a source
+program, but there is no requirement that the encoding method used for
+the source program be the same as the encoding method used for files,
+and different files may use different encoding methods.
+
+The default encoding method for the standard files, and for opened files
+for which no WCEM parameter is given in the FORM string matches the
+wide character encoding specified for the main program (the default
+being brackets encoding if no coding method was specified with -gnatW).
+
+@table @asis
+@item Hex Coding
+In this encoding, a wide character is represented by a five character
+sequence:
+
+@smallexample
+ESC a b c d
+@end smallexample
+
+where @var{a}, @var{b}, @var{c}, @var{d} are the four hexadecimal
+characters (using upper case letters) of the wide character code. For
+example, ESC A345 is used to represent the wide character with code
+16#A345#. This scheme is compatible with use of the full
+@code{Wide_Character} set.
+
+@item Upper Half Coding
+The wide character with encoding 16#abcd#, where the upper bit is on
+(i.e. a is in the range 8-F) is represented as two bytes 16#ab# and
+16#cd#. The second byte may never be a format control character, but is
+not required to be in the upper half. This method can be also used for
+shift-JIS or EUC where the internal coding matches the external coding. 
+
+@item Shift JIS Coding
+A wide character is represented by a two character sequence 16#ab# and
+16#cd#, with the restrictions described for upper half encoding as
+described above. The internal character code is the corresponding JIS
+character according to the standard algorithm for Shift-JIS
+conversion. Only characters defined in the JIS code set table can be
+used with this encoding method.
+
+@item EUC Coding
+A wide character is represented by a two character sequence 16#ab# and
+16#cd#, with both characters being in the upper half. The internal
+character code is the corresponding JIS character according to the EUC
+encoding algorithm. Only characters defined in the JIS code set table
+can be used with this encoding method.
+
+@item UTF-8 Coding
+A wide character is represented using
+UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
+10646-1/Am.2.  Depending on the character value, the representation
+is a one, two, or three byte sequence:
+
+@smallexample
+16#0000#-16#007f#: 2#0xxxxxxx#
+16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
+16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
+@end smallexample
+
+where the xxx bits correspond to the left-padded bits of the
+16-bit character value. Note that all lower half ASCII characters
+are represented as ASCII bytes and all upper half characters and
+other wide characters are represented as sequences of upper-half
+(The full UTF-8 scheme allows for encoding 31-bit characters as
+6-byte sequences, but in this implementation, all UTF-8 sequences
+of four or more bytes length will raise a Constraint_Error, as
+will all illegal UTF-8 sequences.)
+
+@item Brackets Coding
+In this encoding, a wide character is represented by the following eight
+character sequence:
+
+@smallexample
+[ " a b c d " ]
+@end smallexample
+
+Where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
+characters (using uppercase letters) of the wide character code. For
+example, @code{["A345"]} is used to represent the wide character with code
+@code{16#A345#}.
+This scheme is compatible with use of the full Wide_Character set.
+On input, brackets coding can also be used for upper half characters,
+e.g. @code{["C1"]} for lower case a. However, on output, brackets notation
+is only used for wide characters with a code greater than @code{16#FF#}.
+
+@end table
+
+For the coding schemes other than Hex and Brackets encoding,
+not all wide character
+values can be represented. An attempt to output a character that cannot
+be represented using the encoding scheme for the file causes
+Constraint_Error to be raised. An invalid wide character sequence on
+input also causes Constraint_Error to be raised.
+
+@menu
+* Wide_Text_IO Stream Pointer Positioning::  
+* Wide_Text_IO Reading and Writing Non-Regular Files::  
+@end menu
+
+@node Wide_Text_IO Stream Pointer Positioning
+@subsection Stream Pointer Positioning
+
+@noindent
+@code{Ada.Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
+of stream pointer positioning (@pxref{Text_IO}). There is one additional
+case:
+
+If @code{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the
+normal lower ASCII set (i.e. a character in the range:
+
+@smallexample
+Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
+@end smallexample
+
+@noindent
+then although the logical position of the file pointer is unchanged by
+the @code{Look_Ahead} call, the stream is physically positioned past the
+wide character sequence. Again this is to avoid the need for buffering
+or backup, and all @code{Wide_Text_IO} routines check the internal
+indication that this situation has occurred so that this is not visible
+to a normal program using @code{Wide_Text_IO}. However, this discrepancy
+can be observed if the wide text file shares a stream with another file.
+
+@node Wide_Text_IO Reading and Writing Non-Regular Files
+@subsection Reading and Writing Non-Regular Files
+
+@noindent
+As in the case of Text_IO, when a non-regular file is read, it is
+assumed that the file contains no page marks (any form characters are
+treated as data characters), and @code{End_Of_Page} always returns
+@code{False}. Similarly, the end of file indication is not sticky, so
+it is possible to read beyond an end of file.
+
+@node Stream_IO
+@section Stream_IO
+
+@noindent
+A stream file is a sequence of bytes, where individual elements are
+written to the file as described in the Ada 95 reference manual. The type
+@code{Stream_Element} is simply a byte. There are two ways to read or
+write a stream file.
+
+@itemize @bullet
+@item
+The operations @code{Read} and @code{Write} directly read or write a
+sequence of stream elements with no control information.
+
+@item
+The stream attributes applied to a stream file transfer data in the
+manner described for stream attributes.
+@end itemize
+
+@node Shared Files
+@section Shared Files
+
+@noindent
+Section A.14 of the Ada 95 Reference Manual allows implementations to
+provide a wide variety of behavior if an attempt is made to access the
+same external file with two or more internal files.
+
+To provide a full range of functionality, while at the same time
+minimizing the problems of portability caused by this implementation
+dependence, GNAT handles file sharing as follows:
+
+@itemize @bullet
+@item
+In the absence of a @samp{shared=@var{xxx}} form parameter, an attempt
+to open two or more files with the same full name is considered an error
+and is not supported. The exception @code{Use_Error} will be
+raised. Note that a file that is not explicitly closed by the program
+remains open until the program terminates.
+
+@item
+If the form parameter @samp{shared=no} appears in the form string, the
+file can be opened or created with its own separate stream identifier,
+regardless of whether other files sharing the same external file are
+opened. The exact effect depends on how the C stream routines handle
+multiple accesses to the same external files using separate streams.
+
+@item
+If the form parameter @samp{shared=yes} appears in the form string for
+each of two or more files opened using the same full name, the same
+stream is shared between these files, and the semantics are as described
+in Ada 95 Reference Manual, Section A.14.
+@end itemize
+
+When a program that opens multiple files with the same name is ported
+from another Ada compiler to GNAT, the effect will be that
+@code{Use_Error} is raised.
+
+The documentation of the original compiler and the documentation of the
+program should then be examined to determine if file sharing was
+expected, and @samp{shared=@var{xxx}} parameters added to @code{Open}
+and @code{Create} calls as required.
+
+When a program is ported from GNAT to some other Ada compiler, no
+special attention is required unless the @samp{shared=@var{xxx}} form
+parameter is used in the program. In this case, you must examine the
+documentation of the new compiler to see if it supports the required
+file sharing semantics, and form strings modified appropriately. Of
+course it may be the case that the program cannot be ported if the
+target compiler does not support the required functionality. The best
+approach in writing portable code is to avoid file sharing (and hence
+the use of the @samp{shared=@var{xxx}} parameter in the form string)
+completely.
+
+One common use of file sharing in Ada 83 is the use of instantiations of
+Sequential_IO on the same file with different types, to achieve
+heterogeneous input-output. Although this approach will work in GNAT if
+@samp{shared=yes} is specified, it is preferable in Ada 95 to use Stream_IO
+for this purpose (using the stream attributes)
+
+@node Open Modes
+@section Open Modes
+
+@noindent
+@code{Open} and @code{Create} calls result in a call to @code{fopen}
+using the mode shown in Table 6.1
+
+@sp 2
+@center Table 6-1 @code{Open} and @code{Create} Call Modes
+@smallexample
+                               @b{OPEN }           @b{CREATE}
+Append_File                    "r+"             "w+"
+In_File                        "r"              "w+"
+Out_File (Direct_IO)           "r+"             "w"
+Out_File (all other cases)     "w"              "w"
+Inout_File                     "r+"             "w+"
+@end smallexample
+
+If text file translation is required, then either @samp{b} or @samp{t}
+is added to the mode, depending on the setting of Text. Text file
+translation refers to the mapping of CR/LF sequences in an external file
+to LF characters internally. This mapping only occurs in DOS and
+DOS-like systems, and is not relevant to other systems.
+
+A special case occurs with Stream_IO. As shown in the above table, the
+file is initially opened in @samp{r} or @samp{w} mode for the
+@code{In_File} and @code{Out_File} cases. If a @code{Set_Mode} operation
+subsequently requires switching from reading to writing or vice-versa,
+then the file is reopened in @samp{r+} mode to permit the required operation.
+
+@node Operations on C Streams
+@section Operations on C Streams
+The package @code{Interfaces.C_Streams} provides an Ada program with direct
+access to the C library functions for operations on C streams:
+
+@smallexample
+package Interfaces.C_Streams is
+  -- Note: the reason we do not use the types that are in
+  -- Interfaces.C is that we want to avoid dragging in the
+  -- code in this unit if possible.
+  subtype chars is System.Address;
+  -- Pointer to null-terminated array of characters
+  subtype FILEs is System.Address;
+  -- Corresponds to the C type FILE*
+  subtype voids is System.Address;
+  -- Corresponds to the C type void*
+  subtype int is Integer;
+  subtype long is Long_Integer;
+  -- Note: the above types are subtypes deliberately, and it
+  -- is part of this spec that the above correspondences are
+  -- guaranteed. This means that it is legitimate to, for
+  -- example, use Integer instead of int. We provide these
+  -- synonyms for clarity, but in some cases it may be
+  -- convenient to use the underlying types (for example to
+  -- avoid an unnecessary dependency of a spec on the spec
+  -- of this unit).
+  type size_t is mod 2 ** Standard'Address_Size;
+  NULL_Stream : constant FILEs;
+  -- Value returned (NULL in C) to indicate an
+  -- fdopen/fopen/tmpfile error
+  ----------------------------------
+  -- Constants Defined in stdio.h --
+  ----------------------------------
+  EOF : constant int;
+  -- Used by a number of routines to indicate error or 
+  -- end of file
+  IOFBF : constant int;
+  IOLBF : constant int;
+  IONBF : constant int;
+  -- Used to indicate buffering mode for setvbuf call
+  SEEK_CUR : constant int;
+  SEEK_END : constant int;
+  SEEK_SET : constant int;
+  -- Used to indicate origin for fseek call
+  function stdin return FILEs;
+  function stdout return FILEs;
+  function stderr return FILEs;
+  -- Streams associated with standard files
+  --------------------------
+  -- Standard C functions --
+  --------------------------
+  -- The functions selected below are ones that are
+  -- available in DOS, OS/2, UNIX and Xenix (but not
+  -- necessarily in ANSI C). These are very thin interfaces
+  -- which copy exactly the C headers. For more
+  -- documentation on these functions, see the Microsoft C 
+  -- "Run-Time Library Reference" (Microsoft Press, 1990,
+  -- ISBN 1-55615-225-6), which includes useful information
+  -- on system compatibility.
+  procedure clearerr (stream : FILEs);
+  function fclose (stream : FILEs) return int;
+  function fdopen (handle : int; mode : chars) return FILEs; 
+  function feof (stream : FILEs) return int; 
+  function ferror (stream : FILEs) return int; 
+  function fflush (stream : FILEs) return int; 
+  function fgetc (stream : FILEs) return int; 
+  function fgets (strng : chars; n : int; stream : FILEs) 
+      return chars; 
+  function fileno (stream : FILEs) return int; 
+  function fopen (filename : chars; Mode : chars) 
+      return FILEs;
+  -- Note: to maintain target independence, use
+  -- text_translation_required, a boolean variable defined in
+  -- a-sysdep.c to deal with the target dependent text
+  -- translation requirement. If this variable is set, 
+  -- then  b/t should be appended to the standard mode
+  -- argument to set the text translation mode off or on 
+  -- as required.
+  function fputc (C : int; stream : FILEs) return int;
+  function fputs (Strng : chars; Stream : FILEs) return int;
+  function fread
+     (buffer : voids;
+      size : size_t;
+      count : size_t;
+      stream : FILEs)
+      return size_t;
+  function freopen
+     (filename : chars;
+      mode : chars;
+      stream : FILEs)
+      return FILEs;
+  function fseek
+     (stream : FILEs;
+      offset : long;
+      origin : int)
+      return int;
+  function ftell (stream : FILEs) return long;
+  function fwrite
+     (buffer : voids;
+      size : size_t;
+      count : size_t;
+      stream : FILEs)
+      return size_t; 
+  function isatty (handle : int) return int;
+  procedure mktemp (template : chars);
+  -- The return value (which is just a pointer to template)
+  -- is discarded
+  procedure rewind (stream : FILEs);
+  function rmtmp return int;
+  function setvbuf
+     (stream : FILEs;
+      buffer : chars;
+      mode : int;
+      size : size_t)
+      return int;
+
+  function tmpfile return FILEs;
+  function ungetc (c : int; stream : FILEs) return int;
+  function unlink (filename : chars) return int;
+  ---------------------
+  -- Extra functions --
+  ---------------------
+  -- These functions supply slightly thicker bindings than
+  -- those above. They are derived from functions in the 
+  -- C Run-Time Library, but may do a bit more work than
+  -- just directly calling one of the Library functions.
+  function is_regular_file (handle : int) return int;
+  -- Tests if given handle is for a regular file (result 1)
+  -- or for a non-regular file (pipe or device, result 0).
+  ---------------------------------
+  -- Control of Text/Binary Mode --
+  ---------------------------------
+  -- If text_translation_required is true, then the following
+  -- functions may be used to dynamically switch a file from
+  -- binary to text mode or vice versa. These functions have
+  -- no effect if text_translation_required is false (i.e. in
+  -- normal UNIX mode). Use fileno to get a stream handle.
+  procedure set_binary_mode (handle : int);
+  procedure set_text_mode (handle : int);
+  ----------------------------
+  -- Full Path Name support --
+  ----------------------------
+  procedure full_name (nam : chars; buffer : chars);
+  -- Given a NUL terminated string representing a file
+  -- name, returns in buffer a NUL terminated string
+  -- representing the full path name for the file name. 
+  -- On systems where it is relevant the   drive is also
+  -- part of the full path name. It is the responsibility 
+  -- of the caller to pass an actual parameter for buffer
+  -- that is big enough for any full path name. Use
+  -- max_path_len given below as the size of buffer.
+  max_path_len : integer;
+  -- Maximum length of an allowable full path name on the
+  -- system, including a terminating NUL character.
+end Interfaces.C_Streams;
+@end smallexample
+
+@node Interfacing to C Streams
+@section Interfacing to C Streams
+
+@noindent
+The packages in this section permit interfacing Ada files to C Stream
+operations.
+
+@smallexample
+ with Interfaces.C_Streams;
+ package Ada.Sequential_IO.C_Streams is
+    function C_Stream (F : File_Type)  
+       return Interfaces.C_Streams.FILEs;
+    procedure Open
+      (File : in out File_Type;
+       Mode : in File_Mode;
+       C_Stream : in Interfaces.C_Streams.FILEs;
+       Form : in String := "");
+ end Ada.Sequential_IO.C_Streams;
+
+  with Interfaces.C_Streams;
+  package Ada.Direct_IO.C_Streams is
+     function C_Stream (F : File_Type) 
+        return Interfaces.C_Streams.FILEs;
+     procedure Open
+       (File : in out File_Type;
+        Mode : in File_Mode;
+        C_Stream : in Interfaces.C_Streams.FILEs;
+        Form : in String := "");
+  end Ada.Direct_IO.C_Streams;
+
+  with Interfaces.C_Streams;
+  package Ada.Text_IO.C_Streams is
+     function C_Stream (F : File_Type)
+        return Interfaces.C_Streams.FILEs;
+     procedure Open
+       (File : in out File_Type;
+        Mode : in File_Mode;
+        C_Stream : in Interfaces.C_Streams.FILEs;
+        Form : in String := "");
+  end Ada.Text_IO.C_Streams;
+
+  with Interfaces.C_Streams;
+  package Ada.Wide_Text_IO.C_Streams is
+     function C_Stream (F : File_Type)  
+        return Interfaces.C_Streams.FILEs;
+     procedure Open
+       (File : in out File_Type;
+        Mode : in File_Mode;
+        C_Stream : in Interfaces.C_Streams.FILEs;
+        Form : in String := "");
+ end Ada.Wide_Text_IO.C_Streams;
+
+ with Interfaces.C_Streams;
+ package Ada.Stream_IO.C_Streams is
+    function C_Stream (F : File_Type)
+       return Interfaces.C_Streams.FILEs;
+    procedure Open
+      (File : in out File_Type;
+       Mode : in File_Mode;
+       C_Stream : in Interfaces.C_Streams.FILEs;
+       Form : in String := "");
+ end Ada.Stream_IO.C_Streams;
+@end smallexample
+
+In each of these five packages, the @code{C_Stream} function obtains the
+@code{FILE} pointer from a currently opened Ada file. It is then
+possible to use the @code{Interfaces.C_Streams} package to operate on
+this stream, or the stream can be passed to a C program which can
+operate on it directly. Of course the program is responsible for
+ensuring that only appropriate sequences of operations are executed.
+
+One particular use of relevance to an Ada program is that the
+@code{setvbuf} function can be used to control the buffering of the
+stream used by an Ada file. In the absence of such a call the standard
+default buffering is used.
+
+The @code{Open} procedures in these packages open a file giving an
+existing C Stream instead of a file name. Typically this stream is
+imported from a C program, allowing an Ada file to operate on an
+existing C file.
+
+@node The GNAT Library
+@chapter The GNAT Library
+
+@noindent
+The GNAT library contains a number of general and special purpose packages.
+It represents functionality that the GNAT developers have found useful, and
+which is made available to GNAT users. The packages described here are fully
+supported, and upwards compatibility will be maintained in future releases,
+so you can use these facilities with the confidence that the same functionality
+will be available in future releases.
+
+The chapter here simply gives a brief summary of the facilities available.
+The full documentation is found in the spec file for the package. The full
+sources of these library packages, including both spec and body, are provided
+with all GNAT releases. For example, to find out the full specifications of
+the SPITBOL pattern matching capability, including a full tutorial and 
+extensive examples, look in the g-spipat.ads file in the library.
+
+For each entry here, the package name (as it would appear in a @code{with}
+clause) is given, followed by the name of the corresponding spec file in
+parentheses. The packages are children in four hierarchies, @code{Ada},
+@code{Interfaces}, @code{System}, and @code{GNAT}, the latter being a
+GNAT-specific hierarchy.
+
+Note that an application program should only use packages in one of these
+four hierarchies if the package is defined in the Ada Reference Manual,
+or is listed in this section of the GNAT Programmers Reference Manual.
+All other units should be considered internal implementation units and
+should not be directly @code{with}'ed by application code. The use of
+a @code{with} statement that references one of these internal implementation
+units makes an application potentially dependent on changes in versions
+of GNAT, and will generate a warning message.
+
+@menu
+* Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
+* Ada.Command_Line.Remove (a-colire.ads)::
+* Ada.Direct_IO.C_Streams (a-diocst.ads)::
+* Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
+* Ada.Sequential_IO.C_Streams (a-siocst.ads)::
+* Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
+* Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
+* Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
+* Ada.Text_IO.C_Streams (a-tiocst.ads)::
+* Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
+* GNAT.AWK (g-awk.ads)::
+* GNAT.Bubble_Sort_A (g-busora.ads)::
+* GNAT.Bubble_Sort_G (g-busorg.ads)::
+* GNAT.Calendar (g-calend.ads)::
+* GNAT.Calendar.Time_IO (g-catiio.ads)::
+* GNAT.CRC32 (g-crc32.ads)::
+* GNAT.Case_Util (g-casuti.ads)::
+* GNAT.CGI (g-cgi.ads)::
+* GNAT.CGI.Cookie (g-cgicoo.ads)::
+* GNAT.CGI.Debug (g-cgideb.ads)::
+* GNAT.Command_Line (g-comlin.ads)::
+* GNAT.Current_Exception (g-curexc.ads)::
+* GNAT.Debug_Pools (g-debpoo.ads)::
+* GNAT.Debug_Utilities (g-debuti.ads)::
+* GNAT.Directory_Operations (g-dirope.ads)::
+* GNAT.Dynamic_Tables (g-dyntab.ads)::
+* GNAT.Exception_Traces (g-exctra.ads)::
+* GNAT.Expect (g-expect.ads)::
+* GNAT.Float_Control (g-flocon.ads)::
+* GNAT.Heap_Sort_A (g-hesora.ads)::
+* GNAT.Heap_Sort_G (g-hesorg.ads)::
+* GNAT.HTable (g-htable.ads)::
+* GNAT.IO (g-io.ads)::
+* GNAT.IO_Aux (g-io_aux.ads)::
+* GNAT.Lock_Files (g-locfil.ads)::
+* GNAT.Most_Recent_Exception (g-moreex.ads)::
+* GNAT.OS_Lib (g-os_lib.ads)::
+* GNAT.Regexp (g-regexp.ads)::
+* GNAT.Registry (g-regist.ads)::
+* GNAT.Regpat (g-regpat.ads)::
+* GNAT.Sockets (g-socket.ads)::
+* GNAT.Source_Info (g-souinf.ads)::
+* GNAT.Spell_Checker (g-speche.ads)::
+* GNAT.Spitbol.Patterns (g-spipat.ads)::
+* GNAT.Spitbol (g-spitbo.ads)::
+* GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
+* GNAT.Spitbol.Table_Integer (g-sptain.ads)::
+* GNAT.Spitbol.Table_VString (g-sptavs.ads)::
+* GNAT.Table (g-table.ads)::
+* GNAT.Task_Lock (g-tasloc.ads)::
+* GNAT.Threads (g-thread.ads)::
+* GNAT.Traceback (g-traceb.ads)::
+* GNAT.Traceback.Symbolic (g-trasym.ads)::
+* Interfaces.C.Extensions (i-cexten.ads)::
+* Interfaces.C.Streams (i-cstrea.ads)::
+* Interfaces.CPP (i-cpp.ads)::
+* Interfaces.Os2lib (i-os2lib.ads)::
+* Interfaces.Os2lib.Errors (i-os2err.ads)::
+* Interfaces.Os2lib.Synchronization (i-os2syn.ads)::
+* Interfaces.Os2lib.Threads (i-os2thr.ads)::
+* Interfaces.Packed_Decimal (i-pacdec.ads)::
+* Interfaces.VxWorks (i-vxwork.ads)::
+* System.Address_Image (s-addima.ads)::
+* System.Assertions (s-assert.ads)::
+* System.Partition_Interface (s-parint.ads)::
+* System.Task_Info (s-tasinf.ads)::
+* System.Wch_Cnv (s-wchcnv.ads)::
+* System.Wch_Con (s-wchcon.ads)::
+@end menu
+
+@node Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
+@section Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
+@cindex Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
+@cindex  Latin_1 constants for Wide_Character
+
+@noindent
+This child of @code{Ada.Characters}
+provides a set of definitions corresponding to those in the
+RM-defined package @code{Ada.Characters.Latin_1} but with the
+types of the constants being @code{Wide_Character}
+instead of @code{Character}. The provision of such a package
+is specifically authorized by the Ada Reference Manual
+(RM A.3(27)).
+
+@node Ada.Command_Line.Remove (a-colire.ads)
+@section Ada.Command_Line.Remove (a-colire.ads)
+@cindex Ada.Command_Line.Remove (a-colire.ads)
+@cindex  Removing command line arguments
+@cindex  Command line, argument removal
+
+@noindent
+This child of @code{Ada.Command_Line}
+provides a mechanism for logically removing
+arguments from the argument list. Once removed, an argument is not visible
+to further calls on the subprograms in @code{Ada.Command_Line} will not
+see the removed argument.
+
+@node Ada.Direct_IO.C_Streams (a-diocst.ads)
+@section Ada.Direct_IO.C_Streams (a-diocst.ads)
+@cindex Ada.Direct_IO.C_Streams (a-diocst.ads)
+@cindex  C Streams, Interfacing with Direct_IO
+
+@noindent
+This package provides subprograms that allow interfacing between 
+C streams and @code{Direct_IO}. The stream identifier can be
+extracted from a file opened on the Ada side, and an Ada file
+can be constructed from a stream opened on the C side.
+
+@node Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
+@section Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
+@cindex Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
+@cindex  Null_Occurrence, testing for
+
+@noindent
+This child subprogram provides a way of testing for the null 
+exception occurrence (@code{Null_Occurrence}) without raising
+an exception.
+
+@node Ada.Sequential_IO.C_Streams (a-siocst.ads)
+@section Ada.Sequential_IO.C_Streams (a-siocst.ads)
+@cindex Ada.Sequential_IO.C_Streams (a-siocst.ads)
+@cindex  C Streams, Interfacing with Sequential_IO
+
+@noindent
+This package provides subprograms that allow interfacing between 
+C streams and @code{Sequential_IO}. The stream identifier can be
+extracted from a file opened on the Ada side, and an Ada file
+can be constructed from a stream opened on the C side.
+
+@node Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
+@section Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
+@cindex Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
+@cindex  C Streams, Interfacing with Stream_IO
+
+@noindent
+This package provides subprograms that allow interfacing between 
+C streams and @code{Stream_IO}. The stream identifier can be
+extracted from a file opened on the Ada side, and an Ada file
+can be constructed from a stream opened on the C side.
+
+@node Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
+@section Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
+@cindex Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
+@cindex Unbounded_String, IO support
+@cindex Text_IO, extensions for unbounded strings
+
+@noindent
+This package provides subprograms for Text_IO for unbounded
+strings, avoiding the necessity for an intermediate operation
+with ordinary strings.
+
+@node Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
+@section Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
+@cindex Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
+@cindex Unbounded_Wide_String, IO support
+@cindex Text_IO, extensions for unbounded wide strings
+
+@noindent
+This package provides subprograms for Text_IO for unbounded
+wide strings, avoiding the necessity for an intermediate operation
+with ordinary wide strings.
+
+@node Ada.Text_IO.C_Streams (a-tiocst.ads)
+@section Ada.Text_IO.C_Streams (a-tiocst.ads)
+@cindex Ada.Text_IO.C_Streams (a-tiocst.ads)
+@cindex  C Streams, Interfacing with Text_IO
+
+@noindent
+This package provides subprograms that allow interfacing between 
+C streams and @code{Text_IO}. The stream identifier can be
+extracted from a file opened on the Ada side, and an Ada file
+can be constructed from a stream opened on the C side.
+
+@node Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
+@section Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
+@cindex Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
+@cindex  C Streams, Interfacing with Wide_Text_IO
+
+@noindent
+This package provides subprograms that allow interfacing between 
+C streams and @code{Wide_Text_IO}. The stream identifier can be
+extracted from a file opened on the Ada side, and an Ada file
+can be constructed from a stream opened on the C side.
+
+@node GNAT.AWK (g-awk.ads)
+@section GNAT.AWK (g-awk.ads)
+@cindex GNAT.AWK (g-awk.ads)
+@cindex Parsing
+
+@noindent
+Provides AWK-like parsing functions, with an easy interface for parsing one
+or more files containing formatted data. The file is viewed as a database
+where each record is a line and a field is a data element in this line.
+
+@node GNAT.Bubble_Sort_A (g-busora.ads)
+@section GNAT.Bubble_Sort_A (g-busora.ads)
+@cindex GNAT.Bubble_Sort_A (g-busora.ads)
+@cindex Sorting
+
+@noindent
+Provides a general implementation of bubble sort usable for sorting arbitrary
+data items. Move and comparison procedures are provided by passing
+access-to-procedure values.
+
+@node GNAT.Bubble_Sort_G (g-busorg.ads)
+@section GNAT.Bubble_Sort_G (g-busorg.ads)
+@cindex GNAT.Bubble_Sort_G (g-busorg.ads)
+@cindex Sorting
+
+@noindent
+Similar to @code{Bubble_Sort_A} except that the move and sorting procedures
+are provided as generic parameters, this improves efficiency, especially
+if the procedures can be inlined, at the expense of duplicating code for
+multiple instantiations.
+
+@node GNAT.Calendar (g-calend.ads)
+@section GNAT.Calendar (g-calend.ads)
+@cindex GNAT.Calendar (g-calend.ads)
+@cindex Calendar
+
+@noindent
+Extends the facilities provided by @code{Ada.Calendar} to include handling
+of days of the week, an extended @code{Split} and @code{Time_Of} capability.
+Also provides conversion of @code{Ada.Calendar.Time} values to and from the
+C @code{timeval} format.
+
+@node GNAT.Calendar.Time_IO (g-catiio.ads)
+@section GNAT.Calendar.Time_IO (g-catiio.ads)
+@cindex Calendar
+@cindex Time
+@cindex GNAT.Calendar.Time_IO (g-catiio.ads)
+
+@node GNAT.CRC32 (g-crc32.ads)
+@section GNAT.CRC32 (g-crc32.ads)
+@cindex GNAT.CRC32 (g-crc32.ads)
+@cindex CRC32
+
+@noindent
+This package implements the CRC-32 algorithm. For a full description
+of this algorithm you should have a look at:
+"Computation of Cyclic Redundancy Checks via Table Look-Up", Communications
+of the ACM, Vol. 31 No. 8, pp.1008-1013 Aug. 1988. Sarwate, D.V.
+
+@noindent
+Provides an extended capability for formatted output of time values with
+full user control over the format. Modeled on the GNU Date specification.
+
+@node GNAT.Case_Util (g-casuti.ads)
+@section GNAT.Case_Util (g-casuti.ads)
+@cindex GNAT.Case_Util (g-casuti.ads)
+@cindex Casing utilities
+
+@noindent
+A set of simple routines for handling upper and lower casing of strings
+without the overhead of the full casing tables
+in @code{Ada.Characters.Handling}.
+
+@node GNAT.CGI (g-cgi.ads)
+@section GNAT.CGI (g-cgi.ads)
+@cindex GNAT.CGI (g-cgi.ads)
+@cindex CGI (Common Gateway Interface)
+
+@noindent
+This is a package for interfacing a GNAT program with a Web server via the
+Common Gateway Interface (CGI). Basically this package parse the CGI
+parameters which are a set of key/value pairs sent by the Web server. It
+builds a table whose index is the key and provides some services to deal
+with this table.
+
+@node GNAT.CGI.Cookie (g-cgicoo.ads)
+@section GNAT.CGI.Cookie (g-cgicoo.ads)
+@cindex GNAT.CGI.Cookie (g-cgicoo.ads)
+@cindex CGI (Common Gateway Interface) Cookie support
+
+@noindent
+This is a package to interface a GNAT program with a Web server via the
+Common Gateway Interface (CGI). It exports services to deal with Web
+cookies (piece of information kept in the Web client software).
+
+@node GNAT.CGI.Debug (g-cgideb.ads)
+@section GNAT.CGI.Debug (g-cgideb.ads)
+@cindex GNAT.CGI.Debug (g-cgideb.ads)
+@cindex CGI (Common Gateway Interface) debugging
+
+@noindent
+This is a package to help debugging CGI (Common Gateway Interface)
+programs written in Ada.
+
+@node GNAT.Command_Line (g-comlin.ads)
+@section GNAT.Command_Line (g-comlin.ads)
+@cindex GNAT.Command_Line (g-comlin.ads)
+@cindex Command line
+
+@noindent
+Provides a high level interface to @code{Ada.Command_Line} facilities,
+including the ability to scan for named switches with optional parameters
+and expand file names using wild card notations.
+
+@node GNAT.Current_Exception (g-curexc.ads)
+@section GNAT.Current_Exception (g-curexc.ads)
+@cindex GNAT.Current_Exception (g-curexc.ads)
+@cindex Current exception
+@cindex Exception retrieval
+
+@noindent
+Provides access to information on the current exception that has been raised
+without the need for using the Ada-95 exception choice parameter specification
+syntax. This is particularly useful in mimicking typical facilities for
+obtaining information about exceptions provided by Ada 83 compilers.
+
+@node GNAT.Debug_Pools (g-debpoo.ads)
+@section GNAT.Debug_Pools (g-debpoo.ads)
+@cindex GNAT.Debug_Pools (g-debpoo.ads)
+@cindex Debugging
+
+@noindent
+Provide a debugging storage pools that helps tracking memory corruption
+problems. See section "Finding memory problems with GNAT Debug Pool" in
+the GNAT User's guide.
+
+@node GNAT.Debug_Utilities (g-debuti.ads)
+@section GNAT.Debug_Utilities (g-debuti.ads)
+@cindex GNAT.Debug_Utilities (g-debuti.ads)
+@cindex Debugging
+
+@noindent
+Provides a few useful utilities for debugging purposes, including conversion
+to and from string images of address values.
+
+@node GNAT.Directory_Operations (g-dirope.ads)
+@section GNAT.Directory_Operations (g-dirope.ads)
+@cindex GNAT.Directory_Operations (g-dirope.ads)
+@cindex Directory operations
+
+@noindent
+Provides a set of routines for manipulating directories, including changing
+the current directory, making new directories, and scanning the files in a
+directory.
+
+@node GNAT.Dynamic_Tables (g-dyntab.ads)
+@section GNAT.Dynamic_Tables (g-dyntab.ads)
+@cindex GNAT.Dynamic_Tables (g-dyntab.ads)
+@cindex Table implementation
+@cindex Arrays, extendable
+
+@noindent
+A generic package providing a single dimension array abstraction where the
+length of the array can be dynamically modified.
+
+@noindent
+This package provides a facility similar to that of GNAT.Table, except 
+that this package declares a type that can be used to define dynamic
+instances of the table, while an instantiation of GNAT.Table creates a
+single instance of the table type.
+
+@node GNAT.Exception_Traces (g-exctra.ads)
+@section GNAT.Exception_Traces (g-exctra.ads)
+@cindex GNAT.Exception_Traces (g-exctra.ads)
+@cindex Exception traces
+@cindex Debugging
+
+@noindent
+Provides an interface allowing to control automatic output upon exception
+occurrences.
+
+@node GNAT.Expect (g-expect.ads)
+@section GNAT.Expect (g-expect.ads)
+@cindex GNAT.Expect (g-expect.ads)
+
+@noindent
+Provides a set of subprograms similar to what is available
+with the standard Tcl Expect tool.
+It allows you to easily spawn and communicate with an external process.
+You can send commands or inputs to the process, and compare the output
+with some expected regular expression.
+Currently GNAT.Expect is implemented on all native GNAT ports except for
+OpenVMS. It is not implemented for cross ports, and in particular is not
+implemented for VxWorks or LynxOS.
+
+@node GNAT.Float_Control (g-flocon.ads)
+@section GNAT.Float_Control (g-flocon.ads)
+@cindex GNAT.Float_Control (g-flocon.ads)
+@cindex Floating-Point Processor
+
+@noindent
+Provides an interface for resetting the floating-point processor into the
+mode required for correct semantic operation in Ada. Some third party
+library calls may cause this mode to be modified, and the Reset procedure
+in this package can be used to reestablish the required mode.
+
+@node GNAT.Heap_Sort_A (g-hesora.ads)
+@section GNAT.Heap_Sort_A (g-hesora.ads)
+@cindex GNAT.Heap_Sort_A (g-hesora.ads)
+@cindex Sorting
+
+@noindent
+Provides a general implementation of heap sort usable for sorting arbitrary
+data items. Move and comparison procedures are provided by passing
+access-to-procedure values. The algorithm used is a modified heap sort
+that performs approximately N*log(N) comparisons in the worst case.
+
+@node GNAT.Heap_Sort_G (g-hesorg.ads)
+@section GNAT.Heap_Sort_G (g-hesorg.ads)
+@cindex GNAT.Heap_Sort_G (g-hesorg.ads)
+@cindex Sorting
+
+@noindent
+Similar to @code{Heap_Sort_A} except that the move and sorting procedures
+are provided as generic parameters, this improves efficiency, especially
+if the procedures can be inlined, at the expense of duplicating code for
+multiple instantiations.
+
+@node GNAT.HTable (g-htable.ads)
+@section GNAT.HTable (g-htable.ads)
+@cindex GNAT.HTable (g-htable.ads)
+@cindex Hash tables
+
+@noindent
+A generic implementation of hash tables that can be used to hash arbitrary
+data. Provides two approaches, one a simple static approach, and the other
+allowing arbitrary dynamic hash tables.
+
+@node GNAT.IO (g-io.ads)
+@section GNAT.IO (g-io.ads)
+@cindex GNAT.IO (g-io.ads)
+@cindex Simple I/O
+@cindex Input/Output facilities
+
+@noindent
+A simple preealborable input-output package that provides a subset of
+simple Text_IO functions for reading characters and strings from
+Standard_Input, and writing characters, strings and integers to either
+Standard_Output or Standard_Error.
+
+@node GNAT.IO_Aux (g-io_aux.ads)
+@section GNAT.IO_Aux (g-io_aux.ads)
+@cindex GNAT.IO_Aux (g-io_aux.ads)
+@cindex Text_IO
+@cindex Input/Output facilities
+
+Provides some auxiliary functions for use with Text_IO, including a test
+for whether a file exists, and functions for reading a line of text.
+
+@node GNAT.Lock_Files (g-locfil.ads)
+@section GNAT.Lock_Files (g-locfil.ads)
+@cindex GNAT.Lock_Files (g-locfil.ads)
+@cindex File locking
+@cindex Locking using files
+
+@noindent
+Provides a general interface for using files as locks. Can be used for
+providing program level synchronization. 
+
+@node GNAT.Most_Recent_Exception (g-moreex.ads)
+@section GNAT.Most_Recent_Exception (g-moreex.ads)
+@cindex GNAT.Most_Recent_Exception (g-moreex.ads)
+@cindex Exception, obtaining most recent
+
+@noindent
+Provides access to the most recently raised exception. Can be used for
+various logging purposes, including duplicating functionality of some
+Ada 83 implementation dependent extensions.
+
+@node GNAT.OS_Lib (g-os_lib.ads)
+@section GNAT.OS_Lib (g-os_lib.ads)
+@cindex GNAT.OS_Lib (g-os_lib.ads)
+@cindex Operating System interface
+@cindex Spawn capability
+
+@noindent
+Provides a range of target independent operating system interface functions,
+including time/date management, file operations, subprocess management,
+including a portable spawn procedure, and access to environment variables
+and error return codes.
+
+@node GNAT.Regexp (g-regexp.ads)
+@section GNAT.Regexp (g-regexp.ads)
+@cindex GNAT.Regexp (g-regexp.ads)
+@cindex Regular expressions
+@cindex Pattern matching
+
+@noindent
+A simple implementation of regular expressions, using a subset of regular
+expression syntax copied from familiar Unix style utilities. This is the
+simples of the three pattern matching packages provided, and is particularly
+suitable for "file globbing" applications.
+
+@node GNAT.Registry (g-regist.ads)
+@section GNAT.Registry (g-regist.ads)
+@cindex GNAT.Registry (g-regist.ads)
+@cindex Windows Registry
+
+@noindent
+This is a high level binding to the Windows registry. It is possible to
+do simple things like reading a key value, creating a new key. For full
+registry API, but at a lower level of abstraction, refer to the Win32.Winreg
+package provided with the Win32Ada binding
+
+@node GNAT.Regpat (g-regpat.ads)
+@section GNAT.Regpat (g-regpat.ads)
+@cindex GNAT.Regpat (g-regpat.ads)
+@cindex Regular expressions
+@cindex Pattern matching
+
+@noindent
+A complete implementation of Unix-style regular expression matching, copied
+from the original V7 style regular expression library written in C by
+Henry Spencer (and binary compatible with this C library).
+
+@node GNAT.Sockets (g-socket.ads)
+@section GNAT.Sockets (g-socket.ads)
+@cindex GNAT.Sockets (g-socket.ads)
+@cindex Sockets
+
+@noindent
+A high level and portable interface to develop sockets based applications.
+This package is based on the sockets thin binding found in GNAT.Sockets.Thin.
+Currently GNAT.Sockets is implemented on all native GNAT ports except for
+OpenVMS. It is not implemented for cross ports, and in particular is not
+implemented for VxWorks or LynxOS.
+
+@node GNAT.Source_Info (g-souinf.ads)
+@section GNAT.Source_Info (g-souinf.ads)
+@cindex GNAT.Source_Info (g-souinf.ads)
+@cindex Source Information
+
+@noindent
+Provides subprograms that give access to source code information known at
+compile time, such as the current file name and line number.
+
+@node GNAT.Spell_Checker (g-speche.ads)
+@section GNAT.Spell_Checker (g-speche.ads)
+@cindex GNAT.Spell_Checker (g-speche.ads)
+@cindex Spell checking
+
+@noindent
+Provides a function for determining whether one string is a plausible
+near misspelling of another string.
+
+@node GNAT.Spitbol.Patterns (g-spipat.ads)
+@section GNAT.Spitbol.Patterns (g-spipat.ads)
+@cindex GNAT.Spitbol.Patterns (g-spipat.ads)
+@cindex SPITBOL pattern matching
+@cindex Pattern matching
+
+@noindent
+A complete implementation of SNOBOL4 style pattern matching. This is the
+most elaborate of the pattern matching packages provided. It fully duplicates
+the SNOBOL4 dynamic pattern construction and matching capabilities, using the
+efficient algorithm developed by Robert Dewar for the SPITBOL system.
+
+@node GNAT.Spitbol (g-spitbo.ads)
+@section GNAT.Spitbol (g-spitbo.ads)
+@cindex GNAT.Spitbol (g-spitbo.ads)
+@cindex SPITBOL interface
+
+@noindent
+The top level package of the collection of SPITBOL-style functionality, this
+package provides basic SNOBOL4 string manipulation functions, such as
+Pad, Reverse, Trim, Substr capability, as well as a generic table function
+useful for constructing arbitrary mappings from strings in the style of
+the SNOBOL4 TABLE function.
+
+@node GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
+@section GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
+@cindex GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
+@cindex Sets of strings
+@cindex SPITBOL Tables
+
+@noindent
+A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
+for type @code{Standard.Boolean}, giving an implementation of sets of
+string values.
+
+@node GNAT.Spitbol.Table_Integer (g-sptain.ads)
+@section GNAT.Spitbol.Table_Integer (g-sptain.ads)
+@cindex GNAT.Spitbol.Table_Integer (g-sptain.ads)
+@cindex Integer maps
+@cindex Maps
+@cindex SPITBOL Tables
+
+@noindent
+A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
+for type @code{Standard.Integer}, giving an implementation of maps
+from string to integer values.
+
+@node GNAT.Spitbol.Table_VString (g-sptavs.ads)
+@section GNAT.Spitbol.Table_VString (g-sptavs.ads)
+@cindex GNAT.Spitbol.Table_VString (g-sptavs.ads)
+@cindex String maps
+@cindex Maps
+@cindex SPITBOL Tables
+
+@noindent
+A library level of instantiation of GNAT.Spitbol.Patterns.Table for 
+a variable length string type, giving an implementation of general
+maps from strings to strings.
+
+@node GNAT.Table (g-table.ads)
+@section GNAT.Table (g-table.ads)
+@cindex GNAT.Table (g-table.ads)
+@cindex Table implementation
+@cindex Arrays, extendable
+
+@noindent
+A generic package providing a single dimension array abstraction where the
+length of the array can be dynamically modified.
+
+@noindent
+This package provides a facility similar to that of GNAT.Dynamic_Tables,
+except that this package declares a single instance of the table type,
+while an instantiation of GNAT.Dynamic_Tables creates a type that can be
+used to define dynamic instances of the table.
+
+@node GNAT.Task_Lock (g-tasloc.ads)
+@section GNAT.Task_Lock (g-tasloc.ads)
+@cindex GNAT.Task_Lock (g-tasloc.ads)
+@cindex Task synchronization
+@cindex Task locking
+@cindex Locking
+
+@noindent
+A very simple facility for locking and unlocking sections of code using a
+single global task lock. Appropriate for use in situations where contention
+between tasks is very rarely expected.
+
+@node GNAT.Threads (g-thread.ads)
+@section GNAT.Threads (g-thread.ads)
+@cindex GNAT.Threads (g-thread.ads)
+@cindex Foreign threads
+@cindex Threads, foreign
+
+@noindent
+Provides facilities for creating and destroying threads with explicit calls.
+These threads are known to the GNAT run-time system. These subprograms are
+exported C-convention procedures intended to be called from foreign code.
+By using these primitives rather than directly calling operating systems
+routines, compatibility with the Ada tasking runt-time is provided.
+
+@node GNAT.Traceback (g-traceb.ads)
+@section GNAT.Traceback (g-traceb.ads)
+@cindex GNAT.Traceback (g-traceb.ads)
+@cindex Trace back facilities
+
+@noindent
+Provides a facility for obtaining non-symbolic traceback information, useful
+in various debugging situations.
+
+@node GNAT.Traceback.Symbolic (g-trasym.ads)
+@section GNAT.Traceback.Symbolic (g-trasym.ads)
+@cindex GNAT.Traceback.Symbolic (g-trasym.ads)
+@cindex Trace back facilities
+
+@noindent
+Provides symbolic traceback information that includes the subprogram
+name and line number information.
+
+@node Interfaces.C.Extensions (i-cexten.ads)
+@section Interfaces.C.Extensions (i-cexten.ads)
+@cindex Interfaces.C.Extensions (i-cexten.ads)
+
+@noindent
+This package contains additional C-related definitions, intended
+for use with either manually or automatically generated bindings
+to C libraries.
+
+@node Interfaces.C.Streams (i-cstrea.ads)
+@section Interfaces.C.Streams (i-cstrea.ads)
+@cindex Interfaces.C.Streams (i-cstrea.ads)
+@cindex  C streams, interfacing
+
+@noindent
+This package is a binding for the most commonly used operations
+on C streams.
+
+@node Interfaces.CPP (i-cpp.ads)
+@section Interfaces.CPP (i-cpp.ads)
+@cindex Interfaces.CPP (i-cpp.ads)
+@cindex  C++ interfacing
+@cindex  Interfacing, to C++
+
+@noindent
+This package provides facilities for use in interfacing to C++. It
+is primarily intended to be used in connection with automated tools
+for the generation of C++ interfaces.
+
+@node Interfaces.Os2lib (i-os2lib.ads)
+@section Interfaces.Os2lib (i-os2lib.ads)
+@cindex Interfaces.Os2lib (i-os2lib.ads)
+@cindex Interfacing, to OS/2
+@cindex OS/2 interfacing
+
+@noindent
+This package provides interface definitions to the OS/2 library.
+It is a thin binding which is a direct translation of the
+various @file{<bse@.h>} files.
+
+@node Interfaces.Os2lib.Errors (i-os2err.ads)
+@section Interfaces.Os2lib.Errors (i-os2err.ads)
+@cindex Interfaces.Os2lib.Errors (i-os2err.ads)
+@cindex OS/2 Error codes
+@cindex Interfacing, to OS/2
+@cindex OS/2 interfacing
+
+@noindent
+This package provides definitions of the OS/2 error codes.
+
+@node Interfaces.Os2lib.Synchronization (i-os2syn.ads)
+@section Interfaces.Os2lib.Synchronization (i-os2syn.ads)
+@cindex Interfaces.Os2lib.Synchronization (i-os2syn.ads)
+@cindex Interfacing, to OS/2
+@cindex Synchronization, OS/2
+@cindex OS/2 synchronization primitives
+
+@noindent
+This is a child package that provides definitions for interfacing
+to the @code{OS/2} synchronization primitives.
+
+@node Interfaces.Os2lib.Threads (i-os2thr.ads)
+@section Interfaces.Os2lib.Threads (i-os2thr.ads)
+@cindex Interfaces.Os2lib.Threads (i-os2thr.ads)
+@cindex Interfacing, to OS/2
+@cindex Thread control, OS/2
+@cindex OS/2 thread interfacing
+
+@noindent
+This is a child package that provides definitions for interfacing
+to the @code{OS/2} thread primitives.
+
+@node Interfaces.Packed_Decimal (i-pacdec.ads)
+@section Interfaces.Packed_Decimal (i-pacdec.ads)
+@cindex Interfaces.Packed_Decimal (i-pacdec.ads)
+@cindex  IBM Packed Format
+@cindex  Packed Decimal
+
+@noindent
+This package provides a set of routines for conversions to and
+from a packed decimal format compatible with that used on IBM
+mainframes.
+
+@node Interfaces.VxWorks (i-vxwork.ads)
+@section Interfaces.VxWorks (i-vxwork.ads)
+@cindex Interfaces.VxWorks (i-vxwork.ads)
+@cindex Interfacing to VxWorks
+@cindex VxWorks, interfacing
+
+@noindent
+This package provides a limited binding to the VxWorks API
+In particular, it interfaces with the
+VxWorks hardware interrupt facilities
+
+@node System.Address_Image (s-addima.ads)
+@section System.Address_Image (s-addima.ads)
+@cindex System.Address_Image (s-addima.ads)
+@cindex Address image
+@cindex Image, of an address
+
+@noindent
+This function provides a useful debugging
+function that gives an (implementation dependent)
+string which identifies an address.
+
+@node System.Assertions (s-assert.ads)
+@section System.Assertions (s-assert.ads)
+@cindex System.Assertions (s-assert.ads)
+@cindex  Assertions
+@cindex  Assert_Failure, exception
+
+@noindent
+This package provides the declaration of the exception raised
+by an run-time assertion failure, as well as the routine that
+is used internally to raise this assertion.
+
+@node System.Partition_Interface (s-parint.ads)
+@section System.Partition_Interface (s-parint.ads)
+@cindex System.Partition_Interface (s-parint.ads)
+@cindex Partition intefacing functions
+
+@noindent
+This package provides facilities for partition interfacing. It
+is used primarily in a distribution context when using Annex E
+with @code{GLADE}.
+
+@node System.Task_Info (s-tasinf.ads)
+@section System.Task_Info (s-tasinf.ads)
+@cindex System.Task_Info (s-tasinf.ads)
+@cindex  Task_Info pragma
+
+@noindent
+This package provides target dependent functionality that is used
+to support the @code{Task_Info} pragma
+
+@node System.Wch_Cnv (s-wchcnv.ads)
+@section System.Wch_Cnv (s-wchcnv.ads)
+@cindex System.Wch_Cnv (s-wchcnv.ads)
+@cindex Wide Character, Representation
+@cindex Wide String, Conversion
+@cindex Representation of wide characters
+
+@noindent
+This package provides routines for converting between
+wide characters and a representation as a value of type
+@code{Standard.String}, using a specified wide character
+encoding method. Uses definitions in
+package @code{System.Wch_Con}
+
+@node System.Wch_Con (s-wchcon.ads)
+@section System.Wch_Con (s-wchcon.ads)
+@cindex System.Wch_Con (s-wchcon.ads)
+
+@noindent
+This package provides definitions and descriptions of
+the various methods used for encoding wide characters
+in ordinary strings. These definitions are used by
+the package @code{System.Wch_Cnv}.
+
+@node Interfacing to Other Languages
+@chapter Interfacing to Other Languages
+@noindent
+The facilities in annex B of the Ada 95 Reference Manual are fully
+implemented in GNAT, and in addition, a full interface to C++ is
+provided.
+
+@menu
+* Interfacing to C::          
+* Interfacing to C++::          
+* Interfacing to COBOL::        
+* Interfacing to Fortran::      
+* Interfacing to non-GNAT Ada code::
+@end menu
+
+@node Interfacing to C
+@section Interfacing to C
+
+@noindent
+Interfacing to C with GNAT can use one of two approaches:
+
+@enumerate
+@item
+The types in the package @code{Interfaces.C} may be used.
+@item
+Standard Ada types may be used directly. This may be less portable to
+other compilers, but will work on all GNAT compilers, which guarantee
+correspondence between the C and Ada types.
+@end enumerate
+
+@noindent
+Pragma @code{Convention C} maybe applied to Ada types, but mostly has no
+effect, since this is the default. The following table shows the
+correspondence between Ada scalar types and the corresponding C types.
+
+@table @code
+@item Integer
+@code{int}
+@item Short_Integer
+@code{short}
+@item Short_Short_Integer
+@code{signed char}
+@item Long_Integer
+@code{long}
+@item Long_Long_Integer
+@code{long long}
+@item Short_Float
+@code{float}
+@item Float
+@code{float}
+@item Long_Float
+@code{double}
+@item Long_Long_Float
+This is the longest floating-point type supported by the hardware.
+@end table
+
+@itemize @bullet
+@item
+Ada enumeration types map to C enumeration types directly if pragma
+@code{Convention C} is specified, which causes them to have int
+length. Without pragma @code{Convention C}, Ada enumeration types map to
+8, 16, or 32 bits (i.e. C types signed char, short, int respectively)
+depending on the number of values passed. This is the only case in which
+pragma @code{Convention C} affects the representation of an Ada type.
+
+@item
+Ada access types map to C pointers, except for the case of pointers to
+unconstrained types in Ada, which have no direct C equivalent.
+
+@item
+Ada arrays map directly to C arrays.
+
+@item
+Ada records map directly to C structures.
+
+@item
+Packed Ada records map to C structures where all members are bit fields
+of the length corresponding to the @code{@var{type}'Size} value in Ada.
+@end itemize
+
+@node Interfacing to C++
+@section Interfacing to C++
+
+@noindent
+The interface to C++ makes use of the following pragmas, which are
+primarily intended to be constructed automatically using a binding generator
+tool, although it is possible to construct them by hand. Ada Core 
+Technologies does not currently supply a suitable binding generator tool.
+
+Using these pragmas it is possible to achieve complete
+inter-operability between Ada tagged types and C class definitions.
+See @ref{Implementation Defined Pragmas} for more details.
+
+@table @code
+@item pragma CPP_Class ([Entity =>] @var{local_name})
+The argument denotes an entity in the current declarative region that is
+declared as a tagged or untagged record type. It indicates that the type
+corresponds to an externally declared C++ class type, and is to be laid
+out the same way that C++ would lay out the type.
+
+@item pragma CPP_Constructor ([Entity =>] @var{local_name})
+This pragma identifies an imported function (imported in the usual way
+with pragma @code{Import}) as corresponding to a C++ constructor.
+
+@item pragma CPP_Vtable @dots{}
+One @code{CPP_Vtable} pragma can be present for each component of type
+@code{CPP.Interfaces.Vtable_Ptr} in a record to which pragma @code{CPP_Class}
+applies.
+@end table
+
+@node Interfacing to COBOL
+@section Interfacing to COBOL
+
+@noindent
+Interfacing to COBOL is achieved as described in section B.4 of
+the Ada 95 reference manual.
+
+@node Interfacing to Fortran
+@section Interfacing to Fortran
+
+@noindent
+Interfacing to Fortran is achieved as described in section B.5 of the
+reference manual. The pragma @code{Convention Fortran}, applied to a
+multi- dimensional array causes the array to be stored in column-major
+order as required for convenient interface to Fortran.
+
+@node Interfacing to non-GNAT Ada code
+@section Interfacing to non-GNAT Ada code
+
+It is possible to specify the convention Ada in a pragma Import or
+pragma Export. However this refers to the calling conventions used
+by GNAT, which may or may not be similar enough to those used by
+some other Ada 83 or Ada 95 compiler to allow interoperation.
+
+If arguments types are kept simple, and if the foreign compiler generally
+follows system calling conventions, then it may be possible to integrate
+files compiled by other Ada compilers, provided that the elaboration
+issues are adequately addressed (for example by eliminating the 
+need for any load time elaboration).
+
+In particular, GNAT running on VMS is designed to
+be highly compatible with the DEC Ada 83 compiler, so this is one
+case in which it is possible to import foreign units of this type,
+provided that the data items passed are restricted to simple scalar
+values or simple record types without variants, or simple array
+types with fixed bounds.
+
+@node Machine Code Insertions
+@chapter Machine Code Insertions
+
+@noindent
+Package @code{Machine_Code} provides machine code support as described
+in the Ada 95 Reference Manual in two separate forms:
+@itemize @bullet
+@item
+Machine code statements, consisting of qualified expressions that
+fit the requirements of RM section 13.8.
+@item
+An intrinsic callable procedure, providing an alternative mechanism of
+including machine instructions in a subprogram.
+@end itemize
+
+The two features are similar, and both closely related to the mechanism
+provided by the asm instruction in the GNU C compiler. Full understanding
+and use of the facilities in this package requires understanding the asm
+instruction as described in @cite{Using and Porting GNU CC} by Richard
+Stallman.  Calls to the function @code{Asm} and the procedure @code{Asm}
+have identical semantic restrictions and effects as described below.
+Both are provided so that the procedure call can be used as a statement,
+and the function call can be used to form a code_statement.
+
+The first example given in the GNU CC documentation is the C @code{asm}
+instruction:
+@smallexample
+   asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
+@end smallexample
+
+@noindent
+The equivalent can be written for GNAT as:
+
+@smallexample
+Asm ("fsinx %1 %0",
+     My_Float'Asm_Output ("=f", result),
+     My_Float'Asm_Input  ("f",  angle));
+@end smallexample
+
+The first argument to @code{Asm} is the assembler template, and is
+identical to what is used in GNU CC. This string must be a static
+expression.  The second argument is the output operand list. It is
+either a single @code{Asm_Output} attribute reference, or a list of such
+references enclosed in parentheses (technically an array aggregate of
+such references).
+
+The @code{Asm_Output} attribute denotes a function that takes two
+parameters.  The first is a string, the second is the name of a variable
+of the type designated by the attribute prefix. The first (string)
+argument is required to be a static expression and designates the
+constraint for the parameter (e.g. what kind of register is
+required). The second argument is the variable to be updated with the
+result. The possible values for constraint are the same as those used in
+the RTL, and are dependent on the configuration file used to build the
+GCC back end.  If there are no output operands, then this argument may
+either be omitted, or explicitly given as @code{No_Output_Operands}.
+
+The second argument of @code{@var{my_float}'Asm_Output} functions as
+though it were an @code{out} parameter, which is a little curious, but
+all names have the form of expressions, so there is no syntactic
+irregularity, even though normally functions would not be permitted
+@code{out} parameters.  The third argument is the list of input
+operands. It is either a single @code{Asm_Input} attribute reference, or
+a list of such references enclosed in parentheses (technically an array
+aggregate of such references).
+
+The @code{Asm_Input} attribute denotes a function that takes two
+parameters.  The first is a string, the second is an expression of the
+type designated by the prefix. The first (string) argument is required
+to be a static expression, and is the constraint for the parameter,
+(e.g. what kind of register is required). The second argument is the
+value to be used as the input argument. The possible values for the
+constant are the same as those used in the RTL, and are dependent on
+the configuration file used to built the GCC back end.
+
+If there are no input operands, this argument may either be omitted, or
+explicitly given as @code{No_Input_Operands}.  The fourth argument, not
+present in the above example, is a list of register names, called the
+@dfn{clobber} argument. This argument, if given, must be a static string
+expression, and is a space or comma separated list of names of registers
+that must be considered destroyed as a result of the @code{Asm} call. If
+this argument is the null string (the default value), then the code
+generator assumes that no additional registers are destroyed.
+
+The fifth argument, not present in the above example, called the
+@dfn{volatile} argument, is by default @code{False}. It can be set to
+the literal value @code{True} to indicate to the code generator that all
+optimizations with respect to the instruction specified should be
+suppressed, and that in particular, for an instruction that has outputs,
+the instruction will still be generated, even if none of the outputs are
+used. See the full description in the GCC manual for further details.
+
+The @code{Asm} subprograms may be used in two ways. First the procedure
+forms can be used anywhere a procedure call would be valid, and
+correspond to what the RM calls ``intrinsic'' routines. Such calls can
+be used to intersperse machine instructions with other Ada statements.
+Second, the function forms, which return a dummy value of the limited
+private type @code{Asm_Insn}, can be used in code statements, and indeed
+this is the only context where such calls are allowed.  Code statements
+appear as aggregates of the form:
+
+@smallexample
+Asm_Insn'(Asm (@dots{}));
+Asm_Insn'(Asm_Volatile (@dots{}));
+@end smallexample
+
+In accordance with RM rules, such code statements are allowed only
+within subprograms whose entire body consists of such statements.  It is
+not permissible to intermix such statements with other Ada statements.
+
+Typically the form using intrinsic procedure calls is more convenient
+and more flexible. The code statement form is provided to meet the RM
+suggestion that such a facility should be made available.  The following
+is the exact syntax of the call to @code{Asm} (of course if named notation is
+used, the arguments may be given in arbitrary order, following the
+normal rules for use of positional and named arguments)
+
+@smallexample
+ASM_CALL ::= Asm (
+                 [Template =>] static_string_EXPRESSION
+               [,[Outputs  =>] OUTPUT_OPERAND_LIST      ]
+               [,[Inputs   =>] INPUT_OPERAND_LIST       ]
+               [,[Clobber  =>] static_string_EXPRESSION ]
+               [,[Volatile =>] static_boolean_EXPRESSION] )
+OUTPUT_OPERAND_LIST ::=
+  No_Output_Operands
+| OUTPUT_OPERAND_ATTRIBUTE
+| (OUTPUT_OPERAND_ATTRIBUTE @{,OUTPUT_OPERAND_ATTRIBUTE@})
+OUTPUT_OPERAND_ATTRIBUTE ::=
+  SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME)
+INPUT_OPERAND_LIST ::=
+  No_Input_Operands
+| INPUT_OPERAND_ATTRIBUTE
+| (INPUT_OPERAND_ATTRIBUTE @{,INPUT_OPERAND_ATTRIBUTE@})
+INPUT_OPERAND_ATTRIBUTE ::=
+  SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
+@end smallexample
+
+@node GNAT Implementation of Tasking
+@chapter GNAT Implementation of Tasking
+@menu
+* Mapping Ada Tasks onto the Underlying Kernel Threads::
+* Ensuring Compliance with the Real-Time Annex::
+@end menu
+
+@node Mapping Ada Tasks onto the Underlying Kernel Threads
+@section Mapping Ada Tasks onto the Underlying Kernel Threads
+
+GNAT run-time system comprises two layers:
+
+@itemize @bullet
+@item GNARL (GNAT Run-time  Layer)
+@item GNULL (GNAT Low-level Library)
+@end itemize
+
+In GNAT, Ada's tasking services rely on a platform and OS independent
+layer known as GNARL. This code is responsible for implementing the
+correct semantics of Ada's task creation, rendezvous, protected
+operations etc.
+
+GNARL decomposes Ada's tasking semantics into simpler lower level
+operations such as create a thread, set the priority of a thread,
+yield, create a lock, lock/unlock, etc. The spec for these low-level
+operations constitutes GNULLI, the GNULL Interface. This interface is
+directly inspired from the POSIX real-time API.
+
+If the underlying executive or OS implements the POSIX standard
+faithfully, the GNULL Interface maps as is to the services offered by
+the underlying kernel. Otherwise, some target dependent glue code maps
+the services offered by the underlying kernel to the semantics expected
+by GNARL.
+
+Whatever the underlying OS (VxWorks, UNIX, OS/2, Windows NT, etc.) the
+key point is that each Ada task is mapped on a thread in the underlying 
+kernel. For example, in the case of VxWorks
+
+     1 Ada task = 1 VxWorks task
+
+In addition Ada task priorities map onto the underlying thread priorities.
+Mapping Ada tasks onto the underlying kernel threads has several advantages:
+
+@enumerate
+
+@item
+The underlying scheduler is used to schedule the Ada tasks. This
+makes Ada tasks as efficient as kernel threads from a scheduling
+standpoint.  
+
+@item
+Interaction with code written in C containing threads is eased
+since at the lowest level Ada tasks and C threads map onto the same
+underlying kernel concept.
+
+@item
+When an Ada task is blocked during I/O the remaining Ada tasks are
+able to proceed.
+
+@item
+On multi-processor systems Ada Tasks can execute in parallel.
+@end enumerate
+
+@node Ensuring Compliance with the Real-Time Annex
+@section Ensuring Compliance with the Real-Time Annex
+
+The reader will be quick to notice that while mapping Ada tasks onto
+the underlying threads has significant advantages, it does create some
+complications when it comes to respecting the scheduling semantics
+specified in the real-time annex (Annex D).
+
+For instance Annex D requires that for the FIFO_Within_Priorities
+scheduling policy we have:
+
+@smallexample
+When the active priority of a ready task that is not running
+changes, or the setting of its base priority takes effect, the
+task is removed from the ready queue for its old active priority
+and is added at the tail of the ready queue for its new active
+priority, except in the case where the active priority is lowered
+due to the loss of inherited priority, in which case the task is
+added at the head of the ready queue for its new active priority.
+@end smallexample
+
+While most kernels do put tasks at the end of the priority queue when
+a task changes its priority, (which respects the main
+FIFO_Within_Priorities requirement), almost none keep a thread at the
+beginning of its priority queue when its priority drops from the loss
+of inherited priority.
+
+As a result most vendors have provided incomplete Annex D implementations.
+
+The GNAT run-time, has a nice cooperative solution to this problem
+which ensures that accurate FIFO_Within_Priorities semantics are
+respected.
+
+The principle is as follows. When an Ada task T is about to start
+running, it checks whether some other Ada task R with the same
+priority as T has been suspended due to the loss of priority
+inheritance. If this is the case, T yields and is placed at the end of
+its priority queue. When R arrives at the front of the queue it
+executes. 
+
+Note that this simple scheme preserves the relative order of the tasks
+that were ready to execute in the priority queue where R has been
+placed at the end.
+
+@node    Code generation for array aggregates
+@chapter  Code generation for array aggregates
+
+@menu
+* Static constant aggregates with static bounds::
+* Constant aggregates with an unconstrained nominal types::
+* Aggregates with static bounds::
+* Aggregates with non-static bounds::
+* Aggregates in assignments statements::
+@end menu
+ 
+Aggregate have a rich syntax and allow the user to specify the values of
+complex data structures by means of a single construct. As a result, the
+code generated for aggregates can be quite complex and involve loops, case
+statements and multiple assignments. In the simplest cases, however, the
+compiler will recognize aggregates whose components and constraints are
+fully static, and in those cases the compiler will generate little or no
+executable code. The following is an outline of the code that GNAT generates
+for various aggregate constructs. For further details, the user will find it
+useful to examine the output produced by the -gnatG flag to see the expanded
+source that is input to the code generator.  The user will also want to examine
+the assembly code generated at various levels of optimization.
+
+The code generated for aggregates depends on the context, the component values,
+and the type. In the context of an object declaration the code generated is
+generally simpler than in the case of an assignment. As a general rule, static
+component values and static subtypes also lead to simpler code.
+ 
+@node Static constant aggregates with static bounds
+@section Static constant aggregates with static bounds
+ 
+ For the declarations:
+@smallexample 
+    type One_Dim is array (1..10) of integer;
+    ar0 : constant One_Dim := ( 1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
+@end smallexample 
+
+GNAT generates no executable code: the constant ar0 is placed in static memory.
+The same is true for constant aggregates with named associations:
+ 
+@smallexample 
+    Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1=> 1);
+    Cr3 : constant One_Dim := (others => 7777);
+@end smallexample 
+ 
+ The same is true for multidimensional constant arrays such as:
+ 
+@smallexample 
+    type two_dim is array (1..3, 1..3) of integer;
+    Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
+@end smallexample 
+ 
+The same is true for arrays of one-dimensional arrays: the following are
+static:
+ 
+@smallexample 
+type ar1b is array (1..3) of boolean;
+type ar_ar is array (1..3) of ar1b;
+None : constant ar1b := (others => false);      --  fully static
+None2 : constant ar_ar := (1..3 => None);       --  fully static
+@end smallexample 
+ 
+However, for multidimensional aggregates with named associations, GNAT will
+generate assignments and loops, even if all associations are static. The
+following two declarations generate a loop for the first dimension, and
+individual component assignments for the second dimension:
+ 
+@smallexample 
+Zero1: constant two_dim := (1..3 => (1..3 => 0));
+Zero2: constant two_dim := (others => (others => 0));     
+@end smallexample 
+ 
+@node Constant aggregates with an unconstrained nominal types
+@section Constant aggregates with an unconstrained nominal types
+ 
+In such cases the aggregate itself establishes the subtype, so that associations
+with "others" cannot be used. GNAT determines the bounds for the actual
+subtype of the aggregate, and allocates the aggregate statically as well. No
+code is generated for the following:
+ 
+@smallexample 
+    type One_Unc is array (natural range <>) of integer;
+    Cr_Unc : constant One_Unc := (12,24,36);
+@end smallexample 
+ 
+@node Aggregates with static bounds
+@section Aggregates with static bounds
+ 
+In all previous examples the aggregate was the initial (and immutable) value
+of a constant. If the aggregate initializes a variable, then code is generated
+for it as a combination of individual assignments and loops over the target
+object. The declarations
+ 
+@smallexample 
+       Cr_Var1 : One_Dim := (2, 5, 7, 11);
+       Cr_Var2 : One_Dim := (others > -1);
+@end smallexample 
+ 
+generate the equivalent of
+ 
+@smallexample 
+       Cr_Var1 (1) := 2;
+       Cr_Var1 (2) := 3;
+       Cr_Var1 (3) := 5;
+       Cr_Var1 (4) := 11;
+ 
+       for I in Cr_Var2'range loop
+          Cr_Var2 (I) := =-1;
+       end loop;
+@end smallexample 
+ 
+@node Aggregates with non-static bounds
+@section Aggregates with non-static bounds
+ 
+If the bounds of the aggregate are not statically compatible with the bounds
+of the nominal subtype  of the target, then constraint checks have to be
+generated on the bounds. For a multidimensional array, constraint checks may
+have to be applied to sub-arrays individually, if they do not have statically
+compatible subtypes.
+ 
+@node Aggregates in assignments statements
+@section Aggregates in assignments statements
+ 
+In general, aggregate assignment requires the construction of a temporary,
+and a copy from the temporary to the target of the assignment. This is because
+it is not always possible to convert the assignment into a series of individual 
+component assignments. For example, consider the simple case:
+ 
+@smallexample 
+@end smallexample 
+        A := (A(2), A(1));
+ 
+This cannot be converted into:
+ 
+@smallexample 
+        A(1) := A(2);
+        A(2) := A(1);
+@end smallexample 
+ 
+So the aggregate has to be built first in a separate location, and then
+copied into the target. GNAT recognizes simple cases where this intermediate
+step is not required, and the assignments can be performed in place, directly
+into the target. The following sufficient criteria are applied:
+
+@enumerate 
+@item The bounds of the aggregate are static, and the associations are static.
+@item  The components of the aggregate are static constants, names of
+    simple variables that are not renamings, or expressions not involving
+    indexed components whose operands obey these rules.
+@end enumerate
+ 
+If any of these conditions are violated, the aggregate will be built in
+a temporary (created either by the front-end or the code generator) and then
+that temporary will be copied onto the target.
+ 
+ 
+@node Specialized Needs Annexes
+@chapter Specialized Needs Annexes
+
+@noindent
+Ada 95 defines a number of specialized needs annexes, which are not
+required in all implementations. However, as described in this chapter,
+GNAT implements all of these special needs annexes:
+
+@table @asis
+@item Systems Programming (Annex C)
+The systems programming annex is fully implemented.
+
+@item Real-Time Systems (Annex D)
+The real-time systems annex is fully implemented.
+
+@item Distributed Systems (Annex E)
+Stub generation is fully implemented in the @code{GNAT} compiler. In addition,
+a complete compatible PCS is available as part of the @code{GLADE} system,
+a separate product available from Ada Core Technologies. When the two
+products are used in conjunction, this annex is fully implemented.
+
+@item Information Systems (Annex F)
+The information systems annex is fully implemented.
+
+@item Numerics (Annex G)
+The numerics annex is fully implemented.
+
+@item Safety and Security (Annex H)
+The safety and security annex is fully implemented.
+
+@end table
+
+@node Compatibility Guide
+@chapter Compatibility Guide
+
+@noindent
+This chapter contains sections that describe compatibility issues between
+GNAT and other Ada 83 and Ada 95 compilation systems, to aid in porting
+applications developed in other Ada environments.
+
+@menu
+* Compatibility with Ada 83::       
+* Compatibility with DEC Ada 83::
+* Compatibility with Other Ada 95 Systems::
+* Representation Clauses::
+@end menu
+
+@node Compatibility with Ada 83
+@section Compatibility with Ada 83
+
+@noindent
+Ada 95 is designed to be highly upwards compatible with Ada 83. In
+particular, the design intention is that the difficulties associated
+with moving from Ada 83 to Ada 95 should be no greater than those
+that occur when moving from one Ada 83 system to another.
+
+However, there are a number of points at which there are minor
+incompatibilities. The Ada 95 Annotated Reference Manual contains
+full details of these issues,
+and should be consulted for a complete treatment.
+In practice the
+following are the most likely issues to be encountered.
+
+@table @asis
+@item Character range
+The range of Standard.Character is now the full 256 characters of Latin-1,
+whereas in most Ada 83 implementations it was restricted to 128 characters.
+This may show up as compile time or runtime errors. The desirable fix is to
+adapt the program to accommodate the full character set, but in some cases
+it may be convenient to define a subtype or derived type of Character that
+covers only the restricted range.
+
+@item New reserved words
+The identifiers @code{abstract}, @code{aliased}, @code{protected},
+@code{requeue}, @code{tagged}, and @code{until} are reserved in Ada 95.
+Existing Ada 83 code using any of these identifiers must be edited to
+use some alternative name.
+
+@item Freezing rules
+The rules in Ada 95 are slightly different with regard to the point at
+which entities are frozen, and representation pragmas and clauses are
+not permitted past the freeze point. This shows up most typically in
+the form of an error message complaining that a representation item
+appears too late, and the appropriate corrective action is to move
+the item nearer to the declaration of the entity to which it refers.
+
+A particular case is that representation pragmas (including the
+extended DEC Ada 83 compatibility pragmas such as Export_Procedure), cannot
+be applied to a subprogram body. If necessary, a separate subprogram 
+declaration must be introduced to which the pragma can be applied.
+
+@item Optional bodies for library packages
+In Ada 83, a package that did not require a package body was nevertheless
+allowed to have one. This lead to certain surprises in compiling large
+systems (situations in which the body could be unexpectedly ignored). In
+Ada 95, if a package does not require a body then it is not permitted to
+have a body. To fix this problem, simply remove a redundant body if it
+is empty, or, if it is non-empty, introduce a dummy declaration into the
+spec that makes the body required. One approach is to add a private part
+to the package declaration (if necessary), and define a parameterless
+procedure called Requires_Body, which must then be given a dummy
+procedure body in the package body, which then becomes required.
+
+@item Numeric_Error is now the same as Constraint_Error
+In Ada 95, the exception Numeric_Error is a renaming of Constraint_Error.
+This means that it is illegal to have separate exception handlers for
+the two exceptions. The fix is simply to remove the handler for the
+Numeric_Error case (since even in Ada 83, a compiler was free to raise
+Constraint_Error in place of Numeric_Error in all cases).
+
+@item Indefinite subtypes in generics
+In Ada 83, it was permissible to pass an indefinite type (e.g. String) as
+the actual for a generic formal private type, but then the instantiation
+would be illegal if there were any instances of declarations of variables
+of this type in the generic body. In Ada 95, to avoid this clear violation
+of the contract model, the generic declaration clearly indicates whether
+or not such instantiations are permitted. If a generic formal parameter
+has explicit unknown discriminants, indicated by using (<>) after the
+type name, then it can be instantiated with indefinite types, but no
+variables can be declared of this type. Any attempt to declare a variable
+will result in an illegality at the time the generic is declared. If the
+(<>) notation is not used, then it is illegal to instantiate the generic
+with an indefinite type. This will show up as a compile time error, and
+the fix is usually simply to add the (<>) to the generic declaration.
+@end table
+
+All implementations of GNAT provide a switch that causes GNAT to operate
+in Ada 83 mode. In this mode, some but not all compatibility problems
+of the type described above are handled automatically. For example, the
+new Ada 95 protected keywords are not recognized in this mode. However,
+in practice, it is usually advisable to make the necessary modifications
+to the program to remove the need for using this switch.
+
+@node Compatibility with Other Ada 95 Systems
+@section Compatibility with Other Ada 95 Systems
+
+@noindent
+Providing that programs avoid the use of implementation dependent and
+implementation defined features of Ada 95, as documented in the Ada 95
+reference manual, there should be a high degree of portability between
+GNAT and other Ada 95 systems. The following are specific items which
+have proved troublesome in moving GNAT programs to other Ada 95
+compilers, but do not affect porting code to GNAT.
+
+@table @asis
+@item Ada 83 Pragmas and Attributes
+Ada 95 compilers are allowed, but not required, to implement the missing
+Ada 83 pragmas and attributes that are no longer defined in Ada 95.
+GNAT implements all such pragmas and attributes, eliminating this as
+a compatibility concern, but some other Ada 95 compilers reject these
+pragmas and attributes.
+
+@item Special-needs Annexes
+GNAT implements the full set of special needs annexes. At the
+current time, it is the only Ada 95 compiler to do so. This means that
+programs making use of these features may not be portable to other Ada
+95 compilation systems.
+
+@item Representation Clauses
+Some other Ada 95 compilers implement only the minimal set of
+representation clauses required by the Ada 95 reference manual. GNAT goes
+far beyond this minimal set, as described in the next section.
+@end table
+
+@node Representation Clauses
+@section Representation Clauses
+
+@noindent
+The Ada 83 reference manual was quite vague in describing both the minimal
+required implementation of representation clauses, and also their precise
+effects. The Ada 95 reference manual is much more explicit, but the minimal
+set of capabilities required in Ada 95 is quite limited.
+
+GNAT implements the full required set of capabilities described in the
+Ada 95 reference manual, but also goes much beyond this, and in particular
+an effort has been made to be compatible with existing Ada 83 usage to the
+greatest extent possible.
+
+A few cases exist in which Ada 83 compiler behavior is incompatible with
+requirements in the Ada 95 reference manual. These are instances of
+intentional or accidental dependence on specific implementation dependent
+characteristics of these Ada 83 compilers. The following is a list of
+the cases most likely to arise in existing legacy Ada 83 code.
+
+@table @asis
+@item Implicit Packing
+Some Ada 83 compilers allowed a Size specification to cause implicit
+packing of an array or record. This could cause expensive implicit
+conversions for change of representation in the presence of derived
+types, and the Ada design intends to avoid this possibility.
+Subsequent AI's were issued to make it clear that such implicit
+change of representation in response to a Size clause is inadvisable,
+and this recommendation is represented explicitly in the Ada 95 RM
+as implementation advice that is followed by GNAT.
+The problem will show up as an error
+message rejecting the size clause. The fix is simply to provide
+the explicit pragma Pack, or for more fine tuned control, provide
+a Component_Size clause.
+
+@item Meaning of Size Attribute
+The Size attribute in Ada 95 for discrete types is defined as being the
+minimal number of bits required to hold values of the type. For example,
+on a 32-bit machine, the size of Natural will typically be 31 and not
+32 (since no sign bit is required). Some Ada 83 compilers gave 31, and
+some 32 in this situation. This problem will usually show up as a compile
+time error, but not always. It is a good idea to check all uses of the
+'Size attribute when porting Ada 83 code. The GNAT specific attribute
+Object_Size can provide a useful way of duplicating the behavior of
+some Ada 83 compiler systems.
+
+@item Size of Access Types
+A common assumption in Ada 83 code is that an access type is in fact a pointer,
+and that therefore it will be the same size as a System.Address value. This
+assumption is true for GNAT in most cases with one exception. For the case of
+a pointer to an unconstrained array type (where the bounds may vary from one
+value of the access type to another), the default is to use a "fat pointer",
+which is represented as two separate pointers, one to the bounds, and one to
+the array. This representation has a number of advantages, including improved
+efficiency. However, it may cause some difficulties in porting existing Ada 83
+code which makes the assumption that, for example, pointers fit in 32 bits on
+a machine with 32-bit addressing.
+
+To get around this problem, GNAT also permits the use of "thin pointers" for
+access types in this case (where the designated type is an unconstrained array
+type). These thin pointers are indeed the same size as a System.Address value.
+To specify a thin pointer, use a size clause for the type, for example:
+
+@smallexample
+type X is access all String;
+for X'Size use Standard'Address_Size;
+@end smallexample
+
+@noindent
+which will cause the type X to be represented using a single pointer. When using
+this representation, the bounds are right behind the array. This representation
+is slightly less efficient, and does not allow quite such flexibility in the
+use of foreign pointers or in using the Unrestricted_Access attribute to create
+pointers to non-aliased objects. But for any standard portable use of the access
+type it will work in a functionally correct manner and allow porting of existing
+code. Note that another way of forcing a thin pointer representation is to use
+a component size clause for the element size in an array, or a record 
+representation clause for an access field in a record.
+@end table
+
+@node Compatibility with DEC Ada 83
+@section Compatibility with DEC Ada 83
+
+@noindent
+The VMS version of GNAT fully implements all the pragmas and attributes
+provided by DEC Ada 83, as well as providing the standard DEC Ada 83
+libraries, including Starlet. In addition, data layouts and parameter
+passing conventions are highly compatible. This means that porting
+existing DEC Ada 83 code to GNAT in VMS systems should be easier than
+most other porting efforts. The following are some of the most
+significant differences between GNAT and DEC Ada 83.
+
+@table @asis
+@item Default floating-point representation
+In GNAT, the default floating-point format is IEEE, whereas in DEC Ada 83,
+it is VMS format. GNAT does implement the necessary pragmas
+(Long_Float, Float_Representation) for changing this default.
+
+@item System
+The package System in GNAT exactly corresponds to the definition in the
+Ada 95 reference manual, which means that it excludes many of the 
+DEC Ada 83 extensions. However, a separate package Aux_DEC is provided
+that contains the additional definitions, and a special pragma,
+Extend_System allows this package to be treated transparently as an
+extension of package System.
+
+@item To_Address
+The definitions provided by Aux_DEC are exactly compatible with those
+in the DEC Ada 83 version of System, with one exception. DEC Ada provides
+the following declarations:
+
+@smallexample
+TO_ADDRESS(INTEGER)
+TO_ADDRESS(UNSIGNED_LONGWORD)
+TO_ADDRESS(universal_integer)
+@end smallexample
+
+@noindent
+The version of TO_ADDRESS taking a universal integer argument is in fact
+an extension to Ada 83 not strictly compatible with the reference manual.
+In GNAT, we are constrained to be exactly compatible with the standard,
+and this means we cannot provide this capability. In DEC Ada 83, the
+point of this definition is to deal with a call like:
+
+@smallexample
+   TO_ADDRESS (16#12777#);
+@end smallexample
+
+@noindent
+Normally, according to the Ada 83 standard, one would expect this to be
+ambiguous, since it matches both the INTEGER and UNSIGNED_LONGWORD forms
+of TO_ADDRESS. However, in DEC Ada 83, there is no ambiguity, since the
+definition using universal_integer takes precedence.
+
+In GNAT, since the version with universal_integer cannot be supplied, it is
+not possible to be 100% compatible. Since there are many programs using
+numeric constants for the argument to TO_ADDRESS, the decision in GNAT was
+to change the name of the function in the UNSIGNED_LONGWORD case, so the
+declarations provided in the GNAT version of AUX_Dec are:
+
+@smallexample
+function To_Address (X : Integer) return Address;
+pragma Pure_Function (To_Address);
+
+function To_Address_Long (X : Unsigned_Longword)
+ return Address;
+pragma Pure_Function (To_Address_Long);
+@end smallexample
+
+@noindent
+This means that programs using TO_ADDRESS for UNSIGNED_LONGWORD must
+change the name to TO_ADDRESS_LONG.
+
+@item Task_Id values
+The Task_Id values assigned will be different in the two systems, and GNAT
+does not provide a specified value for the Task_Id of the environment task,
+which in GNAT is treated like any other declared task.
+@end table
+
+For full details on these and other less significant compatibility issues,
+see appendix E of the Digital publication entitled "DEC Ada, Technical
+Overview and Comparison on DIGITAL Platforms".
+
+For GNAT running on other than VMS systems, all the DEC Ada 83 pragmas and
+attributes are recognized, although only a subset of them can sensibly
+be implemented. The description of pragmas in this reference manual
+indicates whether or not they are applicable to non-VMS systems.
+
+@include gfdl.texi
+@c GNU Free Documentation License
+
+@node Index,,GNU Free Documentation License, Top
+@unnumbered Index
+
+@printindex cp
+
+@contents
+
+@bye