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authorUlrich Drepper <drepper@redhat.com>1997-09-16 00:42:43 +0000
committerUlrich Drepper <drepper@redhat.com>1997-09-16 00:42:43 +0000
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1997-09-16 02:14 Ulrich Drepper <drepper@cygnus.com> Implementation of Hesiod NSS module by Mark Kettenis. * hesiod/Makefile: New file. * hesiod/hesiod.c: New file. * hesiod/hesiod.h: New file. * hesiod/hesiod_p.h: New file. * hesiod/libnss_hesiod.map: New file. * hesiod/nss_hesiod/hesiod-grp.c: New file. * hesiod/nss_hesiod/hesiod-pwd.c: New file. * hesiod/nss_hesiod/hesiod-service.c: New file. * sysdeps/unix/inet/Subdirs: Add hesiod. * shlib-versions: Add version number for libnss_hesiod. * libio/iolibio.h: Remove definition of _IO_* macros. * libio/fileops.c: Define close, fstat, lseek, read, and write as macros to use __ protected versions. Use those functions instead of _IO_* functions. * libio/iopopen.c: Define _IO_close to close. * manual/math.texi: Explain the use of the optimizing inline functions. Describe rand_r function and tell about SysV RNGs in introduction. * resolv/res_send.c (res_send): Use socklen_t type for `fromlen' variable. * string/Makefile (tests): Add noinl-tester. * string/noinl-tester.c: New file. * string/tester.c: Add more stpcpy tests for constant arguments for all short lengths. * string/string.h: Always declare __bzero. Describe __NO_STRING_INLINES. Always include <bits/string.h>. * string/bits/string2.h: Add warning about direct use. Change __strcpy_small and __stpcpy_small implementation to use macros and provide alternative for platforms which cannot do unaligned stores. * sysdeps/i386/bits/string.h: Don't define anything is __NO_STRING_INLINES is defined. * sysdeps/i386/i486/bits/string.h: Change __strcpy_small and __stpcpy_small implementation to use macros and provide alternative for platforms which cannot do unaligned stores. * sysdeps/alpha/bzero.S: Define bzero as weak alias of __bzero. * sysdeps/generic/bzero.c: Likewise. * sysdeps/i386/bzero.c: Likewise. * sysdeps/i386/i586/bzero.S: Likewise. * sysdeps/vax/bzero.s: Likewise. * sysdeps/generic/bits/select.h: Don't use ugly casts to access array. * sysdeps/i386/bits/select.h: Likewise. * sysdeps/i386/fpu/bits/mathinline.c (__finite): Relax register constraints a bit. Don't define and test for _BITS_MATHINLINE_H. Emit warning if used directly and not through math.h. * sysdeps/i386/i486/atomicity.h: Change return type of compare_and_swap to char to get better code. Fix typo. * sysdeps/stub/atomicity.h: Fix typo. 1997-09-14 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * sysdeps/generic/stpcpy.c: #undef stpcpy and __stpcpy. 1997-09-14 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * string/bits/string2.h: Add prototypes to avoid warning. 1997-09-14 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * string/bits/string2.h (strsep): Fix handling of empty REJECT. (__strsep_1c): Handle NULL and empty string. (__strsep_g): Likewise. 1997-09-13 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * catgets/Makefile (extra-objs): Set this instead of generated. * md5-crypt/Makefile (extra-objs): Add all object file variants of onlymd5-entry. 1997-09-12 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * sysdeps/generic/sysd-stdio.c (__stdio_read): Fix typo in last change. 1997-09-12 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * sysdeps/m68k/m68020/atomicity.h: New file. 1997-09-15 05:11 Ulrich Drepper <drepper@cygnus.com> * posix/Makefile (distribute): Add globtest.c and globtest.sh. Compile and run globtest if not cross-compiling. * posix/globtest.c: New file. * posix/globtest.sh: New file. * posix/glob.c: Pretty print preprocessor stuff. (glob_in_dir): If PATTERN is not really a pattern still check whether it is a real file in the current directory and return error if not. Reported by Eugene Mamchits <eugin@ips.ras.ru>. * libio/fileops.c (_IO_file_sync): Acquire lock before doing the work. * libio/ioseekoff.c (_IO_seekoff): Likewise. * libio/ioseekpos.c (_IO_seekpos): Likewise. 1997-09-13 18:06 Ulrich Drepper <drepper@cygnus.com> * configure.in: Prevent configuration for unsupported platforms. 1997-09-13 04:07 Ulrich Drepper <drepper@cygnus.com> * elf/rtld.c (dl_main): Make sure we always have a file argument by testing for < 2 arguments after recognizing the options. 1997-09-12 11:47 Fila Kolodny <fila@ibi.com> * string/bits/string2.h (__strsep_1c): Cast out const from __retval. (__strsep_g): Likewise.
Diffstat (limited to 'manual/math.texi')
-rw-r--r--manual/math.texi64
1 files changed, 62 insertions, 2 deletions
diff --git a/manual/math.texi b/manual/math.texi
index 2b7cb82..15a2075 100644
--- a/manual/math.texi
+++ b/manual/math.texi
@@ -54,6 +54,7 @@ in case of double using @code{double} is a good compromise.
constant.
* FP Comparison Functions:: Special functions to compare floating-point
numbers.
+* FP Function Optimizations:: Fast code or small code.
* Trig Functions:: Sine, cosine, and tangent.
* Inverse Trig Functions:: Arc sine, arc cosine, and arc tangent.
* Exponents and Logarithms:: Also includes square root.
@@ -704,6 +705,35 @@ that the comparison for equality and unequality do @emph{not} throw an
exception if one of the arguments is an unordered value.
+@node FP Function Optimizations
+@section Is Fast Code or Small Code preferred?
+@cindex Optimization
+
+If an application uses many floating point function it is often the case
+that the costs for the function calls itseld are not neglectable.
+Modern processor implementation often can execute the operation itself
+very fast but the call means a disturbance of the control flow.
+
+For this reason the GNU C Library provides optimizations for many of the
+frequently used math functions. When the GNU CC is used and the user
+activates the optimizer several new inline functions and macros get
+defined. These new functions and macros have the same names as the
+library function and so get used instead of the later. In case of
+inline functions the compiler will decide whether it is reasonable to
+use the inline function and this decision is usually correct.
+
+For the generated code this means that no calls to the library functions
+are necessary. This increases the speed significantly. But the
+drawback is that the code size increases and this increase is not always
+neglectable.
+
+In cases where the inline functions and macros are not wanted the symbol
+@code{__NO_MATH_INLINES} should be defined before any system header is
+included. This will make sure only library functions are used. Of
+course it can be determined for each single file in the project whether
+giving this option is preferred or not.
+
+
@node Trig Functions
@section Trigonometric Functions
@cindex trigonometric functions
@@ -1430,8 +1460,14 @@ the same seed, used in different C libraries or on different CPU types,
will give you different random numbers.
The GNU library supports the standard @w{ISO C} random number functions
-plus another set derived from BSD. We recommend you use the standard
-ones, @code{rand} and @code{srand}.
+plus two other sets derived from BSD and SVID. We recommend you use the
+standard ones, @code{rand} and @code{srand} if only a small number of
+random bits are required. The SVID functions provide an interface which
+allows better randon number generator algorithms and they return up to
+48 random bits in one calls and they also return random floating-point
+numbers if wanted. The SVID function might not be available on some BSD
+derived systems but since they are required in the XPG they are
+available on all Unix-conformant systems.
@menu
* ISO Random:: @code{rand} and friends.
@@ -1478,6 +1514,30 @@ To produce truly random numbers (not just pseudo-random), do @code{srand
(time (0))}.
@end deftypefun
+A completely broken interface was designed by the POSIX.1 committee to
+support reproducible random numbers in multi-threaded programs.
+
+@comment stdlib.h
+@comment POSIX.1
+@deftypefun int rand_r (unsigned int *@var{seed})
+This function returns a random number in the range 0 to @code{RAND_MAX}
+just as @code{rand} does. But this function does not keep an internal
+state for the RNG. Instead the @code{unsigned int} variable pointed to
+by the argument @var{seed} is the only state. Before the value is
+returned the state will be updated so that the next call will return a
+new number.
+
+I.e., the state of the RNG can only have as much bits as the type
+@code{unsigned int} has. This is far too few to provide a good RNG.
+This interface is broken by design.
+
+If the program requires reproducible random numbers in multi-threaded
+programs the reentrant SVID functions are probably a better choice. But
+these functions are GNU extensions and therefore @code{rand_r}, as being
+standardized in POSIX.1, should always be kept as a default method.
+@end deftypefun
+
+
@node BSD Random
@subsection BSD Random Number Functions