Target FP: Perform Ada fixed-point scaling in target format

One of the few still remaining uses of DOUBLEST in GDB is the Ada front-end
code that handles scaling of Ada fixed-point types.  The target format for
those types is some integer format; to convert those values to standard
floating-point representation, that integer needs to be multiplied by a
rational scale factor, given as a pair of numerator and denominator.

To avoid having to deal with long integer arithmetic, the current Ada
front-end code currently performs those scaling operations in host
DOUBLEST arithmetic.  To eliminate this use of DOUBLEST, this patch
changes the front-end to instead perform those operations in the
*target* floating-point format (chosing to use the target "long double").

The implementation is mostly straight-forward, using value_cast and
value_binop to perform the target operations.

Scanning in the scale numerator and denominator is now done into
a host "long long" instead of a DOUBLEST, which should be large
enough to hold all possible values.  (Otherwise, this can be replaced
by target-format target_float_from_string operations as well.)

Printing fixed-point types and values should be completely unchanges,
using target_float_to_string with the same format strings as current code.

gdb/ChangeLog:
2017-11-06  Ulrich Weigand  <uweigand@de.ibm.com>

	* ada-lang.c (cast_to_fixed): Reimplement in target arithmetic.
	(cast_from_fixed): Likewise.
	(ada_scaling_type): New function.
	(ada_delta): Return value instead of DOUBLEST.  Perform target
	arithmetic instead of host arithmetic.
	(scaling_factor): Rename to ...
	(ada_scaling_factor) ... this.  Make non-static.  Return value instead
	of DOUBLEST.  Perform target arithmetic instead of host arithmetic.
	(ada_fixed_to_float): Remove.
	(ada_float_to_fixed): Remove.
	* ada-lang.h (ada_fixed_to_float): Remove.
	(ada_float_to_fixed): Remove.
	(ada_delta): Return value instead of DOUBLEST.
	(ada_scaling_factor): Add prototype.

	* ada-typeprint.c: Include "target-float.h".
	(print_fixed_point_type): Perform target arithmetic instead of
	host arithmetic.
	* ada-valprint.c: Include "target-float.h".
	(ada_val_print_num): Perform target arithmetic instead of
	host arithmetic for fixed-point types.

1 files changed, 10 insertions, 4 deletions

diff --git a/gdb/ada-valprint.c b/gdb/ada-valprint.c
index 8095eed..91dc301 100644
--- a/gdb/ada-valprint.c
+++ b/gdb/ada-valprint.c
@@ -31,6 +31,7 @@
 #include "c-lang.h"
 #include "infcall.h"
 #include "objfiles.h"
+#include "target-float.h"
 
 static int print_field_values (struct type *, const gdb_byte *,
 			       int,
@@ -796,10 +797,15 @@ ada_val_print_num (struct type *type, const gdb_byte *valaddr,
 {
   if (ada_is_fixed_point_type (type))
     {
-      LONGEST v = unpack_long (type, valaddr + offset_aligned);
-
-      fprintf_filtered (stream, TYPE_LENGTH (type) < 4 ? "%.11g" : "%.17g",
-			(double) ada_fixed_to_float (type, v));
+      struct value *scale = ada_scaling_factor (type);
+      struct value *v = value_from_contents (type, valaddr + offset_aligned);
+      v = value_cast (value_type (scale), v);
+      v = value_binop (v, scale, BINOP_MUL);
+
+      const char *fmt = TYPE_LENGTH (type) < 4 ? "%.11g" : "%.17g";
+      std::string str
+	= target_float_to_string (value_contents (v), value_type (v), fmt);
+      fputs_filtered (str.c_str (), stream);
       return;
     }
   else if (TYPE_CODE (type) == TYPE_CODE_RANGE)