[Bug ada/35194] New: floating point truncation error on intel platform

["jerome dot duquennoy at wanadoo dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

In some situations (after a call to a C oracle function, or when running the
program on top of valgrind), floats behave strangely : a given, hard coded
float value displays erroneously.
For exemple, a float value of 1.2001 would print as "1.20831E+0".

Our analysis :
We reproduced the problem either using functions from the Oracle C library or
running the software on top of valgrind.
The tests were done on a Suse Linux 10.0 and a centos 5.1, using a 4.1.2
compiler and a 4.2.3 compiler, running on an intel-based machine (core2duo and
pentium D).
We COULD NOT reproduce the problem on a solaris 9 UltraSPARC III based machine.

Using a customized img_real package, we found that the bad behaving code is the
Long_Long_Float'Truncation attribute, called in the Convert_Integer procedure
of the Set_Image_Real procedure, in package img_real.

This function seems to be platform-dependent, this is coherent with the
behaviour difference between a sparc-based machine and an pentium-based one.

The problem can be reproduced easily by compiling this simple code, and running
the executable under Valgrind :


with 
        ada.text_io, 
        Ada.Strings.Fixed,
        System.img_real;

use 
        Ada.Strings.Fixed, 
        ada.text_io,
        System.img_real;

procedure test_fio is  
   value : Long_Long_Float;

        resulting_string : string(1..15);
        nat : natural;
begin
   value := 1.2001;
   resulting_string := (others => ' '); 
        nat := 0;

        set_image_real(value, resulting_string, nat, 2, 4, 2);

        put_line ("resulting_string : '" & resulting_string & "'");
end test_fio;


-- 
           Summary: floating point truncation error on intel platform
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: ada
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jerome dot duquennoy at wanadoo dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35194