other/8974: fabs error with -ansi

[warren at eng dot up dot ac dot za]

>Number:         8974
>Category:       other
>Synopsis:       fabs error with -ansi
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 17 02:16:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Warren du Plessis
>Release:        unknown-1.0
>Organization:
>Environment:
Output of gcc -v
Configured with: /var/tmp/portage/gcc-3.2-r1/work/gcc-3.2/configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --target=i686-pc-linux-gnu --with-system-zlib --enable-languages=c,c++,ada,f77,objc,java --enable-threads=posix --enable-long-long --disable-checking --enable-cstdio=stdio --enable-clocale=generic --enable-__cxa_atexit --enable-version-specific-runtime-libs --with-gxx-include-dir=/usr/include/g++-v32 --with-local-prefix=/usr/local --enable-shared --enable-nls --without-included-gettext
Thread model: posix
gcc version 3.2
>Description:
fabs() gives garbage (output included below) when I compile the code below with gcc 3.2 with the -ansi flag and run it on a PentiumIV 2.4 GHz I have access to.  The same code compiled with any other version of gcc or with icc works properly.  Running the same binary on a different spec machine works properly, but gives the same problem on other machines of the same type.  The problem only occurs when the -ansi flag is used (When I compile the code below with:
	gcc -ansi -lm -o test test.c
it gives problems, but when I compile with:
	gcc -lm -o test test.c
it works properly.).


Source file:
/* Test fabs problem */

#include<stdio.h>
#include<math.h>

int main()
{
  int count1;
  double value;

  /* Use a loop to show the behaviour as the values change. */
  for(count1 = 0; count1 < 8; count1++)
    {
      value = -1.35 + 0.01*count1;
      printf("%f\t%f\n", value, fabs(value));
    }

  /* Just to prove that the same thing happens with constants. */
  printf("\n%f\t%f\n", -1.29, fabs(-1.29));
  printf("%f\t%f\n", -1.28, fabs(-1.28));

  return 0;
}


Output:
-1.350000       0.000000
-1.340000       1972025612002701974956562650445561404174954378236176687125875831578843553978832422898371277103679201670561005568.000000
-1.330000       0.000000
-1.320000       427698125597735782527681486701155185015946591284413207628408209475262279918486665822208.000000
-1.310000       0.000000
-1.300000       92559680389175149863256792315491644408430319360732995401023488.000000
-1.290000       0.000000
-1.280000       19991593113087055742149331948245352448.000000

-1.290000       0.000000
-1.280000       19991593113087055742149331948245352448.000000
>How-To-Repeat:
Compile and run on a similar machine.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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