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optimization/10825: GCC 2.3.2 cannot compare two double
- From: lethiec at lirmm dot fr
- To: gcc-gnats at gcc dot gnu dot org
- Cc: guindon at lirmm dot fr
- Date: 16 May 2003 18:32:17 -0000
- Subject: optimization/10825: GCC 2.3.2 cannot compare two double
- Reply-to: lethiec at lirmm dot fr
>Number: 10825
>Category: optimization
>Synopsis: GCC 2.3.2 cannot compare two double
>Confidential: no
>Severity: critical
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Fri May 16 18:36:02 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator: Franck Le Thiec
>Release: 3.2.3
>Organization:
>Environment:
i386-linux 2.4.17
>Description:
in a loop a multiple of M_PI is put into two variables,
one is an array of double allocated by malloc
the other is a double.
they compare equal when using gcc with options "-lm" or "-O1 -lm"
they compare different when using gcc with "-O2 -lm" or "-O3 -lm" or "-O4 -lm"
>How-To-Repeat:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(int argc, char **argv)
{
double *a1,a2;
int i;
a1 = (double*)malloc(sizeof(double));
a1[0]=a2=0.0;
for(i=1;i<15;i++)
{ /*if we loop until 13 no problem!*/
a1[0] += M_PI;
a2 += M_PI;
}
printf("%.50f\n%.50f\n",a1[0], a2);
if (a1[0]==a2)
printf("equal\n");
else
printf("different\n");
free(a1);
}
>Fix:
no known fixes !
>Release-Note:
>Audit-Trail:
>Unformatted: