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From: "dilyan.palauzov at aegee dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/113679] long long minus double with gcc -m32 produces
 different results than other compilers or gcc -m64
Date: Wed, 31 Jan 2024 14:32:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113679

--- Comment #8 from =D0=94=D0=B8=D0=BB=D1=8F=D0=BD =D0=9F=D0=B0=D0=BB=D0=B0=
=D1=83=D0=B7=D0=BE=D0=B2 <dilyan.palauzov at aegee dot org> ---
-fexcess-precision=3Dstandard does not ensure consistent behaviour between =
gcc
13.2.1 20231205 (Red Hat 13.2.1-6) and clang 17.0.5.  -msse2 -mfpmath=3Dsse=
 does
for diff.c:

#include <stdio.h>
#include <math.h>
int main(void) {
  long long l =3D 9223372036854775806;
  double d =3D 9223372036854775808.0;
  printf("%f\n", (double)l - d);
  printf("%i\n", pow(3.3, 4.4) =3D=3D 191.18831051580915);
  return 0;
}


$ gcc -lm -fexcess-precision=3Dstandard -m32 -o diff diff.c && ./diff
0.000000
0
$ clang -lm -fexcess-precision=3Dstandard -m32 -o diff diff.c && ./diff
0.000000
1
$ gcc -lm -fexcess-precision=3Dstandard -m64 -o diff diff.c && ./diff
0.000000
1
$ clang -lm -fexcess-precision=3Dstandard -m64 -o diff diff.c && ./diff
0.000000
1
$ gcc -lm -fexcess-precision=3Dfast -m32 -o diff diff.c && ./diff
-2.000000
1
$ clang -lm -fexcess-precision=3Dfast -m32 -o diff diff.c && ./diff
0.000000
1
$ gcc -lm -fexcess-precision=3Dfast -m64 -o diff diff.c && ./diff
0.000000
1
$ clang -lm -fexcess-precision=3Dfast -m64 -o diff diff.c && ./diff
0.000000
1
$ gcc -lm -msse2 -mfpmath=3Dsse -m32 -o diff diff.c && ./diff
0.000000
1
$ clang -lm -msse2 -mfpmath=3Dsse -m32 -o diff diff.c && ./diff
0.000000
1
$ gcc -lm -msse2 -mfpmath=3Dsse -m64 -o diff diff.c && ./diff
0.000000
1
$ clang -lm -msse2 -mfpmath=3Dsse -m64 -o diff diff.c && ./diff
0.000000
1

cl.exe also prints 0.000000 and 1=