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From: "adhemerval.zanella at linaro dot org"
 <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug math/31603] New: math: x86 trunc traps when FE_INEXACT is
 enabled
Date: Wed, 03 Apr 2024 19:28:22 +0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: math
X-Bugzilla-Version: 2.39
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: adhemerval.zanella at linaro dot org
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31603

            Bug ID: 31603
           Summary: math: x86 trunc traps when FE_INEXACT is enabled
           Product: glibc
           Version: 2.39
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: adhemerval.zanella at linaro dot org
  Target Milestone: ---

The implementations of trunc functions using x87 floating point (i386 and
x86_64 long double only) traps when FE_INEXACT is enabled. Although this is=
 a
GNU extension outside the scope of the C standard, other architectures that
also support traps do not show this behavior (aarch64, powerpc64).

The following test shows that issue:

$ cat test-ceil.c
#include <assert.h>
#include <math.h>
#include <fenv.h>

int main (int argc, char *argv[])
{
  feenableexcept (FE_INEXACT);
  volatile long double a =3D 1.5;
  volatile long double b  __attribute__ ((unused));
  b =3D truncl (a);
  assert (fegetexcept () =3D=3D FE_INEXACT);

  return 0;
}
$ gcc -Wall -D_GNU_SOURCE test-ceil.c -lm && ./a.out
Floating point exception (core dumped)

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