[Bug libgcc/122020] New: isnan raises FE_INEXACT

[tydeman at tybor dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122020

            Bug ID: 122020
           Summary: isnan raises FE_INEXACT
           Product: gcc
           Version: 15.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tydeman at tybor dot com
  Target Milestone: ---

I reported this against glibc and they said the bug is in libgcc.

It appears that certain NANs causes isnan() to raise FE_INEXACT.

/* Prereq: dnf install libdfp-devel */
#define __STDC_WANT_DEC_FP__ 1
#define __STDC_WANT_IEC_60559_DFP_EXT__ 1

#include <assert.h>
#include <stdio.h>
#include <limits.h>
#include <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>

#pragma STDC FENV_ACCESS ON
#pragma STDC FP_CONTRACT OFF
#pragma STDC FENV_ROUND FE_TONEAREST
#pragma STDC FENV_DEC_ROUND FE_DEC_TONEAREST
#pragma STDC CX_LIMITED_RANGE OFF

int main(void){

  if(1){
    _Decimal128 dfp33_128 = DEC_NAN;
    long double ld33;
    double d33;
    float f33;
    int flags;
    feclearexcept(FE_ALL_EXCEPT);
    f33 = d33 = ld33 = dfp33_128;
    flags = fetestexcept(FE_ALL_EXCEPT);
    assert( 0 == flags );
    feclearexcept(FE_ALL_EXCEPT);
    assert( isnan(f33) );
    assert( isnan(d33) );
    assert( isnan(ld33) );
    flags = fetestexcept(FE_ALL_EXCEPT);
    assert( FE_INEXACT != flags );      /* fails here */
  }
  return 0;
}