feholdexcept() does not seem to clear the exception flags correctly

[Bernard WEISSER]

Hello,

I used the feholdexcept() function and it does not seem to follow 
exactly the behaviour described in the "fenv" man page.

My configuration is :

gcc version 3.3.4
glibc-2.3.2-i486-6
Linux mars 2.4.26 #6 Mon Jun 14 19:07:27 PDT 2004 i686
>Release:       libc-2.3.2
>Environment:
        <machine, os, target, libraries (multiple lines)>
Host type: i486-slackware-linux-gnu
System: Linux mars 2.4.26 #6 Mon Jun 14 19:07:27 PDT 2004 i686 unknown 
unknown GNU/Linux
Architecture: i686

Addons: linuxthreads
Build CFLAGS: -g -O2 -march=i486 -mcpu=i686
Build CC: i486-slackware-linux-gcc
Compiler version: 3.3.3
Kernel headers: 2.4.26
Symbol versioning: yes
Build static: yes
Build shared: yes
Build pic-default: no
Build profile: yes
Build omitfp: no
Build bounded: no
Build static-nss: no


Here is the code :

/*
* Execution gives that output :
*
* at start, we have :
*  no exception flags are set
*  no traps are enabled
*  --
* after raising FE_INVALID exception, we have :
*  invalid operation flag set
*  no traps are enabled
*  --
* after enabling FE_DIVBYZERO trap, we have :
*  invalid operation flag set
*  division by zero trap enabled
*  --
* saving environment
* after saving environment, we have :
*  invalid operation flag set               <===== should be cleared
*  no traps are enabled
*  --
*
* Manual page "fenv.h" says that calling "feholdexcept()" clears all 
exceptions
* flags and sets a non-stop (continue on exceptions) mode, if available.
*
* What I see here is that the non-stop mode is correctly set, but that
* exception flags ARE NOT RESET.
*/

#define _GNU_SOURCE     /* pour feenableexcept */

#include <stdio.h>
#include <stdlib.h>
#include <fenv.h>

static void print_fe(void)
{
  int   flags ;
  int   traps ;

  flags = fetestexcept (FE_ALL_EXCEPT) ;
  traps = fegetexcept () ;

  if (flags & FE_INEXACT)       printf(" inexact result flag set\n");
  if (flags & FE_UNDERFLOW)     printf(" underflow flag set\n");
  if (flags & FE_OVERFLOW)      printf(" overflow flag set\n");
  if (flags & FE_DIVBYZERO)     printf(" division by zero flag set\n");
  if (flags & FE_INVALID)       printf(" invalid operation flag set\n");
  if (!(flags & FE_ALL_EXCEPT)) printf(" no exception flags are set\n");
  if (traps & FE_INEXACT)       printf(" inexact result trap enabled\n");
  if (traps & FE_UNDERFLOW)     printf(" underflow trap enabled\n");
  if (traps & FE_OVERFLOW)      printf(" overflow trap enabled\n");
  if (traps & FE_DIVBYZERO)     printf(" division by zero trap enabled\n");
  if (traps & FE_INVALID)       printf(" invalid operation trap
enabled\n");
  if (!(traps & FE_ALL_EXCEPT)) printf(" no traps are enabled\n");
  printf (" --\n") ;
}

int main(void)
{
  fenv_t holdenv;

/* Env initial value */

  printf("at start, we have :\n");
  print_fe();

/* Raise FE_INVALID exception */

  feraiseexcept(FE_INVALID) ;
  printf("after raising FE_INVALID exception, we have :\n");
  print_fe() ;

/* Enable FE_DIVBYZERO trap */

  if (feenableexcept(FE_DIVBYZERO) == -1) {
     fprintf (stderr, "feenableexcept(FE_DIVBYZERO) error\n") ;
     exit (1) ;
  }
  printf("after enabling FE_DIVBYZERO trap, we have :\n");
  print_fe() ;

/* feholdexcept */

  printf("saving environment\n");
  if (feholdexcept(&holdenv) != 0) {
     fprintf (stderr, "feholdexcept error\n");
     exit (1) ;
  }

  printf("after saving environment, we have :\n");
  print_fe() ;

  return 0;
}

Do you think this is a bug ?