Message-Id: <200005181522.RAA01200@cerbere.u-strasbg.fr>
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Date: Thu, 18 May 2000 17:04:04 +0200
To: djgpp-workers AT delorie DOT com
From: Pierre Muller <muller AT cerbere DOT u-strasbg DOT fr>
Subject: Simple C program showing FPU problem !
References: <200005181208 DOT OAA08131 AT lws256 DOT lu DOT erisoft DOT se>
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Reply-To: djgpp-workers AT delorie DOT com


  I already had a discussion with Eli about some FPU
exceptions problems with specific processors.

 I send the source code of a very simple C program that should this bug

The source follows Eli's restriction's that the FPU must be reset 
inside the signal handler but when run on a Pentium II 200 MHz (non MMX)
under Win95 
I still get a nonzero overridecount 
meaning that a second exception is sometimes raised inside 
the signal handler itself.
This behavior is documented in the Intel docs, that say the 
the FPU status word should be reset before
resetting the IO port.

A possible solution to this problem is to store the fpu state inside
___djgpp_npx_hndlr
and to use this value when clear87 function is called.

  All this hassle is due to the fact that Free Pascal compiler should be
able to deal with 
FPU exceptions and convert them into software exceptions if the
code is inside a try ... except  block !
(Like Delphi does)

>>>>Start of testd.c source
#include <signal.h>
#include <setjmp.h>
#include <float.h>

#define COUNT 100000

jmp_buf t;

int level,count,overridecount,maxlevel;
short fpustate;


void
setfpucontrol ()
  {
    asm("
      movl $0x1332,%eax
      pushl %eax
      fldcw (%esp)
      popl %eax");
  }

void
fpesig (i)
  int i;
  {
    level++;
    fpustate=_clear87();
    longjmp(t,1);
  }

void
test ()
  {
   int i;

   for (i=0; i < COUNT; i++)
     if (setjmp(t)==0)
       {
         double j,e;
         int k;
         k=100;
         j=0.0;
         e=k/j;
         printf("No exception ");
       }
     else
       {
         if (level > 1)
           overridecount++;
         if (level>maxlevel)
           maxlevel=level;
         setfpucontrol();
         count++;
         level=0;
       }
   }


int
maintest ()
{
  count=0;
  signal(SIGFPE,fpesig);
  overridecount=0;
  maxlevel=0;
  setfpucontrol();
  test();
  printf("Number of signal %d, overridecount %d\r\n",count,overridecount);
  if (count != COUNT || overridecount != 0)
    {
      printf("Problems !!! maxlevel = %d",maxlevel);
      return 1;
    }
  return 0;
}


int
main ()
{
  return maintest();
}
>>> End of source


Pierre Muller
Institut Charles Sadron
6,rue Boussingault
F 67083 STRASBOURG CEDEX (France)
mailto:muller AT ics DOT u-strasbg DOT fr
Phone : (33)-3-88-41-40-07  Fax : (33)-3-88-41-40-99