Xref: news2.mv.net comp.os.msdos.djgpp:8209
From: c533483 AT showme DOT missouri DOT edu
Newsgroups: comp.os.msdos.djgpp
Subject: divide by zero under win95
Date: Mon, 02 Sep 96 17:51:24 GMT
Organization: University of Missouri - Columbia
Lines: 94
Message-ID: <50f6p1$16gc@news.missouri.edu>
NNTP-Posting-Host: mizzou-ts7-09.missouri.edu
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

The following code to catch a divide by zero interrupt works perfectly under 
DOS, but fails under win95.  I would prefer to use win95 than have to go out 
to DOS everytime to run my program.  If anyone out there has experience and 
can offer me some help in trying to fix it, I would appreciate it.

#include <dpmi.h>
#include <stdio.h>

__dpmi_paddr                    old_interrupt_vector;
typedef long                    Fixed32;

#define INT_TO_FIXED(x)         ( (x) << 16 )
#define FIXED_TO_INT(x)         ( (x) >> 16 )


Fixed32 FixedDiv(Fixed32 numer, Fixed32 denom)
{
Fixed32 temp;

__asm__
(
"       xorl    %%eax, %%eax            \n
        shrdl   $16, %%edx, %%eax       \n
        sarl    $16, %%edx              \n
        idivl   %%ebx                   "
        :"=a" (temp)
        :"d" (numer), "b" (denom)
        :"eax", "ebx", "edx"
);

return(temp);
}


void divide_overflow(void)
{
__asm__
(
"       popl    %ebp;                   \n
        cmpl    $0, %ebx                \n
        jz      overflo                 \n
        shll    $4, %ebx                \n
        iret                            \n
overflo:movl    $0x00000001, %ebx       \n
        iret                            "
);
}


void set_divide_interrupt(void)
{
__dpmi_paddr    new_vector;
__dpmi_get_protected_mode_interrupt_vector(0x00, &old_interrupt_vector);

new_vector.selector = _go32_my_cs();
new_vector.offset32 = (long)divide_overflow;
__dpmi_set_protected_mode_interrupt_vector(0x00, &new_vector);
}


void restore_divide_interrupt(void)
{
__dpmi_set_protected_mode_interrupt_vector(0x00, &old_interrupt_vector);
}


main()
{
Fixed32 a, b, c;

set_divide_interrupt();

a = 0x80000;
b = 0x0;
c = FixedDiv(a, b);

printf("Fixed = %x, Int %d\n", c, c);

restore_divide_interrupt();
}

This is almost the same code as was posted by Graham Sturmy in the mailing 
list (you can find his article in the archives).  He never received a 
response, but I'm hoping to fair a little better :).  I can't see any reason 
why it shouldn't work, but then again i'm new to djgpp.  I have tried to read 
the FAQ, but i find the explanation confusing.

I just wanna finish off this post by saying that I think djgpp is a great 
compiler.  I have had little problem in getting help, whether posted by me or 
just reading problems that other people have.  Thanks to everyone that's 
making it and helping people like me :).

L8R,
Tom Hildrich