To: BILLM AT vaxc DOT cc DOT monash DOT edu DOT au, DJGPP AT SUN DOT SOE DOT CLARKSON DOT EDU
From: A DOT APPLEYARD AT fs1 DOT mt DOT umist DOT ac DOT uk
Date: 10 Nov 93 14:59:53 GMT
Subject: Re: Not trapping overflow etc in Gnu C

  As in my previous messages, I want to run a Gnu C (or C++) program in a mode
where "infinity and NaN (overflow, divide by zero) do not cause an error, but
the program continues". I can write my own code to find if a value is infinity
or NaN before I print it. I tried to do it by resetting the CW, as in the
short test programs hereinunder (dividing by zero in line 'z=y/x') hereinunder,
but I always got the same fault remark:-

variorum listfile on Wed Nov 10 14:39:51 1993 of the 4 programs:-
file 1 = t$.cc, 9 lines
file 2 = t$$.cc, 10 lines
file 3 = t$$$.cc, 10 lines
file 4 = t$$$$.cc, 10 lines
[F 1][F 2][F 3][F 4]
    1    1    1    1 #include<stdio.h>
    2    2    2    2 short i; double x=1,y=0,z;
    3    3    3    3 main(){
    4    4    4    4 asm("fstcw _i");
    5    5    5    5 printf("%8x\n",i);
                   6 i&=0xffc0;
              6      i|=3;
         6           i&=0xffc0; i|=3;
    6    7    7    7 asm("fldcw _i");
    7    8    8    8 printf("%8x\n",i); fflush(stdout);
    8    9    9    9 z=x/y;
    9   10   10   10 }

variorum listfile on Wed Nov 10 14:42:34 1993 of their screen outputs:-
file 1 = t$.res, 25 lines
file 2 = t$$.res, 25 lines
file 3 = t$$$.res, 25 lines
file 4 = t$$$$.res, 25 lines
[F 1][F 2][F 3][F 4]
    1    1    1    1   !
                   2 C:\WORK>t$$$$
              2      C:\WORK>t$$$
         2           C:\WORK>t$$
    2                C:\WORK>t$
    3    3    3    3      37a
                   4      340
              4           37b
         4                343
    4                     37a
              5    5 Exception 117 at eip=10d6
         5           Exception 117 at eip=10dd
    5                Exception 117 at eip=10cf
    6    6    6    6 
    7    7    7    7 C:\WORK>call \am\readscr

  Line 1 was the top line of the screen when the screen dumps were made.
  Lines 8 to end were empty.
  The '!' in line 1 appeared there as the program was running. Why!?
  Line 2 is where I called the compiled forms of the programs.
  Before calling each of these compiled forms, I called CLS (clear screen).
  My maths coprocessor manual says that 'exception 117' is an exception
defined by an application.
  Line 7 is where I call a program that I wrote to copy the screen to a file.

  P.S. How to suppress interrupt at divide by zero in int arithmetic?