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From: scott@othervax.UUCP (Scott Pace)
Newsgroups: net.unix-wizards
Subject: floating point overflows (and how to catch them), HELP!
Message-ID: <691@othervax.UUCP>
Date: Thu, 29-Aug-85 09:59:33 EDT
Article-I.D.: othervax.691
Posted: Thu Aug 29 09:59:33 1985
Date-Received: Sun, 1-Sep-85 05:59:57 EDT
Reply-To: scott@otherva.UUCP (Scott Pace)
Organization: Philips Information Systems - St. Laurent  P.Q., Canada
Lines: 38

If I compile and run the following program, it will continue until
a floating point overflow occurs and will then go and proccess
the interrupt routine. However, it seems that the return from the
interrupt routine is returning to the start of the instruction
which caused the overflow in the first place. Therefore, the program
just goes into an infinite loop printing the overflow message.
What exactly is happening here or what am I doing wrong ? Any help
greatly appreciated.

By the way, this is on a VAX11/780 running 4.1BSD


#include <signal.h>

int fpe_flag = 0;

main()
{
    double a = 1.0,b = 2.0;
    int fltover();

    sigset(SIGFPE,fltover);
    for (;;) {
	a *= b;		/* overflow here */
	if (fpe_flag)
	    exit(1);
    }
}

fltover()
{
    printf("Floating point overflow\n");
    fpe_flag = 1;
}


Cheers,
	Scott Pace, ...!philabs!micomvax!othervax!scott