Date: Wed, 26 Aug 1998 14:43:02 +0200 From: Martin Cracauer <cracauer@cons.org> To: Stephen Hocking-Senior Programmer PGS Tensor Perth <shocking@prth.pgs.com>, current@FreeBSD.ORG Subject: Re: Floating Point Exceptions, signal handlers & subsequent ops Message-ID: <19980826144302.C20511@cons.org> In-Reply-To: <19980825180559.A9890@cons.org>; from Martin Cracauer on Tue, Aug 25, 1998 at 06:05:59PM %2B0200 References: <199808250753.PAA29567@ariadne.tensor.pgs.com> <19980825180559.A9890@cons.org>
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In <19980825180559.A9890@cons.org>, Martin Cracauer wrote:
> In <199808250753.PAA29567@ariadne.tensor.pgs.com>, Stephen Hocking-Senior Programmer PGS Tensor Perth wrote:
> >
> > I've noticed in one of my applications that the first FP operation after
> > return from a caught SIGFPE is invalid. I have a signal handler installed that
> > just prints out some basic info (like "SIGFPE caught"). The first FP op after
> > this (in my case, converting a long to a double) just gives garbage. Repeat
> > the same statement and it gives a sensible result. Has anyone else seen this
> > before I file a PR with code to reproduce the problem?
>
> I just did a short test and for me the next FP operation after a
> caught SIGFPE (division by zero) is still sane (without
> setjump/jumpjump).
I'm afraid I was talking nonsense here :-( This test program shows the
problem. Now the question, why did my other test work well...?
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
void
handler(int s)
{
write(1, "sig\n", 4);
}
int
main(void)
{
double f0;
double f2;
double f4;
double f8;
double res;
/* Prevent optimization */
f0 = atof("0.0");
f2 = atof("2.0");
f4 = atof("4.0");
f8 = atof("8.0");
signal (SIGFPE, handler);
res = f2 / f0;
printf("After division by zero: %g\n", res);
res = f4 + f8;
if (res != 12.0) {
printf("Next operation didn't work: %g\n", res);
}
else {
printf("Next operation worked: %g\n", res);
}
return 0;
}
--
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Martin Cracauer <cracauer@cons.org> http://www.cons.org/cracauer
BSD User Group Hamburg, Germany http://www.bsdhh.org/
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