From: Waldemar Schultz <schultz AT ma DOT tum DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Floating point exception
Date: Tue, 04 Jul 2000 19:10:56 +0200
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Eli Zaretskii schrieb:
> > if I don't use FPE
> >   double a=0;
> >   double b=1;
> >   double c=b/a;
> >   double d=a*c;
> >   printf("%g %g\n",c,d);
> > just prints 'Inf NaN'
> 
> Even if you unmask numerical exceptions in the FPU?  What about the
> FPU status word--does it have the corresponding exception bits set?

if I call the sigfpe() function I posted before, it behaves much like
how I intended: It throws the SIGABRT telling me [DIVBYZERO] or [INVALID].
The only odd thing is that I have to call symify manually. And of course
the fact tat I DO USE exceptions in that case.(as you discussed before/below) 

> But you could place such checkpoints in strategic places and zero in
> on the problem.  (IMHO, you will want to leave these safeguards in the
> production code anyway, whereas FP exceptions generally cannot remain
> unmasked beyond the debugging period.)

of course, I agree.
My actual intent is to use it (mainly) in the development phase.

> It's the exception itself, long before it gets converted into SIGFPE.
> (To do this, DJGPP startup code installs a handler for Int 75h in
> protected mode, and when the interrupt hits, it invalidates the DS
> selector, exactly like the keyboard handler does with Ctrl-C.)
> 
> >   print_symified_traceback(...); // anyone did that before ???
> 
> Yes.  See the docs for the function __djgpp_traceback_exit.  However,
> SIGABRT is not your problem, so this won't help you.

Thanks for clarification.
a __djgpp_symified_traceback_exit() would be handy though :-)

-- 
 Gruss Waldemar Schultz.
 Technische Universität München, Zentrum Mathematik M1, D 80290 München
 Tel: +49 (0)89 2892 8226        FAX: +49 (0)89 2892 8228