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 15:33:52 +0200
Organization:	[posted via] Leibniz-Rechenzentrum, Muenchen (Germany)
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Eli Zaretskii schrieb:
> 
> Isn't it better to link against libm.a and write a custom version of
> `matherr'?  See "info libc alpha matherr" for more information.

matherr usage of course works fine with math FUNCTIONS.
 
> > The second problem is: is it possible to throw an exception when a number
> > becomes NaN (NOTaNUMBER) ir Inf (Infinite) ?
> 
> You will have to give more details about how exactly do these come
> into existence.  Does it happen in an FP instruction such as division
> or multiplication?  Does it happen in a function?  The answer depends
> on these details.

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', so if I don't have the printf, I wouldn't be notified
by matherr of course. Because of the huge amount of math operations in the whole
program it isn't feaseable to add something like 'if(fabs(a)<EPS) ...'
ir 'if(!finite(c)) ...' before any aritmetic operation.

so forehand I think I will use a combination of both and try to avoid
an environment where FPE is supposed to crash.
Or anyone a still better idea?

BTW: is it FPE or raise(SIGABRT) which causes the problems?
so if it were raise(SIGABRT) I would be fine if I could do somthing like
  print_symified_traceback(...); // anyone did that before ???
  exit(1);
instead.

Many thanks for your immediate help

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

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