Date: Fri, 24 Feb 1995 03:54:29 -0400 (AST)
From: Bill Davidson <bdavidson AT ra DOT isisnet DOT com>
Subject: Re: strange fp exception
To: Erwin Kok <ttgrx AT win DOT tue DOT nl>
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu



On Thu, 23 Feb 1995, Erwin Kok wrote:

> A while ago I had a similar fp-exception:
> 
> I made up a program compiled it and it worked (under DJGPP FPU-emulation), 
> but when I bought a co-processor, I compiled it and a strange floating-point 
> exception appeared...
> 
> After a few debugging hours I found that the result from an arithmetic 
> statement was NAN (Not A Number), and when you do another statement with a NAN
> an exception appears. So, the FPU-emulator under DJGPP didn't had a problem with
> a NAN it runned right through it. But the real FPU didn't except the NAN and 
> gave an exception.  So maybe MSC ran through some NAN and when you ported it to
> DJGPP/GRX the exception appeared.
> 
> My advise is check if any variabeles are NAN's.

A couple of weeks ago (?) someone posted a lovely little ctrl87.c program 
that allows one to diddle the '87 control word.  It works like a charm  
and allows one to do just this sort of thing without resorting to asm.

Bill Davidson
bdavidson AT ra DOT isisnet DOT com