Xref: news2.mv.net comp.os.msdos.djgpp:7104
From: Thomas Demmer <demmer AT LSTM DOT Ruhr-UNI-Bochum DOT De>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: problem with libm.a "pow" function (and comment on ran())
Date: Mon, 12 Aug 1996 09:26:05 +0100
Organization: Lehrstuhl fuer Stroemungsmechanik
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To: djgpp AT delorie DOT com
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Francois Charton wrote:
> 
> I posted something last week on FPU exceptions compiling povray 3.0 with
> -lm.
> I tried since to isolate the bug (if it is one)
> Here is a small program :
> 
> MYPROG.C
> #include <math.h>
> 
> void main(void)
> {
> int i;
> for(i=1;i<1000000;i++) pow(i/1000000.0,90.0);
> }
> 
> /* EOF */
> 
> When I compile it with  :
> gcc -o myprog myprog.c
> (I link the libc.a pow function), everything works great
> 
> but if I say
> gcc -o myprog myprog.c -lm
> I get (at i==257) a Floating Point exception error
> 
> This is pretty strange as my program only calculate power 90 of values
> strictly between 0 and 1, so the result HAVE to be betweeen 0 and 1, and
> there can be no overflow.
Are you sure this is _numeric_ over/underflow?
libm had a problem with Coprocessor stack underflow that caused
unexpected crashes.
Try the libm from

ftp://ftp.lstm.ruhr-uni-bochum.de/pub/djgpp

I just tried you program and it runs fine. Without -O and -O2.

Sorry, but I haven't seen your posting last week (Or it did not ring
a bell).

-- 
Ciao
Tom

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* Thomas Demmer                                             *
* Lehrstuhl fuer Stroemungsmechanik                         *
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