Subject: Re: Maths ruined when optimizing in gcc
From: [email-masked] (Mumit Khan)

25 Nov 1996 20:58:46 -0800
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Distribution: cygnus
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Original-Cc: "Pedro A. Aranda =?iso-8859-1?Q?Guti=E9rrez?=" <[email-masked]>,
        [email-masked]
In-Reply-To: Your message of "Mon, 18 Nov 1996 10:09:27 EST."
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Original-Sender: [email-masked]

Woodrow Setzer <[email-masked]> writes:
> On Fri, 15 Nov 1996, Pedro A. Aranda [iso-8859-1] Guti=E9rrez wrote:
> 
> > ...
> > When I compile WITHOUT optimization, floating point
> > ops are ok. If I dare do any optimization, I always
> > get all sorts of errors.
> >=20
> > Has anyone experieced a similar thing?
> 
> This may be related.  I am working with an f2c-converted version of
> dmngb.f, one of the routines for optimization from the ATT PORT library.=20
> It compiles and works OK using gcc 2.7.2.1 under Solaris 2.3 on a Sun
> Sparc 20 using the option -O.  Under cyg-win32 and the same option, the
> code compiles and runs without compile-time or run-time errors, but I get
> the wrong answer.  If I omit the -O flag on the compiler invocation under
> cyg-win32, I get essentially the same answer as I do on the Sun.=20
> 
> --

Another data point here. I'm in the process of testing g77 port to 
cygwin32 (it was quite simple once I figured out the right flags to
libfI77) and the big gotcha is the every time I use -O, some of the
programs produce NaNs all over the place! Haven't been able to pin
point where it happens yet, but hopefully soon.

Anybody have a short program that screws up the numerics with -O? If
so, please email it me (if fortran, then either original or f2c'd will
do fine).

regards,
Mumit -- [email-masked]
http://www.xraylith.wisc.edu/~khan/

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