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Message-ID:	<19980713232742.60239@cerebro.laendle>
Date:	Mon, 13 Jul 1998 23:27:42 +0200
From:	Marc Lehmann <pcg AT goof DOT com>
To:	David Reiss <reiss AT astro DOT washington DOT edu>, beastium-list AT Desk DOT nl
Subject:	Re: differences in output between c++ and pg++ compiled programs?
Mail-Followup-To:	David Reiss <reiss AT astro DOT washington DOT edu>,
	beastium-list AT Desk DOT nl
References:	<35A52723 DOT 883F3139 AT astro DOT washington DOT edu>
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In-Reply-To:	<35A52723.883F3139@astro.washington.edu>; from David Reiss on Thu, Jul 09, 1998 at 08:25:07PM +0000
X-Operating-System:	Linux version 2.1.108 (root AT cerebro) (gcc version pgcc-2.91.43 19980628 (gcc2 ss-980502 experimental))
Status:	RO
Lines:	39

On Thu, Jul 09, 1998 at 08:25:07PM +0000, David Reiss wrote:
> Hi. I just discovered pgcc/pg++ and thought it would be great to try on
> my scientific programs which usually take hours to run. I tried
> compiling one program of mine (which uses lots of math routines and some
> C++ classes, etc) in pg++. It compiled fine using -O6 and ran about 4x
> faster than the g++ with -O2! But the numerical output is slightly
> different, basically about 10% off. (Sorry I can't give more detauls w/o

whoaw, great speed improvement ;) alas, the result shouldn't be
10% of.

is it possible to create a (preferably small) testcase that shows this problem?

> explaining what the program does, which would take another 2 pages of 
> typing...suffice it to say its a bunch of operations on floats and float
> arrays with many do loops and reading input data files. It uses a lot of
> routines from the Numerical Recipes text.)

hmm.. does the output agree if you use "-mieee -ffloat-store" (and possibly
-lieee") with both compilers?

> g++ output is exactly the same as the Sun Ultra...so my guess is there's
> something interesting going on with pg++ that I don't understand.

I guess its a bug in pgcc then.

> thanks for any help...it would be great to get this working!

Is that program available anywhere to download? I need to reproduce the
problem on my machine to fix it... (so downloading many megabytes of source
and data is impossible)

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      ---==---(_)__  __ ____  __       Marc Lehmann       +--
      --==---/ / _ \/ // /\ \/ /       pcg AT goof DOT com       |e|
      -=====/_/_//_/\_,_/ /_/\_\                          --+
    The choice of a GNU generation                        |
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