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Message-ID: <35A52723.883F3139@astro.washington.edu>
Date: Thu, 09 Jul 1998 20:25:07 +0000
From: David Reiss <reiss AT astro DOT washington DOT edu>
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Subject: differences in output between c++ and pg++ compiled programs?
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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
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.)

Just to check I tested the output vs. that from g++ on a Sun Ultra. My
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.

PS. the other flags I use other than -O2 (g++) or -O6 (pg++) are:
-fhandle-exceptions -w
and I use the -m486 option with g++ on my Pentium machine.

Does anyone have any thoughts?
I dont subscribe to this list, so please email me!
thanks for any help...it would be great to get this working!

-David
reiss AT astro DOT washington DOT edu