Date:	Tue, 20 Jul 1999 09:09:06 +0200
To:	pgcc AT delorie DOT com
Cc:	derrick AT cco DOT caltech DOT edu
Subject:	Re: Do underflows cause a slowdown? Can I fix it?
Message-ID:	<19990720090906.E263@cerebro.laendle>
Mail-Followup-To:	pgcc AT delorie DOT com, derrick AT cco DOT caltech DOT edu
References:	<378F9D37 DOT EC6D3B6B AT cco DOT caltech DOT edu>
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In-Reply-To:	<378F9D37.EC6D3B6B@cco.caltech.edu>; from Derrick Bass on Fri, Jul 16, 1999 at 01:59:35PM -0700
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From:	Marc Lehmann <pcg AT goof DOT com>
Reply-To:	pgcc AT delorie DOT com
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On Fri, Jul 16, 1999 at 01:59:35PM -0700, Derrick Bass wrote:
> I am using a Pentium Pro (180 MHz, Redhat 5.2) and some of my FP
> intesive code occassionally slows by a factor of 4-6.  I think I've
> traced this to underflow. . .
> 
> Does handling underflow slow down floating point?

Yes, it can, however it does not do so on all steps of the cpu.

> switch or library call to make the underflows silently get replaced by
> zero?

No. You might experiment with setting the precision (see fpu_control.h) to
something else, but that might not help.

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