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From: davec@nucleus.amd.com (Dave Christie)
Newsgroups: comp.arch
Subject: Re: DeNorms (was Alignment on RS/6000)
Message-ID: <1990Nov29.200543.15059@mozart.amd.com>
Date: 29 Nov 90 20:05:43 GMT
References: <46866@apple.Apple.COM> <1990Nov28.154221.26355@Solbourne.COM> <46899@apple.Apple.COM>
Sender: usenet@mozart.amd.com (Usenet News)
Reply-To: davec@nucleus.amd.com (Dave Christie)
Organization: Advanced Micro Devices, Austin, TX
Lines: 22

In article <46899@apple.Apple.COM> baum@apple.UUCP (Allen Baum) writes:
[regarding the frequency of IEEE denorms in the real world]

>                                      I did get one explanation from
> lucier@math.purdue.edu   who said that using spectral methods to
>compute solutions of time-dependent PDEs with very smooth solutions
>(most of the time) then you can have tons of denorms (50% or more) in
>the fourier coefficients of the solution. This is the first concrete
>example I've heard, for real problems. He went on to say that often you can
>just flush to zero in these cases.

For another real-world example, I once dealt with a flight simulation
benchmark (for commercial flight simulators, not gameware) that really
bogged down on a MIPS (denorms handled by software) relative to CDC
machines (denorms in CDC FP format == 0).  As you can imagine,
flight simulation constantly deals with very small rotations in three
dimensions.  A niche application, but certainly real-world.
I don't really know whether denorm values are actually necessary 
for this application, though...

-------------------------
Dave Christie         My opinions only.