Path: utzoo!utgpu!watserv1!watmath!att!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!apple!baum
From: baum@Apple.COM (Allen J. Baum)
Newsgroups: comp.arch
Subject: Re: DeNorms (was Alignment on RS/6000)
Message-ID: <46899@apple.Apple.COM>
Date: 28 Nov 90 17:49:56 GMT
References: <13342@encore.Encore.COM> <46866@apple.Apple.COM> <1990Nov28.154221.26355@Solbourne.COM>
Reply-To: baum@apple.UUCP (Allen Baum)
Organization: Apple Computer, Inc.
Lines: 25

[]
>In article <1990Nov28.154221.26355@Solbourne.COM> joel@kaprap.Solbourne.COM (Joel Boney) writes:
>Statistically denormalized numbers almost never occur (surely less than 1%).
>That doesn't mean they are not useful. They make writing robust floating 
>point codes much easier. However, if your algorithm is producing lots of
>denorms then it probably is time to reconsider your algorithm.....
>
>It is fine (and certainly in the spirit of the IEEE standard) to implement 
>some rare functions such as generating and computing with denorms via 
>a combination of hardware and software....

Well, this is what I wanted to hear. What I heard before was that some 
machine was horribly slow because it trapped denorms and handled them
in software. Since I was under the impression that denorms were rare, I
didn't understand why that should be. 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.

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