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Subject: Re: Beowulf hot spots shown pictorially

Author: Dieter Buerssner

Date: 08:51:45 06/21/02

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On June 21, 2002 at 04:01:41, Sven Reichard wrote:

>Maybe I'm missing something here, but if you furthermore agree to use a hash
>table of size 2^i, i <= 32, you can replace all mods, divs and muls by a 32 bit
>'and'.

Yes.

>The performance hit of the slightly smaller table (less than factor 2)
>should be outweighed by the faster access.

I didn't find a performance penalty using arbitrary hash table sizes for my
program, so I prefer it. However, I can imagine, that a long long modulo (which
I don't use) really hurts. It will probably need a subroutine call. While doing
longer arithmetic than the word size for + and - (and all the logical operators)
manually is rather easy, div/modulo are rather complicated.

Regards,
Dieter



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