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Subject: Re: Bit Operation Does

Author: J. Wesley Cleveland

Date: 18:15:37 05/22/02

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On May 22, 2002 at 18:43:09, Dan Andersson wrote:

>If the function is fast to compute, faster than a memory access. And the LUT
>can't be guaranteed to be in the cache. Then it will be a bad idea. YMMV.
>
If the code is executed enough to matter, the LUT is almost surely in the cache.
You need to compute the probability of it being in each level of cache or memory
times the cost (in cycles) for each to have an estimate of the speed of the
routine. Then you will find that adding some code or a variable can dramatically
change the real speed of your routine or it is very different on a different x86
processor. X86 optimization is lots of "fun", and is to a large extent avoiding
cache misses.



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