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Subject: Beating Bitscan to Death

Author: Matt Taylor

Date: 20:28:27 12/24/02


http://65.186.75.165/~mtaylor/bitscan/bitscan.html

The posted source is outdated, but as my school conveniently decided to turn off
all the power without warning me, I can't update the source. (My source
highlighter is on the school servers.)

I think the older tests were not completely valid. While you can bitscan in a
loop, I was caching data in registers, and that is not very likely to happen in
a general loop. I moved the loop constructs outside of the timed code, and I
also eliminated the caching that I was doing in registers. I think these results
will be a little more fair.

As a natural consequence of my changes, all timings will be inflated (biased by
timing code latency), but they will be biased equally. It is not worthwhile to
compare timings between processors, but it is valid to compare timings for
different pattersn on the same processor.

Also, I'm quite sure that the MMX routines could be written better. If someone
wants to look over them and make some suggestions, I would invite them to do so.

One last thing... merry Christmas!

-Matt



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