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Subject: Re: just another reverse bitscan

Author: Zach Wegner

Date: 13:19:58 12/22/05

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Hi Gerd,

Very interesting. I find this line to be particularly elegant:

>  l   = (h & -m) | (l & m-1);

Unfortunately, in my prototype program it's a tad bit slower (<1%) than the
branch/lookup approach you mention. But, it's only in perft, and I had to add a
couple shifts so that it returns 0x88 coordinates. In a full program where the
lookup tables aren't cached, this method could quite possibly be faster. Do you
think this approach could also be used for the LSB, without adding extra
instructions? It seems you would have to have compares instead of subtracts, or
some NOTs.

Regards,
Zach



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