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Subject: Re: Why using Zobrist keys for Pawn Hashing?

Author: Sune Fischer

Date: 06:56:44 12/05/01

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On December 05, 2001 at 09:37:42, Gerd Isenberg wrote:

>the white and black pawns are disjunct, obviously there is no one-bit in the
>white pawn BitBoard that is also set in the black pawn BitBoard - and each of
>the two BitBoards are unique for each pawn position, so the difference is IMO
>also unique.

So if you have a row of pawns like this:
w=01000000 (white)
b=00000010 (black)

you will take the difference like this:
w&(~b) = 01000000 (=w) ?
you loose the info on the black pawns.

or like this:
w-b = 00111110 ?
But as we all know that loses information too:
7-4=6-3=5-2... etc.

Probably better to AND, but still one can't distinguish between black and
white's, so that will be a problem when a pawn captures a pawn (who captured
who).


> The only thing to do is a 64 bit subtraction with masking the 48
>relevant bits via shift/and - not a big task and not worth to do it
>imcrementally.

Perhaps I have misunderstood, I often do ;)

>Gerd

-S.



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