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Subject: Re: Pawn hashing without Zobrist keys

Author: Dann Corbit

Date: 11:50:11 09/12/03

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On September 12, 2003 at 14:39:46, Dieter Buerssner wrote:

>Hi Gerd,
>
>my answer is not exactly referring to your post, but an idea I always had.
>Instead of Zorbrist type hashing, one could use some "classical" hashing
>function: See all the position data (or pawn pos data) as a string, and
>calculate a hash - perhaps a 32 bit hash. Many schemes don't need any modulo.
>One could use a (32-bit) modulo in the last step. Perhaps one could try the
>typical CRC scheme (source available for example in zip). Crypto experts
>certainly could suggest even better schemes. Incremental updates would perhaps
>be difficult or impossible, but might be possible in some schemes. For pawn
>hashing, storing the whole pawn structure as 2 bitboards, plus perhaps 12 bytes
>for the KK pos for verification of clashes might be no problem (I guess, most
>that use pawn hashing already store lot's of things about the pawnstructure
>anyway, so the size overhead should not be too bad, and would have the
>advantage, that one really has certainty).

An n-bit SDBM hash scheme would be a good one, I bet.
Perhaps 2^20 entries (1,048,576) and a simple and operation will finish the
hash.  (Or you could even have an unsigned:20 type).

The SDBM hash is super simple and yet of high quality.
http://www.cs.yorku.ca/~oz/hash.html



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