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Subject: Re: Pawn hashing without Zobrist keys

Author: Vincent Diepeveen

Date: 17:58:33 09/12/03

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On September 12, 2003 at 17:00:25, Gian-Carlo Pascutto wrote:

minimum number of bits to store somehow either by index or non-index is

48 bits (1 = pawn, 0 = no pawn) + 16 bits ( 1 = white, 0 = black ) = 64 bits.

So that is going to be massive overwriting. of similar structures at the same
adress. Very poor for hash %.

Skip bitboards.

Just use Zobrist and AND.

DIEP's pawnhashtable is like 4MB anyway and never bigger. I never understood
those large sizes for pawn hashtables. Soon i can get rid of the thing
completely when the last couple of hundreds of patterns get extra conditions, so
getting difficult to cache.

Then i can save out a potential penalty of 2 x 400ns, which in future perhaps
will be too much anyway for a lookup :)

>On September 12, 2003 at 16:53:44, Omid David Tabibi wrote:
>
>>assuming 'table_size' is a power of 2, the following two expressions are
>>equivalent:
>>
>>address = key % table_size;
>>address = key & (table_size - 1);
>
>That's exactly the problem. He generates his hashkeys by
>taking the differnce of the white and black pawn bitboard.
>
>If you 'AND' off a piece of that, you're just cutting out a part
>of your board - with massive hash collisions as a result.
>
>You want something more nonlinear.
>
>--
>GCP



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