Author: Gerd Isenberg
Date: 09:45:54 12/05/01
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On December 05, 2001 at 10:30:38, Robert Hyatt wrote: >On December 05, 2001 at 08:22:40, Gerd Isenberg wrote: > >>About the pawn hash key discussions: Why using Zobrist keys for pawn hashing at >>all, at least in BitBoard programs? Isn't it smarter to use a unique 46 Bit >>(Rank2-7) Difference of two colored Pawn-BitBoards instead of zobrist keys for >>pawns? No key collisions and key and index (key mod nEntries) calculation on the >>fly. >> >>Gerd > >The problem is that you have 56 bits of information. 48 possible pawn >positions + 8 possible en passant target files. Which N bits of that are >you going to use to produce the table index? _that_ is the problem. >Because for hashing, _every_ pawn needs to influence the signature and >table address. Using a real position, some pawns won't influence >anything unless you take the position, fold it in half, and so forth, and >then you discover that invites collisions like mad. Isn't it possible to choose a special prime number for nEntries to ensure that every pawn or most combinations of pawns change the remainder in a pseudo random way?
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