Author: Robert Hyatt
Date: 07:30:38 12/05/01
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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.
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