Author: Ricardo Gibert
Date: 22:51:58 12/05/01
Go up one level in this thread
On December 05, 2001 at 22:41:48, Andrew Dados wrote: >On December 05, 2001 at 18:09:48, Ricardo Gibert wrote: > >>On December 05, 2001 at 15:41:12, Bruce Moreland 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 >>> >>>Even if you could generate a Godel number for each pawn structure, there would >>>still be some problems. Zobrist keys are wildly different even with small >>>changes in pawn structure, so the keys tend to disperse well in the table. >>>Depending upon how you generate the Godel number, things might not disperse as >>>well. This could be solved by applying a function to the Godel number that >>>translated it to another unique number that was not particularly like the >>>original number, but this sounds like a challenge in a few different ways. >>> >>>Please pardon logic errors in the above, I spent too much time doing research >>>for this answer and now I'm late to go do something. >>> >>>I calculated 2^85 different pawn structures, but I believe this is somewhat >>>wrong. >> >>You only need a 48 bit bitmap for the location for all pawns, then since there >>are only 16 pawns, you only need an additional 16 bits for color for 64 bits >>total. You can do better than 64 bits with Rube Goldberg like tricks, but it is >>not worth the trouble. >> >>> >>>bruce > >15 bits for color. Which makes 2^63 max pawn positions I doubt you can use that trick (last pawn color is forced when all pawns are present) without adding code that can only slow you down without saving any space in a pawn hash table scheme. What you mention was one of the Rube Goldberg tricks I alluded to. You can better than 63 too, but so what? Just for the heck of it, I think I once got it down something like 58 (I can't remember exactly) without doing anything too elaborate.
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