Author: Vincent Diepeveen
Date: 03:22:27 12/06/01
Go up one level in this thread
On December 06, 2001 at 05:54:34, Ricardo Gibert wrote: yes short after i posted i realized it, thanks. Anyway it's waste of time. you already have for free the pawn zobrist hashing. i don't see why waste system time generating a different hashkey. when i measured some years ago mishits then i got 0. >On December 06, 2001 at 04:37:55, Vincent Diepeveen wrote: > >>On December 05, 2001 at 22:41:48, Andrew Dados wrote: >> >>how do you know in your hashscheme how many pawns you have? > >The 48 bit bitmap (used to give the locations of all the pawns) contains [part >of] the information for that. You just have to do some type of pop count on it >to get the total number of pawns on the board (call it x). If this number is 16, >then you automatically know there are 8 white pawns and 8 black pawns. >Otherwise, you do a pop count of the first x bits of the 15 bits used for color >(call this y) to know how many there are of each color. > >Example: Lets say x = 12 and y = 7, then there are y = 7 white pawns and x - y = >5 black pawns. > >> >>>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
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