Author: Tord Romstad
Date: 13:46:14 06/13/04
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On June 13, 2004 at 14:24:57, GeoffW wrote: >Hi > >I was thinking how I would add pawn hashing to my program. Having read a little >of the Crafty source I have a rough grasp of the idea, however there are a >couple of things I am hazy on. > >Q1) >I understand the pawn hash score stored must not contain any piece related >scoring as that must be factored in later. In my program even the simple choice >of which pawn position look up table is determined by the phase of the game, i.e >it will be piece dependent. How would I get over that obstacle ? Score the pawns >for end game, opening and middle in the hash, and choose which one to use later >? I don't store any scores at all in the pawn hash table, but just lots of computations which is used by the evaluation function. I store things like the location of all passed, isolated, double or backward pawns, pawn chains, number of pawns on black/white squares for both sides, a classification of the centre (open, closed, semi-closed, etc.), and so on. >Q2) >Crafty uses an 8 bit bitmap to store file for passers, this is ok for a bitboard >program as it is probably trivial to find the exact location later. However for >a non bitboard program it is non trivial to find the exact locations. Do I have >any alternative but to store the passer locations in the hash ? That would be 16 >bytes just for the passed pawns for both sides? My program also doesn't use bitboards. I simply store all the exact locations. This is not a problem, you can afford to use lots of space for your pawn hash table entries. My entries are 128 bytes big. Keep in mind that the number of pawn structures seen in a single search isn't very big, and that this means that you don't need to store a big number of entries. I found that increasing the pawn hash table size beyond 256 entries gave only a tiny increase in speed (about 3%, IIRC). Tord
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