Author: James Swafford
Date: 07:07:43 12/03/01
Go up one level in this thread
On December 03, 2001 at 07:11:41, David Rasmussen wrote: >On December 02, 2001 at 23:58:43, Robert Hyatt wrote: > >>On December 02, 2001 at 22:38:30, David Rasmussen wrote: >> >>>Many people use 32-bit pawn hashkeys. But I've found that 32 bits is not enough >>>to avoid collisions. 64-bit seems to be enough, and maybe less could do the job. >>>Why do people use 32-bit keys, when it screws up evaluation this way? >>> >>>/David >> >> >>32 is ok for pawns. To see why, figure out how many _different_ positions >>there are with only pawns on the board. The number is not as large as you >>might think, which makes collisions unlikely so long as you _only_ hash pawn >>positions. > >I get the first collision after about 5 seconds of search, and the the rate >increases as the search progresses. I believe I have good random numbers, I have >checked hamming distance etc. I don't use separate values for pawn hashing (as >you did at some point, I think), I just use the first n bits of the normal >hashkeys for pawns, where n=64 now that I've found n=32 not to work. > >/David What do you mean by 'first n bits of normal hashkey'? Are you just taking a chunk of the regular hashkey and calling that the pawn hashkey? You should be computing a separate key that doesn't factor in anything about the position other than pawn location. Maybe you are, I don't fully understand what you meant. -- James
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