Author: Ralf Elvsén
Date: 01:48:05 11/14/01
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On November 13, 2001 at 19:19:46, David Hanley wrote: >It's my understanding that the hash codes used in a chess program are hamming >codes, and they are generated such that > >bit_count( code[x]^ code[y] ) > threshold > >for all combinations of codes, obviously self excluded. > >Is this correct? > >I plan on using 48 bit hash codes, and my threshold for bit mismatches is >hash_length/6, or in the case of 48 bit keys, 8 bit differences. Is this >sufficient? > It has been argued here (and I think it is correct) that the Hamming distance shouldn't be too big either, i.e. 47 is as bad as 1. I did this for 64 bits, and I tried to push all pairwise Hamming distances as close to 32 as possible, e.g. minimize( maximum(abs(32 - Hammingdistance(r_i, r_j)) ) ) where r_i are the random numbers and i != j . I got a value of 24 or so (don't remember exactly). It seems to work fairly well. Ralf
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