Author: Robert Hyatt
Date: 12:58:16 02/21/99
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On February 21, 1999 at 13:23:24, William Bryant wrote: >On February 21, 1999 at 10:21:50, Robert Hyatt wrote: > >>On February 21, 1999 at 01:14:37, KarinsDad wrote: >> >>>I posted this the other day, but it may have been obscured (or not if nobody has >>>any information on it). >>> >>>I have been wondering if changing the Zobrist hash from a set of random number >>>to a set of non-random and very specific numbers could result in a more even >>>distribution in the hash table. Has anyone done any work in this area? >>> >>>KarinsDad >> >> >>Burt Wendroff and Tony Warnock published a paper in the JICCA a few years >>ago discussing this. The main issue is to find the hamming distances between >>_all_ the random numbers, and maximize all of them. Random numbers work fine >>if they have been tested (I ran all of mine thru a hamming distance analysis >>when I first started). >> >>As far as 'distribution' this is done by the low order N bits >>(N=log2(hash_size)) of the hash signature. You _could_ do the hamming analysis >>on just those bits as well. > >I check all my random numbers for uniqueness, ie no duplicates,and use >0xFFFFFFFFFFFFFFFF for the side to move (compliment the side to move), >but would appreciate information on 'hamming distance analysis' in not to >complicated to post or send via email. > >Thank you, > >William >wbryant@ix.netcom.com "hamming distance" is simply the number of bits two numbers differ in. To compute the hamming distance for a and b, you just compute popcnt(a^b). Two numbers can differ in all bits. But more than two can not... I shoot for no worse than 32 bits that are the same in two random numbers... Assuming 64 bit values...
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