Author: Sune Fischer
Date: 02:38:03 05/30/03
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On May 30, 2003 at 04:31:58, Fermin Serrano wrote: >I have developed my engine with a trasposition table and a incremental move >generator (hash move + captures + killers + pasive moves). It is running nice, >except a few possitions. It could "think" about 7/8 plys without problems, but >then and inconsistence arrive, and I think that it is because I use a hash key >length of 32 bits. With this key length, is there any possibility of "real" >colisions? 32 bits is not enough to avoid collisions. If you have never heard of the birthday problem, then here it is in a nutshell: 32 bits gives you 2^32 combinations. Say you have 2^20 entries in your (filled) hash. Now you generate a bran new key and you look it up. The chances of a collision is going to be 2^-12 = 1/4096. Of course not all the keys you generate will be new ones, and the table may not be entirely full, and the zobrist table may not produce perfectly random distributed keys, still you will get many collisions a second. There are enough ways to destabilize a chess engine, no reason to introduce more noise, IMO. 64 bits are used by many (far majority I think) of the chess programs. -S.
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