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Subject: Re: zobrist hashing

Author: Dave Gomboc

Date: 15:34:18 05/28/99

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On May 28, 1999 at 18:07:17, vitor wrote:

>as far as i can tell, zobrist hashing seems to be an imperfect(but fast) hashing
>scheme, meaning it is possible that your program will mistake position X as
>position Y.
>
>so my question is:
>is zobrist hashing the current standard in computer chess? is it just an
>accepted risk or are there any perfect hashing schemes that are used?

Yes, it is the current standard... and an accepted risk.  That risk can be
minimized by using a large enough key.  64 bits is pretty normal today, though
some people use 32+tricks, or 48+tricks.  (Tricks like checking the best move to
make sure it's legal in the position, which is probably a good idea in any
event. :-)  I don't know of anyone using a perfect hashing scheme for a playing
program, but this doesn't mean it isn't possible.

Dave



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