Author: Dann Corbit
Date: 15:50:06 05/28/99
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On May 28, 1999 at 18:34:18, Dave Gomboc wrote: >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. For a perfect hashing scheme, the width of the key will have to be log2(possible positions) bits wide. We could use it as our mapping to all possible chess positions. If anybody finds one, please let me know. ;-) BTW, that would be one whopper of a hash table!
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