Author: Vincent Diepeveen
Date: 07:32:27 02/01/01
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On February 01, 2001 at 05:57:58, Tony Werten wrote: >On January 31, 2001 at 08:13:52, martin fierz wrote: > >>hi, >> >>i recently corrected some code in my connect 4 program and now it is able to >>solve connect 4 in less than a day on a fast PC with a large hashtable (of >>course, connect 4 has been solved long ago). i tried again with a smaller >>hashtable and >>got some strange results, for very long searches (billions of nodes) i don't get >>the same value for >>the root position. for not-so-deep searches i get the same values for both >>versions. i am wondering, [if this is not just a bug :-)] could this be some >>hashcollision-problem? can anybody give me a probability for a hash collision >>occuring when using B-byte key & lock, with a hashtable with S entries after >>searching N nodes? (i am using 4 byte ints for the key and the lock) >>also, i think i remember somebody mentioning here that one can choose the random >>numbers for the XORs in a clever way making hashcollision probabilities >>smaller - can somebody tell me how? > >Ideal would be if every number would change half of the number of bits. > >Currently I'm working on connect 4,5,6 and 7, using hash scheme of 64bits. I >have found no problems. The advantage of using zobrist is you can handle >mirroring very easy. You just have to keep 16 hash values and store the lowest. >It sounds slow, but getting a hashhit saves such a lot of nodes that it's worth >it. I'm working with the falling stones board always, and the game is solved long before i do effort to mirror things :) The only thing needed is a good move ordering. That reduces the search space incredibly as we all know. >Using this hashscheme and some intelligent recognisers (recognizing >win-in-5-moves is a big winner), solving 4 in a row shouldn't cost you more than >2M nodes (with boards >= 6 by 5, wich is the minimum size for a first player >win). > >BTW make sure you include side-to-move in the hashvalue. > >cheers, > >Tony > >> >>cheers >> martin
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