Author: martin fierz
Date: 07:43:41 01/31/01
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On January 31, 2001 at 10:29:51, Carmelo Calzerano wrote: >On January 31, 2001 at 09:39:10, Vincent Diepeveen 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? > >>You're using 32 bits to hash? >> >>I think there are like 7x6 rows or so = 2^42 possibilities which you >>hash in 32 bits. >> >>Easier is to store the entire position. This fits easily in 64 bits >>as with are 7 rows (?) at most 7 open spots are there. >>you can do next: white = 0, black = 1. >>open spots also 0. >>Now also describe how far each row is open. That's 3 bits for 7 rows = 21 >>bits. >>So in 42 + 21 bits you can store the entire position. That's not hashing >>but a true hash. >>For solving a game you definitely need to store the entire position! >>With just 32 bits you ask for trouble! > >Vincent, >which kind of indexing scheme would be suitable for such a table?! >Whichever you use, you are mapping similar positions in the same entry: >you'll get killed by conflicts, unless you plan to use a 2^64 entries table >of course... > >Bye, >Carmelo nobody dies here... you can use any normal indexing scheme, as long as you save a unique hashlock-code in the table you are safe. you can still get two positions indexed the same way, but you will detect it. cheers martin
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