Author: Vincent Diepeveen
Date: 09:29:38 01/31/01
Go up one level in this thread
On January 31, 2001 at 10:53:11, Carmelo Calzerano wrote: >On January 31, 2001 at 10:43:41, martin fierz wrote: > >>On January 31, 2001 at 10:29:51, Carmelo Calzerano wrote: >> >>>>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 f or 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... >>> >>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. > >But it's not a matter of safety, it's a matter of performance: lots of >positions in big subtrees will map in just a bunch of hash entries. >You will be able to easily detect all these conflicts, just comparing the >full hash keys; but the hash table will be almost useless... Sorry you see problems which i don't see. Which problem do you see. You need 2 bytes extra an entry as he's needing now or something. If you put those 21 bits at the most significant bits and the other bits below then you can use the least significant bits even to index into your hashtable! So you only need a few bits more for each entry. I don't understand the dying issue at all! >Bye, >Carmelo
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