Author: Carmelo Calzerano
Date: 11:11:56 01/31/01
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On January 31, 2001 at 12:29:38, Vincent Diepeveen wrote: >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! Right, of course. But you forgot to specify this in your previous post... Instead, you said: > You don't need XOR. You need a bitmap so I assumed you didn't want to use any Zobrist-like algorithm for indexing, and that was my point. Sorry for misunderstanding :-) Bye, Carmelo
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