Author: Antonio Dieguez
Date: 12:31:58 09/24/01
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On September 24, 2001 at 14:33:49, Uri Blass wrote: >On September 24, 2001 at 13:53:58, Antonio Dieguez wrote: > >> >>>Several hash into 2 X 32 bit values. You store one value, you use the other >>>to generate the hash index. This is not quite as safe as a true 64 bit hash >>>signature where all 64 bits are used, but it is pretty good. If you have >>>one million entries in the table, your hash key is 52 bits long, effectively, >>>which is not horrible. Not as good as 64, but not horrible. >> >>hi. isn't one million of entries around 2^20, so just 44 bits are used for the >>key, (not 52) ? > >no >My understanding is that in this case every chess position is practically >compressed to 52 bits(52=32+20) >20 bits are used for the index when 32 bits are used for the position. oops yes I "just" mixed up what Hyatt said... but what does this mean >>>one million entries in the table, your hash key is 52 bits long, effectively, >>>which is not horrible. Not as good as 64, but not horrible. who cares if it is 52 or other? what about more hash entries, then that will surpass 64, funny. We can't compare just that numbers. >If you get another position with the same hash key then the chance that you get >the same number(hash collision) is practically 1/2^32 > >probability of 1/2^32 for hash collision is not bad and in the worst case if you >have a fast machine and a fast searcher you get an average of 1 or 2 hash >collisions in one hour. > >I believe that in more than 99% of these hash collisions the move in the game is >not changed but I do not know if I am right and it is only based on intuition >that says that changing the score of one random node in the tree is not going to >change the move when the tree is huge and have more than 2^26 nodes. > >Uri
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