Author: Uri Blass
Date: 09:51:58 06/20/01
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On June 20, 2001 at 10:20:07, Robert Hyatt wrote: >On June 20, 2001 at 07:35:24, Uri Blass wrote: > >>Crafty needs only 2.2 seconds to calculate perft 5(the number of legal games >>with 5 moves) and only 54.76 seconds to calculate perft 6(119,060,324 nodes) >> >>It is clear that Crafty does not use hash tables to calculate perft faster. >> >>Is there another program (with free or without free source code) that can >>calculate perft (without hash) faster than Crafty? >> >>Uri > > >You can't use hash tables to do this. Otherwise the node count would not be >exact when the hash table cuts off part of the tree. It is possible to use arrays to calculate things faster(maybe these arrays are not called hash tables but bigger arrays can help so bigger memory can help) I will give an example Suppose you calculate perft(5) It is the sum of perft(2) of all the positions after 3 plies. You found after 1.d4 d6 2.e4 that perft(2)=1023 When you search later 1.e4 d6 2.d4 you can use the array that tells you that perft(2) of this position was searched and is 1023 so you do not need to generate the same moves again and you can add 1023 to perft(5). You only need a function to translate positions to numbers and if you have bigger arrays you can translate positions to bigger numbers so the probability that 2 positions will get the same number is smaller. In this case a possible problem if the array is small is that it is possible that 1.e4 d6 2.d4 and 1.a4 a6 a5 are translated to the same number so you find that the hash signature of 1.e4 d6 2.d4 was searched but this number in the array is translated to 1.a4 a6 2.a5 so you find that you cannot use it because the positions are different. Uri
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