Author: vladan
Date: 10:51:47 08/01/04
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Hi Remi, "Extender" is Alfa-Beta procedure we use in terminal nodes instead of static evaluator. Only a fraction of all generated moves are computed (captures, some checks and promotion moves). It is very important to optimize this procedure as much as possible. Hash system used in Axon is simple: 6 bytes (48 bit): 24 bit - fractional position key, 16 bit - best move, 8 bit - other flags. Using this compressed hash system we have tested Axon with 32 million positions/best moves memory. All nodes (included ones generated by the extender) could be supplied with best moves efficiently. Of course, 24-bit is not enough to determine positions exactly (like Zobrist 64-bit hash); different positions could generate the same 24-bit hash key. But those cases (hash failure) are not fatal for searcher - they only could decrease quality of move ordering. But if the best move is found, Alfa-Beta, Null-Move and Extender procedures could make a great number of cutoffs. This is the main reason why our hash could be used for searcher and not for draw-detector. Best regards, Vladan (Axon programmer)
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