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Subject: Re: Draw Detection by Move Repetition Procedure -- Comments

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

Best regards,

Vladan      (Axon programmer)

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