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Subject: Re: A New Approach to Draw Detection by Move Repetition in Computer Chess Pr

Author: Mathieu Pagé

Date: 10:57:31 07/29/04

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On July 29, 2004 at 06:26:52, Gian-Carlo Pascutto wrote:

>I stumbled onto this when doing a search for Axon.
>Not seen it mentioned here yet.
>They also have a paper about hashing out which I can't


  I just read it and I was surprised to red that the classical way of detecting
draw is by comparing all the board. I know, as other have confirm, that cheking
only the zobrist hash key is enought to detect draw.

  Now I am wondering if my repetition detection is "classical". I use a small
hash table of 256 positions that I fill with the zobrist key of the position
after each MakeMove (That I remove just before UnMakeMove)(Note that I clear all
entries if an irreversible move is played on the board (not in the game tree)).
If the position was already in the hash table it is a repetition. If there is a
collision I do up to four re-hash (using other bits from the 64 bits key) if the
position is not found in 4 try I assume there is no repetition. In this way I do
at most 4 64bits comparisons.

  Is this what you all do, or some of you look back in the positions history of
the game and compare the actual zobrist key with every other since a
irreversible move is found ?

Mathieu Pagé

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