Author: Robert Hyatt
Date: 15:00:00 07/29/04
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On July 29, 2004 at 17:34:11, Christophe Theron wrote: >On July 29, 2004 at 14:07:10, Robert Hyatt wrote: > >>On July 29, 2004 at 06:26:52, Gian-Carlo Pascutto wrote: >> >>>http://arxiv.org/ftp/cs/papers/0406/0406038.pdf >>> >>>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 >>>download. >>> >>>-- >>>GCP >> >> >>Doesn't strike me as particularly interesting. IE it almost seems that they >>don't realize that most programs store positions in a repetition list as 64 bit >>Zobrist integers... > > > >Actually I think it might be interesting. > >Recently, when I was rewriting the core of the Chess Tiger engine, I realized >that I could get even more speed by not computing the hash keys during the >quiescence search for example. I've tried that. Hurts in endgames where there is little q-search and the extra cache traffic hurt performance. Helped in the middlegame. > >In my case, it would have meant some more changes in the engine and the way I do >QSearch. But for some programs, it could be interesting. > >The problem then is how do you check for repetitions? I don't in the q-search as I don't do checks or anything other than captures. That's why I originally decided to try this idea... has some merit to try again however. > >If you allow checks and escape from checks in your QSearch, and if you actually >extend them in some way, you have to detect repetitions. Right... > >So a lightweight, hash key free, repetitions detector is a must in this case. > >It could also be interesting for people who want to write a very small chess >program for portable units. > >But I think there is a better method than the one given in the paper. I would >use an array of integers, one per piece on the board. The array starts filled >with 0. Every time a piece is moved I would add the move vector to the integer >in the array. > >A repetition is detected when all the array is filled with 0 (nul vectors). It >is possible to use a "master vector" that receives all the individual vectors >after every move. One has to check the whole array only when the master vector >is nul, otherwise there cannot be a repetition. > >This method also works backwards (from the current move back to the last >irreversible move), but avoids any search in the concatenation list. > >It should be significantly faster than their method. > >Now I should write a paper. :) > > Always. :) > > Christophe
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