Author: Ed Schröder
Date: 07:14:51 07/30/04
Go up one level in this thread
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. > >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? > >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. > >So a lightweight, hash key free, repetitions detector is a must in this case. Father Christophe, For QS in the case you are using checks consider to compare moves only as most repetitions go as follows: Qh6-g6+ (depth-3) Kg8-h8 (depth-2) Qg6-h6+ (depth-1) Kh8-g8 (depth+0) -> current position if (from[depth+0]==to[depth-2] && to[depth+0]==from[depth-2] && from[depth-1]==to[depth-3] && to[depth-1]==from[depth-3]) -> draw I have used this in my 6502 days in QS only and it worked like a charm. Regarding speed (IMO) nothing can beat this because in 90% of all cases the first compare will fail, so actually you are doing just one compare in 90% of all QS cases. Ed (grandfather)
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