Author: Robert Hyatt
Date: 05:04:42 10/20/98
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On October 20, 1998 at 04:17:35, Steve Maughan wrote: >What is the easiest way to detect draw by repetition during a search? > >I have thought that setting a flag in the hash entries of the main line would >work. Does anyone use a similar technique? What happens when there are no hash >tables. > >Thanks in advance. > >Steve Maughan There are two easy approaches. (1) use the hash table as you suggest. When you create an active position by making a move, you "open" the position in the hash table by storing the key if it isn't already there, and setting the "open" bit. When you unmake that move, you clear the "open flag". Now, if you get a hash hit, and "open" is set, you can return repetition. (2) use a list of hash signatures, one for each ply in the search, plus 1 for each move since the last non-capture/non-pawn-push in the game history. (2) is the most flexible because (1) will give you significantl problems if you ever want to do a parallel search. (2) done carefully is not expensive. I don't spend more than 1% of the total time in this code, usually way less...
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