Author: Dieter Buerssner
Date: 13:55:02 04/04/03
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On April 04, 2003 at 16:40:07, Russell Reagan wrote: >I wonder if a different kind of hashing would work here, involving not a hash of >the position, but of the moves. A key could be computed during each movegen >involving the from and to squares, along with the piece type and maybe a move >type. > >Are there positions which are different, but have the same moves? Yes. For example, double a pawn for the side to move in such a way, that the additional pawn has no (pseudo) legal move - it will be very easy to find many such positions. Also the game theoretical result of such a position can certainly change, by adding that pawn. Anyway, I think normal hashing works well, if done carefully (including ep and castling rights). The main problem I see, is the wrong handling of reptetions (when you reach the same position after different moves, it is not really the same ...), and possibly some subtle points including extensions. Say you reach a position after a capture, you might do a recapture extension. On another path, you might not trigger that recapture extension. In general you just do not search the same tree. This can yield in some search inconsistencies. I think, there is no cure, that does not take away many of the nice advantages of HTs. Regards, Dieter Regards, Dieter
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