Author: Mike Siler
Date: 21:00:07 04/15/03
Up until recently, my chess program generated all pseudo-legal moves, made each move, checked to see if it's in check and unmakes the move if so. This annoyed me a bit because my attack function that sees if the program is in check was not too quick. So I came up with a method of avoiding calling the attack function as often. Assuming the program is not in check at this particular node, we know that there are only 2 ways the program can enter check: either the program moves a piece and discovers a check on itself (it was pinned to the king by a sliding piece) or the king moves into check. I wrote a function to determine which (if any) of the program's pieces are pinned to its king. Then if a pseudo-legal move involves the pinned piece, we know already that the movement will cause the king to be in check, so we don't have to call the time-consuming make_move function, attack function, or unmake_move function. Of course if the move involves the king, we can't skip the attack function. Using this method, I experienced a very nice speed-up: from about 300knps to about 375-400 knps. I've never seen another program that uses this. I'm just curious if there is some down side I don't see or if programs do use this and I just didn't notice. Michael
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Last modified: Thu, 15 Apr 21 08:11:13 -0700
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