Author: Robert Hyatt
Date: 08:59:16 04/17/03
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On April 16, 2003 at 00:51:37, Anthony Cozzie wrote: >On April 16, 2003 at 00:00:07, Mike Siler wrote: > >>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 > >I actually wrote something very similar today ;) > >However, I think I'm going to use Hyatts method of simply capturing the king. >Since I have a get_check_evasions() routine, and I don't let the king move onto >an attacked square, very few moves are actually illegal. > >anthony I would not call that "Hyatt's method". I do it that way, but it wasn't original to me. I did this in Cray Blitz. I believe that chess 4.x did it also and that predated Cray Blitz. Earlier versions of my program (prior to cray blitz) did things completely differently. The only down-side here is I can't recall exactly who started the "pseudo-legal" approach to things using capturing the king as a legality refutation... Most likely Dave Slate deserves the credit...
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