Author: Serge Desmarais
Date: 23:06:21 09/19/98
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On September 19, 1998 at 13:19:07, Robert Hyatt wrote: >On September 19, 1998 at 11:14:40, Guillem Barnolas wrote: > >> >> I am currently developing a pascal chess program which I think will be >>quite weak, because to generate legal moves I'm generating all the moves and >>then discarding the ones that leave the king in check... Generating only legal >>ones seems quite tough.. I now crafty does, but considering it's in C and uses >>bitboards, it's quite difficult for me to understand it.. I tried tscp, but it >>uses the same technique that me (I should say i use the same that it uses..;) I >>have thought of some way of doing this, but seem a little weird... I'll try to >>explain in few words... I thought I could go from the king_position looking if >>there are friendly pieces blocking possible attacks...(I think I might have seen >>this in Crafty or some other program, as X_ray attacks...) and mark those >>friendly pieces...afterwards i go through all the board and for non-marked >>pieces I generate all the movements.. for pieces marked once I generate captures >>to the attacking piece and movements on that direction.. for the pieces marked >>more than once I generate no movements... I don't know If this would miss >>anything... I haven't implemented it because I'm still fighting with the program >>;-D... >> > >this is not really necessary. I generate legal moves only if I start off in >check, because it is more efficient (in my code) to generate only legal moves >than it is to generate a bunch of moves and cull them one at a time by noting >that the king is in check after making them... > >But for the normal case, I generate all moves, and let the search at the next >ply reject a move from this ply if it can capture the king, which means that >move was illegal. It doesn't happen often, *except* when you are in check. Then >almost all moves are illegal... [Snip] Ah! So that is the reason why sometimes I see illegal moves in the end of the PV of certain programs? I thought it was caused by the selective extensions! Serge Desmarais
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