Author: Robert Hyatt
Date: 14:06:18 12/10/03
Go up one level in this thread
On December 10, 2003 at 16:46:37, Matthew McKnight wrote: >On December 10, 2003 at 16:40:45, Robert Hyatt wrote: > >>On December 10, 2003 at 16:14:11, Gerd Isenberg wrote: >> >>>On December 10, 2003 at 15:38:43, Robert Hyatt wrote: >>> >>>>On December 10, 2003 at 12:54:13, Romang Jean-Francois wrote: >>>> >>>>>Hello, >>>>> >>>>>Is there a fast technique to detect that a king is in check in a bitboard engine >>>>>? In my engine I generate all capture moves and try them to see if the king can >>>>>be captured...but this seems very slow ! >>>> >>>>Do it backward. Find the king. Ask does a knight on this square attack >>>>a square that contains a knight? If so that knight is checking the king. >>>>Repeat for all your different piece types. >>>> >>>> >>>>> >>>>>I use check detection mainly in two parts of the engine : >>>>>- During move generation to avoid generating illegal moves >>>>>- To activate check extensions >>>>> >>>>>Is there a way to avoid check detection during move generation ? >>>> >>>>Don't do it. When you go to the next ply, and you capture a king there, >>>>return a special score to the previous ply that says "that move was >>>>illegal, unmake it and try something else." >>> >>>you really generate and even try all pseudo-legal moves if in check? >> >>No. If I know I am in check to start with, I have a GenerateCheckEvasions() >>generator that only generates legal moves out of check. Avoids the high >>overhead of making each illegal move and advancing to the next ply to >>generate captures to refute them... >> >> > >In addition, if you use something like checkEvasions(), then you shouldn't have >to check for legality after making these moves. This saves a little bit of time >too. Remember, I don't check for legality in Crafty. I just make the move, legal or not, and go to the next ply. The move generator will notice it can capture the opponent's king and return an illegal move indicator to the previous ply. After GenerateCheckEvasions() this simply doesn't happen as the moves are all legal. > > >>> >>>> >>>>> >>>>>Thank you :) >>>>>Jean-Francois
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