Author: Tord Romstad
Date: 06:54:55 02/06/04
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On February 06, 2004 at 09:08:28, Anthony Cozzie wrote: >On February 06, 2004 at 07:22:19, Tord Romstad wrote: > >>It is much more expensive than that. Remember that all squares are not >>equally important, and that the bishop cannot safely move to all the squares >>you attack. For each square the bishop attacks, you must see if it can >>move there without getting captured, and consider how useful it is to be >>able to move to this square. For each friendly pawn which obstructs the >>bishop, you must consider how easy it is to advance this pawn. Most of >>this is quite expensive to compute, and I have been forced to do some >>dubious shortcuts and approximations in order not to slow my engine down >>too much. Some day I should probably have a look at how Bob does this, >>and see if there are some ideas there which I could use. >> > > >With rotated bitboards it is practically free; it is just a popcount8. > >Basically just popcount your index. I don't see how you can do this with just a popcount. First of all, how do you get a bitboard containing all the squares the bishop can *safely* reach? Assuming that you can calculate such a bitboard quickly, how do you use it to calculate the bishop's mobility? A raw popcount is obviously not enough, because all squares are not equally valuable. And finally, you still have to look closely at all the blockers to determine their importance. I am not claiming that you are wrong, of course -- I am just curious about how this is done with bitboards. Tord
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