Author: Sune Fischer
Date: 07:16:47 02/06/04
Go up one level in this thread
On February 06, 2004 at 09:54:55, Tord Romstad wrote: >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? You can mask out bad squares before you popcount, that's what I do currently. >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. It's not so easy to figure out what the squares are worth. Although an SME says you can't safely move there it might still be worth something to attack it. >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. You can easily mask out all the blocked pawns before you popcount, no problem. -S. >Tord
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