Author: Anthony Cozzie
Date: 06:08:28 02/06/04
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On February 06, 2004 at 07:22:19, Tord Romstad wrote: >On February 06, 2004 at 06:06:07, Vasik Rajlich wrote: > >>Interesting discussion. One other thing to throw in: it seems to me that a >>rook's mobility being hindered by a pawn is more serious than a bishop's >>mobility being hindered by a pawn, because it's easier to move a pawn off of a >>diagonal (ie just push the pawn) than to move it away from a file. So, it makes >>some sense to emphasize rooks on open files (rather than rook mobility), and to >>give this a higher value than a bishop on an open diagonal. Ideally, a bishop's >>diagonal would be evaluated to see how easy it is for any blocking pawns to >>move, because sometimes a bishop can be totally without prospects because of one >>pawn. > >Yes, it is essential to consider which pawns are blocked and unblocked when >doing mobility evaluation, especially for bishops. > >>Also, it doesn't seem super-cheap cheap to get bishop mobility, you need to do a >>CountBitboardBits (), while open file is just an "&" operation and a boolean >>test. > >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. > >Tord With rotated bitboards it is practically free; it is just a popcount8. Basically just popcount your index. anthony
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