Author: Robert Hyatt
Date: 08:13:14 07/01/04
Go up one level in this thread
On July 01, 2004 at 02:50:35, Tony Werten wrote: >Hi all, > >although I like the principle of bitboards, it really bothers me that I can't >seem to find a decent/fast way to evaluate weighted safe squares. > >Suppose I want to (simple) evaluate a rook, I generate a bitboard with all >reachable squares and mask off the squares attacked by lower pieces (that's no >problem). > >(This doesn't exacly generate safe squares, only the ones that aren't attacked >at all by opponents pieces are, for the remaining squares one would need a SEE, >but that's not the point ) > >Now I can use this bitboard ( say rook on e4 ), mask the rank state, and look in >a precomputed table how this rankstate scores on an e rank. No problem. > >But how to do the files ? If I use the rotated board, I need to have the >opponents attackboard in this rotated board as well, wich would be very costly >to compute (ie also for the bishops,queens ) and very complicated. > >Any ideas ? Am I missing something ? > >BTW, doing a popcount isn't a solution, since it violates the elegance of >bitboards ( and is slow ?) > >Tony On the Cray there is an elegant solution, but not on X86 so far... You can create a 64-word vector of "weights". How you compute these is up to you. In Cray Blitz I did this as I did the evaluation, figuring out which squares were weak, unimportant, strong, useful, painful for opponent, etc. After the normal eval, I had a vector of values, one per square for all squares on the board. Now I computed the "attack bitmap" for a piece, and stuck that in the vector mask register. Now when I sum up the square value vector, it only sums the values with a corresponding bit mask of 1, meaning this piece attacks that square safely. I obviously don't do that at present, since X86 has no such direct capability and the software approach is expensive... In any case, I believe there are plenty of viable alternatives to this kind of mobility concept that it isn't that important... IE mobility has many forms of expression. A rook on an open file is one such idea...
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.