Author: Tony Werten
Date: 22:20:17 11/30/04
Go up one level in this thread
On November 30, 2004 at 15:44:47, James Swafford wrote: >On November 30, 2004 at 14:59:04, Dan Honeycutt wrote: > >>On November 30, 2004 at 13:42:39, Dann Corbit wrote: >> >>>On November 30, 2004 at 13:25:08, James Swafford wrote: >>> >>>>On November 30, 2004 at 12:51:38, Andrew N. Hunt wrote: >>>> >>>>>Hi! >>>>> >>>>>I've recently implemented bitboards (standard and rotated) and have a question >>>>>about pre-computing moves which contain blocked squares. Let's say I have the >>>>>occupied rank: >>>>> >>>>>bQ, wN, _, wR, _, bP, bN, _ >>>>> >>>>>and I want to find the valid moves for the white Rook. How do I handle modifying >>>>>its bitboard rank: 11010110 to remove the blocked squares and only store the >>>>>available squares: 01101100? (which I can then And with the white/black pieces >>>>>to find valid Rook moves) >>>>> >>>>>Maybe I'm missing something obvious... :-? >>>> >>>>You need to precompute a two dimension array >>>>Bitboard rank_moves[64][256]. The first index is the square >>>>the rook is on. The second index is the state of the rank >>>>(in this case 11010110 base 2). >>>> >>>>You'll need a similar array for files and diagonals >>>>(one for the a1->h8 direction and one more for the h1->a8 >>>>direction). >>>> >>>>Just build these arrays in your program initialization >>>>by doing some looping. >>> >>>You can get by with 128 entries instead of 256 in most cases, because a piece >>>never attacks or defends the square it is standing on. >> >>I use [64][128] by simply throwing away the h file. I could use [64][64] by >>likewise throwing away the a file but it would cost me an extra add for my shift >>(ie I'd have to shift by 8*(rank-1) + 1 instead of 8*(rank-1)). Getting rid of >>the square the piece is on could, I guess, get you to [64][32] but looks like it >>would also require some extra math. > >I don't think you could get to 32. What if the square you're on >is in the A or H file? 32 Might be better to change the declaration to [33][64] for easier indexcalculation. Tony > >-- >James > > >> >>Dan H.
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