Author: James Swafford
Date: 05:19:55 12/01/04
Go up one level in this thread
On December 01, 2004 at 01:20:17, Tony Werten wrote: >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. I don't see it. I'f I'm on the A1, I could potentially travel (on this rank) to B1->H1, depending on the occupancy of those squares. The set of squares I can travel to doesn't depend on H1 (if we ignore captures of own pieces). So, I care about the occupancy of B1->G1 = 6 squares = 2^6 states = 64. Would you further explain how to reduce this to 32? -- James > >Tony > >> >>-- >>James >> >> >>> >>>Dan H.
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