Author: Anthony Cozzie
Date: 10:35:56 12/01/04
Go up one level in this thread
On December 01, 2004 at 08:19:55, James Swafford wrote: >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? Because you have the order wrong. anthony
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