Author: Tony Werten
Date: 22:00:08 08/26/05
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On August 26, 2005 at 15:04:55, Robert Hyatt wrote: >I'm fixing to change the way I number bits to make bit 0 the LSB (as the BSF/BSR >instructions count on the X86) rather than the MSB as the leading zero >instruction counts on the Cray-1 architecture. > >I have four choices for which square bit 0 represents (four logical choices, >anyway, I guess one could number bits randomly should they choose). > >A1 = 0 >H1 = 0 >A8 = 0 >H8 = 0 > >For those of you using bitboards, which did you use? Since it doesn't matter to >me at all, since I am having to rewrite a bunch of stuff to make this work, I >thought I would try to match the most common layout which will make the programs >more compatible if we share any ideas. > >I am leaning toward H1 = 0, H2 = 8, ..., H8 = 56 and A8 = 63, but I've not made >any decision yet... The reason for this is that it is easier to visualize if >you think of the chess board as being composed of the 1 rank and the rightmost 8 >bits of the bitboard, the 2nd rank is the next 8 bits, etc. > >The alternative is H8=0, etc, so that the last rank is the rightmost bits, the >seventh rank is the next 8 bits, etc. Anything else requires "mentally >mirroring" so that if A1 or A8 is bit zero, the bits are backward, since A8 is >the left end of a rank, and bit 0 is the right end of a set of 8 bits... I use A1=0,H1=7,H8=63. Same for pawnbytes. A pawn on the A file will the 0 bit set. It seemed logical from programming point of view. You just have to get used to it. I did however make a function ShowBB() wich shows the bitboard in a chessboard view, for checking bitboard patterns. BTW since you start changing anyway, you might want to reconsider your diagonally rotated bitboards. Making them 8 times 8 bits each by lining up A1-H8,A2-G8+H1,A3-F8+G1-H2 etc makes them a lot easier to visualize. In addition it gives the possibility to get "ranks" by charptr[rank] rather than a shift. Well, at least that's nice for my program, I swap a lot between bb and 0x88 Tony
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