Author: Robert Hyatt
Date: 13:58:05 08/26/05
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On August 26, 2005 at 16:45:48, Peter Fendrich wrote: >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 always used A1=0, B1=2,...,A2=8,...,H8=63. >I never thought about it as mentally mirrored but maybe my brain is twisted >somewhere... :-) >/Peter In the PC, bit 0 is the rightmost bit. That's what makes it "mentally mirrored" since a1 is the leftmost square... :)
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