Author: Gerd Isenberg
Date: 13:03:57 09/30/02
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On September 30, 2002 at 15:57:14, Gerd Isenberg wrote: >On September 30, 2002 at 15:39:09, Sune Fischer wrote: > >>On September 30, 2002 at 14:34:48, Gerd Isenberg wrote: >> >>>Hi all, >>> >>>i recently thought about and played with the x^(x-2) idea, introduced to me by >>>"The Hyperbola Project" some time ago. >> >>Isn't this the old reversed bitboards trick? >>How can you use this to generate the upper attack board, it only works on the >>lower bits? >> >>> It works fine with bit 0, and i thought >>>that shifting to file zero is required, before generationg the attacks. >>>But that seems not to be necessary. The generalized term for one rank is simply >>> >>> Occupied ^ (Occupied - 2*RookMover) >>> >>>where RookMover is subset of Occupied. >> >>What is RookMover, how do you generate it? >> >>-S. >> > >Hi Sune, > >RookMover are Rooks and the "Rook Part" of a Queen, which opposite "part" is a >BishopMover. If you only need all tabu squares for the king, or you need to >generate an "attackedBy"-bitboard for a square, then you save the >"getQueenAttacks". > OK, in the routine RookMover is like a formal parameter, the actual one may be a set of one or more rooks, or for the purpose i mentioned, the "bitwise or" of the Rooks and Queen(s), the Rook-Mover. >Gerd > > >>>This term produces all rank attacks of all RookMover in positve direction >>>(increasing file index, here A=0,8...;B=1,9...). >>> >>>What a surprise (at least for me)! >>> >>>sample rank (consider the reversed bit order due to bit0 is A): >>>BitIndex 01234567 >>>Occupied(O) 01011101 >>>RookMover(R) 01001000 >>> 2*R 00100100 >>>-2*R 00111011 >>>Occupied(O) 01011101 >>> (O-2R) 01101001 >>>O^(O-2R) 00110100 >>> >>> >>>With 64-bit mmx-registers this can be done simultaniously with all eight ranks: >>> >>>input: mm1 = RookMover subset of Occupied >>> (may be forced by "por mm6,mm1") >>> mm6 = Occupied >>>output: mm0 = (right)RookAttacks >>> >>> movq mm0, mm6 ; Occupied >>> psubb mm0, mm1 ; Occupied - RookMover >>> psubb mm0, mm1 ; Occupied - 2*RookMover >>> pxor mm0, mm6 ; Occupied ^ (Occupied - 2*RookMover) >>> >>>I tried it with up/down Kogge-Stone and leftDumb7Fill. >>>But only a few percent better performance (24secs instead of 26secs /10**9). >>>With pure dumb7fill, the performance win was even less. The seven unrolled >>>fill-iterations with four independent mmx-instructions are not so much slower >>>than with three for the remaining directions. >>> >>>Cheers, >>>Gerd
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