Author: Gerd Isenberg
Date: 00:58:50 10/01/02
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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? oups, it was little late yesterday... My intention so far is to use this x^(x-2) trick only to replace one direction fill in Kogge-Stone or dumb7fill. So it improves shlightly the getRookAttacksMMX, but a few percents more the getQueenAttacksMMX, due to easier register usage, where finally dumb7fill fills five directions simultaniously (left, leftup, leftdown, rightup, rightdown). Up/Down is done with KoggeStone, right by this x^(x-2) trick. I dont't like the reversed bitboard idea in the matter to work in parallel with two incompatible reversed attack sets. I even don't understand how "The Hyperbola Project" handles file- or diagonal attacks without rotated bitboards, so that these rays fit into one byte with consecutive bits on this ray. Gerd > >> 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. > >>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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