Author: Alessandro Damiani
Date: 10:02:02 09/15/02
Go up one level in this thread
On September 15, 2002 at 12:22:21, Gerd Isenberg wrote:
>The mmx-routine to get bishop-attacks is similar of course.
>
>If you call it whith a set of two opposite colored bishops of one side, it's
>easy to extract the single bishop attack bitboards by anding the combined with
>the appropriate square color bitboards.
>
>This feature is not so easy to implement with either rooks or queens. But even
>with a combined rookattack board, it's also possible to gain some informations
>about single rooks: anding the combined rook attacks with the rooks attacks from
>one rook square on an otherwise empty board (determined by "Kogge-Stone parallel
>prefix algorithm" or cheap table lookup), produces exactly the single rook
>attack bitboard, if no other rook(s) shares the same file or rank. Otherwise it
>includes all xray attacks through these rooks.
>
>
>BitBoard getBishopAttacksMMX(BitBoard freeSquares, BitBoard bishops)
>{
> static const BitBoard eight = 8;
> static const BitBoard notH = 0x7f7f7f7f7f7f7f7f;
> __asm
> {
> movd mm6, [freeSquares]
> punpckldq mm6, [freeSquares+4]
> movd mm1, [bishops]
> punpckldq mm1, [bishops+4] ; rightup
> pxor mm0, mm0 ; bishopsAttacks := 0
> movq mm5, [eight] ; saves some bytes in unrolled loop
> movq mm7, [notH] ; saves some bytes in unrolled loop
> movq mm2, mm1 ; leftup
> movq mm3, mm1 ; rightdown
> movq mm4, mm1 ; leftdown
> // 1. diagonal fill in each direction
> paddb mm1, mm1 ; right
> psllq mm2, 7 ; leftup
> paddb mm3, mm3 ; right
> psllq mm1, mm5 ; rightup
> pand mm2, mm7 ; clear left h-file wraps
> por mm0, mm1 ; bishopsAttacks |= rightup
> psrlq mm3, mm5 ; rightdown
> pand mm1, mm6 ; clear rightup occupied
> psrlq mm4, 9 ; leftdown
> pand mm2, mm7 ; clear left h-file wraps
> por mm0, mm3 ; bishopsAttacks |= rightdown
> por mm0, mm4 ; bishopsAttacks |= leftdown
> pand mm3, mm6 ; clear rightdown occupied
> por mm0, mm2 ; bishopsAttacks |= leftup
> pand mm4, mm6 ; clear leftdown occupied
> pand mm2, mm6 ; clear leftup occupied
> // 2. diagonal fill in each direction
> // ....
Did you already have the time to compare the flood-fill approach to rotated
bitboards or mine (rotated indices)?
I am sitting and waiting. :)
Alessandro
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