Changes

While using eight lookups to intersect sounds expensive on the first glance, SISSY Bitboards yields up to eight [[Direction#RayDirections|ray-directions]] of a queen in one run with cheap instructions and high [https://en.wikipedia.org/wiki/Instructions_per_cycle IPC] potential, and thus may be an alternative for [[Magic Bitboards|magic bitboards]] on architectures with slow 64-bit multiplication, in particular for the queen.

The general SISSY attack getter requires a 3-dimensional 1MByte lookup table, with pre-initialized attack bitboards indexed by 3-bit rank index, 6-bit square, 8-bit rank occupancy and 3-bit rank index.

U64 qss[8][64][256][8];

qss[0][sq][ occ & 255][0] & qss[1][sq][(occ >> 8) & 255][1] & qss[2][sq][(occ >> 16) & 255][2] & qss[3][sq][(occ >> 24) & 255][3] & qss[4][sq][(occ >> 32) & 255][4] & qss[5][sq][(occ >> 40) & 255][5] & qss[6][sq][(occ >> 48) & 255][6] & qss[7][sq][(occ >> 56) & 255][7] ; }

[7][d4][0x80] [76] [d4][0x41] [65] [d4][0xA2] [54] [d4][0x04][4]

1 . . 1 . . 1 . * 1 . . 1 . . 1 .* 0 . . 1 . . 0 . 0 . . 1 . . 1 .

[3][d4][0x28] [32] [d4][0x05] [21] [d4][0x4a] [10] [d4][0x00][0]

Rather then using shift/and instructions to get the ranrank-wise occupancies, and similar to [[Sherwin Bitboards]], one may use a [[C#Union|union]] of a bitboard and a struct or array of eight [[Byte|bytes]] (Portability concerning [[Endianness|endianness]] is an issue), to appear the code looking simpler.

U64 qss[8][64][256][8]; // 1M

qss[0][sq][o.b08.r1][0] & qss[1][sq][o.b08.r2][1] & qss[2][sq][o.b08.r3][2] & qss[3][sq][o.b08.r4][3] & qss[4][sq][o.b08.r5][4] & qss[5][sq][o.b08.r6][5] & qss[6][sq][o.b08.r7][6] & qss[7][sq][o.b08.r8][7];};

queenAttacks(unsigned long long, int): # @queenAttacks(unsigned long long, int) mov rdx, rdi

shr rcx, 50 and ecx, -6456 movsxd rdxrsi, esi movzx esiedi, dildl shl rsi, 611 shl rdx, 14 mov rax, rdi shr rax, 2 and movzx eax, 16320dh mov rax, qword ptr [rdx rsi + 8*rax + qss+8131072] and rax, qword ptr [rdx rsi + rsi 8*rdi + qss] mov rsirdi, rdirdx shr rsirdi, 1013 and esiedi, 163202040 and rax, qword ptr [rdx rsi + rsi rdi + qss+16262144] mov rsirdi, rdirdx shr rsirdi, 1821 and esiedi, 163202040 and rax, qword ptr [rdx rsi + rsi rdi + qss+24393216] mov rsirdi, rdirdx shr rsirdi, 2629 and esiedi, 163202040 and rax, qword ptr [rdx rsi + rsi rdi + qss+32524288] mov rsirdi, rdirdx shr rsirdi, 3437 and esiedi, 163202040 and rax, qword ptr [rdx rsi + rsi rdi + qss+40655360] shr rdirdx, 4245 and ediedx, 163202040 and rax, qword ptr [rsi + rdx + rdi + qss+48786432] and rax, qword ptr [rdx rsi + 8*rcx + qss+56917504]

U64 bss[646][64][664]; // 192 K

rss bss[0][sq][(occ >> 9) & 63][0] & // 2nd rank rss bss[1][sq][(occ >> 17) & 63][1] & rss bss[2][sq][(occ >> 25) & 63][2] & rss bss[3][sq][(occ >> 33) & 63][3] & rss bss[4][sq][(occ >> 41) & 63][4] & rss bss[5][sq][(occ >> 49) & 63][5] ; // 7th rank}

One may There is a more recent attempt to half the table size number of lookups by [[Martin Sedlak]] but using much larger tables <ref>[http://www.talkchess.com/forum3/viewtopic.php?f=7&t=73083&start=55 Re: Split Index Super Set Yielding (SISSY) Bitboards] by combining occupancy indices of two consecutive ranks, since their relevant bits on [[Diagonals|diagonalMartin Sedlak]] and , [[Anti-Diagonals|anti-diagonalCCC]] are always disjoint, February 14, 2021</ref>.

If combined with the [[First Rank Attacks#AttacksOnAllRanks|rank lookup]] to for SISSY fileAttacks only, one can dense the occupy index range to 2, considering only blockers on the same file, SISSY file attack generation looks not that competitive compared to other techniques as well, see for instance [[Kindergarten Bitboards#File-Attacks|Kindergarten file attacks]] or [[Hyperbola Quintessence]].

U64 rss[6][64][2][6]; // 6K

rss[0][sq][(occ >> 8) & 1][0] & // 2nd rank rss[1][sq][(occ >> 16) & 1][1] & rss[2][sq][(occ >> 24) & 1][2] & rss[3][sq][(occ >> 32) & 1][3] & rss[4][sq][(occ >> 40) & 1][4] & rss[5][sq][(occ >> 48) & 1][5] ; // 7th rank}