X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fbitboard.cpp;h=b36f8a291d77647b5af8d1888bc83efabf0542d3;hp=073487e99cf252a02f9ed6656a31578048264279;hb=e870afa5d5a45925c3f2b5677cb15f5ffe2b4e0e;hpb=b706165527b5449fefa20bb31ac66d0274b066ea diff --git a/src/bitboard.cpp b/src/bitboard.cpp index 073487e9..b36f8a29 100644 --- a/src/bitboard.cpp +++ b/src/bitboard.cpp @@ -19,6 +19,7 @@ #include #include +#include #include "bitboard.h" #include "bitcount.h" @@ -26,15 +27,15 @@ // Global bitboards definitions with static storage duration are // automatically set to zero before enter main(). -Bitboard RMask[64]; -Bitboard RMult[64]; +Bitboard RMasks[64]; +Bitboard RMagics[64]; Bitboard* RAttacks[64]; -int RShift[64]; +int RShifts[64]; -Bitboard BMask[64]; -Bitboard BMult[64]; +Bitboard BMasks[64]; +Bitboard BMagics[64]; Bitboard* BAttacks[64]; -int BShift[64]; +int BShifts[64]; Bitboard SetMaskBB[65]; Bitboard ClearMaskBB[65]; @@ -63,11 +64,11 @@ namespace { CACHE_LINE_ALIGNMENT int BSFTable[64]; - Bitboard RAttacksTable[0x19000]; - Bitboard BAttacksTable[0x1480]; + Bitboard RookTable[0x19000]; // Storage space for rook attacks + Bitboard BishopTable[0x1480]; // Storage space for bishop attacks - void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[], - Bitboard mask[], int shift[], Square delta[]); + void init_magic_bitboards(PieceType pt, Bitboard* attacks[], Bitboard magics[], + Bitboard masks[], int shifts[]); } @@ -160,7 +161,7 @@ void init_bitboards() { for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++) for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++) - SquareDistance[s1][s2] = Max(file_distance(s1, s2), rank_distance(s1, s2)); + SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2)); SquaresByColorBB[DARK] = 0xAA55AA55AA55AA55ULL; SquaresByColorBB[LIGHT] = ~SquaresByColorBB[DARK]; @@ -227,11 +228,8 @@ void init_bitboards() { set_bit(&StepAttacksBB[make_piece(c, pt)][s], to); } - Square RDelta[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W }; - Square BDelta[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW }; - - init_sliding_attacks(BMult, BAttacks, BAttacksTable, BMask, BShift, BDelta); - init_sliding_attacks(RMult, RAttacks, RAttacksTable, RMask, RShift, RDelta); + init_magic_bitboards(ROOK, RAttacks, RMagics, RMasks, RShifts); + init_magic_bitboards(BISHOP, BAttacks, BMagics, BMasks, BShifts); for (Square s = SQ_A1; s <= SQ_H8; s++) { @@ -244,22 +242,22 @@ void init_bitboards() { for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++) if (bit_is_set(QueenPseudoAttacks[s1], s2)) { - int f = file_distance(s1, s2); - int r = rank_distance(s1, s2); - - Square d = (s2 - s1) / Max(f, r); + Square delta = (s2 - s1) / square_distance(s1, s2); - for (Square s3 = s1 + d; s3 != s2; s3 += d) - set_bit(&BetweenBB[s1][s2], s3); + for (Square s = s1 + delta; s != s2; s += delta) + set_bit(&BetweenBB[s1][s2], s); } } namespace { - Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[]) { + Bitboard sliding_attacks(PieceType pt, Square sq, Bitboard occupied) { + Square deltas[][4] = { { DELTA_N, DELTA_E, DELTA_S, DELTA_W }, + { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW } }; Bitboard attacks = 0; + Square* delta = (pt == ROOK ? deltas[0] : deltas[1]); for (int i = 0; i < 4; i++) { @@ -278,7 +276,7 @@ namespace { return attacks; } - Bitboard pick_magic(Bitboard mask, RKISS& rk, int booster) { + Bitboard pick_random(Bitboard mask, RKISS& rk, int booster) { Bitboard magic; @@ -299,51 +297,75 @@ namespace { } } - void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[], - Bitboard mask[], int shift[], Square delta[]) { - const int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 }, - { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } }; + // init_magic_bitboards() computes all rook and bishop magics at startup. + // Magic bitboards are used to look up attacks of sliding pieces. As reference + // see chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we + // use the so called "fancy" approach. + + void init_magic_bitboards(PieceType pt, Bitboard* attacks[], Bitboard magics[], + Bitboard masks[], int shifts[]) { + + int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 }, + { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } }; RKISS rk; Bitboard occupancy[4096], reference[4096], edges, b; - int key, maxKey, index, booster, offset = 0; + int i, size, index, booster; + + // attacks[s] is a pointer to the beginning of the attacks table for square 's' + attacks[SQ_A1] = (pt == ROOK ? RookTable : BishopTable); for (Square s = SQ_A1; s <= SQ_H8; s++) { + // Board edges are not considered in the relevant occupancies edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s)); - attack[s] = &attTable[offset]; - mask[s] = sliding_attacks(s, EmptyBoardBB, delta) & ~edges; - shift[s] = (CpuIs64Bit ? 64 : 32) - count_1s(mask[s]); - - // Use Carry-Rippler trick to enumerate all subsets of mask[s] - b = maxKey = 0; + // Given a square 's', the mask is the bitboard of sliding attacks from + // 's' computed on an empty board. The index must be big enough to contain + // all the attacks for each possible subset of the mask and so is 2 power + // the number of 1s of the mask. Hence we deduce the size of the shift to + // apply to the 64 or 32 bits word to get the index. + masks[s] = sliding_attacks(pt, s, EmptyBoardBB) & ~edges; + shifts[s] = (CpuIs64Bit ? 64 : 32) - count_1s(masks[s]); + + // Use Carry-Rippler trick to enumerate all subsets of masks[s] and + // store the corresponding sliding attacks bitboard in reference[]. + b = size = 0; do { - occupancy[maxKey] = b; - reference[maxKey++] = sliding_attacks(s, b, delta); - b = (b - mask[s]) & mask[s]; + occupancy[size] = b; + reference[size++] = sliding_attacks(pt, s, b); + b = (b - masks[s]) & masks[s]; } while (b); - offset += maxKey; - booster = MagicBoosters[CpuIs64Bit][square_rank(s)]; + // Set the offset for the table of the next square. We have individual + // table sizes for each square with "Fancy Magic Bitboards". + if (s < SQ_H8) + attacks[s + 1] = attacks[s] + size; - // Then find a possible magic and the corresponding attacks - do { - magic[s] = pick_magic(mask[s], rk, booster); - memset(attack[s], 0, maxKey * sizeof(Bitboard)); + booster = MagicBoosters[CpuIs64Bit][rank_of(s)]; - for (key = 0; key < maxKey; key++) + // Find a magic for square 's' picking up an (almost) random number + // until we find the one that passes the verification test. + do { + magics[s] = pick_random(masks[s], rk, booster); + memset(attacks[s], 0, size * sizeof(Bitboard)); + + // A good magic must map every possible occupancy to an index that + // looks up the correct sliding attack in the attacks[s] database. + // Note that we build up the database for square 's' as a side + // effect of verifying the magic. + for (i = 0; i < size; i++) { - index = CpuIs64Bit ? unsigned((occupancy[key] * magic[s]) >> shift[s]) - : unsigned(occupancy[key] * magic[s] ^ (occupancy[key] >> 32) * (magic[s] >> 32)) >> shift[s]; + index = (pt == ROOK ? rook_index(s, occupancy[i]) + : bishop_index(s, occupancy[i])); - if (!attack[s][index]) - attack[s][index] = reference[key]; + if (!attacks[s][index]) + attacks[s][index] = reference[i]; - else if (attack[s][index] != reference[key]) + else if (attacks[s][index] != reference[i]) break; } - } while (key != maxKey); + } while (i != size); } } }