2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 uint8_t PopCnt16[1 << 16];
27 int SquareDistance[SQUARE_NB][SQUARE_NB];
29 Bitboard SquareBB[SQUARE_NB];
30 Bitboard FileBB[FILE_NB];
31 Bitboard RankBB[RANK_NB];
32 Bitboard AdjacentFilesBB[FILE_NB];
33 Bitboard ForwardRanksBB[COLOR_NB][RANK_NB];
34 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
35 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
36 Bitboard DistanceRingBB[SQUARE_NB][8];
37 Bitboard ForwardFileBB[COLOR_NB][SQUARE_NB];
38 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
39 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
40 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
41 Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
43 Magic RookMagics[SQUARE_NB];
44 Magic BishopMagics[SQUARE_NB];
48 Bitboard RookTable[0x19000]; // To store rook attacks
49 Bitboard BishopTable[0x1480]; // To store bishop attacks
51 void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
53 // popcount16() counts the non-zero bits using SWAR-Popcount algorithm
55 unsigned popcount16(unsigned u) {
56 u -= (u >> 1) & 0x5555U;
57 u = ((u >> 2) & 0x3333U) + (u & 0x3333U);
58 u = ((u >> 4) + u) & 0x0F0FU;
59 return (u * 0x0101U) >> 8;
64 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
65 /// to be printed to standard output. Useful for debugging.
67 const std::string Bitboards::pretty(Bitboard b) {
69 std::string s = "+---+---+---+---+---+---+---+---+\n";
71 for (Rank r = RANK_8; r >= RANK_1; --r)
73 for (File f = FILE_A; f <= FILE_H; ++f)
74 s += b & make_square(f, r) ? "| X " : "| ";
76 s += "|\n+---+---+---+---+---+---+---+---+\n";
83 /// Bitboards::init() initializes various bitboard tables. It is called at
84 /// startup and relies on global objects to be already zero-initialized.
86 void Bitboards::init() {
88 for (unsigned i = 0; i < (1 << 16); ++i)
89 PopCnt16[i] = (uint8_t) popcount16(i);
91 for (Square s = SQ_A1; s <= SQ_H8; ++s)
92 SquareBB[s] = (1ULL << s);
94 for (File f = FILE_A; f <= FILE_H; ++f)
95 FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
97 for (Rank r = RANK_1; r <= RANK_8; ++r)
98 RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
100 for (File f = FILE_A; f <= FILE_H; ++f)
101 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
103 for (Rank r = RANK_1; r < RANK_8; ++r)
104 ForwardRanksBB[WHITE][r] = ~(ForwardRanksBB[BLACK][r + 1] = ForwardRanksBB[BLACK][r] | RankBB[r]);
106 for (Color c = WHITE; c <= BLACK; ++c)
107 for (Square s = SQ_A1; s <= SQ_H8; ++s)
109 ForwardFileBB [c][s] = ForwardRanksBB[c][rank_of(s)] & FileBB[file_of(s)];
110 PawnAttackSpan[c][s] = ForwardRanksBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
111 PassedPawnMask[c][s] = ForwardFileBB [c][s] | PawnAttackSpan[c][s];
114 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
115 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
118 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
119 DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
122 int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
124 for (Color c = WHITE; c <= BLACK; ++c)
125 for (PieceType pt : { PAWN, KNIGHT, KING })
126 for (Square s = SQ_A1; s <= SQ_H8; ++s)
127 for (int i = 0; steps[pt][i]; ++i)
129 Square to = s + Direction(c == WHITE ? steps[pt][i] : -steps[pt][i]);
131 if (is_ok(to) && distance(s, to) < 3)
134 PawnAttacks[c][s] |= to;
136 PseudoAttacks[pt][s] |= to;
140 Direction RookDirections[] = { NORTH, EAST, SOUTH, WEST };
141 Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
143 init_magics(RookTable, RookMagics, RookDirections);
144 init_magics(BishopTable, BishopMagics, BishopDirections);
146 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
148 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
149 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
151 for (PieceType pt : { BISHOP, ROOK })
152 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
154 if (!(PseudoAttacks[pt][s1] & s2))
157 LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
158 BetweenBB[s1][s2] = attacks_bb(pt, s1, SquareBB[s2]) & attacks_bb(pt, s2, SquareBB[s1]);
166 Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
170 for (int i = 0; i < 4; ++i)
171 for (Square s = sq + directions[i];
172 is_ok(s) && distance(s, s - directions[i]) == 1;
185 // init_magics() computes all rook and bishop attacks at startup. Magic
186 // bitboards are used to look up attacks of sliding pieces. As a reference see
187 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
188 // use the so called "fancy" approach.
190 void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
192 // Optimal PRNG seeds to pick the correct magics in the shortest time
193 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
194 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
196 Bitboard occupancy[4096], reference[4096], edges, b;
197 int epoch[4096] = {}, cnt = 0, size = 0;
199 for (Square s = SQ_A1; s <= SQ_H8; ++s)
201 // Board edges are not considered in the relevant occupancies
202 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
204 // Given a square 's', the mask is the bitboard of sliding attacks from
205 // 's' computed on an empty board. The index must be big enough to contain
206 // all the attacks for each possible subset of the mask and so is 2 power
207 // the number of 1s of the mask. Hence we deduce the size of the shift to
208 // apply to the 64 or 32 bits word to get the index.
209 Magic& m = magics[s];
210 m.mask = sliding_attack(directions, s, 0) & ~edges;
211 m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
213 // Set the offset for the attacks table of the square. We have individual
214 // table sizes for each square with "Fancy Magic Bitboards".
215 m.attacks = s == SQ_A1 ? table : magics[s - 1].attacks + size;
217 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
218 // store the corresponding sliding attack bitboard in reference[].
222 reference[size] = sliding_attack(directions, s, b);
225 m.attacks[pext(b, m.mask)] = reference[size];
228 b = (b - m.mask) & m.mask;
234 PRNG rng(seeds[Is64Bit][rank_of(s)]);
236 // Find a magic for square 's' picking up an (almost) random number
237 // until we find the one that passes the verification test.
238 for (int i = 0; i < size; )
240 for (m.magic = 0; popcount((m.magic * m.mask) >> 56) < 6; )
241 m.magic = rng.sparse_rand<Bitboard>();
243 // A good magic must map every possible occupancy to an index that
244 // looks up the correct sliding attack in the attacks[s] database.
245 // Note that we build up the database for square 's' as a side
246 // effect of verifying the magic. Keep track of the attempt count
247 // and save it in epoch[], little speed-up trick to avoid resetting
248 // m.attacks[] after every failed attempt.
249 for (++cnt, i = 0; i < size; ++i)
251 unsigned idx = m.index(occupancy[i]);
253 if (epoch[idx] < cnt)
256 m.attacks[idx] = reference[i];
258 else if (m.attacks[idx] != reference[i])