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) 2015-2019 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/>.
27 uint8_t PopCnt16[1 << 16];
28 uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
30 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
31 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
32 Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
33 Bitboard SquareBB[SQUARE_NB];
35 Bitboard KingFlank[FILE_NB] = {
36 QueenSide ^ FileDBB, QueenSide, QueenSide,
37 CenterFiles, CenterFiles,
38 KingSide, KingSide, KingSide ^ FileEBB
41 Magic RookMagics[SQUARE_NB];
42 Magic BishopMagics[SQUARE_NB];
46 Bitboard RookTable[0x19000]; // To store rook attacks
47 Bitboard BishopTable[0x1480]; // To store bishop attacks
49 void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
53 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
54 /// to be printed to standard output. Useful for debugging.
56 const std::string Bitboards::pretty(Bitboard b) {
58 std::string s = "+---+---+---+---+---+---+---+---+\n";
60 for (Rank r = RANK_8; r >= RANK_1; --r)
62 for (File f = FILE_A; f <= FILE_H; ++f)
63 s += b & make_square(f, r) ? "| X " : "| ";
65 s += "|\n+---+---+---+---+---+---+---+---+\n";
72 /// Bitboards::init() initializes various bitboard tables. It is called at
73 /// startup and relies on global objects to be already zero-initialized.
75 void Bitboards::init() {
77 for (unsigned i = 0; i < (1 << 16); ++i)
78 PopCnt16[i] = std::bitset<16>(i).count();
80 for (Square s = SQ_A1; s <= SQ_H8; ++s)
81 SquareBB[s] = (1ULL << s);
83 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
84 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
85 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
87 int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
89 for (Color c = WHITE; c <= BLACK; ++c)
90 for (PieceType pt : { PAWN, KNIGHT, KING })
91 for (Square s = SQ_A1; s <= SQ_H8; ++s)
92 for (int i = 0; steps[pt][i]; ++i)
94 Square to = s + Direction(c == WHITE ? steps[pt][i] : -steps[pt][i]);
96 if (is_ok(to) && distance(s, to) < 3)
99 PawnAttacks[c][s] |= to;
101 PseudoAttacks[pt][s] |= to;
105 Direction RookDirections[] = { NORTH, EAST, SOUTH, WEST };
106 Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
108 init_magics(RookTable, RookMagics, RookDirections);
109 init_magics(BishopTable, BishopMagics, BishopDirections);
111 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
113 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
114 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
116 for (PieceType pt : { BISHOP, ROOK })
117 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
118 if (PseudoAttacks[pt][s1] & s2)
119 LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
126 Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
130 for (int i = 0; i < 4; ++i)
131 for (Square s = sq + directions[i];
132 is_ok(s) && distance(s, s - directions[i]) == 1;
145 // init_magics() computes all rook and bishop attacks at startup. Magic
146 // bitboards are used to look up attacks of sliding pieces. As a reference see
147 // www.chessprogramming.org/Magic_Bitboards. In particular, here we use the so
148 // called "fancy" approach.
150 void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
152 // Optimal PRNG seeds to pick the correct magics in the shortest time
153 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
154 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
156 Bitboard occupancy[4096], reference[4096], edges, b;
157 int epoch[4096] = {}, cnt = 0, size = 0;
159 for (Square s = SQ_A1; s <= SQ_H8; ++s)
161 // Board edges are not considered in the relevant occupancies
162 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
164 // Given a square 's', the mask is the bitboard of sliding attacks from
165 // 's' computed on an empty board. The index must be big enough to contain
166 // all the attacks for each possible subset of the mask and so is 2 power
167 // the number of 1s of the mask. Hence we deduce the size of the shift to
168 // apply to the 64 or 32 bits word to get the index.
169 Magic& m = magics[s];
170 m.mask = sliding_attack(directions, s, 0) & ~edges;
171 m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
173 // Set the offset for the attacks table of the square. We have individual
174 // table sizes for each square with "Fancy Magic Bitboards".
175 m.attacks = s == SQ_A1 ? table : magics[s - 1].attacks + size;
177 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
178 // store the corresponding sliding attack bitboard in reference[].
182 reference[size] = sliding_attack(directions, s, b);
185 m.attacks[pext(b, m.mask)] = reference[size];
188 b = (b - m.mask) & m.mask;
194 PRNG rng(seeds[Is64Bit][rank_of(s)]);
196 // Find a magic for square 's' picking up an (almost) random number
197 // until we find the one that passes the verification test.
198 for (int i = 0; i < size; )
200 for (m.magic = 0; popcount((m.magic * m.mask) >> 56) < 6; )
201 m.magic = rng.sparse_rand<Bitboard>();
203 // A good magic must map every possible occupancy to an index that
204 // looks up the correct sliding attack in the attacks[s] database.
205 // Note that we build up the database for square 's' as a side
206 // effect of verifying the magic. Keep track of the attempt count
207 // and save it in epoch[], little speed-up trick to avoid resetting
208 // m.attacks[] after every failed attempt.
209 for (++cnt, i = 0; i < size; ++i)
211 unsigned idx = m.index(occupancy[i]);
213 if (epoch[idx] < cnt)
216 m.attacks[idx] = reference[i];
218 else if (m.attacks[idx] != reference[i])