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 // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
49 const uint64_t DeBruijn64 = 0x3F79D71B4CB0A89ULL;
50 const uint32_t DeBruijn32 = 0x783A9B23;
52 int MSBTable[256]; // To implement software msb()
53 Square BSFTable[SQUARE_NB]; // To implement software bitscan
54 Bitboard RookTable[0x19000]; // To store rook attacks
55 Bitboard BishopTable[0x1480]; // To store bishop attacks
57 void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
59 // bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
60 // Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
62 unsigned bsf_index(Bitboard b) {
64 return Is64Bit ? (b * DeBruijn64) >> 58
65 : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn32) >> 26;
69 // popcount16() counts the non-zero bits using SWAR-Popcount algorithm
71 unsigned popcount16(unsigned u) {
72 u -= (u >> 1) & 0x5555U;
73 u = ((u >> 2) & 0x3333U) + (u & 0x3333U);
74 u = ((u >> 4) + u) & 0x0F0FU;
75 return (u * 0x0101U) >> 8;
81 /// Software fall-back of lsb() and msb() for CPU lacking hardware support
83 Square lsb(Bitboard b) {
85 return BSFTable[bsf_index(b)];
88 Square msb(Bitboard b) {
114 return Square(result + MSBTable[b32]);
117 #endif // ifdef NO_BSF
120 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
121 /// to be printed to standard output. Useful for debugging.
123 const std::string Bitboards::pretty(Bitboard b) {
125 std::string s = "+---+---+---+---+---+---+---+---+\n";
127 for (Rank r = RANK_8; r >= RANK_1; --r)
129 for (File f = FILE_A; f <= FILE_H; ++f)
130 s += b & make_square(f, r) ? "| X " : "| ";
132 s += "|\n+---+---+---+---+---+---+---+---+\n";
139 /// Bitboards::init() initializes various bitboard tables. It is called at
140 /// startup and relies on global objects to be already zero-initialized.
142 void Bitboards::init() {
144 for (unsigned i = 0; i < (1 << 16); ++i)
145 PopCnt16[i] = (uint8_t) popcount16(i);
147 for (Square s = SQ_A1; s <= SQ_H8; ++s)
149 SquareBB[s] = 1ULL << s;
150 BSFTable[bsf_index(SquareBB[s])] = s;
153 for (Bitboard b = 2; b < 256; ++b)
154 MSBTable[b] = MSBTable[b - 1] + !more_than_one(b);
156 for (File f = FILE_A; f <= FILE_H; ++f)
157 FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
159 for (Rank r = RANK_1; r <= RANK_8; ++r)
160 RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
162 for (File f = FILE_A; f <= FILE_H; ++f)
163 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
165 for (Rank r = RANK_1; r < RANK_8; ++r)
166 ForwardRanksBB[WHITE][r] = ~(ForwardRanksBB[BLACK][r + 1] = ForwardRanksBB[BLACK][r] | RankBB[r]);
168 for (Color c = WHITE; c <= BLACK; ++c)
169 for (Square s = SQ_A1; s <= SQ_H8; ++s)
171 ForwardFileBB [c][s] = ForwardRanksBB[c][rank_of(s)] & FileBB[file_of(s)];
172 PawnAttackSpan[c][s] = ForwardRanksBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
173 PassedPawnMask[c][s] = ForwardFileBB [c][s] | PawnAttackSpan[c][s];
176 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
177 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
180 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
181 DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
184 int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
186 for (Color c = WHITE; c <= BLACK; ++c)
187 for (PieceType pt : { PAWN, KNIGHT, KING })
188 for (Square s = SQ_A1; s <= SQ_H8; ++s)
189 for (int i = 0; steps[pt][i]; ++i)
191 Square to = s + Direction(c == WHITE ? steps[pt][i] : -steps[pt][i]);
193 if (is_ok(to) && distance(s, to) < 3)
196 PawnAttacks[c][s] |= to;
198 PseudoAttacks[pt][s] |= to;
202 Direction RookDirections[] = { NORTH, EAST, SOUTH, WEST };
203 Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
205 init_magics(RookTable, RookMagics, RookDirections);
206 init_magics(BishopTable, BishopMagics, BishopDirections);
208 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
210 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
211 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
213 for (PieceType pt : { BISHOP, ROOK })
214 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
216 if (!(PseudoAttacks[pt][s1] & s2))
219 LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
220 BetweenBB[s1][s2] = attacks_bb(pt, s1, SquareBB[s2]) & attacks_bb(pt, s2, SquareBB[s1]);
228 Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
232 for (int i = 0; i < 4; ++i)
233 for (Square s = sq + directions[i];
234 is_ok(s) && distance(s, s - directions[i]) == 1;
247 // init_magics() computes all rook and bishop attacks at startup. Magic
248 // bitboards are used to look up attacks of sliding pieces. As a reference see
249 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
250 // use the so called "fancy" approach.
252 void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
254 // Optimal PRNG seeds to pick the correct magics in the shortest time
255 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
256 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
258 Bitboard occupancy[4096], reference[4096], edges, b;
259 int epoch[4096] = {}, cnt = 0, size = 0;
261 for (Square s = SQ_A1; s <= SQ_H8; ++s)
263 // Board edges are not considered in the relevant occupancies
264 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
266 // Given a square 's', the mask is the bitboard of sliding attacks from
267 // 's' computed on an empty board. The index must be big enough to contain
268 // all the attacks for each possible subset of the mask and so is 2 power
269 // the number of 1s of the mask. Hence we deduce the size of the shift to
270 // apply to the 64 or 32 bits word to get the index.
271 Magic& m = magics[s];
272 m.mask = sliding_attack(directions, s, 0) & ~edges;
273 m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
275 // Set the offset for the attacks table of the square. We have individual
276 // table sizes for each square with "Fancy Magic Bitboards".
277 m.attacks = s == SQ_A1 ? table : magics[s - 1].attacks + size;
279 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
280 // store the corresponding sliding attack bitboard in reference[].
284 reference[size] = sliding_attack(directions, s, b);
287 m.attacks[pext(b, m.mask)] = reference[size];
290 b = (b - m.mask) & m.mask;
296 PRNG rng(seeds[Is64Bit][rank_of(s)]);
298 // Find a magic for square 's' picking up an (almost) random number
299 // until we find the one that passes the verification test.
300 for (int i = 0; i < size; )
302 for (m.magic = 0; popcount((m.magic * m.mask) >> 56) < 6; )
303 m.magic = rng.sparse_rand<Bitboard>();
305 // A good magic must map every possible occupancy to an index that
306 // looks up the correct sliding attack in the attacks[s] database.
307 // Note that we build up the database for square 's' as a side
308 // effect of verifying the magic. Keep track of the attempt count
309 // and save it in epoch[], little speed-up trick to avoid resetting
310 // m.attacks[] after every failed attempt.
311 for (++cnt, i = 0; i < size; ++i)
313 unsigned idx = m.index(occupancy[i]);
315 if (epoch[idx] < cnt)
318 m.attacks[idx] = reference[i];
320 else if (m.attacks[idx] != reference[i])