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) 2015-2017 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 Magic RookMagics[SQUARE_NB];
30 Magic BishopMagics[SQUARE_NB];
32 Bitboard SquareBB[SQUARE_NB];
33 Bitboard FileBB[FILE_NB];
34 Bitboard RankBB[RANK_NB];
35 Bitboard AdjacentFilesBB[FILE_NB];
36 Bitboard InFrontBB[COLOR_NB][RANK_NB];
37 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
38 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
39 Bitboard DistanceRingBB[SQUARE_NB][8];
40 Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
41 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
42 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
43 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
44 Bitboard PawnAttacks[COLOR_NB][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 typedef unsigned (Fn)(Square, Bitboard);
59 void init_magics(Bitboard table[], Magic magics[], Square deltas[], Fn index);
61 // bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
62 // Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
64 unsigned bsf_index(Bitboard b) {
66 return Is64Bit ? (b * DeBruijn64) >> 58
67 : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn32) >> 26;
71 // popcount16() counts the non-zero bits using SWAR-Popcount algorithm
73 unsigned popcount16(unsigned u) {
74 u -= (u >> 1) & 0x5555U;
75 u = ((u >> 2) & 0x3333U) + (u & 0x3333U);
76 u = ((u >> 4) + u) & 0x0F0FU;
77 return (u * 0x0101U) >> 8;
83 /// Software fall-back of lsb() and msb() for CPU lacking hardware support
85 Square lsb(Bitboard b) {
87 return BSFTable[bsf_index(b)];
90 Square msb(Bitboard b) {
116 return Square(result + MSBTable[b32]);
119 #endif // ifdef NO_BSF
122 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
123 /// to be printed to standard output. Useful for debugging.
125 const std::string Bitboards::pretty(Bitboard b) {
127 std::string s = "+---+---+---+---+---+---+---+---+\n";
129 for (Rank r = RANK_8; r >= RANK_1; --r)
131 for (File f = FILE_A; f <= FILE_H; ++f)
132 s += b & make_square(f, r) ? "| X " : "| ";
134 s += "|\n+---+---+---+---+---+---+---+---+\n";
141 /// Bitboards::init() initializes various bitboard tables. It is called at
142 /// startup and relies on global objects to be already zero-initialized.
144 void Bitboards::init() {
146 for (unsigned i = 0; i < (1 << 16); ++i)
147 PopCnt16[i] = (uint8_t) popcount16(i);
149 for (Square s = SQ_A1; s <= SQ_H8; ++s)
151 SquareBB[s] = 1ULL << s;
152 BSFTable[bsf_index(SquareBB[s])] = s;
155 for (Bitboard b = 2; b < 256; ++b)
156 MSBTable[b] = MSBTable[b - 1] + !more_than_one(b);
158 for (File f = FILE_A; f <= FILE_H; ++f)
159 FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
161 for (Rank r = RANK_1; r <= RANK_8; ++r)
162 RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
164 for (File f = FILE_A; f <= FILE_H; ++f)
165 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
167 for (Rank r = RANK_1; r < RANK_8; ++r)
168 InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
170 for (Color c = WHITE; c <= BLACK; ++c)
171 for (Square s = SQ_A1; s <= SQ_H8; ++s)
173 ForwardBB[c][s] = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
174 PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
175 PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
178 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
179 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
182 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
183 DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
186 int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
188 for (Color c = WHITE; c <= BLACK; ++c)
189 for (PieceType pt : { PAWN, KNIGHT, KING })
190 for (Square s = SQ_A1; s <= SQ_H8; ++s)
191 for (int i = 0; steps[pt][i]; ++i)
193 Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
195 if (is_ok(to) && distance(s, to) < 3)
198 PawnAttacks[c][s] |= to;
200 PseudoAttacks[pt][s] |= to;
204 Square RookDeltas[] = { NORTH, EAST, SOUTH, WEST };
205 Square BishopDeltas[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
207 init_magics(RookTable, RookMagics, RookDeltas, magic_index<ROOK>);
208 init_magics(BishopTable, BishopMagics, BishopDeltas, magic_index<BISHOP>);
210 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
212 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
213 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
215 for (PieceType pt : { BISHOP, ROOK })
216 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
218 if (!(PseudoAttacks[pt][s1] & s2))
221 LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
222 BetweenBB[s1][s2] = attacks_bb(pt, s1, SquareBB[s2]) & attacks_bb(pt, s2, SquareBB[s1]);
230 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
234 for (int i = 0; i < 4; ++i)
235 for (Square s = sq + deltas[i];
236 is_ok(s) && distance(s, s - deltas[i]) == 1;
249 // init_magics() computes all rook and bishop attacks at startup. Magic
250 // bitboards are used to look up attacks of sliding pieces. As a reference see
251 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
252 // use the so called "fancy" approach.
254 void init_magics(Bitboard table[], Magic magics[], Square deltas[], Fn index) {
256 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
257 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
259 Bitboard occupancy[4096], reference[4096], edges, b;
260 int age[4096] = {0}, current = 0, i, size;
262 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
263 magics[SQ_A1].attacks = table;
265 for (Square s = SQ_A1; s <= SQ_H8; ++s)
267 // Board edges are not considered in the relevant occupancies
268 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
270 // Given a square 's', the mask is the bitboard of sliding attacks from
271 // 's' computed on an empty board. The index must be big enough to contain
272 // all the attacks for each possible subset of the mask and so is 2 power
273 // the number of 1s of the mask. Hence we deduce the size of the shift to
274 // apply to the 64 or 32 bits word to get the index.
275 magics[s].mask = sliding_attack(deltas, s, 0) & ~edges;
276 magics[s].shift = (Is64Bit ? 64 : 32) - popcount(magics[s].mask);
278 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
279 // store the corresponding sliding attack bitboard in reference[].
283 reference[size] = sliding_attack(deltas, s, b);
286 magics[s].attacks[pext(b, magics[s].mask)] = reference[size];
289 b = (b - magics[s].mask) & magics[s].mask;
292 // Set the offset for the table of the next square. We have individual
293 // table sizes for each square with "Fancy Magic Bitboards".
295 magics[s + 1].attacks = magics[s].attacks + size;
300 PRNG rng(seeds[Is64Bit][rank_of(s)]);
302 // Find a magic for square 's' picking up an (almost) random number
303 // until we find the one that passes the verification test.
306 magics[s].magic = rng.sparse_rand<Bitboard>();
307 while (popcount((magics[s].magic * magics[s].mask) >> 56) < 6);
309 // A good magic must map every possible occupancy to an index that
310 // looks up the correct sliding attack in the attacks[s] database.
311 // Note that we build up the database for square 's' as a side
312 // effect of verifying the magic.
313 for (++current, i = 0; i < size; ++i)
315 unsigned idx = index(s, occupancy[i]);
317 if (age[idx] < current)
320 magics[s].attacks[idx] = reference[i];
322 else if (magics[s].attacks[idx] != reference[i])