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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 int SquareDistance[SQUARE_NB][SQUARE_NB];
28 Bitboard RookMasks [SQUARE_NB];
29 Bitboard RookMagics [SQUARE_NB];
30 Bitboard* RookAttacks[SQUARE_NB];
31 unsigned RookShifts [SQUARE_NB];
33 Bitboard BishopMasks [SQUARE_NB];
34 Bitboard BishopMagics [SQUARE_NB];
35 Bitboard* BishopAttacks[SQUARE_NB];
36 unsigned BishopShifts [SQUARE_NB];
38 Bitboard SquareBB[SQUARE_NB];
39 Bitboard FileBB[FILE_NB];
40 Bitboard RankBB[RANK_NB];
41 Bitboard AdjacentFilesBB[FILE_NB];
42 Bitboard InFrontBB[COLOR_NB][RANK_NB];
43 Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
44 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
45 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
46 Bitboard DistanceRingBB[SQUARE_NB][8];
47 Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
48 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
49 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
50 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
54 // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
55 const uint64_t DeBruijn64 = 0x3F79D71B4CB0A89ULL;
56 const uint32_t DeBruijn32 = 0x783A9B23;
58 int MSBTable[256]; // To implement software msb()
59 Square BSFTable[SQUARE_NB]; // To implement software bitscan
60 Bitboard RookTable[0x19000]; // To store rook attacks
61 Bitboard BishopTable[0x1480]; // To store bishop attacks
63 typedef unsigned (Fn)(Square, Bitboard);
65 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
66 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
68 // bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
69 // Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
71 unsigned bsf_index(Bitboard b) {
73 return Is64Bit ? (b * DeBruijn64) >> 58
74 : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn32) >> 26;
80 /// Software fall-back of lsb() and msb() for CPU lacking hardware support
82 Square lsb(Bitboard b) {
83 return BSFTable[bsf_index(b)];
86 Square msb(Bitboard b) {
111 return Square(result + MSBTable[b32]);
114 #endif // ifndef USE_BSFQ
117 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
118 /// to be printed to standard output. Useful for debugging.
120 const std::string Bitboards::pretty(Bitboard b) {
122 std::string s = "+---+---+---+---+---+---+---+---+\n";
124 for (Rank r = RANK_8; r >= RANK_1; --r)
126 for (File f = FILE_A; f <= FILE_H; ++f)
127 s += b & make_square(f, r) ? "| X " : "| ";
129 s += "|\n+---+---+---+---+---+---+---+---+\n";
136 /// Bitboards::init() initializes various bitboard tables. It is called at
137 /// startup and relies on global objects to be already zero-initialized.
139 void Bitboards::init() {
141 for (Square s = SQ_A1; s <= SQ_H8; ++s)
143 SquareBB[s] = 1ULL << s;
144 BSFTable[bsf_index(SquareBB[s])] = s;
147 for (Bitboard b = 2; b < 256; ++b)
148 MSBTable[b] = MSBTable[b - 1] + !more_than_one(b);
150 for (File f = FILE_A; f <= FILE_H; ++f)
151 FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
153 for (Rank r = RANK_1; r <= RANK_8; ++r)
154 RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
156 for (File f = FILE_A; f <= FILE_H; ++f)
157 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
159 for (Rank r = RANK_1; r < RANK_8; ++r)
160 InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
162 for (Color c = WHITE; c <= BLACK; ++c)
163 for (Square s = SQ_A1; s <= SQ_H8; ++s)
165 ForwardBB[c][s] = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
166 PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
167 PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
170 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
171 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
174 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
175 DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
178 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
179 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
181 for (Color c = WHITE; c <= BLACK; ++c)
182 for (PieceType pt = PAWN; pt <= KING; ++pt)
183 for (Square s = SQ_A1; s <= SQ_H8; ++s)
184 for (int i = 0; steps[pt][i]; ++i)
186 Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
188 if (is_ok(to) && distance(s, to) < 3)
189 StepAttacksBB[make_piece(c, pt)][s] |= to;
192 Square RookDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
193 Square BishopDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
195 init_magics(RookTable, RookAttacks, RookMagics, RookMasks, RookShifts, RookDeltas, magic_index<ROOK>);
196 init_magics(BishopTable, BishopAttacks, BishopMagics, BishopMasks, BishopShifts, BishopDeltas, magic_index<BISHOP>);
198 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
200 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
201 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
203 for (Piece pc = W_BISHOP; pc <= W_ROOK; ++pc)
204 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
206 if (!(PseudoAttacks[pc][s1] & s2))
209 LineBB[s1][s2] = (attacks_bb(pc, s1, 0) & attacks_bb(pc, s2, 0)) | s1 | s2;
210 BetweenBB[s1][s2] = attacks_bb(pc, s1, SquareBB[s2]) & attacks_bb(pc, s2, SquareBB[s1]);
218 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
222 for (int i = 0; i < 4; ++i)
223 for (Square s = sq + deltas[i];
224 is_ok(s) && distance(s, s - deltas[i]) == 1;
237 // init_magics() computes all rook and bishop attacks at startup. Magic
238 // bitboards are used to look up attacks of sliding pieces. As a reference see
239 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
240 // use the so called "fancy" approach.
242 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
243 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
245 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
246 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
248 Bitboard occupancy[4096], reference[4096], edges, b;
249 int age[4096] = {0}, current = 0, i, size;
251 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
252 attacks[SQ_A1] = table;
254 for (Square s = SQ_A1; s <= SQ_H8; ++s)
256 // Board edges are not considered in the relevant occupancies
257 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
259 // Given a square 's', the mask is the bitboard of sliding attacks from
260 // 's' computed on an empty board. The index must be big enough to contain
261 // all the attacks for each possible subset of the mask and so is 2 power
262 // the number of 1s of the mask. Hence we deduce the size of the shift to
263 // apply to the 64 or 32 bits word to get the index.
264 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
265 shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
267 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
268 // store the corresponding sliding attack bitboard in reference[].
272 reference[size] = sliding_attack(deltas, s, b);
275 attacks[s][pext(b, masks[s])] = reference[size];
278 b = (b - masks[s]) & masks[s];
281 // Set the offset for the table of the next square. We have individual
282 // table sizes for each square with "Fancy Magic Bitboards".
284 attacks[s + 1] = attacks[s] + size;
289 PRNG rng(seeds[Is64Bit][rank_of(s)]);
291 // Find a magic for square 's' picking up an (almost) random number
292 // until we find the one that passes the verification test.
295 magics[s] = rng.sparse_rand<Bitboard>();
296 while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
298 // A good magic must map every possible occupancy to an index that
299 // looks up the correct sliding attack in the attacks[s] database.
300 // Note that we build up the database for square 's' as a side
301 // effect of verifying the magic.
302 for (++current, i = 0; i < size; ++i)
304 unsigned idx = index(s, occupancy[i]);
306 if (age[idx] < current)
309 attacks[s][idx] = reference[i];
311 else if (attacks[s][idx] != reference[i])