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) 2015-2016 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 RookMasks [SQUARE_NB];
30 Bitboard RookMagics [SQUARE_NB];
31 Bitboard* RookAttacks[SQUARE_NB];
32 unsigned RookShifts [SQUARE_NB];
34 Bitboard BishopMasks [SQUARE_NB];
35 Bitboard BishopMagics [SQUARE_NB];
36 Bitboard* BishopAttacks[SQUARE_NB];
37 unsigned BishopShifts [SQUARE_NB];
39 Bitboard SquareBB[SQUARE_NB];
40 Bitboard FileBB[FILE_NB];
41 Bitboard RankBB[RANK_NB];
42 Bitboard AdjacentFilesBB[FILE_NB];
43 Bitboard InFrontBB[COLOR_NB][RANK_NB];
44 Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
45 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
46 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
47 Bitboard DistanceRingBB[SQUARE_NB][8];
48 Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
49 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
50 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
51 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
55 // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
56 const uint64_t DeBruijn64 = 0x3F79D71B4CB0A89ULL;
57 const uint32_t DeBruijn32 = 0x783A9B23;
59 int MSBTable[256]; // To implement software msb()
60 Square BSFTable[SQUARE_NB]; // To implement software bitscan
61 Bitboard RookTable[0x19000]; // To store rook attacks
62 Bitboard BishopTable[0x1480]; // To store bishop attacks
64 typedef unsigned (Fn)(Square, Bitboard);
66 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
67 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
69 // bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
70 // Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
72 unsigned bsf_index(Bitboard b) {
74 return Is64Bit ? (b * DeBruijn64) >> 58
75 : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn32) >> 26;
79 // popcount16() counts the non-zero bits using SWAR-Popcount algorithm
81 unsigned popcount16(unsigned u) {
82 u -= (u >> 1) & 0x5555U;
83 u = ((u >> 2) & 0x3333U) + (u & 0x3333U);
84 u = ((u >> 4) + u) & 0x0F0FU;
85 return (u * 0x0101U) >> 8;
91 /// Software fall-back of lsb() and msb() for CPU lacking hardware support
93 Square lsb(Bitboard b) {
95 return BSFTable[bsf_index(b)];
98 Square msb(Bitboard b) {
124 return Square(result + MSBTable[b32]);
127 #endif // ifdef NO_BSF
130 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
131 /// to be printed to standard output. Useful for debugging.
133 const std::string Bitboards::pretty(Bitboard b) {
135 std::string s = "+---+---+---+---+---+---+---+---+\n";
137 for (Rank r = RANK_8; r >= RANK_1; --r)
139 for (File f = FILE_A; f <= FILE_H; ++f)
140 s += b & make_square(f, r) ? "| X " : "| ";
142 s += "|\n+---+---+---+---+---+---+---+---+\n";
149 /// Bitboards::init() initializes various bitboard tables. It is called at
150 /// startup and relies on global objects to be already zero-initialized.
152 void Bitboards::init() {
154 for (unsigned i = 0; i < (1 << 16); ++i)
155 PopCnt16[i] = (uint8_t) popcount16(i);
157 for (Square s = SQ_A1; s <= SQ_H8; ++s)
159 SquareBB[s] = 1ULL << s;
160 BSFTable[bsf_index(SquareBB[s])] = s;
163 for (Bitboard b = 2; b < 256; ++b)
164 MSBTable[b] = MSBTable[b - 1] + !more_than_one(b);
166 for (File f = FILE_A; f <= FILE_H; ++f)
167 FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
169 for (Rank r = RANK_1; r <= RANK_8; ++r)
170 RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
172 for (File f = FILE_A; f <= FILE_H; ++f)
173 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
175 for (Rank r = RANK_1; r < RANK_8; ++r)
176 InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
178 for (Color c = WHITE; c <= BLACK; ++c)
179 for (Square s = SQ_A1; s <= SQ_H8; ++s)
181 ForwardBB[c][s] = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
182 PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
183 PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
186 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
187 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
190 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
191 DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
194 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
195 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
197 for (Color c = WHITE; c <= BLACK; ++c)
198 for (PieceType pt = PAWN; pt <= KING; ++pt)
199 for (Square s = SQ_A1; s <= SQ_H8; ++s)
200 for (int i = 0; steps[pt][i]; ++i)
202 Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
204 if (is_ok(to) && distance(s, to) < 3)
205 StepAttacksBB[make_piece(c, pt)][s] |= to;
208 Square RookDeltas[] = { NORTH, EAST, SOUTH, WEST };
209 Square BishopDeltas[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
211 init_magics(RookTable, RookAttacks, RookMagics, RookMasks, RookShifts, RookDeltas, magic_index<ROOK>);
212 init_magics(BishopTable, BishopAttacks, BishopMagics, BishopMasks, BishopShifts, BishopDeltas, magic_index<BISHOP>);
214 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
216 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
217 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
219 for (Piece pc = W_BISHOP; pc <= W_ROOK; ++pc)
220 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
222 if (!(PseudoAttacks[pc][s1] & s2))
225 LineBB[s1][s2] = (attacks_bb(pc, s1, 0) & attacks_bb(pc, s2, 0)) | s1 | s2;
226 BetweenBB[s1][s2] = attacks_bb(pc, s1, SquareBB[s2]) & attacks_bb(pc, s2, SquareBB[s1]);
234 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
238 for (int i = 0; i < 4; ++i)
239 for (Square s = sq + deltas[i];
240 is_ok(s) && distance(s, s - deltas[i]) == 1;
253 // init_magics() computes all rook and bishop attacks at startup. Magic
254 // bitboards are used to look up attacks of sliding pieces. As a reference see
255 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
256 // use the so called "fancy" approach.
258 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
259 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
261 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
262 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
264 Bitboard occupancy[4096], reference[4096], edges, b;
265 int age[4096] = {0}, current = 0, i, size;
267 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
268 attacks[SQ_A1] = table;
270 for (Square s = SQ_A1; s <= SQ_H8; ++s)
272 // Board edges are not considered in the relevant occupancies
273 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
275 // Given a square 's', the mask is the bitboard of sliding attacks from
276 // 's' computed on an empty board. The index must be big enough to contain
277 // all the attacks for each possible subset of the mask and so is 2 power
278 // the number of 1s of the mask. Hence we deduce the size of the shift to
279 // apply to the 64 or 32 bits word to get the index.
280 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
281 shifts[s] = (Is64Bit ? 64 : 32) - popcount(masks[s]);
283 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
284 // store the corresponding sliding attack bitboard in reference[].
288 reference[size] = sliding_attack(deltas, s, b);
291 attacks[s][pext(b, masks[s])] = reference[size];
294 b = (b - masks[s]) & masks[s];
297 // Set the offset for the table of the next square. We have individual
298 // table sizes for each square with "Fancy Magic Bitboards".
300 attacks[s + 1] = attacks[s] + size;
305 PRNG rng(seeds[Is64Bit][rank_of(s)]);
307 // Find a magic for square 's' picking up an (almost) random number
308 // until we find the one that passes the verification test.
311 magics[s] = rng.sparse_rand<Bitboard>();
312 while (popcount((magics[s] * masks[s]) >> 56) < 6);
314 // A good magic must map every possible occupancy to an index that
315 // looks up the correct sliding attack in the attacks[s] database.
316 // Note that we build up the database for square 's' as a side
317 // effect of verifying the magic.
318 for (++current, i = 0; i < size; ++i)
320 unsigned idx = index(s, occupancy[i]);
322 if (age[idx] < current)
325 attacks[s][idx] = reference[i];
327 else if (attacks[s][idx] != reference[i])