2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 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/>.
30 Bitboard RMasks[SQUARE_NB];
31 Bitboard RMagics[SQUARE_NB];
32 Bitboard* RAttacks[SQUARE_NB];
33 unsigned RShifts[SQUARE_NB];
35 Bitboard BMasks[SQUARE_NB];
36 Bitboard BMagics[SQUARE_NB];
37 Bitboard* BAttacks[SQUARE_NB];
38 unsigned BShifts[SQUARE_NB];
40 Bitboard SquareBB[SQUARE_NB];
41 Bitboard FileBB[FILE_NB];
42 Bitboard RankBB[RANK_NB];
43 Bitboard AdjacentFilesBB[FILE_NB];
44 Bitboard InFrontBB[COLOR_NB][RANK_NB];
45 Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
46 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
47 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
48 Bitboard DistanceRingsBB[SQUARE_NB][8];
49 Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
50 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
51 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
52 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
54 int SquareDistance[SQUARE_NB][SQUARE_NB];
58 // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
59 const uint64_t DeBruijn_64 = 0x3F79D71B4CB0A89ULL;
60 const uint32_t DeBruijn_32 = 0x783A9B23;
65 Square BSFTable[SQUARE_NB];
66 Bitboard RTable[0x19000]; // Storage space for rook attacks
67 Bitboard BTable[0x1480]; // Storage space for bishop attacks
69 typedef unsigned (Fn)(Square, Bitboard);
71 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
72 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
74 FORCE_INLINE unsigned bsf_index(Bitboard b) {
76 // Matt Taylor's folding for 32 bit systems, extended to 64 bits by Kim Walisch
78 return Is64Bit ? (b * DeBruijn_64) >> 58
79 : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
83 /// lsb()/msb() finds the least/most significant bit in a non-zero bitboard.
84 /// pop_lsb() finds and clears the least significant bit in a non-zero bitboard.
88 Square lsb(Bitboard b) { return BSFTable[bsf_index(b)]; }
90 Square pop_lsb(Bitboard* b) {
94 return BSFTable[bsf_index(bb)];
97 Square msb(Bitboard b) {
122 return Square(result + MS1BTable[b32]);
125 #endif // ifndef USE_BSFQ
128 /// Bitboards::pretty() returns an ASCII representation of a bitboard to be
129 /// printed to standard output. This is sometimes useful for debugging.
131 const std::string Bitboards::pretty(Bitboard b) {
133 std::ostringstream ss;
135 for (Rank rank = RANK_8; rank >= RANK_1; --rank)
137 ss << "+---+---+---+---+---+---+---+---+" << '\n';
139 for (File file = FILE_A; file <= FILE_H; ++file)
140 ss << "| " << (b & (file | rank) ? "X " : " ");
144 ss << "+---+---+---+---+---+---+---+---+";
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 (Square s = SQ_A1; s <= SQ_H8; ++s)
155 BSFTable[bsf_index(SquareBB[s] = 1ULL << s)] = s;
157 for (Bitboard b = 1; b < 256; ++b)
158 MS1BTable[b] = more_than_one(b) ? MS1BTable[b - 1] : lsb(b);
160 for (File f = FILE_A; f <= FILE_H; ++f)
161 FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
163 for (Rank r = RANK_1; r <= RANK_8; ++r)
164 RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
166 for (File f = FILE_A; f <= FILE_H; ++f)
167 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
169 for (Rank r = RANK_1; r < RANK_8; ++r)
170 InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
172 for (Color c = WHITE; c <= BLACK; ++c)
173 for (Square s = SQ_A1; s <= SQ_H8; ++s)
175 ForwardBB[c][s] = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
176 PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
177 PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
180 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
181 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
184 SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
185 DistanceRingsBB[s1][SquareDistance[s1][s2] - 1] |= s2;
188 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
189 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
191 for (Color c = WHITE; c <= BLACK; ++c)
192 for (PieceType pt = PAWN; pt <= KING; ++pt)
193 for (Square s = SQ_A1; s <= SQ_H8; ++s)
194 for (int i = 0; steps[pt][i]; ++i)
196 Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
198 if (is_ok(to) && square_distance(s, to) < 3)
199 StepAttacksBB[make_piece(c, pt)][s] |= to;
202 Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
203 Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
205 init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
206 init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
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 (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
215 Piece pc = (PseudoAttacks[BISHOP][s1] & s2) ? W_BISHOP :
216 (PseudoAttacks[ROOK][s1] & s2) ? W_ROOK : NO_PIECE;
221 LineBB[s1][s2] = (attacks_bb(pc, s1, 0) & attacks_bb(pc, s2, 0)) | s1 | s2;
222 BetweenBB[s1][s2] = attacks_bb(pc, s1, SquareBB[s2]) & attacks_bb(pc, 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) && square_distance(s, s - deltas[i]) == 1;
249 Bitboard pick_random(RKISS& rk, int booster) {
251 // Values s1 and s2 are used to rotate the candidate magic of a
252 // quantity known to be optimal to quickly find the magics.
253 int s1 = booster & 63, s2 = (booster >> 6) & 63;
255 Bitboard m = rk.rand<Bitboard>();
256 m = (m >> s1) | (m << (64 - s1));
257 m &= rk.rand<Bitboard>();
258 m = (m >> s2) | (m << (64 - s2));
259 return m & rk.rand<Bitboard>();
263 // init_magics() computes all rook and bishop attacks at startup. Magic
264 // bitboards are used to look up attacks of sliding pieces. As a reference see
265 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
266 // use the so called "fancy" approach.
268 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
269 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
271 int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
272 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
274 Bitboard occupancy[4096], reference[4096], edges, b;
275 int i, size, booster;
277 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
278 attacks[SQ_A1] = table;
280 for (Square s = SQ_A1; s <= SQ_H8; ++s)
282 // Board edges are not considered in the relevant occupancies
283 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
285 // Given a square 's', the mask is the bitboard of sliding attacks from
286 // 's' computed on an empty board. The index must be big enough to contain
287 // all the attacks for each possible subset of the mask and so is 2 power
288 // the number of 1s of the mask. Hence we deduce the size of the shift to
289 // apply to the 64 or 32 bits word to get the index.
290 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
291 shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
293 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
294 // store the corresponding sliding attack bitboard in reference[].
298 reference[size++] = sliding_attack(deltas, s, b);
299 b = (b - masks[s]) & masks[s];
302 // Set the offset for the table of the next square. We have individual
303 // table sizes for each square with "Fancy Magic Bitboards".
305 attacks[s + 1] = attacks[s] + size;
307 booster = MagicBoosters[Is64Bit][rank_of(s)];
309 // Find a magic for square 's' picking up an (almost) random number
310 // until we find the one that passes the verification test.
312 do magics[s] = pick_random(rk, booster);
313 while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
315 std::memset(attacks[s], 0, size * sizeof(Bitboard));
317 // A good magic must map every possible occupancy to an index that
318 // looks up the correct sliding attack in the attacks[s] database.
319 // Note that we build up the database for square 's' as a side
320 // effect of verifying the magic.
321 for (i = 0; i < size; ++i)
323 Bitboard& attack = attacks[s][index(s, occupancy[i])];
325 if (attack && attack != reference[i])
328 assert(reference[i] != 0);
330 attack = reference[i];