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/>.
31 Bitboard RMasks[SQUARE_NB];
32 Bitboard RMagics[SQUARE_NB];
33 Bitboard* RAttacks[SQUARE_NB];
34 unsigned RShifts[SQUARE_NB];
36 Bitboard BMasks[SQUARE_NB];
37 Bitboard BMagics[SQUARE_NB];
38 Bitboard* BAttacks[SQUARE_NB];
39 unsigned BShifts[SQUARE_NB];
41 Bitboard SquareBB[SQUARE_NB];
42 Bitboard FileBB[FILE_NB];
43 Bitboard RankBB[RANK_NB];
44 Bitboard AdjacentFilesBB[FILE_NB];
45 Bitboard InFrontBB[COLOR_NB][RANK_NB];
46 Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
47 Bitboard BetweenBB[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 nonzero bitboard.
84 /// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
86 #if !defined(USE_BSFQ)
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 // !defined(USE_BSFQ)
128 /// Bitboards::print() prints a bitboard in an easily readable format to the
129 /// standard output. This is sometimes useful for debugging.
131 void Bitboards::print(Bitboard b) {
135 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
137 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
139 for (File file = FILE_A; file <= FILE_H; file++)
140 std::cout << "| " << (b & (file | rank) ? "X " : " ");
144 std::cout << "+---+---+---+---+---+---+---+---+" << sync_endl;
148 /// Bitboards::init() initializes various bitboard arrays. It is called during
149 /// program initialization.
151 void Bitboards::init() {
153 for (int k = 0, i = 0; i < 8; i++)
157 for (int i = 0; i < 64; i++)
158 BSFTable[bsf_index(1ULL << i)] = Square(i);
160 for (Square s = SQ_A1; s <= SQ_H8; s++)
161 SquareBB[s] = 1ULL << s;
163 FileBB[FILE_A] = FileABB;
164 RankBB[RANK_1] = Rank1BB;
166 for (int i = 1; i < 8; i++)
168 FileBB[i] = FileBB[i - 1] << 1;
169 RankBB[i] = RankBB[i - 1] << 8;
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++)
188 SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
190 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
191 for (int d = 1; d < 8; d++)
192 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
193 if (SquareDistance[s1][s2] == d)
194 DistanceRingsBB[s1][d - 1] |= s2;
196 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
197 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
199 for (Color c = WHITE; c <= BLACK; c++)
200 for (PieceType pt = PAWN; pt <= KING; pt++)
201 for (Square s = SQ_A1; s <= SQ_H8; s++)
202 for (int k = 0; steps[pt][k]; k++)
204 Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
206 if (is_ok(to) && square_distance(s, to) < 3)
207 StepAttacksBB[make_piece(c, pt)][s] |= to;
210 Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
211 Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
213 init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
214 init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
216 for (Square s = SQ_A1; s <= SQ_H8; s++)
218 PseudoAttacks[QUEEN][s] = PseudoAttacks[BISHOP][s] = attacks_bb<BISHOP>(s, 0);
219 PseudoAttacks[QUEEN][s] |= PseudoAttacks[ ROOK][s] = attacks_bb< ROOK>(s, 0);
222 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
223 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
224 if (PseudoAttacks[QUEEN][s1] & s2)
226 Square delta = (s2 - s1) / square_distance(s1, s2);
228 for (Square s = s1 + delta; s != s2; s += delta)
229 BetweenBB[s1][s2] |= s;
236 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
240 for (int i = 0; i < 4; i++)
241 for (Square s = sq + deltas[i];
242 is_ok(s) && square_distance(s, s - deltas[i]) == 1;
255 Bitboard pick_random(RKISS& rk, int booster) {
257 // Values s1 and s2 are used to rotate the candidate magic of a
258 // quantity known to be the optimal to quickly find the magics.
259 int s1 = booster & 63, s2 = (booster >> 6) & 63;
261 Bitboard m = rk.rand<Bitboard>();
262 m = (m >> s1) | (m << (64 - s1));
263 m &= rk.rand<Bitboard>();
264 m = (m >> s2) | (m << (64 - s2));
265 return m & rk.rand<Bitboard>();
269 // init_magics() computes all rook and bishop attacks at startup. Magic
270 // bitboards are used to look up attacks of sliding pieces. As a reference see
271 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
272 // use the so called "fancy" approach.
274 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
275 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
277 int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
278 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
280 Bitboard occupancy[4096], reference[4096], edges, b;
281 int i, size, booster;
283 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
284 attacks[SQ_A1] = table;
286 for (Square s = SQ_A1; s <= SQ_H8; s++)
288 // Board edges are not considered in the relevant occupancies
289 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
291 // Given a square 's', the mask is the bitboard of sliding attacks from
292 // 's' computed on an empty board. The index must be big enough to contain
293 // all the attacks for each possible subset of the mask and so is 2 power
294 // the number of 1s of the mask. Hence we deduce the size of the shift to
295 // apply to the 64 or 32 bits word to get the index.
296 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
297 shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
299 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
300 // store the corresponding sliding attack bitboard in reference[].
304 reference[size++] = sliding_attack(deltas, s, b);
305 b = (b - masks[s]) & masks[s];
308 // Set the offset for the table of the next square. We have individual
309 // table sizes for each square with "Fancy Magic Bitboards".
311 attacks[s + 1] = attacks[s] + size;
313 booster = MagicBoosters[Is64Bit][rank_of(s)];
315 // Find a magic for square 's' picking up an (almost) random number
316 // until we find the one that passes the verification test.
318 do magics[s] = pick_random(rk, booster);
319 while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
321 std::memset(attacks[s], 0, size * sizeof(Bitboard));
323 // A good magic must map every possible occupancy to an index that
324 // looks up the correct sliding attack in the attacks[s] database.
325 // Note that we build up the database for square 's' as a side
326 // effect of verifying the magic.
327 for (i = 0; i < size; i++)
329 Bitboard& attack = attacks[s][index(s, occupancy[i])];
331 if (attack && attack != reference[i])
334 assert(reference[i] != 0);
336 attack = reference[i];