2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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/>.
33 Bitboard* RAttacks[64];
38 Bitboard* BAttacks[64];
41 Bitboard SquareBB[64];
44 Bitboard AdjacentFilesBB[8];
45 Bitboard ThisAndAdjacentFilesBB[8];
46 Bitboard InFrontBB[2][8];
47 Bitboard StepAttacksBB[16][64];
48 Bitboard BetweenBB[64][64];
49 Bitboard DistanceRingsBB[64][8];
50 Bitboard ForwardBB[2][64];
51 Bitboard PassedPawnMask[2][64];
52 Bitboard AttackSpanMask[2][64];
53 Bitboard PseudoAttacks[6][64];
55 int SquareDistance[64][64];
59 // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
60 const uint64_t DeBruijn_64 = 0x3F79D71B4CB0A89ULL;
61 const uint32_t DeBruijn_32 = 0x783A9B23;
67 Bitboard RTable[0x19000]; // Storage space for rook attacks
68 Bitboard BTable[0x1480]; // Storage space for bishop attacks
69 uint8_t BitCount8Bit[256];
71 typedef unsigned (Fn)(Square, Bitboard);
73 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
74 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
76 FORCE_INLINE unsigned bsf_index(Bitboard b) {
78 // Matt Taylor's folding for 32 bit systems, extended to 64 bits by Kim Walisch
80 return Is64Bit ? (b * DeBruijn_64) >> 58
81 : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
85 /// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
86 /// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
88 #if !defined(USE_BSFQ)
90 Square lsb(Bitboard b) { return BSFTable[bsf_index(b)]; }
92 Square pop_lsb(Bitboard* b) {
96 return BSFTable[bsf_index(bb)];
99 Square msb(Bitboard b) {
124 return (Square)(result + MS1BTable[b32]);
127 #endif // !defined(USE_BSFQ)
130 /// Bitboards::print() prints a bitboard in an easily readable format to the
131 /// standard output. This is sometimes useful for debugging.
133 void Bitboards::print(Bitboard b) {
137 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
139 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
141 for (File file = FILE_A; file <= FILE_H; file++)
142 std::cout << "| " << (b & (file | rank) ? "X " : " ");
146 std::cout << "+---+---+---+---+---+---+---+---+" << sync_endl;
150 /// Bitboards::init() initializes various bitboard arrays. It is called during
151 /// program initialization.
153 void Bitboards::init() {
155 for (int k = 0, i = 0; i < 8; i++)
159 for (int i = 0; i < 64; i++)
160 BSFTable[bsf_index(1ULL << i)] = Square(i);
162 for (Bitboard b = 0; b < 256; b++)
163 BitCount8Bit[b] = (uint8_t)popcount<Max15>(b);
165 for (Square s = SQ_A1; s <= SQ_H8; s++)
166 SquareBB[s] = 1ULL << s;
168 FileBB[FILE_A] = FileABB;
169 RankBB[RANK_1] = Rank1BB;
171 for (int i = 1; i < 8; i++)
173 FileBB[i] = FileBB[i - 1] << 1;
174 RankBB[i] = RankBB[i - 1] << 8;
177 for (File f = FILE_A; f <= FILE_H; f++)
179 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
180 ThisAndAdjacentFilesBB[f] = FileBB[f] | AdjacentFilesBB[f];
183 for (Rank r = RANK_1; r < RANK_8; r++)
184 InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
186 for (Color c = WHITE; c <= BLACK; c++)
187 for (Square s = SQ_A1; s <= SQ_H8; s++)
189 ForwardBB[c][s] = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
190 PassedPawnMask[c][s] = InFrontBB[c][rank_of(s)] & ThisAndAdjacentFilesBB[file_of(s)];
191 AttackSpanMask[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
194 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
195 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
196 SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
198 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
199 for (int d = 1; d < 8; d++)
200 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
201 if (SquareDistance[s1][s2] == d)
202 DistanceRingsBB[s1][d - 1] |= s2;
204 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
205 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
207 for (Color c = WHITE; c <= BLACK; c++)
208 for (PieceType pt = PAWN; pt <= KING; pt++)
209 for (Square s = SQ_A1; s <= SQ_H8; s++)
210 for (int k = 0; steps[pt][k]; k++)
212 Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
214 if (is_ok(to) && square_distance(s, to) < 3)
215 StepAttacksBB[make_piece(c, pt)][s] |= to;
218 Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
219 Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
221 init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
222 init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
224 for (Square s = SQ_A1; s <= SQ_H8; s++)
226 PseudoAttacks[QUEEN][s] = PseudoAttacks[BISHOP][s] = attacks_bb<BISHOP>(s, 0);
227 PseudoAttacks[QUEEN][s] |= PseudoAttacks[ ROOK][s] = attacks_bb< ROOK>(s, 0);
230 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
231 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
232 if (PseudoAttacks[QUEEN][s1] & s2)
234 Square delta = (s2 - s1) / square_distance(s1, s2);
236 for (Square s = s1 + delta; s != s2; s += delta)
237 BetweenBB[s1][s2] |= s;
244 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
248 for (int i = 0; i < 4; i++)
249 for (Square s = sq + deltas[i];
250 is_ok(s) && square_distance(s, s - deltas[i]) == 1;
263 Bitboard pick_random(RKISS& rk, int booster) {
265 // Values s1 and s2 are used to rotate the candidate magic of a
266 // quantity known to be the optimal to quickly find the magics.
267 int s1 = booster & 63, s2 = (booster >> 6) & 63;
269 Bitboard m = rk.rand<Bitboard>();
270 m = (m >> s1) | (m << (64 - s1));
271 m &= rk.rand<Bitboard>();
272 m = (m >> s2) | (m << (64 - s2));
273 return m & rk.rand<Bitboard>();
277 // init_magics() computes all rook and bishop attacks at startup. Magic
278 // bitboards are used to look up attacks of sliding pieces. As a reference see
279 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
280 // use the so called "fancy" approach.
282 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
283 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
285 int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
286 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
288 Bitboard occupancy[4096], reference[4096], edges, b;
289 int i, size, booster;
291 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
292 attacks[SQ_A1] = table;
294 for (Square s = SQ_A1; s <= SQ_H8; s++)
296 // Board edges are not considered in the relevant occupancies
297 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
299 // Given a square 's', the mask is the bitboard of sliding attacks from
300 // 's' computed on an empty board. The index must be big enough to contain
301 // all the attacks for each possible subset of the mask and so is 2 power
302 // the number of 1s of the mask. Hence we deduce the size of the shift to
303 // apply to the 64 or 32 bits word to get the index.
304 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
305 shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
307 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
308 // store the corresponding sliding attack bitboard in reference[].
312 reference[size++] = sliding_attack(deltas, s, b);
313 b = (b - masks[s]) & masks[s];
316 // Set the offset for the table of the next square. We have individual
317 // table sizes for each square with "Fancy Magic Bitboards".
319 attacks[s + 1] = attacks[s] + size;
321 booster = MagicBoosters[Is64Bit][rank_of(s)];
323 // Find a magic for square 's' picking up an (almost) random number
324 // until we find the one that passes the verification test.
326 do magics[s] = pick_random(rk, booster);
327 while (BitCount8Bit[(magics[s] * masks[s]) >> 56] < 6);
329 memset(attacks[s], 0, size * sizeof(Bitboard));
331 // A good magic must map every possible occupancy to an index that
332 // looks up the correct sliding attack in the attacks[s] database.
333 // Note that we build up the database for square 's' as a side
334 // effect of verifying the magic.
335 for (i = 0; i < size; i++)
337 Bitboard& attack = attacks[s][index(s, occupancy[i])];
339 if (attack && attack != reference[i])
342 assert(reference[i] != 0);
344 attack = reference[i];