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/>.
32 Bitboard* RAttacks[64];
37 Bitboard* BAttacks[64];
40 Bitboard SquareBB[64];
43 Bitboard AdjacentFilesBB[8];
44 Bitboard ThisAndAdjacentFilesBB[8];
45 Bitboard InFrontBB[2][8];
46 Bitboard StepAttacksBB[16][64];
47 Bitboard BetweenBB[64][64];
48 Bitboard DistanceRingsBB[64][8];
49 Bitboard ForwardBB[2][64];
50 Bitboard PassedPawnMask[2][64];
51 Bitboard AttackSpanMask[2][64];
52 Bitboard PseudoAttacks[6][64];
54 int SquareDistance[64][64];
58 // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
59 const uint64_t DeBruijn_64 = 0x218A392CD3D5DBFULL;
60 const uint32_t DeBruijn_32 = 0x783A9B23;
66 Bitboard RTable[0x19000]; // Storage space for rook attacks
67 Bitboard BTable[0x1480]; // Storage space for bishop attacks
68 uint8_t BitCount8Bit[256];
70 typedef unsigned (Fn)(Square, Bitboard);
72 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
73 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
76 /// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
77 /// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
79 #if !defined(USE_BSFQ)
81 Square lsb(Bitboard b) {
84 return Square(BSFTable[((b & -b) * DeBruijn_64) >> 58]);
87 uint32_t fold = unsigned(b) ^ unsigned(b >> 32);
88 return Square(BSFTable[(fold * DeBruijn_32) >> 26]);
91 Square pop_lsb(Bitboard* b) {
97 return Square(BSFTable[((bb & -bb) * DeBruijn_64) >> 58]);
100 uint32_t fold = unsigned(bb) ^ unsigned(bb >> 32);
101 return Square(BSFTable[(fold * DeBruijn_32) >> 26]);
104 Square msb(Bitboard b) {
129 return Square(result + MS1BTable[b32]);
132 #endif // !defined(USE_BSFQ)
135 /// Bitboards::print() prints a bitboard in an easily readable format to the
136 /// standard output. This is sometimes useful for debugging.
138 void Bitboards::print(Bitboard b) {
140 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
142 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
144 for (File file = FILE_A; file <= FILE_H; file++)
145 std::cout << "| " << (b & (file | rank) ? "X " : " ");
149 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
153 /// Bitboards::init() initializes various bitboard arrays. It is called during
154 /// program initialization.
156 void Bitboards::init() {
158 for (int k = 0, i = 0; i < 8; 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 for (int i = 0; i < 64; i++)
205 if (!Is64Bit) // Matt Taylor's folding trick for 32 bit systems
207 Bitboard b = 1ULL << i;
210 BSFTable[(uint32_t)(b * DeBruijn_32) >> 26] = i;
213 BSFTable[((1ULL << i) * DeBruijn_64) >> 58] = i;
215 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
216 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
218 for (Color c = WHITE; c <= BLACK; c++)
219 for (PieceType pt = PAWN; pt <= KING; pt++)
220 for (Square s = SQ_A1; s <= SQ_H8; s++)
221 for (int k = 0; steps[pt][k]; k++)
223 Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
225 if (is_ok(to) && square_distance(s, to) < 3)
226 StepAttacksBB[make_piece(c, pt)][s] |= to;
229 Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
230 Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
232 init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
233 init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
235 for (Square s = SQ_A1; s <= SQ_H8; s++)
237 PseudoAttacks[QUEEN][s] = PseudoAttacks[BISHOP][s] = attacks_bb<BISHOP>(s, 0);
238 PseudoAttacks[QUEEN][s] |= PseudoAttacks[ ROOK][s] = attacks_bb< ROOK>(s, 0);
241 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
242 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
243 if (PseudoAttacks[QUEEN][s1] & s2)
245 Square delta = (s2 - s1) / square_distance(s1, s2);
247 for (Square s = s1 + delta; s != s2; s += delta)
248 BetweenBB[s1][s2] |= s;
255 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
259 for (int i = 0; i < 4; i++)
260 for (Square s = sq + deltas[i];
261 is_ok(s) && square_distance(s, s - deltas[i]) == 1;
274 Bitboard pick_random(RKISS& rk, int booster) {
276 // Values s1 and s2 are used to rotate the candidate magic of a
277 // quantity known to be the optimal to quickly find the magics.
278 int s1 = booster & 63, s2 = (booster >> 6) & 63;
280 Bitboard m = rk.rand<Bitboard>();
281 m = (m >> s1) | (m << (64 - s1));
282 m &= rk.rand<Bitboard>();
283 m = (m >> s2) | (m << (64 - s2));
284 return m & rk.rand<Bitboard>();
288 // init_magics() computes all rook and bishop attacks at startup. Magic
289 // bitboards are used to look up attacks of sliding pieces. As a reference see
290 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
291 // use the so called "fancy" approach.
293 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
294 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
296 int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
297 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
299 Bitboard occupancy[4096], reference[4096], edges, b;
300 int i, size, booster;
302 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
303 attacks[SQ_A1] = table;
305 for (Square s = SQ_A1; s <= SQ_H8; s++)
307 // Board edges are not considered in the relevant occupancies
308 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
310 // Given a square 's', the mask is the bitboard of sliding attacks from
311 // 's' computed on an empty board. The index must be big enough to contain
312 // all the attacks for each possible subset of the mask and so is 2 power
313 // the number of 1s of the mask. Hence we deduce the size of the shift to
314 // apply to the 64 or 32 bits word to get the index.
315 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
316 shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
318 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
319 // store the corresponding sliding attack bitboard in reference[].
323 reference[size++] = sliding_attack(deltas, s, b);
324 b = (b - masks[s]) & masks[s];
327 // Set the offset for the table of the next square. We have individual
328 // table sizes for each square with "Fancy Magic Bitboards".
330 attacks[s + 1] = attacks[s] + size;
332 booster = MagicBoosters[Is64Bit][rank_of(s)];
334 // Find a magic for square 's' picking up an (almost) random number
335 // until we find the one that passes the verification test.
337 do magics[s] = pick_random(rk, booster);
338 while (BitCount8Bit[(magics[s] * masks[s]) >> 56] < 6);
340 memset(attacks[s], 0, size * sizeof(Bitboard));
342 // A good magic must map every possible occupancy to an index that
343 // looks up the correct sliding attack in the attacks[s] database.
344 // Note that we build up the database for square 's' as a side
345 // effect of verifying the magic.
346 for (i = 0; i < size; i++)
348 Bitboard& attack = attacks[s][index(s, occupancy[i])];
350 if (attack && attack != reference[i])
353 assert(reference[i] != 0);
355 attack = reference[i];