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 SquaresInFrontMask[2][64];
49 Bitboard PassedPawnMask[2][64];
50 Bitboard AttackSpanMask[2][64];
51 Bitboard PseudoAttacks[6][64];
53 uint8_t BitCount8Bit[256];
54 int SquareDistance[64][64];
62 Bitboard RTable[0x19000]; // Storage space for rook attacks
63 Bitboard BTable[0x1480]; // Storage space for bishop attacks
65 typedef unsigned (Fn)(Square, Bitboard);
67 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
68 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
71 /// first_1() finds the least significant nonzero bit in a nonzero bitboard.
72 /// pop_1st_bit() finds and clears the least significant nonzero bit in a
75 #if defined(IS_64BIT) && !defined(USE_BSFQ)
77 Square first_1(Bitboard b) {
78 return Square(BSFTable[((b & -b) * 0x218A392CD3D5DBFULL) >> 58]);
81 Square pop_1st_bit(Bitboard* b) {
84 return Square(BSFTable[((bb & -bb) * 0x218A392CD3D5DBFULL) >> 58]);
87 #elif !defined(USE_BSFQ)
89 Square first_1(Bitboard b) {
91 uint32_t fold = unsigned(b) ^ unsigned(b >> 32);
92 return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
100 #if defined (BIGENDIAN)
110 Square pop_1st_bit(Bitboard* b) {
112 const b_union u = *((b_union*)b);
116 ((b_union*)b)->b.l = u.b.l & (u.b.l - 1);
117 return Square(BSFTable[((u.b.l ^ (u.b.l - 1)) * 0x783A9B23) >> 26]);
120 ((b_union*)b)->b.h = u.b.h & (u.b.h - 1);
121 return Square(BSFTable[((~(u.b.h ^ (u.b.h - 1))) * 0x783A9B23) >> 26]);
124 Square last_1(Bitboard b) {
146 return Square(result + MS1BTable[b]);
149 #endif // !defined(USE_BSFQ)
152 /// Bitboards::print() prints a bitboard in an easily readable format to the
153 /// standard output. This is sometimes useful for debugging.
155 void Bitboards::print(Bitboard b) {
157 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
159 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
161 for (File file = FILE_A; file <= FILE_H; file++)
162 std::cout << "| " << ((b & make_square(file, rank)) ? "X " : " ");
166 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
170 /// Bitboards::init() initializes various bitboard arrays. It is called during
171 /// program initialization.
173 void Bitboards::init() {
175 for (int k = 0, i = 0; i < 8; i++)
179 for (Bitboard b = 0; b < 256; b++)
180 BitCount8Bit[b] = (uint8_t)popcount<Max15>(b);
182 for (Square s = SQ_A1; s <= SQ_H8; s++)
183 SquareBB[s] = 1ULL << s;
185 FileBB[FILE_A] = FileABB;
186 RankBB[RANK_1] = Rank1BB;
188 for (int f = FILE_B; f <= FILE_H; f++)
190 FileBB[f] = FileBB[f - 1] << 1;
191 RankBB[f] = RankBB[f - 1] << 8;
194 for (int f = FILE_A; f <= FILE_H; f++)
196 AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
197 ThisAndAdjacentFilesBB[f] = FileBB[f] | AdjacentFilesBB[f];
200 for (int rw = RANK_7, rb = RANK_2; rw >= RANK_1; rw--, rb++)
202 InFrontBB[WHITE][rw] = InFrontBB[WHITE][rw + 1] | RankBB[rw + 1];
203 InFrontBB[BLACK][rb] = InFrontBB[BLACK][rb - 1] | RankBB[rb - 1];
206 for (Color c = WHITE; c <= BLACK; c++)
207 for (Square s = SQ_A1; s <= SQ_H8; s++)
209 SquaresInFrontMask[c][s] = in_front_bb(c, s) & file_bb(s);
210 PassedPawnMask[c][s] = in_front_bb(c, s) & this_and_adjacent_files_bb(file_of(s));
211 AttackSpanMask[c][s] = in_front_bb(c, s) & adjacent_files_bb(file_of(s));
214 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
215 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
216 SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
218 for (int i = 0; i < 64; i++)
219 if (!Is64Bit) // Matt Taylor's folding trick for 32 bit systems
221 Bitboard b = 1ULL << i;
224 BSFTable[(uint32_t)(b * 0x783A9B23) >> 26] = i;
227 BSFTable[((1ULL << i) * 0x218A392CD3D5DBFULL) >> 58] = i;
229 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
230 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
232 for (Color c = WHITE; c <= BLACK; c++)
233 for (PieceType pt = PAWN; pt <= KING; pt++)
234 for (Square s = SQ_A1; s <= SQ_H8; s++)
235 for (int k = 0; steps[pt][k]; k++)
237 Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
239 if (is_ok(to) && square_distance(s, to) < 3)
240 StepAttacksBB[make_piece(c, pt)][s] |= to;
243 Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
244 Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
246 init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
247 init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
249 for (Square s = SQ_A1; s <= SQ_H8; s++)
251 PseudoAttacks[BISHOP][s] = attacks_bb<BISHOP>(s, 0);
252 PseudoAttacks[ROOK][s] = attacks_bb<ROOK>(s, 0);
253 PseudoAttacks[QUEEN][s] = PseudoAttacks[BISHOP][s] | PseudoAttacks[ROOK][s];
256 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
257 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
258 if (PseudoAttacks[QUEEN][s1] & s2)
260 Square delta = (s2 - s1) / square_distance(s1, s2);
262 for (Square s = s1 + delta; s != s2; s += delta)
263 BetweenBB[s1][s2] |= s;
270 Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
274 for (int i = 0; i < 4; i++)
275 for (Square s = sq + deltas[i];
276 is_ok(s) && square_distance(s, s - deltas[i]) == 1;
289 Bitboard pick_random(Bitboard mask, RKISS& rk, int booster) {
293 // Values s1 and s2 are used to rotate the candidate magic of a
294 // quantity known to be the optimal to quickly find the magics.
295 int s1 = booster & 63, s2 = (booster >> 6) & 63;
299 magic = rk.rand<Bitboard>();
300 magic = (magic >> s1) | (magic << (64 - s1));
301 magic &= rk.rand<Bitboard>();
302 magic = (magic >> s2) | (magic << (64 - s2));
303 magic &= rk.rand<Bitboard>();
305 if (BitCount8Bit[(mask * magic) >> 56] >= 6)
311 // init_magics() computes all rook and bishop attacks at startup. Magic
312 // bitboards are used to look up attacks of sliding pieces. As a reference see
313 // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
314 // use the so called "fancy" approach.
316 void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
317 Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
319 int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
320 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
322 Bitboard occupancy[4096], reference[4096], edges, b;
323 int i, size, booster;
325 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
326 attacks[SQ_A1] = table;
328 for (Square s = SQ_A1; s <= SQ_H8; s++)
330 // Board edges are not considered in the relevant occupancies
331 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
333 // Given a square 's', the mask is the bitboard of sliding attacks from
334 // 's' computed on an empty board. The index must be big enough to contain
335 // all the attacks for each possible subset of the mask and so is 2 power
336 // the number of 1s of the mask. Hence we deduce the size of the shift to
337 // apply to the 64 or 32 bits word to get the index.
338 masks[s] = sliding_attack(deltas, s, 0) & ~edges;
339 shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
341 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
342 // store the corresponding sliding attack bitboard in reference[].
346 reference[size++] = sliding_attack(deltas, s, b);
347 b = (b - masks[s]) & masks[s];
350 // Set the offset for the table of the next square. We have individual
351 // table sizes for each square with "Fancy Magic Bitboards".
353 attacks[s + 1] = attacks[s] + size;
355 booster = MagicBoosters[Is64Bit][rank_of(s)];
357 // Find a magic for square 's' picking up an (almost) random number
358 // until we find the one that passes the verification test.
360 magics[s] = pick_random(masks[s], rk, booster);
361 memset(attacks[s], 0, size * sizeof(Bitboard));
363 // A good magic must map every possible occupancy to an index that
364 // looks up the correct sliding attack in the attacks[s] database.
365 // Note that we build up the database for square 's' as a side
366 // effect of verifying the magic.
367 for (i = 0; i < size; i++)
369 Bitboard& attack = attacks[s][index(s, occupancy[i])];
371 if (attack && attack != reference[i])
374 attack = reference[i];