2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
28 // Global bitboards definitions with static storage duration are
29 // automatically set to zero before enter main().
32 Bitboard* RAttacks[64];
37 Bitboard* BAttacks[64];
40 Bitboard SetMaskBB[65];
41 Bitboard ClearMaskBB[65];
43 Bitboard SquaresByColorBB[2];
46 Bitboard NeighboringFilesBB[8];
47 Bitboard ThisAndNeighboringFilesBB[8];
48 Bitboard InFrontBB[2][8];
49 Bitboard StepAttacksBB[16][64];
50 Bitboard BetweenBB[64][64];
51 Bitboard SquaresInFrontMask[2][64];
52 Bitboard PassedPawnMask[2][64];
53 Bitboard AttackSpanMask[2][64];
55 Bitboard BishopPseudoAttacks[64];
56 Bitboard RookPseudoAttacks[64];
57 Bitboard QueenPseudoAttacks[64];
59 uint8_t BitCount8Bit[256];
60 int SquareDistance[64][64];
67 Bitboard RookTable[0x19000]; // Storage space for rook attacks
68 Bitboard BishopTable[0x1480]; // Storage space for bishop attacks
70 void init_magic_bitboards(Bitboard* attacks[], Bitboard magics[],
71 Bitboard masks[], int shifts[], Square deltas[]);
75 /// print_bitboard() prints a bitboard in an easily readable format to the
76 /// standard output. This is sometimes useful for debugging.
78 void print_bitboard(Bitboard b) {
80 for (Rank r = RANK_8; r >= RANK_1; r--)
82 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
83 for (File f = FILE_A; f <= FILE_H; f++)
84 std::cout << "| " << (bit_is_set(b, make_square(f, r)) ? "X " : " ");
88 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
92 /// first_1() finds the least significant nonzero bit in a nonzero bitboard.
93 /// pop_1st_bit() finds and clears the least significant nonzero bit in a
96 #if defined(IS_64BIT) && !defined(USE_BSFQ)
98 Square first_1(Bitboard b) {
99 return Square(BSFTable[((b & -b) * 0x218A392CD3D5DBFULL) >> 58]);
102 Square pop_1st_bit(Bitboard* b) {
105 return Square(BSFTable[((bb & -bb) * 0x218A392CD3D5DBFULL) >> 58]);
108 #elif !defined(USE_BSFQ)
110 Square first_1(Bitboard b) {
112 uint32_t fold = unsigned(b) ^ unsigned(b >> 32);
113 return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
121 #if defined (BIGENDIAN)
131 Square pop_1st_bit(Bitboard* bb) {
140 ret = Square(BSFTable[((u.dw.l ^ (u.dw.l - 1)) * 0x783A9B23) >> 26]);
141 u.dw.l &= (u.dw.l - 1);
145 ret = Square(BSFTable[((~(u.dw.h ^ (u.dw.h - 1))) * 0x783A9B23) >> 26]);
146 u.dw.h &= (u.dw.h - 1);
151 #endif // !defined(USE_BSFQ)
154 /// init_bitboards() initializes various bitboard arrays. It is called during
155 /// program initialization.
157 void init_bitboards() {
159 for (Bitboard b = 0; b < 256; b++)
160 BitCount8Bit[b] = (uint8_t)count_1s<CNT32_MAX15>(b);
162 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
163 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
164 SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
166 SquaresByColorBB[DARK] = 0xAA55AA55AA55AA55ULL;
167 SquaresByColorBB[LIGHT] = ~SquaresByColorBB[DARK];
169 for (Square s = SQ_A1; s <= SQ_H8; s++)
171 SetMaskBB[s] = 1ULL << s;
172 ClearMaskBB[s] = ~SetMaskBB[s];
175 ClearMaskBB[SQ_NONE] = ~EmptyBoardBB;
177 FileBB[FILE_A] = FileABB;
178 RankBB[RANK_1] = Rank1BB;
180 for (int f = FILE_B; f <= FILE_H; f++)
182 FileBB[f] = FileBB[f - 1] << 1;
183 RankBB[f] = RankBB[f - 1] << 8;
186 for (int f = FILE_A; f <= FILE_H; f++)
188 NeighboringFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
189 ThisAndNeighboringFilesBB[f] = FileBB[f] | NeighboringFilesBB[f];
192 for (int rw = RANK_7, rb = RANK_2; rw >= RANK_1; rw--, rb++)
194 InFrontBB[WHITE][rw] = InFrontBB[WHITE][rw + 1] | RankBB[rw + 1];
195 InFrontBB[BLACK][rb] = InFrontBB[BLACK][rb - 1] | RankBB[rb - 1];
198 for (Color c = WHITE; c <= BLACK; c++)
199 for (Square s = SQ_A1; s <= SQ_H8; s++)
201 SquaresInFrontMask[c][s] = in_front_bb(c, s) & file_bb(s);
202 PassedPawnMask[c][s] = in_front_bb(c, s) & this_and_neighboring_files_bb(s);
203 AttackSpanMask[c][s] = in_front_bb(c, s) & neighboring_files_bb(s);
206 for (int i = 0; i < 64; i++)
207 if (!CpuIs64Bit) // Matt Taylor's folding trick for 32 bit systems
209 Bitboard b = 1ULL << i;
212 BSFTable[uint32_t(b * 0x783A9B23) >> 26] = i;
215 BSFTable[((1ULL << i) * 0x218A392CD3D5DBFULL) >> 58] = i;
217 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
218 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
220 for (Color c = WHITE; c <= BLACK; c++)
221 for (PieceType pt = PAWN; pt <= KING; pt++)
222 for (Square s = SQ_A1; s <= SQ_H8; s++)
223 for (int k = 0; steps[pt][k]; k++)
225 Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
227 if (square_is_ok(to) && square_distance(s, to) < 3)
228 set_bit(&StepAttacksBB[make_piece(c, pt)][s], to);
231 Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
232 Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
234 RAttacks[0] = RookTable;
235 BAttacks[0] = BishopTable;
237 init_magic_bitboards(RAttacks, RMagics, RMasks, RShifts, RDeltas);
238 init_magic_bitboards(BAttacks, BMagics, BMasks, BShifts, BDeltas);
240 for (Square s = SQ_A1; s <= SQ_H8; s++)
242 BishopPseudoAttacks[s] = bishop_attacks_bb(s, EmptyBoardBB);
243 RookPseudoAttacks[s] = rook_attacks_bb(s, EmptyBoardBB);
244 QueenPseudoAttacks[s] = queen_attacks_bb(s, EmptyBoardBB);
247 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
248 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
249 if (bit_is_set(QueenPseudoAttacks[s1], s2))
251 int f = file_distance(s1, s2);
252 int r = rank_distance(s1, s2);
254 Square d = (s2 - s1) / std::max(f, r);
256 for (Square s3 = s1 + d; s3 != s2; s3 += d)
257 set_bit(&BetweenBB[s1][s2], s3);
264 Bitboard sliding_attacks(Square sq, Bitboard occupied, Square deltas[]) {
266 Bitboard attacks = 0;
268 for (int i = 0; i < 4; i++)
270 Square s = sq + deltas[i];
272 while (square_is_ok(s) && square_distance(s, s - deltas[i]) == 1)
274 set_bit(&attacks, s);
276 if (bit_is_set(occupied, s))
285 Bitboard pick_random(Bitboard mask, RKISS& rk, int booster) {
289 // Values s1 and s2 are used to rotate the candidate magic of a
290 // quantity known to be the optimal to quickly find the magics.
291 int s1 = booster & 63, s2 = (booster >> 6) & 63;
295 magic = rk.rand<Bitboard>();
296 magic = (magic >> s1) | (magic << (64 - s1));
297 magic &= rk.rand<Bitboard>();
298 magic = (magic >> s2) | (magic << (64 - s2));
299 magic &= rk.rand<Bitboard>();
301 if (BitCount8Bit[(mask * magic) >> 56] >= 6)
307 // init_magic_bitboards() computes all rook and bishop magics at startup.
308 // Magic bitboards are used to look up attacks of sliding pieces. As reference
309 // see chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
310 // use the so called "fancy" approach.
312 void init_magic_bitboards(Bitboard* attacks[], Bitboard magics[],
313 Bitboard masks[], int shifts[], Square deltas[]) {
315 const int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
316 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
318 Bitboard occupancy[4096], reference[4096], edges, b;
319 int key, maxKey, index, booster;
321 for (Square s = SQ_A1; s <= SQ_H8; s++)
323 // Board edges are not considered in the relevant occupancies
324 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
326 // Given a square 's', the mask is the bitboard of sliding attacks from
327 // 's' computed on an empty board. The index must be big enough to contain
328 // all the attacks for each possible subset of the mask and so is 2 power
329 // the number of 1s of the mask. Hence we deduce the size of the shift to
330 // apply to the 64 or 32 bits word to get the index.
331 masks[s] = sliding_attacks(s, EmptyBoardBB, deltas) & ~edges;
332 shifts[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(masks[s]);
334 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
335 // store the corresponding sliding attacks in reference[].
338 occupancy[maxKey] = b;
339 reference[maxKey++] = sliding_attacks(s, b, deltas);
340 b = (b - masks[s]) & masks[s];
343 // Set the offset for the table of the next square. We have individual
344 // table sizes for each square with "Fancy Magic Bitboards".
346 attacks[s + 1] = attacks[s] + maxKey;
348 booster = MagicBoosters[CpuIs64Bit][rank_of(s)];
350 // Find a magic for square 's' picking up an (almost) random number
351 // until we find the one that passes the verification test.
353 magics[s] = pick_random(masks[s], rk, booster);
354 memset(attacks[s], 0, maxKey * sizeof(Bitboard));
356 // A good magic must map every possible occupancy to an index that
357 // looks up the correct sliding attack in the attacks[s] database.
358 // Note that we build up the database for square 's' as a side
359 // effect of verifying the magic.
360 for (key = 0; key < maxKey; key++)
362 index = CpuIs64Bit ? unsigned((occupancy[key] * magics[s]) >> shifts[s])
363 : unsigned(occupancy[key] * magics[s] ^ (occupancy[key] >> 32) * (magics[s] >> 32)) >> shifts[s];
365 if (!attacks[s][index])
366 attacks[s][index] = reference[key];
368 else if (attacks[s][index] != reference[key])
371 } while (key != maxKey);