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/>.
27 // Global bitboards definitions with static storage duration are
28 // automatically set to zero before enter main().
31 Bitboard* RAttacks[64];
36 Bitboard* BAttacks[64];
39 Bitboard SetMaskBB[65];
40 Bitboard ClearMaskBB[65];
42 Bitboard SquaresByColorBB[2];
45 Bitboard NeighboringFilesBB[8];
46 Bitboard ThisAndNeighboringFilesBB[8];
47 Bitboard InFrontBB[2][8];
48 Bitboard StepAttacksBB[16][64];
49 Bitboard BetweenBB[64][64];
50 Bitboard SquaresInFrontMask[2][64];
51 Bitboard PassedPawnMask[2][64];
52 Bitboard AttackSpanMask[2][64];
54 Bitboard BishopPseudoAttacks[64];
55 Bitboard RookPseudoAttacks[64];
56 Bitboard QueenPseudoAttacks[64];
58 uint8_t BitCount8Bit[256];
59 int SquareDistance[64][64];
66 Bitboard RAttacksTable[0x19000];
67 Bitboard BAttacksTable[0x1480];
69 void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[],
70 Bitboard mask[], int shift[], Square delta[]);
74 /// print_bitboard() prints a bitboard in an easily readable format to the
75 /// standard output. This is sometimes useful for debugging.
77 void print_bitboard(Bitboard b) {
79 for (Rank r = RANK_8; r >= RANK_1; r--)
81 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
82 for (File f = FILE_A; f <= FILE_H; f++)
83 std::cout << "| " << (bit_is_set(b, make_square(f, r)) ? "X " : " ");
87 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
91 /// first_1() finds the least significant nonzero bit in a nonzero bitboard.
92 /// pop_1st_bit() finds and clears the least significant nonzero bit in a
95 #if defined(IS_64BIT) && !defined(USE_BSFQ)
97 Square first_1(Bitboard b) {
98 return Square(BSFTable[((b & -b) * 0x218A392CD3D5DBFULL) >> 58]);
101 Square pop_1st_bit(Bitboard* b) {
104 return Square(BSFTable[((bb & -bb) * 0x218A392CD3D5DBFULL) >> 58]);
107 #elif !defined(USE_BSFQ)
109 Square first_1(Bitboard b) {
111 uint32_t fold = unsigned(b) ^ unsigned(b >> 32);
112 return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
120 #if defined (BIGENDIAN)
130 Square pop_1st_bit(Bitboard* bb) {
139 ret = Square(BSFTable[((u.dw.l ^ (u.dw.l - 1)) * 0x783A9B23) >> 26]);
140 u.dw.l &= (u.dw.l - 1);
144 ret = Square(BSFTable[((~(u.dw.h ^ (u.dw.h - 1))) * 0x783A9B23) >> 26]);
145 u.dw.h &= (u.dw.h - 1);
150 #endif // !defined(USE_BSFQ)
153 /// init_bitboards() initializes various bitboard arrays. It is called during
154 /// program initialization.
156 void init_bitboards() {
158 for (Bitboard b = 0; b < 256; b++)
159 BitCount8Bit[b] = (uint8_t)count_1s<CNT32_MAX15>(b);
161 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
162 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
163 SquareDistance[s1][s2] = Max(file_distance(s1, s2), rank_distance(s1, s2));
165 SquaresByColorBB[DARK] = 0xAA55AA55AA55AA55ULL;
166 SquaresByColorBB[LIGHT] = ~SquaresByColorBB[DARK];
168 for (Square s = SQ_A1; s <= SQ_H8; s++)
170 SetMaskBB[s] = 1ULL << s;
171 ClearMaskBB[s] = ~SetMaskBB[s];
174 ClearMaskBB[SQ_NONE] = ~EmptyBoardBB;
176 FileBB[FILE_A] = FileABB;
177 RankBB[RANK_1] = Rank1BB;
179 for (int f = FILE_B; f <= FILE_H; f++)
181 FileBB[f] = FileBB[f - 1] << 1;
182 RankBB[f] = RankBB[f - 1] << 8;
185 for (int f = FILE_A; f <= FILE_H; f++)
187 NeighboringFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
188 ThisAndNeighboringFilesBB[f] = FileBB[f] | NeighboringFilesBB[f];
191 for (int rw = RANK_7, rb = RANK_2; rw >= RANK_1; rw--, rb++)
193 InFrontBB[WHITE][rw] = InFrontBB[WHITE][rw + 1] | RankBB[rw + 1];
194 InFrontBB[BLACK][rb] = InFrontBB[BLACK][rb - 1] | RankBB[rb - 1];
197 for (Color c = WHITE; c <= BLACK; c++)
198 for (Square s = SQ_A1; s <= SQ_H8; s++)
200 SquaresInFrontMask[c][s] = in_front_bb(c, s) & file_bb(s);
201 PassedPawnMask[c][s] = in_front_bb(c, s) & this_and_neighboring_files_bb(s);
202 AttackSpanMask[c][s] = in_front_bb(c, s) & neighboring_files_bb(s);
205 for (int i = 0; i < 64; i++)
206 if (!CpuIs64Bit) // Matt Taylor's folding trick for 32 bit systems
208 Bitboard b = 1ULL << i;
211 BSFTable[uint32_t(b * 0x783A9B23) >> 26] = i;
214 BSFTable[((1ULL << i) * 0x218A392CD3D5DBFULL) >> 58] = i;
216 int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
217 {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
219 for (Color c = WHITE; c <= BLACK; c++)
220 for (PieceType pt = PAWN; pt <= KING; pt++)
221 for (Square s = SQ_A1; s <= SQ_H8; s++)
222 for (int k = 0; steps[pt][k]; k++)
224 Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
226 if (square_is_ok(to) && square_distance(s, to) < 3)
227 set_bit(&StepAttacksBB[make_piece(c, pt)][s], to);
230 Square RDelta[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
231 Square BDelta[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
233 init_sliding_attacks(BMult, BAttacks, BAttacksTable, BMask, BShift, BDelta);
234 init_sliding_attacks(RMult, RAttacks, RAttacksTable, RMask, RShift, RDelta);
236 for (Square s = SQ_A1; s <= SQ_H8; s++)
238 BishopPseudoAttacks[s] = bishop_attacks_bb(s, EmptyBoardBB);
239 RookPseudoAttacks[s] = rook_attacks_bb(s, EmptyBoardBB);
240 QueenPseudoAttacks[s] = queen_attacks_bb(s, EmptyBoardBB);
243 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
244 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
245 if (bit_is_set(QueenPseudoAttacks[s1], s2))
247 int f = file_distance(s1, s2);
248 int r = rank_distance(s1, s2);
250 Square d = (s2 - s1) / Max(f, r);
252 for (Square s3 = s1 + d; s3 != s2; s3 += d)
253 set_bit(&BetweenBB[s1][s2], s3);
260 Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[]) {
262 Bitboard attacks = 0;
264 for (int i = 0; i < 4; i++)
266 Square s = sq + delta[i];
268 while (square_is_ok(s) && square_distance(s, s - delta[i]) == 1)
270 set_bit(&attacks, s);
272 if (bit_is_set(occupied, s))
281 Bitboard pick_magic(Bitboard mask, RKISS& rk, int booster) {
285 // Values s1 and s2 are used to rotate the candidate magic of a
286 // quantity known to be the optimal to quickly find the magics.
287 int s1 = booster & 63, s2 = (booster >> 6) & 63;
291 magic = rk.rand<Bitboard>();
292 magic = (magic >> s1) | (magic << (64 - s1));
293 magic &= rk.rand<Bitboard>();
294 magic = (magic >> s2) | (magic << (64 - s2));
295 magic &= rk.rand<Bitboard>();
297 if (BitCount8Bit[(mask * magic) >> 56] >= 6)
302 void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[],
303 Bitboard mask[], int shift[], Square delta[]) {
305 const int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
306 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
308 Bitboard occupancy[4096], reference[4096], edges, b;
309 int key, maxKey, index, booster, offset = 0;
311 for (Square s = SQ_A1; s <= SQ_H8; s++)
313 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
315 attack[s] = &attTable[offset];
316 mask[s] = sliding_attacks(s, EmptyBoardBB, delta) & ~edges;
317 shift[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(mask[s]);
319 // Use Carry-Rippler trick to enumerate all subsets of mask[s]
322 occupancy[maxKey] = b;
323 reference[maxKey++] = sliding_attacks(s, b, delta);
324 b = (b - mask[s]) & mask[s];
328 booster = MagicBoosters[CpuIs64Bit][rank_of(s)];
330 // Then find a possible magic and the corresponding attacks
332 magic[s] = pick_magic(mask[s], rk, booster);
333 memset(attack[s], 0, maxKey * sizeof(Bitboard));
335 for (key = 0; key < maxKey; key++)
337 index = CpuIs64Bit ? unsigned((occupancy[key] * magic[s]) >> shift[s])
338 : unsigned(occupancy[key] * magic[s] ^ (occupancy[key] >> 32) * (magic[s] >> 32)) >> shift[s];
340 if (!attack[s][index])
341 attack[s][index] = reference[key];
343 else if (attack[s][index] != reference[key])
346 } while (key != maxKey);