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/>.
30 Bitboard* RAttacks[64];
35 Bitboard* BAttacks[64];
38 Bitboard SetMaskBB[65];
39 Bitboard ClearMaskBB[65];
41 Bitboard SquaresByColorBB[2];
44 Bitboard NeighboringFilesBB[8];
45 Bitboard ThisAndNeighboringFilesBB[8];
46 Bitboard InFrontBB[2][8];
47 Bitboard StepAttacksBB[16][64];
48 Bitboard BetweenBB[64][64];
49 Bitboard SquaresInFrontMask[2][64];
50 Bitboard PassedPawnMask[2][64];
51 Bitboard AttackSpanMask[2][64];
53 Bitboard BishopPseudoAttacks[64];
54 Bitboard RookPseudoAttacks[64];
55 Bitboard QueenPseudoAttacks[64];
57 uint8_t BitCount8Bit[256];
58 int SquareDistance[64][64];
65 Bitboard RookTable[0x19000]; // Storage space for rook attacks
66 Bitboard BishopTable[0x1480]; // Storage space for bishop attacks
68 void init_magic_bitboards(PieceType pt, Bitboard* attacks[], Bitboard magics[],
69 Bitboard masks[], int shifts[]);
73 /// print_bitboard() prints a bitboard in an easily readable format to the
74 /// standard output. This is sometimes useful for debugging.
76 void print_bitboard(Bitboard b) {
78 for (Rank r = RANK_8; r >= RANK_1; r--)
80 std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
81 for (File f = FILE_A; f <= FILE_H; f++)
82 std::cout << "| " << (bit_is_set(b, make_square(f, r)) ? "X " : " ");
86 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
90 /// first_1() finds the least significant nonzero bit in a nonzero bitboard.
91 /// pop_1st_bit() finds and clears the least significant nonzero bit in a
94 #if defined(IS_64BIT) && !defined(USE_BSFQ)
96 Square first_1(Bitboard b) {
97 return Square(BSFTable[((b & -b) * 0x218A392CD3D5DBFULL) >> 58]);
100 Square pop_1st_bit(Bitboard* b) {
103 return Square(BSFTable[((bb & -bb) * 0x218A392CD3D5DBFULL) >> 58]);
106 #elif !defined(USE_BSFQ)
108 Square first_1(Bitboard b) {
110 uint32_t fold = unsigned(b) ^ unsigned(b >> 32);
111 return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
119 #if defined (BIGENDIAN)
129 Square pop_1st_bit(Bitboard* bb) {
138 ret = Square(BSFTable[((u.dw.l ^ (u.dw.l - 1)) * 0x783A9B23) >> 26]);
139 u.dw.l &= (u.dw.l - 1);
143 ret = Square(BSFTable[((~(u.dw.h ^ (u.dw.h - 1))) * 0x783A9B23) >> 26]);
144 u.dw.h &= (u.dw.h - 1);
149 #endif // !defined(USE_BSFQ)
152 /// bitboards_init() initializes various bitboard arrays. It is called during
153 /// program initialization.
155 void bitboards_init() {
157 for (Bitboard b = 0; b < 256; b++)
158 BitCount8Bit[b] = (uint8_t)count_1s<CNT32_MAX15>(b);
160 SquaresByColorBB[DARK] = 0xAA55AA55AA55AA55ULL;
161 SquaresByColorBB[LIGHT] = ~SquaresByColorBB[DARK];
163 for (Square s = SQ_A1; s <= SQ_H8; s++)
165 SetMaskBB[s] = 1ULL << s;
166 ClearMaskBB[s] = ~SetMaskBB[s];
169 ClearMaskBB[SQ_NONE] = ~0ULL;
171 FileBB[FILE_A] = FileABB;
172 RankBB[RANK_1] = Rank1BB;
174 for (int f = FILE_B; f <= FILE_H; f++)
176 FileBB[f] = FileBB[f - 1] << 1;
177 RankBB[f] = RankBB[f - 1] << 8;
180 for (int f = FILE_A; f <= FILE_H; f++)
182 NeighboringFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
183 ThisAndNeighboringFilesBB[f] = FileBB[f] | NeighboringFilesBB[f];
186 for (int rw = RANK_7, rb = RANK_2; rw >= RANK_1; rw--, rb++)
188 InFrontBB[WHITE][rw] = InFrontBB[WHITE][rw + 1] | RankBB[rw + 1];
189 InFrontBB[BLACK][rb] = InFrontBB[BLACK][rb - 1] | RankBB[rb - 1];
192 for (Color c = WHITE; c <= BLACK; c++)
193 for (Square s = SQ_A1; s <= SQ_H8; s++)
195 SquaresInFrontMask[c][s] = in_front_bb(c, s) & file_bb(s);
196 PassedPawnMask[c][s] = in_front_bb(c, s) & this_and_neighboring_files_bb(file_of(s));
197 AttackSpanMask[c][s] = in_front_bb(c, s) & neighboring_files_bb(file_of(s));
200 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
201 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
202 SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
204 for (int i = 0; i < 64; i++)
205 if (!CpuIs64Bit) // Matt Taylor's folding trick for 32 bit systems
207 Bitboard b = 1ULL << i;
210 BSFTable[uint32_t(b * 0x783A9B23) >> 26] = i;
213 BSFTable[((1ULL << i) * 0x218A392CD3D5DBFULL) >> 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 (square_is_ok(to) && square_distance(s, to) < 3)
226 set_bit(&StepAttacksBB[make_piece(c, pt)][s], to);
229 init_magic_bitboards(ROOK, RAttacks, RMagics, RMasks, RShifts);
230 init_magic_bitboards(BISHOP, BAttacks, BMagics, BMasks, BShifts);
232 for (Square s = SQ_A1; s <= SQ_H8; s++)
234 BishopPseudoAttacks[s] = bishop_attacks_bb(s, 0);
235 RookPseudoAttacks[s] = rook_attacks_bb(s, 0);
236 QueenPseudoAttacks[s] = queen_attacks_bb(s, 0);
239 for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
240 for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
241 if (bit_is_set(QueenPseudoAttacks[s1], s2))
243 Square delta = (s2 - s1) / square_distance(s1, s2);
245 for (Square s = s1 + delta; s != s2; s += delta)
246 set_bit(&BetweenBB[s1][s2], s);
253 Bitboard sliding_attacks(PieceType pt, Square sq, Bitboard occupied) {
255 Square deltas[][4] = { { DELTA_N, DELTA_E, DELTA_S, DELTA_W },
256 { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW } };
257 Bitboard attacks = 0;
258 Square* delta = (pt == ROOK ? deltas[0] : deltas[1]);
260 for (int i = 0; i < 4; i++)
262 Square s = sq + delta[i];
264 while (square_is_ok(s) && square_distance(s, s - delta[i]) == 1)
266 set_bit(&attacks, s);
268 if (bit_is_set(occupied, s))
278 Bitboard pick_random(Bitboard mask, RKISS& rk, int booster) {
282 // Values s1 and s2 are used to rotate the candidate magic of a
283 // quantity known to be the optimal to quickly find the magics.
284 int s1 = booster & 63, s2 = (booster >> 6) & 63;
288 magic = rk.rand<Bitboard>();
289 magic = (magic >> s1) | (magic << (64 - s1));
290 magic &= rk.rand<Bitboard>();
291 magic = (magic >> s2) | (magic << (64 - s2));
292 magic &= rk.rand<Bitboard>();
294 if (BitCount8Bit[(mask * magic) >> 56] >= 6)
300 // init_magic_bitboards() computes all rook and bishop magics at startup.
301 // Magic bitboards are used to look up attacks of sliding pieces. As reference
302 // see chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
303 // use the so called "fancy" approach.
305 void init_magic_bitboards(PieceType pt, Bitboard* attacks[], Bitboard magics[],
306 Bitboard masks[], int shifts[]) {
308 int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
309 { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
311 Bitboard occupancy[4096], reference[4096], edges, b;
312 int i, size, index, booster;
314 // attacks[s] is a pointer to the beginning of the attacks table for square 's'
315 attacks[SQ_A1] = (pt == ROOK ? RookTable : BishopTable);
317 for (Square s = SQ_A1; s <= SQ_H8; s++)
319 // Board edges are not considered in the relevant occupancies
320 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
322 // Given a square 's', the mask is the bitboard of sliding attacks from
323 // 's' computed on an empty board. The index must be big enough to contain
324 // all the attacks for each possible subset of the mask and so is 2 power
325 // the number of 1s of the mask. Hence we deduce the size of the shift to
326 // apply to the 64 or 32 bits word to get the index.
327 masks[s] = sliding_attacks(pt, s, 0) & ~edges;
328 shifts[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(masks[s]);
330 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
331 // store the corresponding sliding attacks bitboard in reference[].
335 reference[size++] = sliding_attacks(pt, s, b);
336 b = (b - masks[s]) & masks[s];
339 // Set the offset for the table of the next square. We have individual
340 // table sizes for each square with "Fancy Magic Bitboards".
342 attacks[s + 1] = attacks[s] + size;
344 booster = MagicBoosters[CpuIs64Bit][rank_of(s)];
346 // Find a magic for square 's' picking up an (almost) random number
347 // until we find the one that passes the verification test.
349 magics[s] = pick_random(masks[s], rk, booster);
350 memset(attacks[s], 0, size * sizeof(Bitboard));
352 // A good magic must map every possible occupancy to an index that
353 // looks up the correct sliding attack in the attacks[s] database.
354 // Note that we build up the database for square 's' as a side
355 // effect of verifying the magic.
356 for (i = 0; i < size; i++)
358 index = (pt == ROOK ? rook_index(s, occupancy[i])
359 : bishop_index(s, occupancy[i]));
361 if (!attacks[s][index])
362 attacks[s][index] = reference[i];
364 else if (attacks[s][index] != reference[i])