1/*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
6
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
11
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
19*/
20
21#include <algorithm>
22#include <bitset>
23
24#include "bitboard.h"
25#include "misc.h"
26
27uint8_t PopCnt16[1 << 16];
28uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
29
30Bitboard SquareBB[SQUARE_NB];
31Bitboard LineBB[SQUARE_NB][SQUARE_NB];
32Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
33Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
34
35Magic RookMagics[SQUARE_NB];
36Magic BishopMagics[SQUARE_NB];
37
38namespace {
39
40 Bitboard RookTable[0x19000]; // To store rook attacks
41 Bitboard BishopTable[0x1480]; // To store bishop attacks
42
43 void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
44}
45
46
47/// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
48/// to be printed to standard output. Useful for debugging.
49
50const std::string Bitboards::pretty(Bitboard b) {
51
52 std::string s = "+---+---+---+---+---+---+---+---+\n";
53
54 for (Rank r = RANK_8; r >= RANK_1; --r)
55 {
56 for (File f = FILE_A; f <= FILE_H; ++f)
57 s += b & make_square(f, r) ? "| X " : "| ";
58
59 s += "|\n+---+---+---+---+---+---+---+---+\n";
60 }
61
62 return s;
63}
64
65
66/// Bitboards::init() initializes various bitboard tables. It is called at
67/// startup and relies on global objects to be already zero-initialized.
68
69void Bitboards::init() {
70
71 for (unsigned i = 0; i < (1 << 16); ++i)
72 PopCnt16[i] = std::bitset<16>(i).count();
73
74 for (Square s = SQ_A1; s <= SQ_H8; ++s)
75 SquareBB[s] = (1ULL << s);
76
77 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
78 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
79 SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
80
81 int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
82
83 for (Color c : { WHITE, BLACK })
84 for (PieceType pt : { PAWN, KNIGHT, KING })
85 for (Square s = SQ_A1; s <= SQ_H8; ++s)
86 for (int i = 0; steps[pt][i]; ++i)
87 {
88 Square to = s + Direction(c == WHITE ? steps[pt][i] : -steps[pt][i]);
89
90 if (is_ok(to) && distance(s, to) < 3)
91 {
92 if (pt == PAWN)
93 PawnAttacks[c][s] |= to;
94 else
95 PseudoAttacks[pt][s] |= to;
96 }
97 }
98
99 Direction RookDirections[] = { NORTH, EAST, SOUTH, WEST };
100 Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
101
102 init_magics(RookTable, RookMagics, RookDirections);
103 init_magics(BishopTable, BishopMagics, BishopDirections);
104
105 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
106 {
107 PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
108 PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
109
110 for (PieceType pt : { BISHOP, ROOK })
111 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
112 if (PseudoAttacks[pt][s1] & s2)
113 LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
114 }
115}
116
117
118namespace {
119
120 Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
121
122 Bitboard attack = 0;
123
124 for (int i = 0; i < 4; ++i)
125 for (Square s = sq + directions[i];
126 is_ok(s) && distance(s, s - directions[i]) == 1;
127 s += directions[i])
128 {
129 attack |= s;
130
131 if (occupied & s)
132 break;
133 }
134
135 return attack;
136 }
137
138
139 // init_magics() computes all rook and bishop attacks at startup. Magic
140 // bitboards are used to look up attacks of sliding pieces. As a reference see
141 // www.chessprogramming.org/Magic_Bitboards. In particular, here we use the so
142 // called "fancy" approach.
143
144 void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
145
146 // Optimal PRNG seeds to pick the correct magics in the shortest time
147 int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
148 { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
149
150 Bitboard occupancy[4096], reference[4096], edges, b;
151 int epoch[4096] = {}, cnt = 0, size = 0;
152
153 for (Square s = SQ_A1; s <= SQ_H8; ++s)
154 {
155 // Board edges are not considered in the relevant occupancies
156 edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
157
158 // Given a square 's', the mask is the bitboard of sliding attacks from
159 // 's' computed on an empty board. The index must be big enough to contain
160 // all the attacks for each possible subset of the mask and so is 2 power
161 // the number of 1s of the mask. Hence we deduce the size of the shift to
162 // apply to the 64 or 32 bits word to get the index.
163 Magic& m = magics[s];
164 m.mask = sliding_attack(directions, s, 0) & ~edges;
165 m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
166
167 // Set the offset for the attacks table of the square. We have individual
168 // table sizes for each square with "Fancy Magic Bitboards".
169 m.attacks = s == SQ_A1 ? table : magics[s - 1].attacks + size;
170
171 // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
172 // store the corresponding sliding attack bitboard in reference[].
173 b = size = 0;
174 do {
175 occupancy[size] = b;
176 reference[size] = sliding_attack(directions, s, b);
177
178 if (HasPext)
179 m.attacks[pext(b, m.mask)] = reference[size];
180
181 size++;
182 b = (b - m.mask) & m.mask;
183 } while (b);
184
185 if (HasPext)
186 continue;
187
188 PRNG rng(seeds[Is64Bit][rank_of(s)]);
189
190 // Find a magic for square 's' picking up an (almost) random number
191 // until we find the one that passes the verification test.
192 for (int i = 0; i < size; )
193 {
194 for (m.magic = 0; popcount((m.magic * m.mask) >> 56) < 6; )
195 m.magic = rng.sparse_rand<Bitboard>();
196
197 // A good magic must map every possible occupancy to an index that
198 // looks up the correct sliding attack in the attacks[s] database.
199 // Note that we build up the database for square 's' as a side
200 // effect of verifying the magic. Keep track of the attempt count
201 // and save it in epoch[], little speed-up trick to avoid resetting
202 // m.attacks[] after every failed attempt.
203 for (++cnt, i = 0; i < size; ++i)
204 {
205 unsigned idx = m.index(occupancy[i]);
206
207 if (epoch[idx] < cnt)
208 {
209 epoch[idx] = cnt;
210 m.attacks[idx] = reference[i];
211 }
212 else if (m.attacks[idx] != reference[i])
213 break;
214 }
215 }
216 }
217 }
218}
219