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) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
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.
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.
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/>.
32 #define S(mg, eg) make_score(mg, eg)
34 // Isolated pawn penalty
35 const Score Isolated = S(13, 18);
37 // Backward pawn penalty
38 const Score Backward = S(24, 12);
40 // Connected pawn bonus by opposed, phalanx, #support and rank
41 Score Connected[2][2][3][RANK_NB];
43 // Doubled pawn penalty
44 const Score Doubled = S(18, 38);
46 // Lever bonus by rank
47 const Score Lever[RANK_NB] = {
48 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
49 S(17, 16), S(33, 32), S(0, 0), S(0, 0)
52 // Weakness of our pawn shelter in front of the king by [isKingFile][distance from edge][rank].
53 // RANK_1 = 0 is used for files where we have no pawns or our pawn is behind our king.
54 const Value ShelterWeakness[][int(FILE_NB) / 2][RANK_NB] = {
55 { { V( 97), V(17), V( 9), V(44), V( 84), V( 87), V( 99) }, // Not On King file
56 { V(106), V( 6), V(33), V(86), V( 87), V(104), V(112) },
57 { V(101), V( 2), V(65), V(98), V( 58), V( 89), V(115) },
58 { V( 73), V( 7), V(54), V(73), V( 84), V( 83), V(111) } },
59 { { V(104), V(20), V( 6), V(27), V( 86), V( 93), V( 82) }, // On King file
60 { V(123), V( 9), V(34), V(96), V(112), V( 88), V( 75) },
61 { V(120), V(25), V(65), V(91), V( 66), V( 78), V(117) },
62 { V( 81), V( 2), V(47), V(63), V( 94), V( 93), V(104) } }
65 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
66 // For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has
67 // no pawn on the given file, or their pawn is behind our king.
68 const Value StormDanger[][4][RANK_NB] = {
69 { { V( 0), V(-290), V(-274), V(57), V(41) }, // BlockedByKing
70 { V( 0), V( 60), V( 144), V(39), V(13) },
71 { V( 0), V( 65), V( 141), V(41), V(34) },
72 { V( 0), V( 53), V( 127), V(56), V(14) } },
73 { { V( 4), V( 73), V( 132), V(46), V(31) }, // Unopposed
74 { V( 1), V( 64), V( 143), V(26), V(13) },
75 { V( 1), V( 47), V( 110), V(44), V(24) },
76 { V( 0), V( 72), V( 127), V(50), V(31) } },
77 { { V( 0), V( 0), V( 79), V(23), V( 1) }, // BlockedByPawn
78 { V( 0), V( 0), V( 148), V(27), V( 2) },
79 { V( 0), V( 0), V( 161), V(16), V( 1) },
80 { V( 0), V( 0), V( 171), V(22), V(15) } },
81 { { V(22), V( 45), V( 104), V(62), V( 6) }, // Unblocked
82 { V(31), V( 30), V( 99), V(39), V(19) },
83 { V(23), V( 29), V( 96), V(41), V(15) },
84 { V(21), V( 23), V( 116), V(41), V(15) } }
87 // Max bonus for king safety. Corresponds to start position with all the pawns
88 // in front of the king and no enemy pawn on the horizon.
89 const Value MaxSafetyBonus = V(258);
95 Score evaluate(const Position& pos, Pawns::Entry* e) {
97 const Color Them = (Us == WHITE ? BLACK : WHITE);
98 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
99 const Direction Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
100 const Direction Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
102 Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
103 Bitboard lever, leverPush;
105 bool opposed, backward;
106 Score score = SCORE_ZERO;
107 const Square* pl = pos.squares<PAWN>(Us);
109 Bitboard ourPawns = pos.pieces( Us, PAWN);
110 Bitboard theirPawns = pos.pieces(Them, PAWN);
112 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
113 e->semiopenFiles[Us] = 0xFF;
114 e->kingSquares[Us] = SQ_NONE;
115 e->pawnAttacks[Us] = shift<Right>(ourPawns) | shift<Left>(ourPawns);
116 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
117 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
119 // Loop through all pawns of the current color and score each pawn
120 while ((s = *pl++) != SQ_NONE)
122 assert(pos.piece_on(s) == make_piece(Us, PAWN));
126 e->semiopenFiles[Us] &= ~(1 << f);
127 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
130 opposed = theirPawns & forward_file_bb(Us, s);
131 stoppers = theirPawns & passed_pawn_mask(Us, s);
132 lever = theirPawns & PawnAttacks[Us][s];
133 leverPush = theirPawns & PawnAttacks[Us][s + Up];
134 doubled = ourPawns & (s - Up);
135 neighbours = ourPawns & adjacent_files_bb(f);
136 phalanx = neighbours & rank_bb(s);
137 supported = neighbours & rank_bb(s - Up);
139 // A pawn is backward when it is behind all pawns of the same color on the
140 // adjacent files and cannot be safely advanced.
141 if (!neighbours || lever || relative_rank(Us, s) >= RANK_5)
145 // Find the backmost rank with neighbours or stoppers
146 b = rank_bb(backmost_sq(Us, neighbours | stoppers));
148 // The pawn is backward when it cannot safely progress to that rank:
149 // either there is a stopper in the way on this rank, or there is a
150 // stopper on adjacent file which controls the way to that rank.
151 backward = (b | shift<Up>(b & adjacent_files_bb(f))) & stoppers;
153 assert(!(backward && (forward_ranks_bb(Them, s + Up) & neighbours)));
156 // Passed pawns will be properly scored in evaluation because we need
157 // full attack info to evaluate them. Include also not passed pawns
158 // which could become passed after one or two pawn pushes when are
159 // not attacked more times than defended.
160 if ( !(stoppers ^ lever ^ leverPush)
161 && !(ourPawns & forward_file_bb(Us, s))
162 && popcount(supported) >= popcount(lever)
163 && popcount(phalanx) >= popcount(leverPush))
164 e->passedPawns[Us] |= s;
166 else if ( stoppers == SquareBB[s + Up]
167 && relative_rank(Us, s) >= RANK_5)
169 b = shift<Up>(supported) & ~theirPawns;
171 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
172 e->passedPawns[Us] |= s;
176 if (supported | phalanx)
177 score += Connected[opposed][bool(phalanx)][popcount(supported)][relative_rank(Us, s)];
179 else if (!neighbours)
180 score -= Isolated, e->weakUnopposed[Us] += !opposed;
183 score -= Backward, e->weakUnopposed[Us] += !opposed;
185 if (doubled && !supported)
189 score += Lever[relative_rank(Us, s)];
199 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
200 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
201 /// to reduce independent parameters and to allow easier tuning and better insight.
205 static const int Seed[RANK_NB] = { 0, 13, 24, 18, 76, 100, 175, 330 };
207 for (int opposed = 0; opposed <= 1; ++opposed)
208 for (int phalanx = 0; phalanx <= 1; ++phalanx)
209 for (int support = 0; support <= 2; ++support)
210 for (Rank r = RANK_2; r < RANK_8; ++r)
212 int v = 17 * support;
213 v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
215 Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
220 /// Pawns::probe() looks up the current position's pawns configuration in
221 /// the pawns hash table. It returns a pointer to the Entry if the position
222 /// is found. Otherwise a new Entry is computed and stored there, so we don't
223 /// have to recompute all when the same pawns configuration occurs again.
225 Entry* probe(const Position& pos) {
227 Key key = pos.pawn_key();
228 Entry* e = pos.this_thread()->pawnsTable[key];
234 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
235 e->asymmetry = popcount(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
236 e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
241 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
242 /// the king is on, as well as the two closest files.
245 Value Entry::shelter_storm(const Position& pos, Square ksq) {
247 const Color Them = (Us == WHITE ? BLACK : WHITE);
249 enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
251 Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
252 Bitboard ourPawns = b & pos.pieces(Us);
253 Bitboard theirPawns = b & pos.pieces(Them);
254 Value safety = MaxSafetyBonus;
255 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
257 for (File f = File(center - 1); f <= File(center + 1); ++f)
259 b = ourPawns & file_bb(f);
260 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
262 b = theirPawns & file_bb(f);
263 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
265 int d = std::min(f, ~f);
266 safety -= ShelterWeakness[f == file_of(ksq)][d][rkUs]
268 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
269 rkUs == RANK_1 ? Unopposed :
270 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
278 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
279 /// when king square changes, which is about 20% of total king_safety() calls.
282 Score Entry::do_king_safety(const Position& pos, Square ksq) {
284 kingSquares[Us] = ksq;
285 castlingRights[Us] = pos.can_castle(Us);
286 int minKingPawnDistance = 0;
288 Bitboard pawns = pos.pieces(Us, PAWN);
290 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
292 Value bonus = shelter_storm<Us>(pos, ksq);
294 // If we can castle use the bonus after the castling if it is bigger
295 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
296 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
298 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
299 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
301 return make_score(bonus, -16 * minKingPawnDistance);
304 // Explicit template instantiation
305 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
306 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);