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 constexpr Score Isolated = S(13, 18);
37 // Backward pawn penalty
38 constexpr 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 constexpr Score Doubled = S(18, 38);
46 // Strength of pawn shelter for our king by [distance from edge][rank].
47 // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
48 constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
49 { V( -9), V(64), V(77), V( 44), V( 4), V( -1), V(-11) },
50 { V(-15), V(83), V(51), V(-10), V( 1), V(-10), V(-28) },
51 { V(-18), V(84), V(27), V(-12), V(21), V( -7), V(-36) },
52 { V( 12), V(79), V(25), V( 19), V( 9), V( -6), V(-33) }
55 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
56 // For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has
57 // no pawn on the given file, or their pawn is behind our king.
58 constexpr Value StormDanger[][4][RANK_NB] = {
59 { { V( 4), V( 73), V( 132), V(46), V(31) }, // Unopposed
60 { V( 1), V( 64), V( 143), V(26), V(13) },
61 { V( 1), V( 47), V( 110), V(44), V(24) },
62 { V( 0), V( 72), V( 127), V(50), V(31) } },
63 { { V( 0), V( 0), V( 19), V(23), V( 1) }, // BlockedByPawn
64 { V( 0), V( 0), V( 88), V(27), V( 2) },
65 { V( 0), V( 0), V( 101), V(16), V( 1) },
66 { V( 0), V( 0), V( 111), V(22), V(15) } },
67 { { V(22), V( 45), V( 104), V(62), V( 6) }, // Unblocked
68 { V(31), V( 30), V( 99), V(39), V(19) },
69 { V(23), V( 29), V( 96), V(41), V(15) },
70 { V(21), V( 23), V( 116), V(41), V(15) } }
77 Score evaluate(const Position& pos, Pawns::Entry* e) {
79 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
80 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
82 Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
83 Bitboard lever, leverPush;
85 bool opposed, backward;
86 Score score = SCORE_ZERO;
87 const Square* pl = pos.squares<PAWN>(Us);
89 Bitboard ourPawns = pos.pieces( Us, PAWN);
90 Bitboard theirPawns = pos.pieces(Them, PAWN);
92 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
93 e->semiopenFiles[Us] = 0xFF;
94 e->kingSquares[Us] = SQ_NONE;
95 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
96 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
97 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
99 // Loop through all pawns of the current color and score each pawn
100 while ((s = *pl++) != SQ_NONE)
102 assert(pos.piece_on(s) == make_piece(Us, PAWN));
106 e->semiopenFiles[Us] &= ~(1 << f);
107 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
110 opposed = theirPawns & forward_file_bb(Us, s);
111 stoppers = theirPawns & passed_pawn_mask(Us, s);
112 lever = theirPawns & PawnAttacks[Us][s];
113 leverPush = theirPawns & PawnAttacks[Us][s + Up];
114 doubled = ourPawns & (s - Up);
115 neighbours = ourPawns & adjacent_files_bb(f);
116 phalanx = neighbours & rank_bb(s);
117 supported = neighbours & rank_bb(s - Up);
119 // A pawn is backward when it is behind all pawns of the same color
120 // on the adjacent files and cannot be safely advanced.
121 backward = !(ourPawns & pawn_attack_span(Them, s + Up))
122 && (stoppers & (leverPush | (s + Up)));
124 // Passed pawns will be properly scored in evaluation because we need
125 // full attack info to evaluate them. Include also not passed pawns
126 // which could become passed after one or two pawn pushes when are
127 // not attacked more times than defended.
128 if ( !(stoppers ^ lever ^ leverPush)
129 && !(ourPawns & forward_file_bb(Us, s))
130 && popcount(supported) >= popcount(lever) - 1
131 && popcount(phalanx) >= popcount(leverPush))
132 e->passedPawns[Us] |= s;
134 else if ( stoppers == SquareBB[s + Up]
135 && relative_rank(Us, s) >= RANK_5)
137 b = shift<Up>(supported) & ~theirPawns;
139 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
140 e->passedPawns[Us] |= s;
144 if (supported | phalanx)
145 score += Connected[opposed][bool(phalanx)][popcount(supported)][relative_rank(Us, s)];
147 else if (!neighbours)
148 score -= Isolated, e->weakUnopposed[Us] += !opposed;
151 score -= Backward, e->weakUnopposed[Us] += !opposed;
153 if (doubled && !supported)
164 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
165 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
166 /// to reduce independent parameters and to allow easier tuning and better insight.
170 static constexpr int Seed[RANK_NB] = { 0, 13, 24, 18, 65, 100, 175, 330 };
172 for (int opposed = 0; opposed <= 1; ++opposed)
173 for (int phalanx = 0; phalanx <= 1; ++phalanx)
174 for (int support = 0; support <= 2; ++support)
175 for (Rank r = RANK_2; r < RANK_8; ++r)
177 int v = 17 * support;
178 v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
180 Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
185 /// Pawns::probe() looks up the current position's pawns configuration in
186 /// the pawns hash table. It returns a pointer to the Entry if the position
187 /// is found. Otherwise a new Entry is computed and stored there, so we don't
188 /// have to recompute all when the same pawns configuration occurs again.
190 Entry* probe(const Position& pos) {
192 Key key = pos.pawn_key();
193 Entry* e = pos.this_thread()->pawnsTable[key];
199 e->scores[WHITE] = evaluate<WHITE>(pos, e);
200 e->scores[BLACK] = evaluate<BLACK>(pos, e);
201 e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
202 e->asymmetry = popcount( (e->passedPawns[WHITE] | e->passedPawns[BLACK])
203 | (e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]));
209 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
210 /// penalty for a king, looking at the king file and the two closest files.
213 Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
215 enum { Unopposed, BlockedByPawn, Unblocked };
216 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
217 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
218 constexpr Bitboard BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
220 Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
221 Bitboard ourPawns = b & pos.pieces(Us);
222 Bitboard theirPawns = b & pos.pieces(Them);
224 Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
226 if (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq)
229 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
230 for (File f = File(center - 1); f <= File(center + 1); ++f)
232 b = ourPawns & file_bb(f);
233 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
235 b = theirPawns & file_bb(f);
236 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
238 int d = std::min(f, ~f);
239 safety += ShelterStrength[d][rkUs]
240 - StormDanger[rkUs == RANK_1 ? Unopposed :
241 rkUs == rkThem - 1 ? BlockedByPawn : Unblocked]
249 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
250 /// when king square changes, which is about 20% of total king_safety() calls.
253 Score Entry::do_king_safety(const Position& pos, Square ksq) {
255 kingSquares[Us] = ksq;
256 castlingRights[Us] = pos.can_castle(Us);
257 int minKingPawnDistance = 0;
259 Bitboard pawns = pos.pieces(Us, PAWN);
261 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
263 Value bonus = evaluate_shelter<Us>(pos, ksq);
265 // If we can castle use the bonus after the castling if it is bigger
266 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
267 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
269 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
270 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
272 return make_score(bonus, -16 * minKingPawnDistance);
275 // Explicit template instantiation
276 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
277 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);