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
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/>.
31 #define S(mg, eg) make_score(mg, eg)
34 constexpr Score Backward = S( 9, 24);
35 constexpr Score Doubled = S(11, 56);
36 constexpr Score Isolated = S( 5, 15);
38 // Connected pawn bonus
39 constexpr int Connected[RANK_NB] = { 0, 13, 17, 24, 59, 96, 171 };
41 // Strength of pawn shelter for our king by [distance from edge][rank].
42 // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
43 constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
44 { V( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
45 { V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
46 { V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
47 { V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
50 // Danger of enemy pawns moving toward our king by [distance from edge][rank].
51 // RANK_1 = 0 is used for files where the enemy has no pawn, or their pawn
52 // is behind our king.
53 constexpr Value UnblockedStorm[int(FILE_NB) / 2][RANK_NB] = {
54 { V( 89), V(107), V(123), V(93), V(57), V( 45), V( 51) },
55 { V( 44), V(-18), V(123), V(46), V(39), V( -7), V( 23) },
56 { V( 4), V( 52), V(162), V(37), V( 7), V(-14), V( -2) },
57 { V(-10), V(-14), V( 90), V(15), V( 2), V( -7), V(-16) }
64 Score evaluate(const Position& pos, Pawns::Entry* e) {
66 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
67 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
69 Bitboard b, neighbours, stoppers, doubled, support, phalanx;
70 Bitboard lever, leverPush;
72 bool opposed, backward;
73 Score score = SCORE_ZERO;
74 const Square* pl = pos.squares<PAWN>(Us);
76 Bitboard ourPawns = pos.pieces( Us, PAWN);
77 Bitboard theirPawns = pos.pieces(Them, PAWN);
79 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
80 e->kingSquares[Us] = SQ_NONE;
81 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
83 // Loop through all pawns of the current color and score each pawn
84 while ((s = *pl++) != SQ_NONE)
86 assert(pos.piece_on(s) == make_piece(Us, PAWN));
89 Rank r = relative_rank(Us, s);
91 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
94 opposed = theirPawns & forward_file_bb(Us, s);
95 stoppers = theirPawns & passed_pawn_span(Us, s);
96 lever = theirPawns & PawnAttacks[Us][s];
97 leverPush = theirPawns & PawnAttacks[Us][s + Up];
98 doubled = ourPawns & (s - Up);
99 neighbours = ourPawns & adjacent_files_bb(f);
100 phalanx = neighbours & rank_bb(s);
101 support = neighbours & rank_bb(s - Up);
103 // A pawn is backward when it is behind all pawns of the same color
104 // on the adjacent files and cannot be safely advanced.
105 backward = !(ourPawns & pawn_attack_span(Them, s + Up))
106 && (stoppers & (leverPush | (s + Up)));
108 // Passed pawns will be properly scored in evaluation because we need
109 // full attack info to evaluate them. Include also not passed pawns
110 // which could become passed after one or two pawn pushes when are
111 // not attacked more times than defended.
112 if ( !(stoppers ^ lever ^ leverPush)
113 && (support || !more_than_one(lever))
114 && popcount(phalanx) >= popcount(leverPush))
115 e->passedPawns[Us] |= s;
117 else if (stoppers == square_bb(s + Up) && r >= RANK_5)
119 b = shift<Up>(support) & ~theirPawns;
121 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
122 e->passedPawns[Us] |= s;
126 if (support | phalanx)
128 int v = (phalanx ? 3 : 2) * Connected[r];
129 v = 17 * popcount(support) + (v >> (opposed + 1));
130 score += make_score(v, v * (r - 2) / 4);
132 else if (!neighbours)
133 score -= Isolated, e->weakUnopposed[Us] += !opposed;
136 score -= Backward, e->weakUnopposed[Us] += !opposed;
138 if (doubled && !support)
149 /// Pawns::probe() looks up the current position's pawns configuration in
150 /// the pawns hash table. It returns a pointer to the Entry if the position
151 /// is found. Otherwise a new Entry is computed and stored there, so we don't
152 /// have to recompute all when the same pawns configuration occurs again.
154 Entry* probe(const Position& pos) {
156 Key key = pos.pawn_key();
157 Entry* e = pos.this_thread()->pawnsTable[key];
163 e->scores[WHITE] = evaluate<WHITE>(pos, e);
164 e->scores[BLACK] = evaluate<BLACK>(pos, e);
170 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
171 /// penalty for a king, looking at the king file and the two closest files.
174 Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
176 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
177 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
178 constexpr Bitboard BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
180 Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
181 Bitboard ourPawns = b & pos.pieces(Us);
182 Bitboard theirPawns = b & pos.pieces(Them);
184 Value safety = (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq) ?
185 Value(374) : Value(5);
187 File center = clamp(file_of(ksq), FILE_B, FILE_G);
188 for (File f = File(center - 1); f <= File(center + 1); ++f)
190 b = ourPawns & file_bb(f);
191 Rank ourRank = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
193 b = theirPawns & file_bb(f);
194 Rank theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
196 int d = std::min(f, ~f);
197 safety += ShelterStrength[d][ourRank];
198 safety -= (ourRank && (ourRank == theirRank - 1)) ? 66 * (theirRank == RANK_3)
199 : UnblockedStorm[d][theirRank];
206 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
207 /// when king square changes, which is about 20% of total king_safety() calls.
210 Score Entry::do_king_safety(const Position& pos) {
212 Square ksq = pos.square<KING>(Us);
213 kingSquares[Us] = ksq;
214 castlingRights[Us] = pos.castling_rights(Us);
215 int minKingPawnDistance = 0;
217 Bitboard pawns = pos.pieces(Us, PAWN);
219 while (!(DistanceRingBB[ksq][++minKingPawnDistance] & pawns)) {}
221 Value bonus = evaluate_shelter<Us>(pos, ksq);
223 // If we can castle use the bonus after the castling if it is bigger
224 if (pos.can_castle(Us | KING_SIDE))
225 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
227 if (pos.can_castle(Us | QUEEN_SIDE))
228 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
230 return make_score(bonus, -16 * minKingPawnDistance);
233 // Explicit template instantiation
234 template Score Entry::do_king_safety<WHITE>(const Position& pos);
235 template Score Entry::do_king_safety<BLACK>(const Position& pos);