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) 2015-2020 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)
35 constexpr Score Backward = S( 9, 24);
36 constexpr Score Doubled = S(11, 56);
37 constexpr Score Isolated = S( 5, 15);
38 constexpr Score WeakLever = S( 0, 56);
39 constexpr Score WeakUnopposed = S(13, 27);
41 constexpr Score BlockedStorm[RANK_NB] = {S( 0, 0), S( 0, 0), S( 76, 78), S(-10, 15), S(-7, 10), S(-4, 6), S(-1, 2)};
43 // Connected pawn bonus
44 constexpr int Connected[RANK_NB] = { 0, 7, 8, 12, 29, 48, 86 };
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( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
50 { V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
51 { V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
52 { V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
55 // Danger of enemy pawns moving toward our king by [distance from edge][rank].
56 // RANK_1 = 0 is used for files where the enemy has no pawn, or their pawn
57 // is behind our king. Note that UnblockedStorm[0][1-2] accommodate opponent pawn
58 // on edge, likely blocked by our king.
59 constexpr Value UnblockedStorm[int(FILE_NB) / 2][RANK_NB] = {
60 { V( 85), V(-289), V(-166), V(97), V(50), V( 45), V( 50) },
61 { V( 46), V( -25), V( 122), V(45), V(37), V(-10), V( 20) },
62 { V( -6), V( 51), V( 168), V(34), V(-2), V(-22), V(-14) },
63 { V(-15), V( -11), V( 101), V( 4), V(11), V(-15), V(-29) }
70 /// evaluate() calculates a score for the static pawn structure of the given position.
71 /// We cannot use the location of pieces or king in this function, as the evaluation
72 /// of the pawn structure will be stored in a small cache for speed reasons, and will
73 /// be re-used even when the pieces have moved.
76 Score evaluate(const Position& pos, Pawns::Entry* e) {
78 constexpr Color Them = ~Us;
79 constexpr Direction Up = pawn_push(Us);
81 Bitboard neighbours, stoppers, support, phalanx, opposed;
82 Bitboard lever, leverPush, blocked;
84 bool backward, passed, doubled;
85 Score score = SCORE_ZERO;
86 const Square* pl = pos.squares<PAWN>(Us);
88 Bitboard ourPawns = pos.pieces( Us, PAWN);
89 Bitboard theirPawns = pos.pieces(Them, PAWN);
91 Bitboard doubleAttackThem = pawn_double_attacks_bb<Them>(theirPawns);
93 e->passedPawns[Us] = 0;
94 e->kingSquares[Us] = SQ_NONE;
95 e->pawnAttacks[Us] = e->pawnAttacksSpan[Us] = pawn_attacks_bb<Us>(ourPawns);
96 e->blockedCount += popcount(shift<Up>(ourPawns) & (theirPawns | doubleAttackThem));
98 // Loop through all pawns of the current color and score each pawn
99 while ((s = *pl++) != SQ_NONE)
101 assert(pos.piece_on(s) == make_piece(Us, PAWN));
103 Rank r = relative_rank(Us, s);
106 opposed = theirPawns & forward_file_bb(Us, s);
107 blocked = theirPawns & (s + Up);
108 stoppers = theirPawns & passed_pawn_span(Us, s);
109 lever = theirPawns & pawn_attacks_bb(Us, s);
110 leverPush = theirPawns & pawn_attacks_bb(Us, s + Up);
111 doubled = ourPawns & (s - Up);
112 neighbours = ourPawns & adjacent_files_bb(s);
113 phalanx = neighbours & rank_bb(s);
114 support = neighbours & rank_bb(s - Up);
116 // A pawn is backward when it is behind all pawns of the same color on
117 // the adjacent files and cannot safely advance.
118 backward = !(neighbours & forward_ranks_bb(Them, s + Up))
119 && (leverPush | blocked);
121 // Compute additional span if pawn is not backward nor blocked
122 if (!backward && !blocked)
123 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
125 // A pawn is passed if one of the three following conditions is true:
126 // (a) there is no stoppers except some levers
127 // (b) the only stoppers are the leverPush, but we outnumber them
128 // (c) there is only one front stopper which can be levered.
129 // (Refined in Evaluation::passed)
130 passed = !(stoppers ^ lever)
131 || ( !(stoppers ^ leverPush)
132 && popcount(phalanx) >= popcount(leverPush))
133 || ( stoppers == blocked && r >= RANK_5
134 && (shift<Up>(support) & ~(theirPawns | doubleAttackThem)));
136 passed &= !(forward_file_bb(Us, s) & ourPawns);
138 // Passed pawns will be properly scored later in evaluation when we have
141 e->passedPawns[Us] |= s;
144 if (support | phalanx)
146 int v = Connected[r] * (4 + 2 * bool(phalanx) - 2 * bool(opposed) - bool(blocked)) / 2
147 + 21 * popcount(support);
149 score += make_score(v, v * (r - 2) / 4);
152 else if (!neighbours)
155 && (ourPawns & forward_file_bb(Them, s))
156 && !(theirPawns & adjacent_files_bb(s)))
160 + WeakUnopposed * !opposed;
165 + WeakUnopposed * !opposed;
168 score -= Doubled * doubled
169 + WeakLever * more_than_one(lever);
180 /// Pawns::probe() looks up the current position's pawns configuration in
181 /// the pawns hash table. It returns a pointer to the Entry if the position
182 /// is found. Otherwise a new Entry is computed and stored there, so we don't
183 /// have to recompute all when the same pawns configuration occurs again.
185 Entry* probe(const Position& pos) {
187 Key key = pos.pawn_key();
188 Entry* e = pos.this_thread()->pawnsTable[key];
195 e->scores[WHITE] = evaluate<WHITE>(pos, e);
196 e->scores[BLACK] = evaluate<BLACK>(pos, e);
202 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
203 /// penalty for a king, looking at the king file and the two closest files.
206 Score Entry::evaluate_shelter(const Position& pos, Square ksq) const {
208 constexpr Color Them = ~Us;
210 Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
211 Bitboard ourPawns = b & pos.pieces(Us) & ~pawnAttacks[Them];
212 Bitboard theirPawns = b & pos.pieces(Them);
214 Score bonus = make_score(5, 5);
216 File center = Utility::clamp(file_of(ksq), FILE_B, FILE_G);
217 for (File f = File(center - 1); f <= File(center + 1); ++f)
219 b = ourPawns & file_bb(f);
220 int ourRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
222 b = theirPawns & file_bb(f);
223 int theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
225 int d = edge_distance(f);
226 bonus += make_score(ShelterStrength[d][ourRank], 0);
228 if (ourRank && (ourRank == theirRank - 1))
229 bonus -= BlockedStorm[theirRank];
231 bonus -= make_score(UnblockedStorm[d][theirRank], 0);
238 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
239 /// when king square changes, which is about 20% of total king_safety() calls.
242 Score Entry::do_king_safety(const Position& pos) {
244 Square ksq = pos.square<KING>(Us);
245 kingSquares[Us] = ksq;
246 castlingRights[Us] = pos.castling_rights(Us);
247 auto compare = [](Score a, Score b) { return mg_value(a) < mg_value(b); };
249 Score shelter = evaluate_shelter<Us>(pos, ksq);
251 // If we can castle use the bonus after castling if it is bigger
253 if (pos.can_castle(Us & KING_SIDE))
254 shelter = std::max(shelter, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)), compare);
256 if (pos.can_castle(Us & QUEEN_SIDE))
257 shelter = std::max(shelter, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)), compare);
259 // In endgame we like to bring our king near our closest pawn
260 Bitboard pawns = pos.pieces(Us, PAWN);
263 if (pawns & attacks_bb<KING>(ksq))
266 minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
268 return shelter - make_score(0, 16 * minPawnDist);
271 // Explicit template instantiation
272 template Score Entry::do_king_safety<WHITE>(const Position& pos);
273 template Score Entry::do_king_safety<BLACK>(const Position& pos);