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/>.
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 WeakUnopposed = S( 13, 27);
39 constexpr Score Attacked2Unsupported = S( 0, 20);
41 // Connected pawn bonus
42 constexpr int Connected[RANK_NB] = { 0, 7, 8, 12, 29, 48, 86 };
44 // Strength of pawn shelter for our king by [distance from edge][rank].
45 // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
46 constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
47 { V( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
48 { V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
49 { V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
50 { V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
53 // Danger of enemy pawns moving toward our king by [distance from edge][rank].
54 // RANK_1 = 0 is used for files where the enemy has no pawn, or their pawn
55 // is behind our king.
56 // [0][1-2] accommodate opponent pawn on edge (likely blocked by our king)
57 constexpr Value UnblockedStorm[int(FILE_NB) / 2][RANK_NB] = {
58 { V( 89), V(-285), V(-185), V(93), V(57), V( 45), V( 51) },
59 { V( 44), V( -18), V( 123), V(46), V(39), V( -7), V( 23) },
60 { V( 4), V( 52), V( 162), V(37), V( 7), V(-14), V( -2) },
61 { V(-10), V( -14), V( 90), V(15), V( 2), V( -7), V(-16) }
68 Score evaluate(const Position& pos, Pawns::Entry* e) {
70 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
71 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
73 Bitboard b, neighbours, stoppers, doubled, support, phalanx;
74 Bitboard lever, leverPush;
76 bool opposed, backward;
77 Score score = SCORE_ZERO;
78 const Square* pl = pos.squares<PAWN>(Us);
80 Bitboard ourPawns = pos.pieces( Us, PAWN);
81 Bitboard theirPawns = pos.pieces(Them, PAWN);
83 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
84 e->kingSquares[Us] = SQ_NONE;
85 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
87 // Unsupported enemy pawns attacked twice by us
88 score += Attacked2Unsupported * popcount( theirPawns
89 & pawn_double_attacks_bb<Us>(ourPawns)
90 & ~pawn_attacks_bb<Them>(theirPawns));
92 // Loop through all pawns of the current color and score each pawn
93 while ((s = *pl++) != SQ_NONE)
95 assert(pos.piece_on(s) == make_piece(Us, PAWN));
97 Rank r = relative_rank(Us, s);
99 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
102 opposed = theirPawns & forward_file_bb(Us, s);
103 stoppers = theirPawns & passed_pawn_span(Us, s);
104 lever = theirPawns & PawnAttacks[Us][s];
105 leverPush = theirPawns & PawnAttacks[Us][s + Up];
106 doubled = ourPawns & (s - Up);
107 neighbours = ourPawns & adjacent_files_bb(s);
108 phalanx = neighbours & rank_bb(s);
109 support = neighbours & rank_bb(s - Up);
111 // A pawn is backward when it is behind all pawns of the same color on
112 // the adjacent files and cannot safely advance. Phalanx and isolated
113 // pawns will be excluded when the pawn is scored.
114 backward = !(neighbours & forward_ranks_bb(Them, s))
115 && (stoppers & (leverPush | (s + Up)));
117 // Passed pawns will be properly scored in evaluation because we need
118 // full attack info to evaluate them. Include also not passed pawns
119 // which could become passed after one or two pawn pushes when are
120 // not attacked more times than defended.
121 if ( !(stoppers ^ lever) ||
122 (!(stoppers ^ leverPush) && popcount(phalanx) >= popcount(leverPush)))
123 e->passedPawns[Us] |= s;
125 else if (stoppers == square_bb(s + Up) && r >= RANK_5)
127 b = shift<Up>(support) & ~theirPawns;
129 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
130 e->passedPawns[Us] |= s;
134 if (support | phalanx)
136 int v = Connected[r] * (phalanx ? 3 : 2) / (opposed ? 2 : 1)
137 + 17 * popcount(support);
139 score += make_score(v, v * (r - 2) / 4);
142 else if (!neighbours)
143 score -= Isolated + WeakUnopposed * int(!opposed);
146 score -= Backward + WeakUnopposed * int(!opposed);
148 if (doubled && !support)
159 /// Pawns::probe() looks up the current position's pawns configuration in
160 /// the pawns hash table. It returns a pointer to the Entry if the position
161 /// is found. Otherwise a new Entry is computed and stored there, so we don't
162 /// have to recompute all when the same pawns configuration occurs again.
164 Entry* probe(const Position& pos) {
166 Key key = pos.pawn_key();
167 Entry* e = pos.this_thread()->pawnsTable[key];
173 e->scores[WHITE] = evaluate<WHITE>(pos, e);
174 e->scores[BLACK] = evaluate<BLACK>(pos, e);
180 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
181 /// penalty for a king, looking at the king file and the two closest files.
184 void Entry::evaluate_shelter(const Position& pos, Square ksq, Score& shelter) {
186 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
188 Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
189 Bitboard ourPawns = b & pos.pieces(Us);
190 Bitboard theirPawns = b & pos.pieces(Them);
192 Score bonus = make_score(5, 5);
194 File center = clamp(file_of(ksq), FILE_B, FILE_G);
195 for (File f = File(center - 1); f <= File(center + 1); ++f)
197 b = ourPawns & file_bb(f);
198 Rank ourRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
200 b = theirPawns & file_bb(f);
201 Rank theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
203 int d = std::min(f, ~f);
204 bonus += make_score(ShelterStrength[d][ourRank], 0);
206 if (ourRank && (ourRank == theirRank - 1))
207 bonus -= make_score(82 * (theirRank == RANK_3), 82 * (theirRank == RANK_3));
209 bonus -= make_score(UnblockedStorm[d][theirRank], 0);
212 if (mg_value(bonus) > mg_value(shelter))
217 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
218 /// when king square changes, which is about 20% of total king_safety() calls.
221 Score Entry::do_king_safety(const Position& pos) {
223 Square ksq = pos.square<KING>(Us);
224 kingSquares[Us] = ksq;
225 castlingRights[Us] = pos.castling_rights(Us);
227 Bitboard pawns = pos.pieces(Us, PAWN);
228 int minPawnDist = pawns ? 8 : 0;
230 if (pawns & PseudoAttacks[KING][ksq])
234 minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
236 Score shelter = make_score(-VALUE_INFINITE, VALUE_ZERO);
237 evaluate_shelter<Us>(pos, ksq, shelter);
239 // If we can castle use the bonus after the castling if it is bigger
240 if (pos.can_castle(Us | KING_SIDE))
241 evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1), shelter);
243 if (pos.can_castle(Us | QUEEN_SIDE))
244 evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1), shelter);
246 return shelter - make_score(VALUE_ZERO, 16 * minPawnDist);
249 // Explicit template instantiation
250 template Score Entry::do_king_safety<WHITE>(const Position& pos);
251 template Score Entry::do_king_safety<BLACK>(const Position& pos);