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 BlockedStorm = S(82, 82);
37 constexpr Score Doubled = S(11, 56);
38 constexpr Score Isolated = S( 5, 15);
39 constexpr Score WeakLever = S( 0, 56);
40 constexpr Score WeakUnopposed = S(13, 27);
42 // Connected pawn bonus
43 constexpr int Connected[RANK_NB] = { 0, 7, 8, 12, 29, 48, 86 };
45 // Strength of pawn shelter for our king by [distance from edge][rank].
46 // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
47 constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
48 { V( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
49 { V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
50 { V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
51 { V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
54 // Danger of enemy pawns moving toward our king by [distance from edge][rank].
55 // RANK_1 = 0 is used for files where the enemy has no pawn, or their pawn
56 // is behind our king. Note that UnblockedStorm[0][1-2] accommodate opponent pawn
57 // on edge, likely blocked by our king.
58 constexpr Value UnblockedStorm[int(FILE_NB) / 2][RANK_NB] = {
59 { V( 89), V(-285), V(-185), V(93), V(57), V( 45), V( 51) },
60 { V( 44), V( -18), V( 123), V(46), V(39), V( -7), V( 23) },
61 { V( 4), V( 52), V( 162), V(37), V( 7), V(-14), V( -2) },
62 { V(-10), V( -14), V( 90), V(15), V( 2), V( -7), V(-16) }
69 Score evaluate(const Position& pos, Pawns::Entry* e) {
71 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
72 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
74 Bitboard neighbours, stoppers, doubled, support, phalanx;
75 Bitboard lever, leverPush;
77 bool opposed, backward, passed;
78 Score score = SCORE_ZERO;
79 const Square* pl = pos.squares<PAWN>(Us);
81 Bitboard ourPawns = pos.pieces( Us, PAWN);
82 Bitboard theirPawns = pos.pieces(Them, PAWN);
84 Bitboard doubleAttackThem = pawn_double_attacks_bb<Them>(theirPawns);
86 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
87 e->kingSquares[Us] = SQ_NONE;
88 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
90 // Loop through all pawns of the current color and score each pawn
91 while ((s = *pl++) != SQ_NONE)
93 assert(pos.piece_on(s) == make_piece(Us, PAWN));
95 Rank r = relative_rank(Us, s);
97 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
100 opposed = theirPawns & forward_file_bb(Us, s);
101 stoppers = theirPawns & passed_pawn_span(Us, s);
102 lever = theirPawns & PawnAttacks[Us][s];
103 leverPush = theirPawns & PawnAttacks[Us][s + Up];
104 doubled = ourPawns & (s - Up);
105 neighbours = ourPawns & adjacent_files_bb(s);
106 phalanx = neighbours & rank_bb(s);
107 support = neighbours & rank_bb(s - Up);
109 // A pawn is backward when it is behind all pawns of the same color on
110 // the adjacent files and cannot safely advance. Phalanx and isolated
111 // pawns will be excluded when the pawn is scored.
112 backward = !(neighbours & forward_ranks_bb(Them, s))
113 && (stoppers & (leverPush | (s + Up)));
115 // A pawn is passed if one of the three following conditions is true:
116 // (a) there is no stoppers except some levers
117 // (b) the only stoppers are the leverPush, but we outnumber them
118 // (c) there is only one front stopper which can be levered.
119 passed = !(stoppers ^ lever)
120 || ( !(stoppers ^ leverPush)
121 && popcount(phalanx) >= popcount(leverPush))
122 || ( stoppers == square_bb(s + Up) && r >= RANK_5
123 && (shift<Up>(support) & ~(theirPawns | doubleAttackThem)));
125 // Passed pawns will be properly scored later in evaluation when we have
128 e->passedPawns[Us] |= s;
131 if (support | phalanx)
133 int v = Connected[r] * (phalanx ? 3 : 2) / (opposed ? 2 : 1)
134 + 17 * popcount(support);
136 score += make_score(v, v * (r - 2) / 4);
139 else if (!neighbours)
140 score -= Isolated + WeakUnopposed * int(!opposed);
143 score -= Backward + WeakUnopposed * int(!opposed);
145 if (doubled && !support)
149 // Penalize our unsupported pawns attacked twice by enemy pawns
150 score -= WeakLever * popcount( ourPawns
152 & ~e->pawnAttacks[Us]);
161 /// Pawns::probe() looks up the current position's pawns configuration in
162 /// the pawns hash table. It returns a pointer to the Entry if the position
163 /// is found. Otherwise a new Entry is computed and stored there, so we don't
164 /// have to recompute all when the same pawns configuration occurs again.
166 Entry* probe(const Position& pos) {
168 Key key = pos.pawn_key();
169 Entry* e = pos.this_thread()->pawnsTable[key];
175 e->scores[WHITE] = evaluate<WHITE>(pos, e);
176 e->scores[BLACK] = evaluate<BLACK>(pos, e);
182 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
183 /// penalty for a king, looking at the king file and the two closest files.
186 Score Entry::evaluate_shelter(const Position& pos, Square ksq) {
188 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
190 Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
191 Bitboard ourPawns = b & pos.pieces(Us);
192 Bitboard theirPawns = b & pos.pieces(Them);
194 Score bonus = make_score(5, 5);
196 File center = clamp(file_of(ksq), FILE_B, FILE_G);
197 for (File f = File(center - 1); f <= File(center + 1); ++f)
199 b = ourPawns & file_bb(f);
200 int ourRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
202 b = theirPawns & file_bb(f);
203 int theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
205 int d = std::min(f, ~f);
206 bonus += make_score(ShelterStrength[d][ourRank], 0);
208 if (ourRank && (ourRank == theirRank - 1))
209 bonus -= BlockedStorm * int(theirRank == RANK_3);
211 bonus -= make_score(UnblockedStorm[d][theirRank], 0);
218 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
219 /// when king square changes, which is about 20% of total king_safety() calls.
222 Score Entry::do_king_safety(const Position& pos) {
224 Square ksq = pos.square<KING>(Us);
225 kingSquares[Us] = ksq;
226 castlingRights[Us] = pos.castling_rights(Us);
228 Score shelters[3] = { evaluate_shelter<Us>(pos, ksq),
229 make_score(-VALUE_INFINITE, 0),
230 make_score(-VALUE_INFINITE, 0) };
232 // If we can castle use the bonus after castling if it is bigger
233 if (pos.can_castle(Us & KING_SIDE))
234 shelters[1] = evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1));
236 if (pos.can_castle(Us & QUEEN_SIDE))
237 shelters[2] = evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1));
240 if (mg_value(shelters[i]) > mg_value(shelters[0]))
241 shelters[0] = shelters[i];
243 // In endgame we like to bring our king near our closest pawn
244 Bitboard pawns = pos.pieces(Us, PAWN);
245 int minPawnDist = pawns ? 8 : 0;
247 if (pawns & PseudoAttacks[KING][ksq])
250 minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
252 return shelters[0] - make_score(0, 16 * minPawnDist);
255 // Explicit template instantiation
256 template Score Entry::do_king_safety<WHITE>(const Position& pos);
257 template Score Entry::do_king_safety<BLACK>(const Position& pos);