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, 24, 18, 65, 100, 175, 330 };
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->semiopenFiles[Us] = 0xFF;
81 e->kingSquares[Us] = SQ_NONE;
82 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
83 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
84 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
86 // Loop through all pawns of the current color and score each pawn
87 while ((s = *pl++) != SQ_NONE)
89 assert(pos.piece_on(s) == make_piece(Us, PAWN));
93 e->semiopenFiles[Us] &= ~(1 << f);
94 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
97 opposed = theirPawns & forward_file_bb(Us, s);
98 stoppers = theirPawns & passed_pawn_span(Us, s);
99 lever = theirPawns & PawnAttacks[Us][s];
100 leverPush = theirPawns & PawnAttacks[Us][s + Up];
101 doubled = ourPawns & (s - Up);
102 neighbours = ourPawns & adjacent_files_bb(f);
103 phalanx = neighbours & rank_bb(s);
104 support = neighbours & rank_bb(s - Up);
106 // A pawn is backward when it is behind all pawns of the same color
107 // on the adjacent files and cannot be safely advanced.
108 backward = !(ourPawns & pawn_attack_span(Them, s + Up))
109 && (stoppers & (leverPush | (s + Up)));
111 // Passed pawns will be properly scored in evaluation because we need
112 // full attack info to evaluate them. Include also not passed pawns
113 // which could become passed after one or two pawn pushes when are
114 // not attacked more times than defended.
115 if ( !(stoppers ^ lever ^ leverPush)
116 && (support || !more_than_one(lever))
117 && popcount(phalanx) >= popcount(leverPush))
118 e->passedPawns[Us] |= s;
120 else if ( stoppers == square_bb(s + Up)
121 && relative_rank(Us, s) >= RANK_5)
123 b = shift<Up>(support) & ~theirPawns;
125 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
126 e->passedPawns[Us] |= s;
130 if (support | phalanx)
132 int r = relative_rank(Us, s);
133 int v = phalanx ? Connected[r] + Connected[r + 1] : 2 * Connected[r];
134 v = 17 * popcount(support) + (v >> (opposed + 1));
135 score += make_score(v, v * (r - 2) / 4);
137 else if (!neighbours)
138 score -= Isolated, e->weakUnopposed[Us] += !opposed;
141 score -= Backward, e->weakUnopposed[Us] += !opposed;
143 if (doubled && !support)
154 /// Pawns::probe() looks up the current position's pawns configuration in
155 /// the pawns hash table. It returns a pointer to the Entry if the position
156 /// is found. Otherwise a new Entry is computed and stored there, so we don't
157 /// have to recompute all when the same pawns configuration occurs again.
159 Entry* probe(const Position& pos) {
161 Key key = pos.pawn_key();
162 Entry* e = pos.this_thread()->pawnsTable[key];
168 e->scores[WHITE] = evaluate<WHITE>(pos, e);
169 e->scores[BLACK] = evaluate<BLACK>(pos, e);
170 e->passedCount= popcount(e->passedPawns[WHITE] | e->passedPawns[BLACK]);
176 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
177 /// penalty for a king, looking at the king file and the two closest files.
180 Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
182 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
183 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
184 constexpr Bitboard BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
186 Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
187 Bitboard ourPawns = b & pos.pieces(Us);
188 Bitboard theirPawns = b & pos.pieces(Them);
190 Value safety = (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq) ?
191 Value(374) : Value(5);
193 File center = clamp(file_of(ksq), FILE_B, FILE_G);
194 for (File f = File(center - 1); f <= File(center + 1); ++f)
196 b = ourPawns & file_bb(f);
197 Rank ourRank = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
199 b = theirPawns & file_bb(f);
200 Rank theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
202 int d = std::min(f, ~f);
203 safety += ShelterStrength[d][ourRank];
204 safety -= (ourRank && (ourRank == theirRank - 1)) ? 66 * (theirRank == RANK_3)
205 : UnblockedStorm[d][theirRank];
212 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
213 /// when king square changes, which is about 20% of total king_safety() calls.
216 Score Entry::do_king_safety(const Position& pos) {
218 Square ksq = pos.square<KING>(Us);
219 kingSquares[Us] = ksq;
220 castlingRights[Us] = pos.castling_rights(Us);
221 int minKingPawnDistance = 0;
223 Bitboard pawns = pos.pieces(Us, PAWN);
225 while (!(DistanceRingBB[ksq][++minKingPawnDistance] & pawns)) {}
227 Value bonus = evaluate_shelter<Us>(pos, ksq);
229 // If we can castle use the bonus after the castling if it is bigger
230 if (pos.can_castle(Us | KING_SIDE))
231 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
233 if (pos.can_castle(Us | QUEEN_SIDE))
234 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
236 return make_score(bonus, -16 * minKingPawnDistance);
239 // Explicit template instantiation
240 template Score Entry::do_king_safety<WHITE>(const Position& pos);
241 template Score Entry::do_king_safety<BLACK>(const Position& pos);