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);
39 // Connected pawn bonus by opposed, phalanx, #support and rank
40 Score Connected[2][2][3][RANK_NB];
42 // Strength of pawn shelter for our king by [distance from edge][rank].
43 // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
44 constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
45 { V( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
46 { V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
47 { V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
48 { V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
51 // Danger of enemy pawns moving toward our king by [distance from edge][rank].
52 // RANK_1 = 0 is used for files where the enemy has no pawn, or their pawn
53 // is behind our king.
54 constexpr Value UnblockedStorm[int(FILE_NB) / 2][RANK_NB] = {
55 { V( 89), V(107), V(123), V(93), V(57), V( 45), V( 51) },
56 { V( 44), V(-18), V(123), V(46), V(39), V( -7), V( 23) },
57 { V( 4), V( 52), V(162), V(37), V( 7), V(-14), V( -2) },
58 { V(-10), V(-14), V( 90), V(15), V( 2), V( -7), V(-16) }
65 Score evaluate(const Position& pos, Pawns::Entry* e) {
67 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
68 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
70 Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
71 Bitboard lever, leverPush;
73 bool opposed, backward;
74 Score score = SCORE_ZERO;
75 const Square* pl = pos.squares<PAWN>(Us);
77 Bitboard ourPawns = pos.pieces( Us, PAWN);
78 Bitboard theirPawns = pos.pieces(Them, PAWN);
80 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
81 e->semiopenFiles[Us] = 0xFF;
82 e->kingSquares[Us] = SQ_NONE;
83 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
84 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
85 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
87 // Loop through all pawns of the current color and score each pawn
88 while ((s = *pl++) != SQ_NONE)
90 assert(pos.piece_on(s) == make_piece(Us, PAWN));
94 e->semiopenFiles[Us] &= ~(1 << f);
95 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
98 opposed = theirPawns & forward_file_bb(Us, s);
99 stoppers = theirPawns & passed_pawn_mask(Us, s);
100 lever = theirPawns & PawnAttacks[Us][s];
101 leverPush = theirPawns & PawnAttacks[Us][s + Up];
102 doubled = ourPawns & (s - Up);
103 neighbours = ourPawns & adjacent_files_bb(f);
104 phalanx = neighbours & rank_bb(s);
105 supported = neighbours & rank_bb(s - Up);
107 // A pawn is backward when it is behind all pawns of the same color
108 // on the adjacent files and cannot be safely advanced.
109 backward = !(ourPawns & pawn_attack_span(Them, s + Up))
110 && (stoppers & (leverPush | (s + Up)));
112 // Passed pawns will be properly scored in evaluation because we need
113 // full attack info to evaluate them. Include also not passed pawns
114 // which could become passed after one or two pawn pushes when are
115 // not attacked more times than defended.
116 if ( !(stoppers ^ lever ^ leverPush)
117 && popcount(supported) >= popcount(lever) - 1
118 && popcount(phalanx) >= popcount(leverPush))
119 e->passedPawns[Us] |= s;
121 else if ( stoppers == SquareBB[s + Up]
122 && relative_rank(Us, s) >= RANK_5)
124 b = shift<Up>(supported) & ~theirPawns;
126 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
127 e->passedPawns[Us] |= s;
131 if (supported | phalanx)
132 score += Connected[opposed][bool(phalanx)][popcount(supported)][relative_rank(Us, s)];
134 else if (!neighbours)
135 score -= Isolated, e->weakUnopposed[Us] += !opposed;
138 score -= Backward, e->weakUnopposed[Us] += !opposed;
140 if (doubled && !supported)
151 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
152 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
153 /// to reduce independent parameters and to allow easier tuning and better insight.
157 static constexpr int Seed[RANK_NB] = { 0, 13, 24, 18, 65, 100, 175, 330 };
159 for (int opposed = 0; opposed <= 1; ++opposed)
160 for (int phalanx = 0; phalanx <= 1; ++phalanx)
161 for (int support = 0; support <= 2; ++support)
162 for (Rank r = RANK_2; r < RANK_8; ++r)
164 int v = 17 * support;
165 v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
167 Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
172 /// Pawns::probe() looks up the current position's pawns configuration in
173 /// the pawns hash table. It returns a pointer to the Entry if the position
174 /// is found. Otherwise a new Entry is computed and stored there, so we don't
175 /// have to recompute all when the same pawns configuration occurs again.
177 Entry* probe(const Position& pos) {
179 Key key = pos.pawn_key();
180 Entry* e = pos.this_thread()->pawnsTable[key];
186 e->scores[WHITE] = evaluate<WHITE>(pos, e);
187 e->scores[BLACK] = evaluate<BLACK>(pos, e);
188 e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
189 e->asymmetry = popcount( (e->passedPawns[WHITE] | e->passedPawns[BLACK])
190 | (e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]));
196 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
197 /// penalty for a king, looking at the king file and the two closest files.
200 Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
202 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
203 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
204 constexpr Bitboard BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
206 Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
207 Bitboard ourPawns = b & pos.pieces(Us);
208 Bitboard theirPawns = b & pos.pieces(Them);
210 Value safety = (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq) ?
211 Value(374) : Value(5);
213 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
214 for (File f = File(center - 1); f <= File(center + 1); ++f)
216 b = ourPawns & file_bb(f);
217 int ourRank = b ? relative_rank(Us, backmost_sq(Us, b)) : 0;
219 b = theirPawns & file_bb(f);
220 int theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
222 int d = std::min(f, ~f);
223 safety += ShelterStrength[d][ourRank];
224 safety -= (ourRank && (ourRank == theirRank - 1)) ? 66 * (theirRank == RANK_3)
225 : UnblockedStorm[d][theirRank];
232 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
233 /// when king square changes, which is about 20% of total king_safety() calls.
236 Score Entry::do_king_safety(const Position& pos) {
238 Square ksq = pos.square<KING>(Us);
239 kingSquares[Us] = ksq;
240 castlingRights[Us] = pos.can_castle(Us);
241 int minKingPawnDistance = 0;
243 Bitboard pawns = pos.pieces(Us, PAWN);
245 while (!(DistanceRingBB[ksq][++minKingPawnDistance] & pawns)) {}
247 Value bonus = evaluate_shelter<Us>(pos, ksq);
249 // If we can castle use the bonus after the castling if it is bigger
250 if (pos.can_castle(Us | KING_SIDE))
251 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
253 if (pos.can_castle(Us | QUEEN_SIDE))
254 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
256 return make_score(bonus, -16 * minKingPawnDistance);
259 // Explicit template instantiation
260 template Score Entry::do_king_safety<WHITE>(const Position& pos);
261 template Score Entry::do_king_safety<BLACK>(const Position& pos);