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) 2015-2018 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 Isolated = S(13, 16);
36 constexpr Score Backward = S(17, 11);
37 constexpr Score Doubled = S(13, 40);
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( 7), V(76), V( 84), V( 38), V( 7), V( 30), V(-19) },
46 { V(-13), V(83), V( 42), V(-27), V( 2), V(-32), V(-45) },
47 { V(-26), V(63), V( 5), V(-44), V( -5), V( 2), V(-59) },
48 { V(-19), V(53), V(-11), V(-22), V(-12), V(-51), V(-60) }
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( 25), V( 79), V(107), V( 51), V( 27), V( 0), V( 0) },
56 { V( 5), V( 35), V(121), V( -2), V( 15), V(-10), V(-10) },
57 { V(-20), V( 22), V( 98), V( 36), V( 7), V(-20), V(-20) },
58 { V(-27), V( 24), V( 80), V( 25), V( -4), V(-30), V(-30) }
61 // Danger of blocked enemy pawns storming our king, by rank
62 constexpr Value BlockedStorm[RANK_NB] =
63 { V( 0), V( 0), V( 75), V(-10), V(-20), V(-20), V(-20) };
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 b, neighbours, stoppers, doubled, supported, phalanx;
75 Bitboard lever, leverPush;
77 bool opposed, backward;
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 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
85 e->semiopenFiles[Us] = 0xFF;
86 e->kingSquares[Us] = SQ_NONE;
87 e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
88 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
89 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
91 // Loop through all pawns of the current color and score each pawn
92 while ((s = *pl++) != SQ_NONE)
94 assert(pos.piece_on(s) == make_piece(Us, PAWN));
98 e->semiopenFiles[Us] &= ~(1 << f);
99 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
102 opposed = theirPawns & forward_file_bb(Us, s);
103 stoppers = theirPawns & passed_pawn_mask(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(f);
108 phalanx = neighbours & rank_bb(s);
109 supported = neighbours & rank_bb(s - Up);
111 // A pawn is backward when it is behind all pawns of the same color
112 // on the adjacent files and cannot be safely advanced.
113 backward = !(ourPawns & pawn_attack_span(Them, s + Up))
114 && (stoppers & (leverPush | (s + Up)));
116 // Passed pawns will be properly scored in evaluation because we need
117 // full attack info to evaluate them. Include also not passed pawns
118 // which could become passed after one or two pawn pushes when are
119 // not attacked more times than defended.
120 if ( !(stoppers ^ lever ^ leverPush)
121 && !(ourPawns & forward_file_bb(Us, s))
122 && popcount(supported) >= popcount(lever) - 1
123 && popcount(phalanx) >= popcount(leverPush))
124 e->passedPawns[Us] |= s;
126 else if ( stoppers == SquareBB[s + Up]
127 && relative_rank(Us, s) >= RANK_5)
129 b = shift<Up>(supported) & ~theirPawns;
131 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
132 e->passedPawns[Us] |= s;
136 if (supported | phalanx)
137 score += Connected[opposed][bool(phalanx)][popcount(supported)][relative_rank(Us, s)];
139 else if (!neighbours)
140 score -= Isolated, e->weakUnopposed[Us] += !opposed;
143 score -= Backward, e->weakUnopposed[Us] += !opposed;
145 if (doubled && !supported)
156 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
157 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
158 /// to reduce independent parameters and to allow easier tuning and better insight.
162 static constexpr int Seed[RANK_NB] = { 0, 13, 24, 18, 65, 100, 175, 330 };
164 for (int opposed = 0; opposed <= 1; ++opposed)
165 for (int phalanx = 0; phalanx <= 1; ++phalanx)
166 for (int support = 0; support <= 2; ++support)
167 for (Rank r = RANK_2; r < RANK_8; ++r)
169 int v = 17 * support;
170 v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
172 Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
177 /// Pawns::probe() looks up the current position's pawns configuration in
178 /// the pawns hash table. It returns a pointer to the Entry if the position
179 /// is found. Otherwise a new Entry is computed and stored there, so we don't
180 /// have to recompute all when the same pawns configuration occurs again.
182 Entry* probe(const Position& pos) {
184 Key key = pos.pawn_key();
185 Entry* e = pos.this_thread()->pawnsTable[key];
191 e->scores[WHITE] = evaluate<WHITE>(pos, e);
192 e->scores[BLACK] = evaluate<BLACK>(pos, e);
193 e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
194 e->asymmetry = popcount( (e->passedPawns[WHITE] | e->passedPawns[BLACK])
195 | (e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]));
201 /// Entry::evaluate_shelter() calculates the shelter bonus and the storm
202 /// penalty for a king, looking at the king file and the two closest files.
205 Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
207 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
208 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
209 constexpr Bitboard BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
211 Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
212 Bitboard ourPawns = b & pos.pieces(Us);
213 Bitboard theirPawns = b & pos.pieces(Them);
215 Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
217 if (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq)
218 safety += Value(374);
220 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
221 for (File f = File(center - 1); f <= File(center + 1); ++f)
223 b = ourPawns & file_bb(f);
224 int ourRank = b ? relative_rank(Us, backmost_sq(Us, b)) : 0;
226 b = theirPawns & file_bb(f);
227 int theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
229 int d = std::min(f, ~f);
230 safety += ShelterStrength[d][ourRank];
231 safety -= (ourRank && (ourRank == theirRank - 1)) ? BlockedStorm[theirRank]
232 : UnblockedStorm[d][theirRank];
239 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
240 /// when king square changes, which is about 20% of total king_safety() calls.
243 Score Entry::do_king_safety(const Position& pos, Square ksq) {
245 kingSquares[Us] = ksq;
246 castlingRights[Us] = pos.can_castle(Us);
247 int minKingPawnDistance = 0;
249 Bitboard pawns = pos.pieces(Us, PAWN);
251 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
253 Value bonus = evaluate_shelter<Us>(pos, ksq);
255 // If we can castle use the bonus after the castling if it is bigger
256 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
257 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
259 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
260 bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
262 return make_score(bonus, -16 * minKingPawnDistance);
265 // Explicit template instantiation
266 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
267 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);