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) 2015-2017 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)
34 // Isolated pawn penalty by opposed flag
35 const Score Isolated[2] = { S(45, 40), S(30, 27) };
37 // Backward pawn penalty by opposed flag
38 const Score Backward[2] = { S(56, 33), S(41, 19) };
40 // Unsupported pawn penalty for pawns which are neither isolated or backward
41 const Score Unsupported = S(17, 8);
43 // Connected pawn bonus by opposed, phalanx, twice supported and rank
44 Score Connected[2][2][2][RANK_NB];
46 // Doubled pawn penalty
47 const Score Doubled = S(18,38);
49 // Lever bonus by rank
50 const Score Lever[RANK_NB] = {
51 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
52 S(17, 16), S(33, 32), S(0, 0), S(0, 0)
55 // Weakness of our pawn shelter in front of the king by [distance from edge][rank].
56 // RANK_1 = 0 is used for files where we have no pawns, or where our pawn is behind our king.
57 const Value ShelterWeakness[][RANK_NB] = {
58 { V(100), V(20), V(10), V(46), V(82), V( 86), V( 98) },
59 { V(116), V( 4), V(28), V(87), V(94), V(108), V(104) },
60 { V(109), V( 1), V(59), V(87), V(62), V( 91), V(116) },
61 { V( 75), V(12), V(43), V(59), V(90), V( 84), V(112) }
64 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
65 // For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has no pawn
66 // on the given file, or his pawn his behind our king.
67 const Value StormDanger[][4][RANK_NB] = {
68 { { V( 0), V(-290), V(-274), V(57), V(41) }, //BlockedByKing
69 { V( 0), V( 60), V( 144), V(39), V(13) },
70 { V( 0), V( 65), V( 141), V(41), V(34) },
71 { V( 0), V( 53), V( 127), V(56), V(14) } },
72 { { V( 4), V( 73), V( 132), V(46), V(31) }, //Unopposed
73 { V( 1), V( 64), V( 143), V(26), V(13) },
74 { V( 1), V( 47), V( 110), V(44), V(24) },
75 { V( 0), V( 72), V( 127), V(50), V(31) } },
76 { { V( 0), V( 0), V( 79), V(23), V( 1) }, //BlockedByPawn
77 { V( 0), V( 0), V( 148), V(27), V( 2) },
78 { V( 0), V( 0), V( 161), V(16), V( 1) },
79 { V( 0), V( 0), V( 171), V(22), V(15) } },
80 { { V(22), V( 45), V( 104), V(62), V( 6) }, //Unblocked
81 { V(31), V( 30), V( 99), V(39), V(19) },
82 { V(23), V( 29), V( 96), V(41), V(15) },
83 { V(21), V( 23), V( 116), V(41), V(15) } }
86 // Max bonus for king safety. Corresponds to start position with all the pawns
87 // in front of the king and no enemy pawn on the horizon.
88 const Value MaxSafetyBonus = V(258);
94 Score evaluate(const Position& pos, Pawns::Entry* e) {
96 const Color Them = (Us == WHITE ? BLACK : WHITE);
97 const Square Up = (Us == WHITE ? NORTH : SOUTH);
98 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
99 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
101 Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
103 bool opposed, lever, connected, backward;
104 Score score = SCORE_ZERO;
105 const Square* pl = pos.squares<PAWN>(Us);
106 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
108 Bitboard ourPawns = pos.pieces(Us , PAWN);
109 Bitboard theirPawns = pos.pieces(Them, PAWN);
111 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
112 e->semiopenFiles[Us] = 0xFF;
113 e->kingSquares[Us] = SQ_NONE;
114 e->pawnAttacks[Us] = shift<Right>(ourPawns) | shift<Left>(ourPawns);
115 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
116 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
118 // Loop through all pawns of the current color and score each pawn
119 while ((s = *pl++) != SQ_NONE)
121 assert(pos.piece_on(s) == make_piece(Us, PAWN));
125 e->semiopenFiles[Us] &= ~(1 << f);
126 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
129 opposed = theirPawns & forward_bb(Us, s);
130 stoppers = theirPawns & passed_pawn_mask(Us, s);
131 lever = theirPawns & pawnAttacksBB[s];
132 doubled = ourPawns & (s + Up);
133 neighbours = ourPawns & adjacent_files_bb(f);
134 phalanx = neighbours & rank_bb(s);
135 supported = neighbours & rank_bb(s - Up);
136 connected = supported | phalanx;
138 // A pawn is backward when it is behind all pawns of the same color on the
139 // adjacent files and cannot be safely advanced.
140 if (!neighbours || lever || relative_rank(Us, s) >= RANK_5)
144 // Find the backmost rank with neighbours or stoppers
145 b = rank_bb(backmost_sq(Us, neighbours | stoppers));
147 // The pawn is backward when it cannot safely progress to that rank:
148 // either there is a stopper in the way on this rank, or there is a
149 // stopper on adjacent file which controls the way to that rank.
150 backward = (b | shift<Up>(b & adjacent_files_bb(f))) & stoppers;
152 assert(!backward || !(pawn_attack_span(Them, s + Up) & neighbours));
155 // Passed pawns will be properly scored in evaluation because we need
156 // full attack info to evaluate them.
157 if (!stoppers && !(ourPawns & forward_bb(Us, s)))
158 e->passedPawns[Us] |= s;
162 score -= Isolated[opposed];
165 score -= Backward[opposed];
168 score -= Unsupported;
171 score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
177 score += Lever[relative_rank(Us, s)];
187 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
188 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
189 /// to reduce independent parameters and to allow easier tuning and better insight.
193 static const int Seed[RANK_NB] = { 0, 8, 19, 13, 71, 94, 169, 324 };
195 for (int opposed = 0; opposed <= 1; ++opposed)
196 for (int phalanx = 0; phalanx <= 1; ++phalanx)
197 for (int apex = 0; apex <= 1; ++apex)
198 for (Rank r = RANK_2; r < RANK_8; ++r)
200 int v = (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
201 v += (apex ? v / 2 : 0);
202 Connected[opposed][phalanx][apex][r] = make_score(v, v * (r-2) / 4);
207 /// Pawns::probe() looks up the current position's pawns configuration in
208 /// the pawns hash table. It returns a pointer to the Entry if the position
209 /// is found. Otherwise a new Entry is computed and stored there, so we don't
210 /// have to recompute all when the same pawns configuration occurs again.
212 Entry* probe(const Position& pos) {
214 Key key = pos.pawn_key();
215 Entry* e = pos.this_thread()->pawnsTable[key];
221 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
222 e->asymmetry = popcount(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
223 e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
228 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
229 /// the king is on, as well as the two closest files.
232 Value Entry::shelter_storm(const Position& pos, Square ksq) {
234 const Color Them = (Us == WHITE ? BLACK : WHITE);
236 enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
238 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
239 Bitboard ourPawns = b & pos.pieces(Us);
240 Bitboard theirPawns = b & pos.pieces(Them);
241 Value safety = MaxSafetyBonus;
242 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
244 for (File f = center - File(1); f <= center + File(1); ++f)
246 b = ourPawns & file_bb(f);
247 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
249 b = theirPawns & file_bb(f);
250 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
252 safety -= ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
254 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
255 rkUs == RANK_1 ? Unopposed :
256 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
257 [std::min(f, FILE_H - f)][rkThem];
264 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
265 /// when king square changes, which is about 20% of total king_safety() calls.
268 Score Entry::do_king_safety(const Position& pos, Square ksq) {
270 kingSquares[Us] = ksq;
271 castlingRights[Us] = pos.can_castle(Us);
272 int minKingPawnDistance = 0;
274 Bitboard pawns = pos.pieces(Us, PAWN);
276 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
278 Value bonus = shelter_storm<Us>(pos, ksq);
280 // If we can castle use the bonus after the castling if it is bigger
281 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
282 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
284 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
285 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
287 return make_score(bonus, -16 * minKingPawnDistance);
290 // Explicit template instantiation
291 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
292 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);