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[] = { S(27, 30), S(13, 18) };
37 // Backward pawn penalty by opposed flag
38 const Score Backward[] = { S(40, 26), S(24, 12) };
40 // Connected pawn bonus by opposed, phalanx, #support and rank
41 Score Connected[2][2][3][RANK_NB];
43 // Doubled pawn penalty
44 const Score Doubled = S(18, 38);
46 // Lever bonus by rank
47 const Score Lever[RANK_NB] = {
48 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
49 S(17, 16), S(33, 32), S(0, 0), S(0, 0)
52 // Weakness of our pawn shelter in front of the king by [distance from edge][rank].
53 // RANK_1 = 0 is used for files where we have no pawns or our pawn is behind our king.
54 const Value ShelterWeakness[][RANK_NB] = {
55 { V(100), V(20), V(10), V(46), V(82), V( 86), V( 98) },
56 { V(116), V( 4), V(28), V(87), V(94), V(108), V(104) },
57 { V(109), V( 1), V(59), V(87), V(62), V( 91), V(116) },
58 { V( 75), V(12), V(43), V(59), V(90), V( 84), V(112) }
61 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
62 // For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has no pawn
63 // on the given file, or their pawn is behind our king.
64 const Value StormDanger[][4][RANK_NB] = {
65 { { V( 0), V(-290), V(-274), V(57), V(41) }, //BlockedByKing
66 { V( 0), V( 60), V( 144), V(39), V(13) },
67 { V( 0), V( 65), V( 141), V(41), V(34) },
68 { V( 0), V( 53), V( 127), V(56), V(14) } },
69 { { V( 4), V( 73), V( 132), V(46), V(31) }, //Unopposed
70 { V( 1), V( 64), V( 143), V(26), V(13) },
71 { V( 1), V( 47), V( 110), V(44), V(24) },
72 { V( 0), V( 72), V( 127), V(50), V(31) } },
73 { { V( 0), V( 0), V( 79), V(23), V( 1) }, //BlockedByPawn
74 { V( 0), V( 0), V( 148), V(27), V( 2) },
75 { V( 0), V( 0), V( 161), V(16), V( 1) },
76 { V( 0), V( 0), V( 171), V(22), V(15) } },
77 { { V(22), V( 45), V( 104), V(62), V( 6) }, //Unblocked
78 { V(31), V( 30), V( 99), V(39), V(19) },
79 { V(23), V( 29), V( 96), V(41), V(15) },
80 { V(21), V( 23), V( 116), V(41), V(15) } }
83 // Max bonus for king safety. Corresponds to start position with all the pawns
84 // in front of the king and no enemy pawn on the horizon.
85 const Value MaxSafetyBonus = V(258);
91 Score evaluate(const Position& pos, Pawns::Entry* e) {
93 const Color Them = (Us == WHITE ? BLACK : WHITE);
94 const Square Up = (Us == WHITE ? NORTH : SOUTH);
95 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
96 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
98 Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
99 Bitboard lever, leverPush;
101 bool opposed, backward;
102 Score score = SCORE_ZERO;
103 const Square* pl = pos.squares<PAWN>(Us);
105 Bitboard ourPawns = pos.pieces( Us, PAWN);
106 Bitboard theirPawns = pos.pieces(Them, PAWN);
108 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
109 e->semiopenFiles[Us] = 0xFF;
110 e->kingSquares[Us] = SQ_NONE;
111 e->pawnAttacks[Us] = shift<Right>(ourPawns) | shift<Left>(ourPawns);
112 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
113 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
115 // Loop through all pawns of the current color and score each pawn
116 while ((s = *pl++) != SQ_NONE)
118 assert(pos.piece_on(s) == make_piece(Us, PAWN));
122 e->semiopenFiles[Us] &= ~(1 << f);
123 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
126 opposed = theirPawns & forward_file_bb(Us, s);
127 stoppers = theirPawns & passed_pawn_mask(Us, s);
128 lever = theirPawns & PawnAttacks[Us][s];
129 leverPush = theirPawns & PawnAttacks[Us][s + Up];
130 doubled = ourPawns & (s - Up);
131 neighbours = ourPawns & adjacent_files_bb(f);
132 phalanx = neighbours & rank_bb(s);
133 supported = neighbours & rank_bb(s - Up);
135 // A pawn is backward when it is behind all pawns of the same color on the
136 // adjacent files and cannot be safely advanced.
137 if (!neighbours || lever || relative_rank(Us, s) >= RANK_5)
141 // Find the backmost rank with neighbours or stoppers
142 b = rank_bb(backmost_sq(Us, neighbours | stoppers));
144 // The pawn is backward when it cannot safely progress to that rank:
145 // either there is a stopper in the way on this rank, or there is a
146 // stopper on adjacent file which controls the way to that rank.
147 backward = (b | shift<Up>(b & adjacent_files_bb(f))) & stoppers;
149 assert(!(backward && (forward_ranks_bb(Them, s + Up) & neighbours)));
152 // Passed pawns will be properly scored in evaluation because we need
153 // full attack info to evaluate them. Include also not passed pawns
154 // which could become passed after one or two pawn pushes when are
155 // not attacked more times than defended.
156 if ( !(stoppers ^ lever ^ leverPush)
157 && !(ourPawns & forward_file_bb(Us, s))
158 && popcount(supported) >= popcount(lever)
159 && popcount(phalanx) >= popcount(leverPush))
160 e->passedPawns[Us] |= s;
162 else if ( stoppers == SquareBB[s + Up]
163 && relative_rank(Us, s) >= RANK_5)
165 b = shift<Up>(supported) & ~theirPawns;
167 if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
168 e->passedPawns[Us] |= s;
172 if (supported | phalanx)
173 score += Connected[opposed][!!phalanx][popcount(supported)][relative_rank(Us, s)];
175 else if (!neighbours)
176 score -= Isolated[opposed];
179 score -= Backward[opposed];
181 if (doubled && !supported)
185 score += Lever[relative_rank(Us, s)];
195 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
196 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
197 /// to reduce independent parameters and to allow easier tuning and better insight.
201 static const int Seed[RANK_NB] = { 0, 13, 24, 18, 76, 100, 175, 330 };
203 for (int opposed = 0; opposed <= 1; ++opposed)
204 for (int phalanx = 0; phalanx <= 1; ++phalanx)
205 for (int support = 0; support <= 2; ++support)
206 for (Rank r = RANK_2; r < RANK_8; ++r)
208 int v = 17 * support;
209 v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
211 Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
216 /// Pawns::probe() looks up the current position's pawns configuration in
217 /// the pawns hash table. It returns a pointer to the Entry if the position
218 /// is found. Otherwise a new Entry is computed and stored there, so we don't
219 /// have to recompute all when the same pawns configuration occurs again.
221 Entry* probe(const Position& pos) {
223 Key key = pos.pawn_key();
224 Entry* e = pos.this_thread()->pawnsTable[key];
230 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
231 e->asymmetry = popcount(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
232 e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
237 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
238 /// the king is on, as well as the two closest files.
241 Value Entry::shelter_storm(const Position& pos, Square ksq) {
243 const Color Them = (Us == WHITE ? BLACK : WHITE);
245 enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
247 Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
248 Bitboard ourPawns = b & pos.pieces(Us);
249 Bitboard theirPawns = b & pos.pieces(Them);
250 Value safety = MaxSafetyBonus;
251 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
253 for (File f = center - File(1); f <= center + File(1); ++f)
255 b = ourPawns & file_bb(f);
256 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
258 b = theirPawns & file_bb(f);
259 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
261 int d = std::min(f, FILE_H - f);
262 safety -= ShelterWeakness[d][rkUs]
264 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
265 rkUs == RANK_1 ? Unopposed :
266 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
274 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
275 /// when king square changes, which is about 20% of total king_safety() calls.
278 Score Entry::do_king_safety(const Position& pos, Square ksq) {
280 kingSquares[Us] = ksq;
281 castlingRights[Us] = pos.can_castle(Us);
282 int minKingPawnDistance = 0;
284 Bitboard pawns = pos.pieces(Us, PAWN);
286 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
288 Value bonus = shelter_storm<Us>(pos, ksq);
290 // If we can castle use the bonus after the castling if it is bigger
291 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
292 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
294 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
295 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
297 return make_score(bonus, -16 * minKingPawnDistance);
300 // Explicit template instantiation
301 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
302 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);