2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
30 #define S(mg, eg) make_score(mg, eg)
32 // Doubled pawn penalty by opposed flag and file
33 const Score DoubledPawnPenalty[2][FILE_NB] = {
34 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
35 S(23, 48), S(23, 48), S(20, 48), S(13, 43) },
36 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
37 S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
39 // Isolated pawn penalty by opposed flag and file
40 const Score IsolatedPawnPenalty[2][FILE_NB] = {
41 { S(37, 45), S(54, 52), S(60, 52), S(60, 52),
42 S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
43 { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
44 S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
46 // Backward pawn penalty by opposed flag and file
47 const Score BackwardPawnPenalty[2][FILE_NB] = {
48 { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
49 S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
50 { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
51 S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
53 // Pawn chain membership bonus by file
54 const Score ChainBonus[FILE_NB] = {
55 S(11,-1), S(13,-1), S(13,-1), S(14,-1),
56 S(14,-1), S(13,-1), S(13,-1), S(11,-1)
59 // Candidate passed pawn bonus by rank
60 const Score CandidateBonus[RANK_NB] = {
61 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
62 S(34,68), S(83,166), S(0, 0), S( 0, 0)
65 const Score PawnStructureWeight = S(233, 201);
67 // Weakness of our pawn shelter in front of the king indexed by [king pawn][rank]
68 const Value ShelterWeakness[2][RANK_NB] =
69 { { V(141), V(0), V(38), V(102), V(128), V(141), V(141) },
70 { V( 61), V(0), V(16), V( 44), V( 56), V( 61), V( 61) } };
72 // Danger of enemy pawns moving toward our king indexed by [pawn blocked][rank]
73 const Value StormDanger[2][RANK_NB] =
74 { { V(26), V(0), V(128), V(51), V(26) },
75 { V(13), V(0), V( 64), V(25), V(13) } };
77 // Max bonus for king safety. Corresponds to start position with all the pawns
78 // in front of the king and no enemy pawn on the horizont.
79 const Value MaxSafetyBonus = V(263);
85 Score evaluate_pawns(const Position& pos, Bitboard ourPawns,
86 Bitboard theirPawns, Pawns::Entry* e) {
88 const Color Them = (Us == WHITE ? BLACK : WHITE);
94 bool passed, isolated, doubled, opposed, chain, backward, candidate;
95 Score value = SCORE_ZERO;
96 const Square* pl = pos.piece_list(Us, PAWN);
98 // Loop through all pawns of the current color and score each pawn
99 while ((s = *pl++) != SQ_NONE)
101 assert(pos.piece_on(s) == make_piece(Us, PAWN));
106 // This file cannot be half open
107 e->halfOpenFiles[Us] &= ~(1 << f);
109 // Our rank plus previous one. Used for chain detection
110 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
112 // Flag the pawn as passed, isolated, doubled or member of a pawn
113 // chain (but not the backward one).
114 chain = ourPawns & adjacent_files_bb(f) & b;
115 isolated = !(ourPawns & adjacent_files_bb(f));
116 doubled = ourPawns & forward_bb(Us, s);
117 opposed = theirPawns & forward_bb(Us, s);
118 passed = !(theirPawns & passed_pawn_mask(Us, s));
120 // Test for backward pawn
123 // If the pawn is passed, isolated, or member of a pawn chain it cannot
124 // be backward. If there are friendly pawns behind on adjacent files
125 // or if can capture an enemy pawn it cannot be backward either.
126 if ( !(passed | isolated | chain)
127 && !(ourPawns & attack_span_mask(Them, s))
128 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
130 // We now know that there are no friendly pawns beside or behind this
131 // pawn on adjacent files. We now check whether the pawn is
132 // backward by looking in the forward direction on the adjacent
133 // files, and seeing whether we meet a friendly or an enemy pawn first.
134 b = pos.attacks_from<PAWN>(s, Us);
136 // Note that we are sure to find something because pawn is not passed
137 // nor isolated, so loop is potentially infinite, but it isn't.
138 while (!(b & (ourPawns | theirPawns)))
139 Us == WHITE ? b <<= 8 : b >>= 8;
141 // The friendly pawn needs to be at least two ranks closer than the
142 // enemy pawn in order to help the potentially backward pawn advance.
143 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
146 assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
148 // A not passed pawn is a candidate to become passed if it is free to
149 // advance and if the number of friendly pawns beside or behind this
150 // pawn on adjacent files is higher or equal than the number of
151 // enemy pawns in the forward direction on the adjacent files.
152 candidate = !(opposed | passed | backward | isolated)
153 && (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != 0
154 && popcount<Max15>(b) >= popcount<Max15>(attack_span_mask(Us, s) & theirPawns);
156 // Passed pawns will be properly scored in evaluation because we need
157 // full attack info to evaluate passed pawns. Only the frontmost passed
158 // pawn on each file is considered a true passed pawn.
159 if (passed && !doubled)
160 e->passedPawns[Us] |= s;
164 value -= IsolatedPawnPenalty[opposed][f];
167 value -= DoubledPawnPenalty[opposed][f];
170 value -= BackwardPawnPenalty[opposed][f];
173 value += ChainBonus[f];
176 value += CandidateBonus[relative_rank(Us, s)];
185 /// probe() takes a position object as input, computes a Entry object, and returns
186 /// a pointer to it. The result is also stored in a hash table, so we don't have
187 /// to recompute everything when the same pawn structure occurs again.
189 Entry* probe(const Position& pos, Table& entries) {
191 Key key = pos.pawn_key();
192 Entry* e = entries[key];
194 // If e->key matches the position's pawn hash key, it means that we
195 // have analysed this pawn structure before, and we can simply return
196 // the information we found the last time instead of recomputing it.
201 e->passedPawns[WHITE] = e->passedPawns[BLACK] = 0;
202 e->kingSquares[WHITE] = e->kingSquares[BLACK] = SQ_NONE;
203 e->halfOpenFiles[WHITE] = e->halfOpenFiles[BLACK] = 0xFF;
205 Bitboard wPawns = pos.pieces(WHITE, PAWN);
206 Bitboard bPawns = pos.pieces(BLACK, PAWN);
207 e->pawnAttacks[WHITE] = ((wPawns & ~FileHBB) << 9) | ((wPawns & ~FileABB) << 7);
208 e->pawnAttacks[BLACK] = ((bPawns & ~FileHBB) >> 7) | ((bPawns & ~FileABB) >> 9);
210 e->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, e)
211 - evaluate_pawns<BLACK>(pos, bPawns, wPawns, e);
213 e->value = apply_weight(e->value, PawnStructureWeight);
219 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
220 /// the king is on, as well as the two adjacent files.
223 Value Entry::shelter_storm(const Position& pos, Square ksq) {
225 const Color Them = (Us == WHITE ? BLACK : WHITE);
227 Value safety = MaxSafetyBonus;
228 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | rank_bb(ksq));
229 Bitboard ourPawns = b & pos.pieces(Us) & ~rank_bb(ksq);
230 Bitboard theirPawns = b & pos.pieces(Them);
232 File kf = file_of(ksq);
234 kf = (kf == FILE_A) ? FILE_B : (kf == FILE_H) ? FILE_G : kf;
236 for (int f = kf - 1; f <= kf + 1; f++)
238 // Shelter penalty is higher for the pawn in front of the king
239 b = ourPawns & FileBB[f];
240 rkUs = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
241 safety -= ShelterWeakness[f != kf][rkUs];
243 // Storm danger is smaller if enemy pawn is blocked
244 b = theirPawns & FileBB[f];
245 rkThem = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
246 safety -= StormDanger[rkThem == rkUs + 1][rkThem];
253 /// Entry::update_safety() calculates and caches a bonus for king safety. It is
254 /// called only when king square changes, about 20% of total king_safety() calls.
257 Score Entry::update_safety(const Position& pos, Square ksq) {
259 kingSquares[Us] = ksq;
260 castleRights[Us] = pos.can_castle(Us);
261 minKPdistance[Us] = 0;
263 Bitboard pawns = pos.pieces(Us, PAWN);
265 while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
267 if (relative_rank(Us, ksq) > RANK_4)
268 return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
270 Value bonus = shelter_storm<Us>(pos, ksq);
272 // If we can castle use the bonus after the castle if is bigger
273 if (pos.can_castle(make_castle_right(Us, KING_SIDE)))
274 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
276 if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
277 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
279 return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
282 // Explicit template instantiation
283 template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq);
284 template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq);