2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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/>.
29 #define S(mg, eg) make_score(mg, eg)
31 // Doubled pawn penalty by opposed flag and file
32 const Score DoubledPawnPenalty[2][8] = {
33 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
34 S(23, 48), S(23, 48), S(20, 48), S(13, 43) },
35 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
36 S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
38 // Isolated pawn penalty by opposed flag and file
39 const Score IsolatedPawnPenalty[2][8] = {
40 { S(37, 45), S(54, 52), S(60, 52), S(60, 52),
41 S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
42 { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
43 S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
45 // Backward pawn penalty by opposed flag and file
46 const Score BackwardPawnPenalty[2][8] = {
47 { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
48 S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
49 { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
50 S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
52 // Pawn chain membership bonus by file
53 const Score ChainBonus[8] = {
54 S(11,-1), S(13,-1), S(13,-1), S(14,-1),
55 S(14,-1), S(13,-1), S(13,-1), S(11,-1)
58 // Candidate passed pawn bonus by rank
59 const Score CandidateBonus[8] = {
60 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
61 S(34,68), S(83,166), S(0, 0), S( 0, 0)
64 const Score PawnStructureWeight = S(233, 201);
70 // Weakness of our pawn shelter in front of the king indexed by [king pawn][rank]
71 const Value ShelterWeakness[2][8] =
72 { { V(141), V(0), V(38), V(102), V(128), V(141), V(141), V(141) },
73 { V( 61), V(0), V(16), V( 44), V( 56), V( 61), V( 61), V( 61) } };
75 // Danger of enemy pawns moving toward our king indexed by [pawn blocked][rank]
76 const Value StormDanger[2][8] =
77 { { V(26), V(0), V(128), V(51), V(26), V(0), V(0), V(0) },
78 { V(13), V(0), V( 64), V(25), V(13), V(0), V(0), V(0) } };
80 // Max bonus for king safety. Corresponds to start position with all the pawns
81 // in front of the king and no enemy pawns on the horizont.
82 const Value MaxSafetyBonus = V(263);
84 inline Score apply_weight(Score v, Score w) {
85 return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
86 (int(eg_value(v)) * eg_value(w)) / 0x100);
91 /// PawnInfoTable::pawn_info() takes a position object as input, computes
92 /// a PawnInfo object, and returns a pointer to it. The result is also stored
93 /// in an hash table, so we don't have to recompute everything when the same
94 /// pawn structure occurs again.
96 PawnInfo* PawnInfoTable::pawn_info(const Position& pos) const {
98 Key key = pos.pawn_key();
99 PawnInfo* pi = probe(key);
101 // If pi->key matches the position's pawn hash key, it means that we
102 // have analysed this pawn structure before, and we can simply return
103 // the information we found the last time instead of recomputing it.
107 // Initialize PawnInfo entry
109 pi->passedPawns[WHITE] = pi->passedPawns[BLACK] = 0;
110 pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
111 pi->halfOpenFiles[WHITE] = pi->halfOpenFiles[BLACK] = 0xFF;
113 // Calculate pawn attacks
114 Bitboard wPawns = pos.pieces(PAWN, WHITE);
115 Bitboard bPawns = pos.pieces(PAWN, BLACK);
116 pi->pawnAttacks[WHITE] = ((wPawns << 9) & ~FileABB) | ((wPawns << 7) & ~FileHBB);
117 pi->pawnAttacks[BLACK] = ((bPawns >> 7) & ~FileABB) | ((bPawns >> 9) & ~FileHBB);
119 // Evaluate pawns for both colors and weight the result
120 pi->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, pi)
121 - evaluate_pawns<BLACK>(pos, bPawns, wPawns, pi);
123 pi->value = apply_weight(pi->value, PawnStructureWeight);
129 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
132 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
133 Bitboard theirPawns, PawnInfo* pi) {
135 const Color Them = (Us == WHITE ? BLACK : WHITE);
141 bool passed, isolated, doubled, opposed, chain, backward, candidate;
142 Score value = SCORE_ZERO;
143 const Square* pl = pos.piece_list(Us, PAWN);
145 // Loop through all pawns of the current color and score each pawn
146 while ((s = *pl++) != SQ_NONE)
148 assert(pos.piece_on(s) == make_piece(Us, PAWN));
153 // This file cannot be half open
154 pi->halfOpenFiles[Us] &= ~(1 << f);
156 // Our rank plus previous one. Used for chain detection
157 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
159 // Flag the pawn as passed, isolated, doubled or member of a pawn
160 // chain (but not the backward one).
161 passed = !(theirPawns & passed_pawn_mask(Us, s));
162 doubled = ourPawns & squares_in_front_of(Us, s);
163 opposed = theirPawns & squares_in_front_of(Us, s);
164 isolated = !(ourPawns & adjacent_files_bb(f));
165 chain = ourPawns & adjacent_files_bb(f) & b;
167 // Test for backward pawn
170 // If the pawn is passed, isolated, or member of a pawn chain it cannot
171 // be backward. If there are friendly pawns behind on adjacent files
172 // or if can capture an enemy pawn it cannot be backward either.
173 if ( !(passed | isolated | chain)
174 && !(ourPawns & attack_span_mask(Them, s))
175 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
177 // We now know that there are no friendly pawns beside or behind this
178 // pawn on adjacent files. We now check whether the pawn is
179 // backward by looking in the forward direction on the adjacent
180 // files, and seeing whether we meet a friendly or an enemy pawn first.
181 b = pos.attacks_from<PAWN>(s, Us);
183 // Note that we are sure to find something because pawn is not passed
184 // nor isolated, so loop is potentially infinite, but it isn't.
185 while (!(b & (ourPawns | theirPawns)))
186 Us == WHITE ? b <<= 8 : b >>= 8;
188 // The friendly pawn needs to be at least two ranks closer than the
189 // enemy pawn in order to help the potentially backward pawn advance.
190 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
193 assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
195 // A not passed pawn is a candidate to become passed if it is free to
196 // advance and if the number of friendly pawns beside or behind this
197 // pawn on adjacent files is higher or equal than the number of
198 // enemy pawns in the forward direction on the adjacent files.
199 candidate = !(opposed | passed | backward | isolated)
200 && (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != 0
201 && popcount<Max15>(b) >= popcount<Max15>(attack_span_mask(Us, s) & theirPawns);
203 // Passed pawns will be properly scored in evaluation because we need
204 // full attack info to evaluate passed pawns. Only the frontmost passed
205 // pawn on each file is considered a true passed pawn.
206 if (passed && !doubled)
207 pi->passedPawns[Us] |= s;
211 value -= IsolatedPawnPenalty[opposed][f];
214 value -= DoubledPawnPenalty[opposed][f];
217 value -= BackwardPawnPenalty[opposed][f];
220 value += ChainBonus[f];
223 value += CandidateBonus[relative_rank(Us, s)];
230 int PawnInfo::shelter_storm(const Position& pos, Square ksq) {
232 const Color Them = (Us == WHITE ? BLACK : WHITE);
235 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | RankBB[rank_of(ksq)]);
236 Bitboard ourPawns = b & pos.pieces(Us) & ~RankBB[rank_of(ksq)];
237 Bitboard theirPawns = b & pos.pieces(Them);
239 File kf = file_of(ksq);
241 // Compute shelter and storm values for the file the king is on, as well as
242 // the two adjacent files. Computation is done from the white point of view.
243 kf = (kf == FILE_A) ? kf++ : (kf == FILE_H) ? kf-- : kf;
245 for (int f = kf - 1; f <= kf + 1; f++)
247 // Shelter penalty is higher for the pawn in front of the king
248 b = ourPawns & FileBB[f];
249 rkUs = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
250 safety -= ShelterWeakness[f != kf][rkUs];
252 // Storm danger is smaller if enemy pawn is blocked
253 b = theirPawns & FileBB[f];
254 rkThem = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
255 safety -= StormDanger[rkThem == rkUs + 1][rkThem];
262 /// PawnInfo::update_safety() calculates and caches a bonus for king safety. It is
263 /// called only when king square changes, about 20% of total king_safety() calls.
266 Score PawnInfo::update_safety(const Position& pos, Square ksq) {
270 if (relative_rank(Us, ksq) <= RANK_4)
272 bonus = shelter_storm<Us>(pos, ksq);
274 // If we can castle use the bonus after the castle if is bigger
275 if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
276 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
278 if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
279 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
281 bonus += MaxSafetyBonus; // Offset to be sure bonus is always positive
284 kingSquares[Us] = ksq;
285 kingShelters[Us] = make_score(bonus, 0);
286 return kingShelters[Us];
289 // Explicit template instantiation
290 template Score PawnInfo::update_safety<WHITE>(const Position& pos, Square ksq);
291 template Score PawnInfo::update_safety<BLACK>(const Position& pos, Square ksq);