2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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);
68 inline Score apply_weight(Score v, Score w) {
69 return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
70 (int(eg_value(v)) * eg_value(w)) / 0x100);
75 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
76 /// a PawnInfo object, and returns a pointer to it. The result is also stored
77 /// in an hash table, so we don't have to recompute everything when the same
78 /// pawn structure occurs again.
80 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) const {
82 Key key = pos.get_pawn_key();
83 PawnInfo* pi = probe(key);
85 // If pi->key matches the position's pawn hash key, it means that we
86 // have analysed this pawn structure before, and we can simply return
87 // the information we found the last time instead of recomputing it.
91 // Initialize PawnInfo entry
93 pi->passedPawns[WHITE] = pi->passedPawns[BLACK] = 0;
94 pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
95 pi->halfOpenFiles[WHITE] = pi->halfOpenFiles[BLACK] = 0xFF;
97 // Calculate pawn attacks
98 Bitboard wPawns = pos.pieces(PAWN, WHITE);
99 Bitboard bPawns = pos.pieces(PAWN, BLACK);
100 pi->pawnAttacks[WHITE] = ((wPawns << 9) & ~FileABB) | ((wPawns << 7) & ~FileHBB);
101 pi->pawnAttacks[BLACK] = ((bPawns >> 7) & ~FileABB) | ((bPawns >> 9) & ~FileHBB);
103 // Evaluate pawns for both colors and weight the result
104 pi->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, pi)
105 - evaluate_pawns<BLACK>(pos, bPawns, wPawns, pi);
107 pi->value = apply_weight(pi->value, PawnStructureWeight);
113 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
116 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
117 Bitboard theirPawns, PawnInfo* pi) {
119 const BitCountType Max15 = CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
120 const Color Them = (Us == WHITE ? BLACK : WHITE);
126 bool passed, isolated, doubled, opposed, chain, backward, candidate;
127 Score value = SCORE_ZERO;
128 const Square* pl = pos.piece_list(Us, PAWN);
130 // Loop through all pawns of the current color and score each pawn
131 while ((s = *pl++) != SQ_NONE)
133 assert(pos.piece_on(s) == make_piece(Us, PAWN));
138 // This file cannot be half open
139 pi->halfOpenFiles[Us] &= ~(1 << f);
141 // Our rank plus previous one. Used for chain detection
142 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
144 // Flag the pawn as passed, isolated, doubled or member of a pawn
145 // chain (but not the backward one).
146 passed = !(theirPawns & passed_pawn_mask(Us, s));
147 doubled = ourPawns & squares_in_front_of(Us, s);
148 opposed = theirPawns & squares_in_front_of(Us, s);
149 isolated = !(ourPawns & neighboring_files_bb(f));
150 chain = ourPawns & neighboring_files_bb(f) & b;
152 // Test for backward pawn
155 // If the pawn is passed, isolated, or member of a pawn chain it cannot
156 // be backward. If there are friendly pawns behind on neighboring files
157 // or if can capture an enemy pawn it cannot be backward either.
158 if ( !(passed | isolated | chain)
159 && !(ourPawns & attack_span_mask(Them, s))
160 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
162 // We now know that there are no friendly pawns beside or behind this
163 // pawn on neighboring files. We now check whether the pawn is
164 // backward by looking in the forward direction on the neighboring
165 // files, and seeing whether we meet a friendly or an enemy pawn first.
166 b = pos.attacks_from<PAWN>(s, Us);
168 // Note that we are sure to find something because pawn is not passed
169 // nor isolated, so loop is potentially infinite, but it isn't.
170 while (!(b & (ourPawns | theirPawns)))
171 Us == WHITE ? b <<= 8 : b >>= 8;
173 // The friendly pawn needs to be at least two ranks closer than the
174 // enemy pawn in order to help the potentially backward pawn advance.
175 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
178 assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
180 // A not passed pawn is a candidate to become passed if it is free to
181 // advance and if the number of friendly pawns beside or behind this
182 // pawn on neighboring files is higher or equal than the number of
183 // enemy pawns in the forward direction on the neighboring files.
184 candidate = !(opposed | passed | backward | isolated)
185 && (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != EmptyBoardBB
186 && count_1s<Max15>(b) >= count_1s<Max15>(attack_span_mask(Us, s) & theirPawns);
188 // Passed pawns will be properly scored in evaluation because we need
189 // full attack info to evaluate passed pawns. Only the frontmost passed
190 // pawn on each file is considered a true passed pawn.
191 if (passed && !doubled)
192 set_bit(&(pi->passedPawns[Us]), s);
196 value -= IsolatedPawnPenalty[opposed][f];
199 value -= DoubledPawnPenalty[opposed][f];
202 value -= BackwardPawnPenalty[opposed][f];
205 value += ChainBonus[f];
208 value += CandidateBonus[relative_rank(Us, s)];
214 /// PawnInfo::updateShelter() calculates and caches king shelter. It is called
215 /// only when king square changes, about 20% of total king_shelter() calls.
217 Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
219 const int Shift = (Us == WHITE ? 8 : -8);
224 if (relative_rank(Us, ksq) <= RANK_4)
226 pawns = pos.pieces(PAWN, Us) & this_and_neighboring_files_bb(ksq);
228 for (int i = 0; i < 3; i++)
231 shelter += BitCount8Bit[(pawns >> r) & 0xFF] << (6 - i);
234 kingSquares[Us] = ksq;
235 kingShelters[Us] = make_score(shelter, 0);
236 return kingShelters[Us];
239 // Explicit template instantiation
240 template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
241 template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);