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/>.
34 //// Local definitions
39 /// Constants and variables
41 #define S(mg, eg) make_score(mg, eg)
43 // Doubled pawn penalty by file
44 const Score DoubledPawnPenalty[8] = {
45 S(13, 43), S(20, 48), S(23, 48), S(23, 48),
46 S(23, 48), S(23, 48), S(20, 48), S(13, 43)
49 // Isolated pawn penalty by file
50 const Score IsolatedPawnPenalty[8] = {
51 S(25, 30), S(36, 35), S(40, 35), S(40, 35),
52 S(40, 35), S(40, 35), S(36, 35), S(25, 30)
55 // Backward pawn penalty by file
56 const Score BackwardPawnPenalty[8] = {
57 S(20, 28), S(29, 31), S(33, 31), S(33, 31),
58 S(33, 31), S(33, 31), S(29, 31), S(20, 28)
61 // Pawn chain membership bonus by file
62 const Score ChainBonus[8] = {
63 S(11,-1), S(13,-1), S(13,-1), S(14,-1),
64 S(14,-1), S(13,-1), S(13,-1), S(11,-1)
67 // Candidate passed pawn bonus by rank
68 const Score CandidateBonus[8] = {
69 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
70 S(34,68), S(83,166), S(0, 0), S( 0, 0)
81 /// PawnInfoTable c'tor and d'tor instantiated one each thread
83 PawnInfoTable::PawnInfoTable() {
85 entries = new PawnInfo[PawnTableSize];
89 std::cerr << "Failed to allocate " << (PawnTableSize * sizeof(PawnInfo))
90 << " bytes for pawn hash table." << std::endl;
91 Application::exit_with_failure();
93 memset(entries, 0, PawnTableSize * sizeof(PawnInfo));
97 PawnInfoTable::~PawnInfoTable() {
103 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
104 /// a PawnInfo object, and returns a pointer to it. The result is also stored
105 /// in a hash table, so we don't have to recompute everything when the same
106 /// pawn structure occurs again.
108 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) const {
112 Key key = pos.get_pawn_key();
113 unsigned index = unsigned(key & (PawnTableSize - 1));
114 PawnInfo* pi = entries + index;
116 // If pi->key matches the position's pawn hash key, it means that we
117 // have analysed this pawn structure before, and we can simply return
118 // the information we found the last time instead of recomputing it.
122 // Clear the PawnInfo object, and set the key
123 memset(pi, 0, sizeof(PawnInfo));
124 pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
127 // Calculate pawn attacks
128 Bitboard whitePawns = pos.pieces(PAWN, WHITE);
129 Bitboard blackPawns = pos.pieces(PAWN, BLACK);
130 pi->pawnAttacks[WHITE] = ((whitePawns << 9) & ~FileABB) | ((whitePawns << 7) & ~FileHBB);
131 pi->pawnAttacks[BLACK] = ((blackPawns >> 7) & ~FileABB) | ((blackPawns >> 9) & ~FileHBB);
133 // Evaluate pawns for both colors
134 pi->value = evaluate_pawns<WHITE>(pos, whitePawns, blackPawns, pi)
135 - evaluate_pawns<BLACK>(pos, blackPawns, whitePawns, pi);
140 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
143 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
144 Bitboard theirPawns, PawnInfo* pi) const {
149 bool passed, isolated, doubled, opposed, chain, backward, candidate;
150 Score value = SCORE_ZERO;
151 const BitCountType Max15 = CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
152 const Square* ptr = pos.piece_list_begin(Us, PAWN);
154 // Initialize halfOpenFiles[]
155 for (f = FILE_A; f <= FILE_H; f++)
156 if (!(ourPawns & file_bb(f)))
157 pi->halfOpenFiles[Us] |= (1 << f);
159 // Loop through all pawns of the current color and score each pawn
160 while ((s = *ptr++) != SQ_NONE)
162 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
167 // Our rank plus previous one. Used for chain detection.
168 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
170 // Passed, isolated, doubled or member of a pawn
171 // chain (but not the backward one) ?
172 passed = !(theirPawns & passed_pawn_mask(Us, s));
173 doubled = ourPawns & squares_behind(Us, s);
174 opposed = theirPawns & squares_in_front_of(Us, s);
175 isolated = !(ourPawns & neighboring_files_bb(f));
176 chain = ourPawns & neighboring_files_bb(f) & b;
178 // Test for backward pawn
182 // If the pawn is passed, isolated, or member of a pawn chain
183 // it cannot be backward. If can capture an enemy pawn or if
184 // there are friendly pawns behind on neighboring files it cannot
185 // be backward either.
186 if ( !(passed | isolated | chain)
187 && !(ourPawns & attack_span_mask(opposite_color(Us), s))
188 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
190 // We now know that there are no friendly pawns beside or behind this
191 // pawn on neighboring files. We now check whether the pawn is
192 // backward by looking in the forward direction on the neighboring
193 // files, and seeing whether we meet a friendly or an enemy pawn first.
194 b = pos.attacks_from<PAWN>(s, Us);
196 // Note that we are sure to find something because pawn is not passed
197 // nor isolated, so loop is potentially infinite, but it isn't.
198 while (!(b & (ourPawns | theirPawns)))
199 Us == WHITE ? b <<= 8 : b >>= 8;
201 // The friendly pawn needs to be at least two ranks closer than the enemy
202 // pawn in order to help the potentially backward pawn advance.
203 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
206 assert(passed | opposed | (attack_span_mask(Us, s) & theirPawns));
208 // Test for candidate passed pawn
209 candidate = !(opposed | passed)
210 && (b = attack_span_mask(opposite_color(Us), s + pawn_push(Us)) & ourPawns) != EmptyBoardBB
211 && count_1s<Max15>(b) >= count_1s<Max15>(attack_span_mask(Us, s) & theirPawns);
213 // In order to prevent doubled passed pawns from receiving a too big
214 // bonus, only the frontmost passed pawn on each file is considered as
215 // a true passed pawn.
216 if (passed && (ourPawns & squares_in_front_of(Us, s)))
219 // Mark the pawn as passed. Pawn will be properly scored in evaluation
220 // because we need full attack info to evaluate passed pawns.
222 set_bit(&(pi->passedPawns[Us]), s);
227 value -= IsolatedPawnPenalty[f];
229 value -= IsolatedPawnPenalty[f] / 2;
232 value -= DoubledPawnPenalty[f];
236 value -= BackwardPawnPenalty[f];
238 value -= BackwardPawnPenalty[f] / 2;
241 value += ChainBonus[f];
244 value += CandidateBonus[relative_rank(Us, s)];