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 opposed flag and file
44 const Score DoubledPawnPenalty[2][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) },
47 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
48 S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
50 // Isolated pawn penalty by opposed flag and file
51 const Score IsolatedPawnPenalty[2][8] = {
52 { S(37, 45), S(54, 52), S(60, 52), S(60, 52),
53 S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
54 { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
55 S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
57 // Backward pawn penalty by opposed flag and file
58 const Score BackwardPawnPenalty[2][8] = {
59 { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
60 S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
61 { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
62 S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
64 // Pawn chain membership bonus by file
65 const Score ChainBonus[8] = {
66 S(11,-1), S(13,-1), S(13,-1), S(14,-1),
67 S(14,-1), S(13,-1), S(13,-1), S(11,-1)
70 // Candidate passed pawn bonus by rank
71 const Score CandidateBonus[8] = {
72 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
73 S(34,68), S(83,166), S(0, 0), S( 0, 0)
85 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
86 /// a PawnInfo object, and returns a pointer to it. The result is also stored
87 /// in a hash table, so we don't have to recompute everything when the same
88 /// pawn structure occurs again.
90 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) const {
94 Key key = pos.get_pawn_key();
95 PawnInfo* pi = find(key);
97 // If pi->key matches the position's pawn hash key, it means that we
98 // have analysed this pawn structure before, and we can simply return
99 // the information we found the last time instead of recomputing it.
103 // Clear the PawnInfo object, and set the key
104 memset(pi, 0, sizeof(PawnInfo));
105 pi->halfOpenFiles[WHITE] = pi->halfOpenFiles[BLACK] = 0xFF;
106 pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
109 // Calculate pawn attacks
110 Bitboard wPawns = pos.pieces(PAWN, WHITE);
111 Bitboard bPawns = pos.pieces(PAWN, BLACK);
112 pi->pawnAttacks[WHITE] = ((wPawns << 9) & ~FileABB) | ((wPawns << 7) & ~FileHBB);
113 pi->pawnAttacks[BLACK] = ((bPawns >> 7) & ~FileABB) | ((bPawns >> 9) & ~FileHBB);
115 // Evaluate pawns for both colors
116 pi->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, pi)
117 - evaluate_pawns<BLACK>(pos, bPawns, wPawns, pi);
122 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
125 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
126 Bitboard theirPawns, PawnInfo* pi) const {
131 bool passed, isolated, doubled, opposed, chain, backward, candidate;
132 Score value = SCORE_ZERO;
133 const BitCountType Max15 = CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
134 const Square* ptr = pos.piece_list_begin(Us, PAWN);
136 // Loop through all pawns of the current color and score each pawn
137 while ((s = *ptr++) != SQ_NONE)
139 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
144 // This file cannot be half open
145 pi->halfOpenFiles[Us] &= ~(1 << f);
147 // Our rank plus previous one. Used for chain detection.
148 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
150 // Passed, isolated, doubled or member of a pawn
151 // chain (but not the backward one) ?
152 passed = !(theirPawns & passed_pawn_mask(Us, s));
153 doubled = ourPawns & squares_in_front_of(Us, s);
154 opposed = theirPawns & squares_in_front_of(Us, s);
155 isolated = !(ourPawns & neighboring_files_bb(f));
156 chain = ourPawns & neighboring_files_bb(f) & b;
158 // Test for backward pawn
162 // If the pawn is passed, isolated, or member of a pawn chain
163 // it cannot be backward. If can capture an enemy pawn or if
164 // there are friendly pawns behind on neighboring files it cannot
165 // be backward either.
166 if ( !(passed | isolated | chain)
167 && !(ourPawns & attack_span_mask(opposite_color(Us), s))
168 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
170 // We now know that there are no friendly pawns beside or behind this
171 // pawn on neighboring files. We now check whether the pawn is
172 // backward by looking in the forward direction on the neighboring
173 // files, and seeing whether we meet a friendly or an enemy pawn first.
174 b = pos.attacks_from<PAWN>(s, Us);
176 // Note that we are sure to find something because pawn is not passed
177 // nor isolated, so loop is potentially infinite, but it isn't.
178 while (!(b & (ourPawns | theirPawns)))
179 Us == WHITE ? b <<= 8 : b >>= 8;
181 // The friendly pawn needs to be at least two ranks closer than the enemy
182 // pawn in order to help the potentially backward pawn advance.
183 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
186 assert(passed | opposed | (attack_span_mask(Us, s) & theirPawns));
188 // Test for candidate passed pawn
189 candidate = !(opposed | passed)
190 && (b = attack_span_mask(opposite_color(Us), s + pawn_push(Us)) & ourPawns) != EmptyBoardBB
191 && count_1s<Max15>(b) >= count_1s<Max15>(attack_span_mask(Us, s) & theirPawns);
193 // Mark the pawn as passed. Pawn will be properly scored in evaluation
194 // because we need full attack info to evaluate passed pawns. Only the
195 // frontmost passed pawn on each file is considered a true passed pawn.
196 if (passed && !doubled)
197 set_bit(&(pi->passedPawns[Us]), s);
201 value -= IsolatedPawnPenalty[opposed][f];
204 value -= DoubledPawnPenalty[opposed][f];
207 value -= BackwardPawnPenalty[opposed][f];
210 value += ChainBonus[f];
213 value += CandidateBonus[relative_rank(Us, s)];