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);
68 const File ShelterFile[8] = { FILE_B, FILE_B, FILE_C, FILE_D, FILE_E, FILE_F, FILE_G, FILE_G };
70 inline Value score_non_center_file(const Value v) {
71 return Value(v * 7 / 16);
75 // Arrays are indexed by rank. Zeroth value is for when no pawn on that file.
76 const Value PawnShelter[8] = { V(141), V(0), V( 38), V(102), V(128), V(141), V(141), V(141) };
77 const Value PawnStorm[8] = { V( 26), V(0), V(128), V( 51), V( 26), V( 0), V( 0), V( 0) };
78 // We compute shelter as a penalty for the given color, but shelter is used as a bonus, so we invert it using this as the basis.
79 const Value PawnShelterBasis = PawnShelter[0] + score_non_center_file(PawnShelter[0]) * 2;
81 inline Score apply_weight(Score v, Score w) {
82 return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
83 (int(eg_value(v)) * eg_value(w)) / 0x100);
88 /// PawnInfoTable::pawn_info() takes a position object as input, computes
89 /// a PawnInfo object, and returns a pointer to it. The result is also stored
90 /// in an hash table, so we don't have to recompute everything when the same
91 /// pawn structure occurs again.
93 PawnInfo* PawnInfoTable::pawn_info(const Position& pos) const {
95 Key key = pos.pawn_key();
96 PawnInfo* pi = probe(key);
98 // If pi->key matches the position's pawn hash key, it means that we
99 // have analysed this pawn structure before, and we can simply return
100 // the information we found the last time instead of recomputing it.
104 // Initialize PawnInfo entry
106 pi->passedPawns[WHITE] = pi->passedPawns[BLACK] = 0;
107 pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
108 pi->halfOpenFiles[WHITE] = pi->halfOpenFiles[BLACK] = 0xFF;
110 // Calculate pawn attacks
111 Bitboard wPawns = pos.pieces(PAWN, WHITE);
112 Bitboard bPawns = pos.pieces(PAWN, BLACK);
113 pi->pawnAttacks[WHITE] = ((wPawns << 9) & ~FileABB) | ((wPawns << 7) & ~FileHBB);
114 pi->pawnAttacks[BLACK] = ((bPawns >> 7) & ~FileABB) | ((bPawns >> 9) & ~FileHBB);
116 // Evaluate pawns for both colors and weight the result
117 pi->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, pi)
118 - evaluate_pawns<BLACK>(pos, bPawns, wPawns, pi);
120 pi->value = apply_weight(pi->value, PawnStructureWeight);
126 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
129 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
130 Bitboard theirPawns, PawnInfo* pi) {
132 const Color Them = (Us == WHITE ? BLACK : WHITE);
138 bool passed, isolated, doubled, opposed, chain, backward, candidate;
139 Score value = SCORE_ZERO;
140 const Square* pl = pos.piece_list(Us, PAWN);
142 // Loop through all pawns of the current color and score each pawn
143 while ((s = *pl++) != SQ_NONE)
145 assert(pos.piece_on(s) == make_piece(Us, PAWN));
150 // This file cannot be half open
151 pi->halfOpenFiles[Us] &= ~(1 << f);
153 // Our rank plus previous one. Used for chain detection
154 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
156 // Flag the pawn as passed, isolated, doubled or member of a pawn
157 // chain (but not the backward one).
158 passed = !(theirPawns & passed_pawn_mask(Us, s));
159 doubled = ourPawns & squares_in_front_of(Us, s);
160 opposed = theirPawns & squares_in_front_of(Us, s);
161 isolated = !(ourPawns & adjacent_files_bb(f));
162 chain = ourPawns & adjacent_files_bb(f) & b;
164 // Test for backward pawn
167 // If the pawn is passed, isolated, or member of a pawn chain it cannot
168 // be backward. If there are friendly pawns behind on adjacent files
169 // or if can capture an enemy pawn it cannot be backward either.
170 if ( !(passed | isolated | chain)
171 && !(ourPawns & attack_span_mask(Them, s))
172 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
174 // We now know that there are no friendly pawns beside or behind this
175 // pawn on adjacent files. We now check whether the pawn is
176 // backward by looking in the forward direction on the adjacent
177 // files, and seeing whether we meet a friendly or an enemy pawn first.
178 b = pos.attacks_from<PAWN>(s, Us);
180 // Note that we are sure to find something because pawn is not passed
181 // nor isolated, so loop is potentially infinite, but it isn't.
182 while (!(b & (ourPawns | theirPawns)))
183 Us == WHITE ? b <<= 8 : b >>= 8;
185 // The friendly pawn needs to be at least two ranks closer than the
186 // enemy pawn in order to help the potentially backward pawn advance.
187 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
190 assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
192 // A not passed pawn is a candidate to become passed if it is free to
193 // advance and if the number of friendly pawns beside or behind this
194 // pawn on adjacent files is higher or equal than the number of
195 // enemy pawns in the forward direction on the adjacent files.
196 candidate = !(opposed | passed | backward | isolated)
197 && (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != 0
198 && popcount<Max15>(b) >= popcount<Max15>(attack_span_mask(Us, s) & theirPawns);
200 // Passed pawns will be properly scored in evaluation because we need
201 // full attack info to evaluate passed pawns. Only the frontmost passed
202 // pawn on each file is considered a true passed pawn.
203 if (passed && !doubled)
204 pi->passedPawns[Us] |= s;
208 value -= IsolatedPawnPenalty[opposed][f];
211 value -= DoubledPawnPenalty[opposed][f];
214 value -= BackwardPawnPenalty[opposed][f];
217 value += ChainBonus[f];
220 value += CandidateBonus[relative_rank(Us, s)];
226 int computePawnShelter(const Position &pos, Square ksq) {
227 const Color Them = (Us == WHITE ? BLACK : WHITE);
228 const File kingFile = ShelterFile[file_of(ksq)];
229 const Bitboard ourPawns = pos.pieces(PAWN, Us) & in_front_bb(Us, ksq);
230 const Bitboard theirPawns = pos.pieces(PAWN, Them) & (RankBB[rank_of(ksq)] | in_front_bb(Us, ksq));
234 // Compute king shelter and storm values for the file the king is on, as well as the two adjacent files.
235 for (int fileOffset = -1; fileOffset <= 1; fileOffset++) {
236 // Shelter takes full penalty for center file, otherwise it's half penalty
237 Bitboard shelterFile = ourPawns & FileBB[kingFile + fileOffset];
238 Rank shelterClosest = shelterFile ? relative_rank<Us>(shelterFile)
241 shelter += fileOffset == 0 ? PawnShelter[shelterClosest]
242 : score_non_center_file(PawnShelter[shelterClosest]);
244 // Storm takes full penalty, unless there is an enemy pawn blocking us
245 Bitboard stormFile = theirPawns & FileBB[kingFile + fileOffset];
246 Rank stormClosest = stormFile ? relative_rank<Us>(stormFile)
249 shelter += shelterClosest + 1 == stormClosest ? PawnStorm[stormClosest] / 2
250 : PawnStorm[stormClosest];
256 /// PawnInfo::updateShelter() calculates and caches king shelter. It is called
257 /// only when king square changes, about 20% of total king_shelter() calls.
259 Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
262 if (relative_rank(Us, ksq) <= RANK_4)
264 shelter = computePawnShelter<Us>(pos, ksq);
265 if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
266 shelter = std::min(shelter, computePawnShelter<Us>(pos, relative_square(Us, SQ_G1)));
267 if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
268 shelter = std::min(shelter, computePawnShelter<Us>(pos, relative_square(Us, SQ_C1)));
269 shelter = PawnShelterBasis - shelter;
272 kingSquares[Us] = ksq;
273 kingShelters[Us] = make_score(shelter, 0);
274 return kingShelters[Us];
277 // Explicit template instantiation
278 template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
279 template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);