2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 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/>.
30 #define S(mg, eg) make_score(mg, eg)
32 // Doubled pawn penalty by opposed flag and file
33 const Score Doubled[2][FILE_NB] = {
34 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
35 S(23, 48), S(23, 48), S(20, 48), S(13, 43) },
36 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
37 S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
39 // Isolated pawn penalty by opposed flag and file
40 const Score Isolated[2][FILE_NB] = {
41 { S(37, 45), S(54, 52), S(60, 52), S(60, 52),
42 S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
43 { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
44 S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
46 // Backward pawn penalty by opposed flag and file
47 const Score Backward[2][FILE_NB] = {
48 { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
49 S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
50 { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
51 S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
53 // Pawn chain membership bonus by file
54 const Score ChainMember[FILE_NB] = {
55 S(11,-1), S(13,-1), S(13,-1), S(14,-1),
56 S(14,-1), S(13,-1), S(13,-1), S(11,-1)
59 // Candidate passed pawn bonus by rank
60 const Score CandidatePassed[RANK_NB] = {
61 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
62 S(34,68), S(83,166), S(0, 0), S( 0, 0)
65 // Weakness of our pawn shelter in front of the king indexed by [king pawn][rank]
66 const Value ShelterWeakness[2][RANK_NB] =
67 { { V(141), V(0), V(38), V(102), V(128), V(141), V(141) },
68 { V( 61), V(0), V(16), V( 44), V( 56), V( 61), V( 61) } };
70 // Danger of enemy pawns moving toward our king indexed by [pawn blocked][rank]
71 const Value StormDanger[2][RANK_NB] =
72 { { V(26), V(0), V(128), V(51), V(26) },
73 { V(13), V(0), V( 64), V(25), V(13) } };
75 // Max bonus for king safety. Corresponds to start position with all the pawns
76 // in front of the king and no enemy pawn on the horizont.
77 const Value MaxSafetyBonus = V(263);
83 Score evaluate(const Position& pos, Pawns::Entry* e) {
85 const Color Them = (Us == WHITE ? BLACK : WHITE);
86 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
87 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
88 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
94 bool passed, isolated, doubled, opposed, chain, backward, candidate;
95 Score value = SCORE_ZERO;
96 const Square* pl = pos.list<PAWN>(Us);
98 Bitboard ourPawns = pos.pieces(Us, PAWN);
99 Bitboard theirPawns = pos.pieces(Them, PAWN);
101 e->passedPawns[Us] = 0;
102 e->kingSquares[Us] = SQ_NONE;
103 e->semiopenFiles[Us] = 0xFF;
104 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
105 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & BlackSquares);
106 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
108 // Loop through all pawns of the current color and score each pawn
109 while ((s = *pl++) != SQ_NONE)
111 assert(pos.piece_on(s) == make_piece(Us, PAWN));
116 // This file cannot be semi-open
117 e->semiopenFiles[Us] &= ~(1 << f);
119 // Our rank plus previous one. Used for chain detection
120 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
122 // Flag the pawn as passed, isolated, doubled or member of a pawn
123 // chain (but not the backward one).
124 chain = ourPawns & adjacent_files_bb(f) & b;
125 isolated = !(ourPawns & adjacent_files_bb(f));
126 doubled = ourPawns & forward_bb(Us, s);
127 opposed = theirPawns & forward_bb(Us, s);
128 passed = !(theirPawns & passed_pawn_mask(Us, s));
130 // Test for backward pawn
133 // If the pawn is passed, isolated, or member of a pawn chain it cannot
134 // be backward. If there are friendly pawns behind on adjacent files
135 // or if can capture an enemy pawn it cannot be backward either.
136 if ( !(passed | isolated | chain)
137 && !(ourPawns & pawn_attack_span(Them, s))
138 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
140 // We now know that there are no friendly pawns beside or behind this
141 // pawn on adjacent files. We now check whether the pawn is
142 // backward by looking in the forward direction on the adjacent
143 // files, and seeing whether we meet a friendly or an enemy pawn first.
144 b = pos.attacks_from<PAWN>(s, Us);
146 // Note that we are sure to find something because pawn is not passed
147 // nor isolated, so loop is potentially infinite, but it isn't.
148 while (!(b & (ourPawns | theirPawns)))
151 // The friendly pawn needs to be at least two ranks closer than the
152 // enemy pawn in order to help the potentially backward pawn advance.
153 backward = (b | shift_bb<Up>(b)) & theirPawns;
156 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
158 // A not passed pawn is a candidate to become passed if it is free to
159 // advance and if the number of friendly pawns beside or behind this
160 // pawn on adjacent files is higher or equal than the number of
161 // enemy pawns in the forward direction on the adjacent files.
162 candidate = !(opposed | passed | backward | isolated)
163 && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
164 && popcount<Max15>(b) >= popcount<Max15>(pawn_attack_span(Us, s) & theirPawns);
166 // Passed pawns will be properly scored in evaluation because we need
167 // full attack info to evaluate passed pawns. Only the frontmost passed
168 // pawn on each file is considered a true passed pawn.
169 if (passed && !doubled)
170 e->passedPawns[Us] |= s;
174 value -= Isolated[opposed][f];
177 value -= Doubled[opposed][f];
180 value -= Backward[opposed][f];
183 value += ChainMember[f];
186 value += CandidatePassed[relative_rank(Us, s)];
196 /// probe() takes a position object as input, computes a Entry object, and returns
197 /// a pointer to it. The result is also stored in a hash table, so we don't have
198 /// to recompute everything when the same pawn structure occurs again.
200 Entry* probe(const Position& pos, Table& entries) {
202 Key key = pos.pawn_key();
203 Entry* e = entries[key];
209 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
214 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
215 /// the king is on, as well as the two adjacent files.
218 Value Entry::shelter_storm(const Position& pos, Square ksq) {
220 const Color Them = (Us == WHITE ? BLACK : WHITE);
222 Value safety = MaxSafetyBonus;
223 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | rank_bb(ksq));
224 Bitboard ourPawns = b & pos.pieces(Us) & ~rank_bb(ksq);
225 Bitboard theirPawns = b & pos.pieces(Them);
227 File kf = file_of(ksq);
229 kf = (kf == FILE_A) ? FILE_B : (kf == FILE_H) ? FILE_G : kf;
231 for (int f = kf - 1; f <= kf + 1; f++)
233 // Shelter penalty is higher for the pawn in front of the king
234 b = ourPawns & FileBB[f];
235 rkUs = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
236 safety -= ShelterWeakness[f != kf][rkUs];
238 // Storm danger is smaller if enemy pawn is blocked
239 b = theirPawns & FileBB[f];
240 rkThem = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
241 safety -= StormDanger[rkThem == rkUs + 1][rkThem];
248 /// Entry::update_safety() calculates and caches a bonus for king safety. It is
249 /// called only when king square changes, about 20% of total king_safety() calls.
252 Score Entry::update_safety(const Position& pos, Square ksq) {
254 kingSquares[Us] = ksq;
255 castleRights[Us] = pos.can_castle(Us);
256 minKPdistance[Us] = 0;
258 Bitboard pawns = pos.pieces(Us, PAWN);
260 while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
262 if (relative_rank(Us, ksq) > RANK_4)
263 return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
265 Value bonus = shelter_storm<Us>(pos, ksq);
267 // If we can castle use the bonus after the castle if is bigger
268 if (pos.can_castle(make_castle_right(Us, KING_SIDE)))
269 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
271 if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
272 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
274 return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
277 // Explicit template instantiation
278 template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq);
279 template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq);