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_pawns(const Position& pos, Bitboard ourPawns,
84 Bitboard theirPawns, Pawns::Entry* e) {
86 const Color Them = (Us == WHITE ? BLACK : WHITE);
87 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
93 bool passed, isolated, doubled, opposed, chain, backward, candidate;
94 Score value = SCORE_ZERO;
95 const Square* pl = pos.piece_list(Us, PAWN);
97 // Loop through all pawns of the current color and score each pawn
98 while ((s = *pl++) != SQ_NONE)
100 assert(pos.piece_on(s) == make_piece(Us, PAWN));
105 // This file cannot be semi-open
106 e->semiopenFiles[Us] &= ~(1 << f);
108 // Our rank plus previous one. Used for chain detection
109 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
111 // Flag the pawn as passed, isolated, doubled or member of a pawn
112 // chain (but not the backward one).
113 chain = ourPawns & adjacent_files_bb(f) & b;
114 isolated = !(ourPawns & adjacent_files_bb(f));
115 doubled = ourPawns & forward_bb(Us, s);
116 opposed = theirPawns & forward_bb(Us, s);
117 passed = !(theirPawns & passed_pawn_mask(Us, s));
119 // Test for backward pawn
122 // If the pawn is passed, isolated, or member of a pawn chain it cannot
123 // be backward. If there are friendly pawns behind on adjacent files
124 // or if can capture an enemy pawn it cannot be backward either.
125 if ( !(passed | isolated | chain)
126 && !(ourPawns & attack_span_mask(Them, s))
127 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
129 // We now know that there are no friendly pawns beside or behind this
130 // pawn on adjacent files. We now check whether the pawn is
131 // backward by looking in the forward direction on the adjacent
132 // files, and seeing whether we meet a friendly or an enemy pawn first.
133 b = pos.attacks_from<PAWN>(s, Us);
135 // Note that we are sure to find something because pawn is not passed
136 // nor isolated, so loop is potentially infinite, but it isn't.
137 while (!(b & (ourPawns | theirPawns)))
138 Us == WHITE ? b <<= 8 : b >>= 8;
140 // The friendly pawn needs to be at least two ranks closer than the
141 // enemy pawn in order to help the potentially backward pawn advance.
142 backward = (b | shift_bb<Up>(b)) & theirPawns;
145 assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
147 // A not passed pawn is a candidate to become passed if it is free to
148 // advance and if the number of friendly pawns beside or behind this
149 // pawn on adjacent files is higher or equal than the number of
150 // enemy pawns in the forward direction on the adjacent files.
151 candidate = !(opposed | passed | backward | isolated)
152 && (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != 0
153 && popcount<Max15>(b) >= popcount<Max15>(attack_span_mask(Us, s) & theirPawns);
155 // Passed pawns will be properly scored in evaluation because we need
156 // full attack info to evaluate passed pawns. Only the frontmost passed
157 // pawn on each file is considered a true passed pawn.
158 if (passed && !doubled)
159 e->passedPawns[Us] |= s;
163 value -= Isolated[opposed][f];
166 value -= Doubled[opposed][f];
169 value -= Backward[opposed][f];
172 value += ChainMember[f];
175 value += CandidatePassed[relative_rank(Us, s)];
178 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & BlackSquares);
179 e->pawnsOnSquares[Us][WHITE] = pos.piece_count(Us, PAWN) - e->pawnsOnSquares[Us][BLACK];
181 e->pawnsOnSquares[Them][BLACK] = popcount<Max15>(theirPawns & BlackSquares);
182 e->pawnsOnSquares[Them][WHITE] = pos.piece_count(Them, PAWN) - e->pawnsOnSquares[Them][BLACK];
190 /// probe() takes a position object as input, computes a Entry object, and returns
191 /// a pointer to it. The result is also stored in a hash table, so we don't have
192 /// to recompute everything when the same pawn structure occurs again.
194 Entry* probe(const Position& pos, Table& entries) {
196 Key key = pos.pawn_key();
197 Entry* e = entries[key];
199 // If e->key matches the position's pawn hash key, it means that we
200 // have analysed this pawn structure before, and we can simply return
201 // the information we found the last time instead of recomputing it.
206 e->passedPawns[WHITE] = e->passedPawns[BLACK] = 0;
207 e->kingSquares[WHITE] = e->kingSquares[BLACK] = SQ_NONE;
208 e->semiopenFiles[WHITE] = e->semiopenFiles[BLACK] = 0xFF;
210 Bitboard wPawns = pos.pieces(WHITE, PAWN);
211 Bitboard bPawns = pos.pieces(BLACK, PAWN);
212 e->pawnAttacks[WHITE] = shift_bb<DELTA_NE>(wPawns) | shift_bb<DELTA_NW>(wPawns);
213 e->pawnAttacks[BLACK] = shift_bb<DELTA_SE>(bPawns) | shift_bb<DELTA_SW>(bPawns);
215 e->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, e)
216 - evaluate_pawns<BLACK>(pos, bPawns, wPawns, e);
221 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
222 /// the king is on, as well as the two adjacent files.
225 Value Entry::shelter_storm(const Position& pos, Square ksq) {
227 const Color Them = (Us == WHITE ? BLACK : WHITE);
229 Value safety = MaxSafetyBonus;
230 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | rank_bb(ksq));
231 Bitboard ourPawns = b & pos.pieces(Us) & ~rank_bb(ksq);
232 Bitboard theirPawns = b & pos.pieces(Them);
234 File kf = file_of(ksq);
236 kf = (kf == FILE_A) ? FILE_B : (kf == FILE_H) ? FILE_G : kf;
238 for (int f = kf - 1; f <= kf + 1; f++)
240 // Shelter penalty is higher for the pawn in front of the king
241 b = ourPawns & FileBB[f];
242 rkUs = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
243 safety -= ShelterWeakness[f != kf][rkUs];
245 // Storm danger is smaller if enemy pawn is blocked
246 b = theirPawns & FileBB[f];
247 rkThem = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
248 safety -= StormDanger[rkThem == rkUs + 1][rkThem];
255 /// Entry::update_safety() calculates and caches a bonus for king safety. It is
256 /// called only when king square changes, about 20% of total king_safety() calls.
259 Score Entry::update_safety(const Position& pos, Square ksq) {
261 kingSquares[Us] = ksq;
262 castleRights[Us] = pos.can_castle(Us);
263 minKPdistance[Us] = 0;
265 Bitboard pawns = pos.pieces(Us, PAWN);
267 while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
269 if (relative_rank(Us, ksq) > RANK_4)
270 return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
272 Value bonus = shelter_storm<Us>(pos, ksq);
274 // If we can castle use the bonus after the castle if is bigger
275 if (pos.can_castle(make_castle_right(Us, KING_SIDE)))
276 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
278 if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
279 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
281 return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
284 // Explicit template instantiation
285 template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq);
286 template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq);