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/>.
31 #define S(mg, eg) make_score(mg, eg)
33 // Doubled pawn penalty by opposed flag and file
34 const Score Doubled[2][FILE_NB] = {
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) },
37 { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
38 S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
40 // Isolated pawn penalty by opposed flag and file
41 const Score Isolated[2][FILE_NB] = {
42 { S(37, 45), S(54, 52), S(60, 52), S(60, 52),
43 S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
44 { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
45 S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
47 // Backward pawn penalty by opposed flag and file
48 const Score Backward[2][FILE_NB] = {
49 { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
50 S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
51 { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
52 S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
54 // Pawn chain membership bonus by file
55 const Score ChainMember[FILE_NB][RANK_NB] = {
56 { S(0, 0), S(14, 0), S(16, 4), S(18, 9), S(56, 56), S(104, 208), S(236, 472) },
57 { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) },
58 { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) },
59 { S(0, 0), S(17, 0), S(19, 6), S(22, 11), S(66, 66), S(118, 236), S(254, 508) },
60 { S(0, 0), S(17, 0), S(19, 6), S(22, 11), S(66, 66), S(118, 236), S(254, 508) },
61 { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) },
62 { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) },
63 { S(0, 0), S(14, 0), S(16, 4), S(18, 9), S(56, 56), S(104, 208), S(236, 472) }
66 // Candidate passed pawn bonus by rank
67 const Score CandidatePassed[RANK_NB] = {
68 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
69 S(34,68), S(83,166), S(0, 0), S( 0, 0)
72 // Weakness of our pawn shelter in front of the king indexed by [rank]
73 const Value ShelterWeakness[RANK_NB] =
74 { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
76 // Danger of enemy pawns moving toward our king indexed by
77 // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
78 const Value StormDanger[3][RANK_NB] = {
79 { V( 0), V(64), V(128), V(51), V(26) },
80 { V(26), V(32), V( 96), V(38), V(20) },
81 { V( 0), V( 0), V( 64), V(25), V(13) }};
83 // Max bonus for king safety. Corresponds to start position with all the pawns
84 // in front of the king and no enemy pawn on the horizont.
85 const Value MaxSafetyBonus = V(263);
91 Score evaluate(const Position& pos, Pawns::Entry* e) {
93 const Color Them = (Us == WHITE ? BLACK : WHITE);
94 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
95 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
96 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
102 bool passed, isolated, doubled, opposed, chain, backward, candidate;
103 Score value = SCORE_ZERO;
104 const Square* pl = pos.list<PAWN>(Us);
106 Bitboard ourPawns = pos.pieces(Us, PAWN);
107 Bitboard theirPawns = pos.pieces(Them, PAWN);
109 e->passedPawns[Us] = e->candidatePawns[Us] = 0;
110 e->kingSquares[Us] = SQ_NONE;
111 e->semiopenFiles[Us] = 0xFF;
112 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
113 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
114 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
116 // Loop through all pawns of the current color and score each pawn
117 while ((s = *pl++) != SQ_NONE)
119 assert(pos.piece_on(s) == make_piece(Us, PAWN));
122 r = relative_rank(Us, s);
124 // This file cannot be semi-open
125 e->semiopenFiles[Us] &= ~(1 << f);
127 // Our rank plus previous one. Used for chain detection
128 b = rank_bb(s) | rank_bb(s - pawn_push(Us));
130 // Flag the pawn as passed, isolated, doubled or member of a pawn
131 // chain (but not the backward one).
132 chain = ourPawns & adjacent_files_bb(f) & b;
133 isolated = !(ourPawns & adjacent_files_bb(f));
134 doubled = ourPawns & forward_bb(Us, s);
135 opposed = theirPawns & forward_bb(Us, s);
136 passed = !(theirPawns & passed_pawn_mask(Us, s));
138 // Test for backward pawn.
139 // If the pawn is passed, isolated, or member of a pawn chain it cannot
140 // be backward. If there are friendly pawns behind on adjacent files
141 // or if can capture an enemy pawn it cannot be backward either.
142 if ( (passed | isolated | chain)
143 || (ourPawns & pawn_attack_span(Them, s))
144 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
148 // We now know that there are no friendly pawns beside or behind this
149 // pawn on adjacent files. We now check whether the pawn is
150 // backward by looking in the forward direction on the adjacent
151 // files, and picking the closest pawn there.
152 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
153 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
155 // If we have an enemy pawn in the same or next rank, the pawn is
156 // backward because it cannot advance without being captured.
157 backward = (b | shift_bb<Up>(b)) & theirPawns;
160 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
162 // A not passed pawn is a candidate to become passed if it is free to
163 // advance and if the number of friendly pawns beside or behind this
164 // pawn on adjacent files is higher or equal than the number of
165 // enemy pawns in the forward direction on the adjacent files.
166 candidate = !(opposed | passed | backward | isolated)
167 && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
168 && popcount<Max15>(b) >= popcount<Max15>(pawn_attack_span(Us, s) & theirPawns);
170 // Passed pawns will be properly scored in evaluation because we need
171 // full attack info to evaluate passed pawns. Only the frontmost passed
172 // pawn on each file is considered a true passed pawn.
173 if (passed && !doubled)
174 e->passedPawns[Us] |= s;
178 value -= Isolated[opposed][f];
181 value -= Doubled[opposed][f];
184 value -= Backward[opposed][f];
187 value += opposed ? ChainMember[f][r] / 2 : ChainMember[f][r];
191 value += CandidatePassed[r];
194 e->candidatePawns[Us] |= s;
205 /// probe() takes a position object as input, computes a Entry object, and returns
206 /// a pointer to it. The result is also stored in a hash table, so we don't have
207 /// to recompute everything when the same pawn structure occurs again.
209 Entry* probe(const Position& pos, Table& entries) {
211 Key key = pos.pawn_key();
212 Entry* e = entries[key];
218 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
223 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
224 /// the king is on, as well as the two adjacent files.
227 Value Entry::shelter_storm(const Position& pos, Square ksq) {
229 const Color Them = (Us == WHITE ? BLACK : WHITE);
231 Value safety = MaxSafetyBonus;
232 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
233 Bitboard ourPawns = b & pos.pieces(Us);
234 Bitboard theirPawns = b & pos.pieces(Them);
236 File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
238 for (int f = kf - 1; f <= kf + 1; ++f)
240 b = ourPawns & FileBB[f];
241 rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
242 safety -= ShelterWeakness[rkUs];
244 b = theirPawns & FileBB[f];
245 rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
246 safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
253 /// Entry::update_safety() calculates and caches a bonus for king safety. It is
254 /// called only when king square changes, about 20% of total king_safety() calls.
257 Score Entry::update_safety(const Position& pos, Square ksq) {
259 kingSquares[Us] = ksq;
260 castleRights[Us] = pos.can_castle(Us);
261 minKPdistance[Us] = 0;
263 Bitboard pawns = pos.pieces(Us, PAWN);
265 while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
267 if (relative_rank(Us, ksq) > RANK_4)
268 return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
270 Value bonus = shelter_storm<Us>(pos, ksq);
272 // If we can castle use the bonus after the castle if is bigger
273 if (pos.can_castle(make_castle_right(Us, KING_SIDE)))
274 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
276 if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
277 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
279 return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
282 // Explicit template instantiation
283 template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq);
284 template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq);