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 file
34 const Score Doubled[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) };
38 // Isolated pawn penalty by opposed flag and file
39 const Score Isolated[2][FILE_NB] = {
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 Backward[2][FILE_NB] = {
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 and rank (initialized by formula)
53 Score ChainMember[FILE_NB][RANK_NB];
55 // Candidate passed pawn bonus by rank
56 const Score CandidatePassed[RANK_NB] = {
57 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
58 S(34,68), S(83,166), S(0, 0), S( 0, 0) };
60 // Weakness of our pawn shelter in front of the king indexed by [rank]
61 const Value ShelterWeakness[RANK_NB] =
62 { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
64 // Danger of enemy pawns moving toward our king indexed by
65 // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
66 const Value StormDanger[3][RANK_NB] = {
67 { V( 0), V(64), V(128), V(51), V(26) },
68 { V(26), V(32), V( 96), V(38), V(20) },
69 { V( 0), V( 0), V( 64), V(25), V(13) } };
71 // Max bonus for king safety. Corresponds to start position with all the pawns
72 // in front of the king and no enemy pawn on the horizon.
73 const Value MaxSafetyBonus = V(263);
79 Score evaluate(const Position& pos, Pawns::Entry* e) {
81 const Color Them = (Us == WHITE ? BLACK : WHITE);
82 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
83 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
84 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
89 bool passed, isolated, doubled, opposed, chain, backward, candidate;
90 Score value = SCORE_ZERO;
91 const Square* pl = pos.list<PAWN>(Us);
93 Bitboard ourPawns = pos.pieces(Us, PAWN);
94 Bitboard theirPawns = pos.pieces(Them, PAWN);
96 e->passedPawns[Us] = e->candidatePawns[Us] = 0;
97 e->kingSquares[Us] = SQ_NONE;
98 e->semiopenFiles[Us] = 0xFF;
99 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
100 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
101 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
103 // Loop through all pawns of the current color and score each pawn
104 while ((s = *pl++) != SQ_NONE)
106 assert(pos.piece_on(s) == make_piece(Us, PAWN));
110 // This file cannot be semi-open
111 e->semiopenFiles[Us] &= ~(1 << f);
113 // Our rank plus previous one. Used for chain detection
114 b = rank_bb(s) | rank_bb(s - pawn_push(Us));
116 // Flag the pawn as passed, isolated, doubled or member of a pawn
117 // chain (but not the backward one).
118 chain = ourPawns & adjacent_files_bb(f) & b;
119 isolated = !(ourPawns & adjacent_files_bb(f));
120 doubled = ourPawns & forward_bb(Us, s);
121 opposed = theirPawns & forward_bb(Us, s);
122 passed = !(theirPawns & passed_pawn_mask(Us, s));
124 // Test for backward pawn.
125 // If the pawn is passed, isolated, or member of a pawn chain it cannot
126 // be backward. If there are friendly pawns behind on adjacent files
127 // or if can capture an enemy pawn it cannot be backward either.
128 if ( (passed | isolated | chain)
129 || (ourPawns & pawn_attack_span(Them, s))
130 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
134 // We now know that there are no friendly pawns beside or behind this
135 // pawn on adjacent files. We now check whether the pawn is
136 // backward by looking in the forward direction on the adjacent
137 // files, and picking the closest pawn there.
138 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
139 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
141 // If we have an enemy pawn in the same or next rank, the pawn is
142 // backward because it cannot advance without being captured.
143 backward = (b | shift_bb<Up>(b)) & theirPawns;
146 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
148 // A not passed pawn is a candidate to become passed, if it is free to
149 // advance and if the number of friendly pawns beside or behind this
150 // pawn on adjacent files is higher or equal than the number of
151 // enemy pawns in the forward direction on the adjacent files.
152 candidate = !(opposed | passed | backward | isolated)
153 && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
154 && popcount<Max15>(b) >= popcount<Max15>(pawn_attack_span(Us, s) & theirPawns);
156 // Passed pawns will be properly scored in evaluation because we need
157 // full attack info to evaluate passed pawns. Only the frontmost passed
158 // pawn on each file is considered a true passed pawn.
159 if (passed && !doubled)
160 e->passedPawns[Us] |= s;
164 value -= Isolated[opposed][f];
170 value -= Backward[opposed][f];
173 value += ChainMember[f][relative_rank(Us, s)];
177 value += CandidatePassed[relative_rank(Us, s)];
180 e->candidatePawns[Us] |= s;
191 /// init() initializes some tables by formula instead of hard-code their values
195 const int chainByFile[8] = { 1, 3, 3, 4, 4, 3, 3, 1 };
198 for (Rank r = RANK_1; r < RANK_8; ++r)
199 for (File f = FILE_A; f <= FILE_H; ++f)
201 bonus = r * (r-1) * (r-2) + chainByFile[f] * (r/2 + 1);
202 ChainMember[f][r] = make_score(bonus, bonus);
207 /// probe() takes a position object as input, computes a Entry object, and returns
208 /// a pointer to it. The result is also stored in a hash table, so we don't have
209 /// to recompute everything when the same pawn structure occurs again.
211 Entry* probe(const Position& pos, Table& entries) {
213 Key key = pos.pawn_key();
214 Entry* e = entries[key];
220 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
225 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
226 /// the king is on, as well as the two adjacent files.
229 Value Entry::shelter_storm(const Position& pos, Square ksq) {
231 const Color Them = (Us == WHITE ? BLACK : WHITE);
233 Value safety = MaxSafetyBonus;
234 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
235 Bitboard ourPawns = b & pos.pieces(Us);
236 Bitboard theirPawns = b & pos.pieces(Them);
238 File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
240 for (File f = kf - File(1); f <= kf + File(1); ++f)
242 b = ourPawns & file_bb(f);
243 rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
244 safety -= ShelterWeakness[rkUs];
246 b = theirPawns & file_bb(f);
247 rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
248 safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 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 it 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);