2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
32 #define S(mg, eg) make_score(mg, eg)
34 // Isolated pawn penalty by opposed flag
35 const Score Isolated[2] = { S(45, 40), S(30, 27) };
37 // Backward pawn penalty by opposed flag
38 const Score Backward[2] = { S(56, 33), S(41, 19) };
40 // Unsupported pawn penalty for pawns which are neither isolated or backward,
41 // by number of pawns it supports [less than 2 / exactly 2].
42 const Score Unsupported[2] = { S(17, 8), S(21, 12) };
44 // Connected pawn bonus by opposed, phalanx, twice supported and rank
45 Score Connected[2][2][2][RANK_NB];
47 // Doubled pawn penalty
48 const Score Doubled = S(18,38);
50 // Lever bonus by rank
51 const Score Lever[RANK_NB] = {
52 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
53 S(17, 16), S(33, 32), S(0, 0), S(0, 0) };
55 // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
56 const Value ShelterWeakness[][RANK_NB] = {
57 { V( 97), V(21), V(26), V(51), V(87), V( 89), V( 99) },
58 { V(120), V( 0), V(28), V(76), V(88), V(103), V(104) },
59 { V(101), V( 7), V(54), V(78), V(77), V( 92), V(101) },
60 { V( 80), V(11), V(44), V(68), V(87), V( 90), V(119) } };
62 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
63 const Value StormDanger[][4][RANK_NB] = {
64 { { V( 0), V( 67), V( 134), V(38), V(32) },
65 { V( 0), V( 57), V( 139), V(37), V(22) },
66 { V( 0), V( 43), V( 115), V(43), V(27) },
67 { V( 0), V( 68), V( 124), V(57), V(32) } },
68 { { V(20), V( 43), V( 100), V(56), V(20) },
69 { V(23), V( 20), V( 98), V(40), V(15) },
70 { V(23), V( 39), V( 103), V(36), V(18) },
71 { V(28), V( 19), V( 108), V(42), V(26) } },
72 { { V( 0), V( 0), V( 75), V(14), V( 2) },
73 { V( 0), V( 0), V( 150), V(30), V( 4) },
74 { V( 0), V( 0), V( 160), V(22), V( 5) },
75 { V( 0), V( 0), V( 166), V(24), V(13) } },
76 { { V( 0), V(-283), V(-281), V(57), V(31) },
77 { V( 0), V( 58), V( 141), V(39), V(18) },
78 { V( 0), V( 65), V( 142), V(48), V(32) },
79 { V( 0), V( 60), V( 126), V(51), V(19) } } };
81 // Max bonus for king safety. Corresponds to start position with all the pawns
82 // in front of the king and no enemy pawn on the horizon.
83 const Value MaxSafetyBonus = V(258);
89 Score evaluate(const Position& pos, Pawns::Entry* e) {
91 const Color Them = (Us == WHITE ? BLACK : WHITE);
92 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
93 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
94 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
96 Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
98 bool opposed, lever, connected, backward;
99 Score score = SCORE_ZERO;
100 const Square* pl = pos.squares<PAWN>(Us);
101 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
103 Bitboard ourPawns = pos.pieces(Us , PAWN);
104 Bitboard theirPawns = pos.pieces(Them, PAWN);
106 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
107 e->kingSquares[Us] = SQ_NONE;
108 e->semiopenFiles[Us] = 0xFF;
109 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
110 e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
111 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
113 // Loop through all pawns of the current color and score each pawn
114 while ((s = *pl++) != SQ_NONE)
116 assert(pos.piece_on(s) == make_piece(Us, PAWN));
120 e->semiopenFiles[Us] &= ~(1 << f);
121 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
124 opposed = theirPawns & forward_bb(Us, s);
125 stoppers = theirPawns & passed_pawn_mask(Us, s);
126 lever = theirPawns & pawnAttacksBB[s];
127 doubled = ourPawns & forward_bb(Us, s);
128 neighbours = ourPawns & adjacent_files_bb(f);
129 phalanx = neighbours & rank_bb(s);
130 supported = neighbours & rank_bb(s - Up);
131 connected = supported | phalanx;
133 // A pawn is backward when it is behind all pawns of the same color on the
134 // adjacent files and cannot be safely advanced.
135 if (!neighbours || lever || relative_rank(Us, s) >= RANK_5)
139 // Find the backmost rank with neighbours or stoppers
140 b = rank_bb(backmost_sq(Us, neighbours | stoppers));
142 // The pawn is backward when it cannot safely progress to that rank:
143 // either there is a stopper in the way on this rank, or there is a
144 // stopper on adjacent file which controls the way to that rank.
145 backward = (b | shift_bb<Up>(b & adjacent_files_bb(f))) & stoppers;
147 assert(!backward || !(pawn_attack_span(Them, s + Up) & neighbours));
150 // Passed pawns will be properly scored in evaluation because we need
151 // full attack info to evaluate them. Only the frontmost passed
152 // pawn on each file is considered a true passed pawn.
153 if (!(stoppers | doubled))
154 e->passedPawns[Us] |= s;
158 score -= Isolated[opposed];
161 score -= Backward[opposed];
164 score -= Unsupported[more_than_one(neighbours & pawnAttacksBB[s])];
167 score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
170 score -= Doubled / distance<Rank>(s, frontmost_sq(Us, doubled));
173 score += Lever[relative_rank(Us, s)];
176 b = e->semiopenFiles[Us] ^ 0xFF;
177 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
186 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
187 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
188 /// to reduce independent parameters and to allow easier tuning and better insight.
192 static const int Seed[RANK_NB] = { 0, 8, 19, 13, 71, 94, 169, 324 };
194 for (int opposed = 0; opposed <= 1; ++opposed)
195 for (int phalanx = 0; phalanx <= 1; ++phalanx)
196 for (int apex = 0; apex <= 1; ++apex)
197 for (Rank r = RANK_2; r < RANK_8; ++r)
199 int v = (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
200 v += (apex ? v / 2 : 0);
201 Connected[opposed][phalanx][apex][r] = make_score(v, v * 5 / 8);
206 /// Pawns::probe() looks up the current position's pawns configuration in
207 /// the pawns hash table. It returns a pointer to the Entry if the position
208 /// is found. Otherwise a new Entry is computed and stored there, so we don't
209 /// have to recompute all when the same pawns configuration occurs again.
211 Entry* probe(const Position& pos) {
213 Key key = pos.pawn_key();
214 Entry* e = pos.this_thread()->pawnsTable[key];
220 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
221 e->asymmetry = popcount(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
226 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
227 /// the king is on, as well as the two adjacent files.
230 Value Entry::shelter_storm(const Position& pos, Square ksq) {
232 const Color Them = (Us == WHITE ? BLACK : WHITE);
234 enum { NoFriendlyPawn, Unblocked, BlockedByPawn, BlockedByKing };
236 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
237 Bitboard ourPawns = b & pos.pieces(Us);
238 Bitboard theirPawns = b & pos.pieces(Them);
239 Value safety = MaxSafetyBonus;
240 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
242 for (File f = center - File(1); f <= center + File(1); ++f)
244 b = ourPawns & file_bb(f);
245 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
247 b = theirPawns & file_bb(f);
248 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
250 safety -= ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
252 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
253 rkUs == RANK_1 ? NoFriendlyPawn :
254 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
255 [std::min(f, FILE_H - f)][rkThem];
262 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
263 /// when king square changes, which is about 20% of total king_safety() calls.
266 Score Entry::do_king_safety(const Position& pos, Square ksq) {
268 kingSquares[Us] = ksq;
269 castlingRights[Us] = pos.can_castle(Us);
270 int minKingPawnDistance = 0;
272 Bitboard pawns = pos.pieces(Us, PAWN);
274 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
276 Value bonus = shelter_storm<Us>(pos, ksq);
278 // If we can castle use the bonus after the castling if it is bigger
279 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
280 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
282 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
283 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
285 return make_score(bonus, -16 * minKingPawnDistance);
288 // Explicit template instantiation
289 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
290 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);