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
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/>.
32 #define S(mg, eg) make_score(mg, eg)
34 // Doubled pawn penalty by file
35 const Score Doubled[FILE_NB] = {
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 // Connected pawn bonus by opposed, phalanx flags and rank
54 Score Connected[2][2][RANK_NB];
56 // Levers bonus by rank
57 const Score Lever[RANK_NB] = {
58 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
59 S(20,20), S(40,40), S(0, 0), S(0, 0) };
61 // Unsupported pawn penalty
62 const Score UnsupportedPawnPenalty = S(20, 10);
64 // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
65 const Value ShelterWeakness[][RANK_NB] = {
66 { V(100), V(13), V(24), V(64), V(89), V( 93), V(104) },
67 { V(110), V( 1), V(29), V(75), V(96), V(102), V(107) },
68 { V(102), V( 0), V(39), V(74), V(88), V(101), V( 98) },
69 { V( 88), V( 4), V(33), V(67), V(92), V( 94), V(107) } };
71 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
72 const Value StormDanger[][4][RANK_NB] = {
73 { { V( 0), V( 63), V( 128), V(43), V(27) },
74 { V( 0), V( 62), V( 131), V(44), V(26) },
75 { V( 0), V( 59), V( 121), V(50), V(28) },
76 { V( 0), V( 62), V( 127), V(54), V(28) } },
77 { { V(24), V( 40), V( 93), V(42), V(22) },
78 { V(24), V( 28), V( 101), V(38), V(20) },
79 { V(24), V( 32), V( 95), V(36), V(23) },
80 { V(27), V( 24), V( 99), V(36), V(24) } },
81 { { V( 0), V( 0), V( 81), V(16), V( 6) },
82 { V( 0), V( 0), V( 165), V(29), V( 9) },
83 { V( 0), V( 0), V( 163), V(23), V(12) },
84 { V( 0), V( 0), V( 161), V(28), V(13) } },
85 { { V( 0), V(-296), V(-299), V(55), V(25) },
86 { V( 0), V( 67), V( 131), V(46), V(21) },
87 { V( 0), V( 65), V( 135), V(50), V(31) },
88 { V( 0), V( 62), V( 128), V(51), V(24) } } };
90 // Max bonus for king safety. Corresponds to start position with all the pawns
91 // in front of the king and no enemy pawn on the horizon.
92 const Value MaxSafetyBonus = V(257);
98 Score evaluate(const Position& pos, Pawns::Entry* e) {
100 const Color Them = (Us == WHITE ? BLACK : WHITE);
101 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
102 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
103 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
105 Bitboard b, p, doubled, connected;
107 bool passed, isolated, opposed, phalanx, backward, unsupported, lever;
108 Score score = SCORE_ZERO;
109 const Square* pl = pos.list<PAWN>(Us);
110 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
112 Bitboard ourPawns = pos.pieces(Us , PAWN);
113 Bitboard theirPawns = pos.pieces(Them, PAWN);
115 e->passedPawns[Us] = 0;
116 e->kingSquares[Us] = SQ_NONE;
117 e->semiopenFiles[Us] = 0xFF;
118 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
119 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
120 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
122 // Loop through all pawns of the current color and score each pawn
123 while ((s = *pl++) != SQ_NONE)
125 assert(pos.piece_on(s) == make_piece(Us, PAWN));
129 // This file cannot be semi-open
130 e->semiopenFiles[Us] &= ~(1 << f);
133 p = rank_bb(s - pawn_push(Us));
135 // Flag the pawn as passed, isolated, doubled,
136 // unsupported or connected (but not the backward one).
137 connected = ourPawns & adjacent_files_bb(f) & (rank_bb(s) | p);
138 phalanx = connected & rank_bb(s);
139 unsupported = !(ourPawns & adjacent_files_bb(f) & p);
140 isolated = !(ourPawns & adjacent_files_bb(f));
141 doubled = ourPawns & forward_bb(Us, s);
142 opposed = theirPawns & forward_bb(Us, s);
143 passed = !(theirPawns & passed_pawn_mask(Us, s));
144 lever = theirPawns & pawnAttacksBB[s];
146 // Test for backward pawn.
147 // If the pawn is passed, isolated, or connected it cannot be
148 // backward. If there are friendly pawns behind on adjacent files
149 // or if it can capture an enemy pawn it cannot be backward either.
150 if ( (passed | isolated | connected)
151 || (ourPawns & pawn_attack_span(Them, s))
152 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
156 // We now know that there are no friendly pawns beside or behind this
157 // pawn on adjacent files. We now check whether the pawn is
158 // backward by looking in the forward direction on the adjacent
159 // files, and picking the closest pawn there.
160 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
161 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
163 // If we have an enemy pawn in the same or next rank, the pawn is
164 // backward because it cannot advance without being captured.
165 backward = (b | shift_bb<Up>(b)) & theirPawns;
168 assert(opposed | passed | (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 score -= Isolated[opposed][f];
180 if (unsupported && !isolated)
181 score -= UnsupportedPawnPenalty;
184 score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
187 score -= Backward[opposed][f];
190 score += Connected[opposed][phalanx][relative_rank(Us, s)];
193 score += Lever[relative_rank(Us, s)];
196 b = e->semiopenFiles[Us] ^ 0xFF;
197 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
206 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
207 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
208 /// to reduce independent parameters and to allow easier tuning and better insight.
212 static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
214 for (int opposed = 0; opposed <= 1; ++opposed)
215 for (int phalanx = 0; phalanx <= 1; ++phalanx)
216 for (Rank r = RANK_2; r < RANK_8; ++r)
218 int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
219 Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
224 /// Pawns::probe() looks up the current position's pawns configuration in
225 /// the pawns hash table. It returns a pointer to the Entry if the position
226 /// is found. Otherwise a new Entry is computed and stored there, so we don't
227 /// have to recompute all when the same pawns configuration occurs again.
229 Entry* probe(const Position& pos) {
231 Key key = pos.pawn_key();
232 Entry* e = pos.this_thread()->pawnsTable[key];
238 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
243 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
244 /// the king is on, as well as the two adjacent files.
247 Value Entry::shelter_storm(const Position& pos, Square ksq) {
249 const Color Them = (Us == WHITE ? BLACK : WHITE);
251 enum { NoFriendlyPawn, Unblocked, BlockedByPawn, BlockedByKing };
253 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
254 Bitboard ourPawns = b & pos.pieces(Us);
255 Bitboard theirPawns = b & pos.pieces(Them);
256 Value safety = MaxSafetyBonus;
257 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
259 for (File f = center - File(1); f <= center + File(1); ++f)
261 b = ourPawns & file_bb(f);
262 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
264 b = theirPawns & file_bb(f);
265 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
267 safety -= ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
269 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
270 rkUs == RANK_1 ? NoFriendlyPawn :
271 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
272 [std::min(f, FILE_H - f)][rkThem];
279 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
280 /// when king square changes, which is about 20% of total king_safety() calls.
283 Score Entry::do_king_safety(const Position& pos, Square ksq) {
285 kingSquares[Us] = ksq;
286 castlingRights[Us] = pos.can_castle(Us);
287 minKingPawnDistance[Us] = 0;
289 Bitboard pawns = pos.pieces(Us, PAWN);
291 while (!(DistanceRingBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
293 if (relative_rank(Us, ksq) > RANK_4)
294 return make_score(0, -16 * minKingPawnDistance[Us]);
296 Value bonus = shelter_storm<Us>(pos, ksq);
298 // If we can castle use the bonus after the castling if it is bigger
299 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
300 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
302 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
303 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
305 return make_score(bonus, -16 * minKingPawnDistance[Us]);
308 // Explicit template instantiation
309 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
310 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);