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
47 const Score Backward[2] = { S(67, 56), S(49, 40) };
49 // Connected pawn bonus by opposed, phalanx, twice supported and rank
50 Score Connected[2][2][2][RANK_NB];
52 // Levers bonus by rank
53 const Score Lever[RANK_NB] = {
54 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
55 S(20,20), S(40,40), S(0, 0), S(0, 0) };
57 // Unsupported pawn penalty
58 const Score UnsupportedPawnPenalty = S(20, 10);
60 // Center bind bonus: Two pawns controlling the same central square
61 const Bitboard CenterBindMask[COLOR_NB] = {
62 (FileDBB | FileEBB) & (Rank5BB | Rank6BB | Rank7BB),
63 (FileDBB | FileEBB) & (Rank4BB | Rank3BB | Rank2BB)
66 const Score CenterBind = S(16, 0);
68 // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
69 const Value ShelterWeakness[][RANK_NB] = {
70 { V( 99), V(20), V(26), V(54), V(85), V( 92), V(108) },
71 { V(117), V( 1), V(27), V(71), V(94), V(104), V(118) },
72 { V(104), V( 4), V(51), V(76), V(82), V(102), V( 97) },
73 { V( 80), V(12), V(43), V(65), V(88), V( 91), V(115) } };
75 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
76 const Value StormDanger[][4][RANK_NB] = {
77 { { V( 0), V( 65), V( 126), V(36), V(30) },
78 { V( 0), V( 55), V( 135), V(36), V(23) },
79 { V( 0), V( 47), V( 116), V(45), V(26) },
80 { V( 0), V( 62), V( 127), V(57), V(34) } },
81 { { V(21), V( 45), V( 93), V(50), V(19) },
82 { V(23), V( 24), V( 105), V(41), V(13) },
83 { V(23), V( 36), V( 101), V(38), V(20) },
84 { V(30), V( 19), V( 110), V(41), V(27) } },
85 { { V( 0), V( 0), V( 81), V(14), V( 4) },
86 { V( 0), V( 0), V( 169), V(30), V( 3) },
87 { V( 0), V( 0), V( 168), V(24), V( 5) },
88 { V( 0), V( 0), V( 162), V(26), V(10) } },
89 { { V( 0), V(-283), V(-298), V(57), V(29) },
90 { V( 0), V( 63), V( 137), V(42), V(18) },
91 { V( 0), V( 67), V( 145), V(49), V(33) },
92 { V( 0), V( 62), V( 126), V(53), V(21) } } };
94 // Max bonus for king safety. Corresponds to start position with all the pawns
95 // in front of the king and no enemy pawn on the horizon.
96 const Value MaxSafetyBonus = V(258);
102 Score evaluate(const Position& pos, Pawns::Entry* e) {
104 const Color Them = (Us == WHITE ? BLACK : WHITE);
105 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
106 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
107 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
109 Bitboard b, neighbours, doubled, supported, phalanx;
111 bool passed, isolated, opposed, backward, lever, connected;
112 Score score = SCORE_ZERO;
113 const Square* pl = pos.list<PAWN>(Us);
114 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
116 Bitboard ourPawns = pos.pieces(Us , PAWN);
117 Bitboard theirPawns = pos.pieces(Them, PAWN);
119 e->passedPawns[Us] = 0;
120 e->kingSquares[Us] = SQ_NONE;
121 e->semiopenFiles[Us] = 0xFF;
122 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
123 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
124 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
126 // Loop through all pawns of the current color and score each pawn
127 while ((s = *pl++) != SQ_NONE)
129 assert(pos.piece_on(s) == make_piece(Us, PAWN));
133 // This file cannot be semi-open
134 e->semiopenFiles[Us] &= ~(1 << f);
137 neighbours = ourPawns & adjacent_files_bb(f);
138 doubled = ourPawns & forward_bb(Us, s);
139 opposed = theirPawns & forward_bb(Us, s);
140 passed = !(theirPawns & passed_pawn_mask(Us, s));
141 lever = theirPawns & pawnAttacksBB[s];
142 phalanx = neighbours & rank_bb(s);
143 supported = neighbours & rank_bb(s - Up);
144 connected = supported | phalanx;
145 isolated = !neighbours;
147 // Test for backward pawn.
148 // If the pawn is passed, isolated, lever or connected it cannot be
149 // backward. If there are friendly pawns behind on adjacent files
150 // it cannot be backward either.
151 if ( (passed | isolated | lever | connected)
152 || (ourPawns & pawn_attack_span(Them, s)))
156 // We now know 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];
181 score -= Backward[opposed];
184 score -= UnsupportedPawnPenalty;
187 score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
190 score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
193 score += Lever[relative_rank(Us, s)];
196 b = e->semiopenFiles[Us] ^ 0xFF;
197 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
199 // Center binds: Two pawns controlling the same central square
200 b = shift_bb<Right>(ourPawns) & shift_bb<Left>(ourPawns) & CenterBindMask[Us];
201 score += popcount<Max15>(b) * CenterBind;
210 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
211 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
212 /// to reduce independent parameters and to allow easier tuning and better insight.
216 static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
218 for (int opposed = 0; opposed <= 1; ++opposed)
219 for (int phalanx = 0; phalanx <= 1; ++phalanx)
220 for (int apex = 0; apex <= 1; ++apex)
221 for (Rank r = RANK_2; r < RANK_8; ++r)
223 int v = (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
224 v += (apex ? v / 2 : 0);
225 Connected[opposed][phalanx][apex][r] = make_score(3 * v / 2, v);
230 /// Pawns::probe() looks up the current position's pawns configuration in
231 /// the pawns hash table. It returns a pointer to the Entry if the position
232 /// is found. Otherwise a new Entry is computed and stored there, so we don't
233 /// have to recompute all when the same pawns configuration occurs again.
235 Entry* probe(const Position& pos) {
237 Key key = pos.pawn_key();
238 Entry* e = pos.this_thread()->pawnsTable[key];
244 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
249 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
250 /// the king is on, as well as the two adjacent files.
253 Value Entry::shelter_storm(const Position& pos, Square ksq) {
255 const Color Them = (Us == WHITE ? BLACK : WHITE);
257 enum { NoFriendlyPawn, Unblocked, BlockedByPawn, BlockedByKing };
259 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
260 Bitboard ourPawns = b & pos.pieces(Us);
261 Bitboard theirPawns = b & pos.pieces(Them);
262 Value safety = MaxSafetyBonus;
263 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
265 for (File f = center - File(1); f <= center + File(1); ++f)
267 b = ourPawns & file_bb(f);
268 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
270 b = theirPawns & file_bb(f);
271 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
273 safety -= ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
275 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
276 rkUs == RANK_1 ? NoFriendlyPawn :
277 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
278 [std::min(f, FILE_H - f)][rkThem];
285 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
286 /// when king square changes, which is about 20% of total king_safety() calls.
289 Score Entry::do_king_safety(const Position& pos, Square ksq) {
291 kingSquares[Us] = ksq;
292 castlingRights[Us] = pos.can_castle(Us);
293 int minKingPawnDistance = 0;
295 Bitboard pawns = pos.pieces(Us, PAWN);
297 while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
299 if (relative_rank(Us, ksq) > RANK_4)
300 return make_score(0, -16 * minKingPawnDistance);
302 Value bonus = shelter_storm<Us>(pos, ksq);
304 // If we can castle use the bonus after the castling if it is bigger
305 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
306 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
308 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
309 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
311 return make_score(bonus, -16 * minKingPawnDistance);
314 // Explicit template instantiation
315 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
316 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);