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, 42), S(49, 24) };
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 const Score CenterBind = S(16, 0);
62 // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
63 const Value ShelterWeakness[][RANK_NB] = {
64 { V( 97), V(21), V(26), V(51), V(87), V( 89), V( 99) },
65 { V(120), V( 0), V(28), V(76), V(88), V(103), V(104) },
66 { V(101), V( 7), V(54), V(78), V(77), V( 92), V(101) },
67 { V( 80), V(11), V(44), V(68), V(87), V( 90), V(119) } };
69 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
70 const Value StormDanger[][4][RANK_NB] = {
71 { { V( 0), V( 67), V( 134), V(38), V(32) },
72 { V( 0), V( 57), V( 139), V(37), V(22) },
73 { V( 0), V( 43), V( 115), V(43), V(27) },
74 { V( 0), V( 68), V( 124), V(57), V(32) } },
75 { { V(20), V( 43), V( 100), V(56), V(20) },
76 { V(23), V( 20), V( 98), V(40), V(15) },
77 { V(23), V( 39), V( 103), V(36), V(18) },
78 { V(28), V( 19), V( 108), V(42), V(26) } },
79 { { V( 0), V( 0), V( 75), V(14), V( 2) },
80 { V( 0), V( 0), V( 150), V(30), V( 4) },
81 { V( 0), V( 0), V( 160), V(22), V( 5) },
82 { V( 0), V( 0), V( 166), V(24), V(13) } },
83 { { V( 0), V(-283), V(-281), V(57), V(31) },
84 { V( 0), V( 58), V( 141), V(39), V(18) },
85 { V( 0), V( 65), V( 142), V(48), V(32) },
86 { V( 0), V( 60), V( 126), V(51), V(19) } } };
88 // Max bonus for king safety. Corresponds to start position with all the pawns
89 // in front of the king and no enemy pawn on the horizon.
90 const Value MaxSafetyBonus = V(258);
96 Score evaluate(const Position& pos, Pawns::Entry* e) {
98 const Color Them = (Us == WHITE ? BLACK : WHITE);
99 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
100 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
101 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
103 const Bitboard CenterBindMask =
104 Us == WHITE ? (FileDBB | FileEBB) & (Rank5BB | Rank6BB | Rank7BB)
105 : (FileDBB | FileEBB) & (Rank4BB | Rank3BB | Rank2BB);
107 Bitboard b, neighbours, doubled, supported, phalanx;
109 bool passed, isolated, opposed, backward, lever, connected;
110 Score score = SCORE_ZERO;
111 const Square* pl = pos.squares<PAWN>(Us);
112 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
114 Bitboard ourPawns = pos.pieces(Us , PAWN);
115 Bitboard theirPawns = pos.pieces(Them, PAWN);
117 e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
118 e->kingSquares[Us] = SQ_NONE;
119 e->semiopenFiles[Us] = 0xFF;
120 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
121 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
122 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
124 // Loop through all pawns of the current color and score each pawn
125 while ((s = *pl++) != SQ_NONE)
127 assert(pos.piece_on(s) == make_piece(Us, PAWN));
131 e->semiopenFiles[Us] &= ~(1 << f);
132 e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
135 neighbours = ourPawns & adjacent_files_bb(f);
136 doubled = ourPawns & forward_bb(Us, s);
137 opposed = theirPawns & forward_bb(Us, s);
138 passed = !(theirPawns & passed_pawn_mask(Us, s));
139 lever = theirPawns & pawnAttacksBB[s];
140 phalanx = neighbours & rank_bb(s);
141 supported = neighbours & rank_bb(s - Up);
142 connected = supported | phalanx;
143 isolated = !neighbours;
145 // Test for backward pawn.
146 // If the pawn is passed, isolated, lever or connected it cannot be
147 // backward. If there are friendly pawns behind on adjacent files
148 // or if it is sufficiently advanced, it cannot be backward either.
149 if ( (passed | isolated | lever | connected)
150 || (ourPawns & pawn_attack_span(Them, s))
151 || (relative_rank(Us, s) >= RANK_5))
155 // We now know there are no friendly pawns beside or behind this
156 // pawn on adjacent files. We now check whether the pawn is
157 // backward by looking in the forward direction on the adjacent
158 // files, and picking the closest pawn there.
159 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
160 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
162 // If we have an enemy pawn in the same or next rank, the pawn is
163 // backward because it cannot advance without being captured.
164 backward = (b | shift_bb<Up>(b)) & theirPawns;
167 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
169 // Passed pawns will be properly scored in evaluation because we need
170 // full attack info to evaluate passed pawns. Only the frontmost passed
171 // pawn on each file is considered a true passed pawn.
172 if (passed && !doubled)
173 e->passedPawns[Us] |= s;
177 score -= Isolated[opposed][f];
180 score -= Backward[opposed];
183 score -= UnsupportedPawnPenalty;
186 score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
189 score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
192 score += Lever[relative_rank(Us, s)];
195 b = e->semiopenFiles[Us] ^ 0xFF;
196 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
198 // Center binds: Two pawns controlling the same central square
199 b = shift_bb<Right>(ourPawns) & shift_bb<Left>(ourPawns) & CenterBindMask;
200 score += popcount<Max15>(b) * CenterBind;
209 /// Pawns::init() initializes some tables needed by evaluation. Instead of using
210 /// hard-coded tables, when makes sense, we prefer to calculate them with a formula
211 /// to reduce independent parameters and to allow easier tuning and better insight.
215 static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
217 for (int opposed = 0; opposed <= 1; ++opposed)
218 for (int phalanx = 0; phalanx <= 1; ++phalanx)
219 for (int apex = 0; apex <= 1; ++apex)
220 for (Rank r = RANK_2; r < RANK_8; ++r)
222 int v = (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
223 v += (apex ? v / 2 : 0);
224 Connected[opposed][phalanx][apex][r] = make_score(3 * v / 2, v);
229 /// Pawns::probe() looks up the current position's pawns configuration in
230 /// the pawns hash table. It returns a pointer to the Entry if the position
231 /// is found. Otherwise a new Entry is computed and stored there, so we don't
232 /// have to recompute all when the same pawns configuration occurs again.
234 Entry* probe(const Position& pos) {
236 Key key = pos.pawn_key();
237 Entry* e = pos.this_thread()->pawnsTable[key];
243 e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
244 e->asymmetry = popcount<Max15>(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
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);