2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 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 // Connected pawn bonus by opposed, phalanx flags and rank
53 Score Connected[2][2][RANK_NB];
55 // Levers bonus by rank
56 const Score Lever[RANK_NB] = {
57 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
58 S(20,20), S(40,40), S(0, 0), S(0, 0) };
60 // Unsupported pawn penalty
61 const Score UnsupportedPawnPenalty = S(20, 10);
63 // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
64 const Value ShelterWeakness[][RANK_NB] = {
65 { V(101), V(10), V(24), V(68), V(90), V( 95), V(102) },
66 { V(105), V( 1), V(30), V(76), V(95), V(100), V(105) },
67 { V( 99), V( 0), V(32), V(72), V(92), V(101), V(100) },
68 { V( 94), V( 1), V(31), V(68), V(89), V( 98), V(106) } };
70 // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
71 const Value StormDanger[][4][RANK_NB] = {
72 { { V( 0), V( 61), V( 128), V(47), V(27) },
73 { V( 0), V( 66), V( 131), V(49), V(27) },
74 { V( 0), V( 62), V( 126), V(52), V(23) },
75 { V( 0), V( 63), V( 128), V(52), V(26) } },
76 { { V(25), V( 33), V( 95), V(39), V(21) },
77 { V(24), V( 33), V( 97), V(42), V(22) },
78 { V(24), V( 33), V( 93), V(35), V(23) },
79 { V(26), V( 27), V( 96), V(37), V(22) } },
80 { { V( 0), V( 0), V( 80), V(14), V( 8) },
81 { V( 0), V( 0), V( 163), V(28), V(12) },
82 { V( 0), V( 0), V( 163), V(25), V(15) },
83 { V( 0), V( 0), V( 161), V(24), V(14) } },
84 { { V( 0), V(-300), V(-300), V(54), V(23) },
85 { V( 0), V( 67), V( 128), V(46), V(24) },
86 { V( 0), V( 64), V( 130), V(50), V(29) },
87 { V( 0), V( 63), V( 127), V(51), V(24) } } };
89 // Max bonus for king safety. Corresponds to start position with all the pawns
90 // in front of the king and no enemy pawn on the horizon.
91 const Value MaxSafetyBonus = V(261);
97 Score evaluate(const Position& pos, Pawns::Entry* e) {
99 const Color Them = (Us == WHITE ? BLACK : WHITE);
100 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
101 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
102 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
104 Bitboard b, p, doubled, connected;
106 bool passed, isolated, opposed, phalanx, backward, unsupported, lever;
107 Score value = SCORE_ZERO;
108 const Square* pl = pos.list<PAWN>(Us);
109 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
111 Bitboard ourPawns = pos.pieces(Us , PAWN);
112 Bitboard theirPawns = pos.pieces(Them, PAWN);
114 e->passedPawns[Us] = 0;
115 e->kingSquares[Us] = SQ_NONE;
116 e->semiopenFiles[Us] = 0xFF;
117 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
118 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
119 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
121 // Loop through all pawns of the current color and score each pawn
122 while ((s = *pl++) != SQ_NONE)
124 assert(pos.piece_on(s) == make_piece(Us, PAWN));
128 // This file cannot be semi-open
129 e->semiopenFiles[Us] &= ~(1 << f);
132 p = rank_bb(s - pawn_push(Us));
134 // Flag the pawn as passed, isolated, doubled,
135 // unsupported or connected (but not the backward one).
136 connected = ourPawns & adjacent_files_bb(f) & (rank_bb(s) | p);
137 phalanx = connected & rank_bb(s);
138 unsupported = !(ourPawns & adjacent_files_bb(f) & p);
139 isolated = !(ourPawns & adjacent_files_bb(f));
140 doubled = ourPawns & forward_bb(Us, s);
141 opposed = theirPawns & forward_bb(Us, s);
142 passed = !(theirPawns & passed_pawn_mask(Us, s));
143 lever = theirPawns & pawnAttacksBB[s];
145 // Test for backward pawn.
146 // If the pawn is passed, isolated, or connected it cannot be
147 // backward. If there are friendly pawns behind on adjacent files
148 // or if it can capture an enemy pawn it cannot be backward either.
149 if ( (passed | isolated | connected)
150 || (ourPawns & pawn_attack_span(Them, s))
151 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
155 // We now know that 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 value -= Isolated[opposed][f];
179 if (unsupported && !isolated)
180 value -= UnsupportedPawnPenalty;
183 value -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
186 value -= Backward[opposed][f];
189 value += Connected[opposed][phalanx][relative_rank(Us, s)];
192 value += Lever[relative_rank(Us, s)];
195 b = e->semiopenFiles[Us] ^ 0xFF;
196 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
205 /// init() initializes some tables used by evaluation. Instead of hard-coded
206 /// tables, when makes sense, we prefer to calculate them with a formula to
207 /// reduce independent parameters and to allow easier tuning and better insight.
211 static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
213 for (int opposed = 0; opposed <= 1; ++opposed)
214 for (int phalanx = 0; phalanx <= 1; ++phalanx)
215 for (Rank r = RANK_2; r < RANK_8; ++r)
217 int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
218 Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
223 /// probe() takes a position as input, computes a Entry object, and returns a
224 /// pointer to it. The result is also stored in a hash table, so we don't have
225 /// to recompute everything when the same pawn structure occurs again.
227 Entry* probe(const Position& pos, Table& entries) {
229 Key key = pos.pawn_key();
230 Entry* e = entries[key];
236 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
241 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
242 /// the king is on, as well as the two adjacent files.
245 Value Entry::shelter_storm(const Position& pos, Square ksq) {
247 const Color Them = (Us == WHITE ? BLACK : WHITE);
249 enum { NoFriendlyPawn, Unblocked, BlockedByPawn, BlockedByKing };
251 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
252 Bitboard ourPawns = b & pos.pieces(Us);
253 Bitboard theirPawns = b & pos.pieces(Them);
254 Value safety = MaxSafetyBonus;
255 File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
257 for (File f = center - File(1); f <= center + File(1); ++f)
259 b = ourPawns & file_bb(f);
260 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
262 b = theirPawns & file_bb(f);
263 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
265 safety -= ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
267 [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
268 rkUs == RANK_1 ? NoFriendlyPawn :
269 rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
270 [std::min(f, FILE_H - f)][rkThem];
277 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
278 /// when king square changes, which is about 20% of total king_safety() calls.
281 Score Entry::do_king_safety(const Position& pos, Square ksq) {
283 kingSquares[Us] = ksq;
284 castlingRights[Us] = pos.can_castle(Us);
285 minKingPawnDistance[Us] = 0;
287 Bitboard pawns = pos.pieces(Us, PAWN);
289 while (!(DistanceRingsBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
291 if (relative_rank(Us, ksq) > RANK_4)
292 return make_score(0, -16 * minKingPawnDistance[Us]);
294 Value bonus = shelter_storm<Us>(pos, ksq);
296 // If we can castle use the bonus after the castling if it is bigger
297 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
298 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
300 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
301 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
303 return make_score(bonus, -16 * minKingPawnDistance[Us]);
306 // Explicit template instantiation
307 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
308 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);