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 file and rank (initialized by formula)
53 Score Connected[FILE_NB][RANK_NB];
55 // Candidate passed pawn bonus by rank
56 const Score CandidatePassed[RANK_NB] = {
57 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
58 S(34,68), S(83,166), S(0, 0), S( 0, 0) };
60 // Levers bonus by rank
61 const Score Lever[RANK_NB] = {
62 S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
63 S(20,20), S(40,40), S(0, 0), S(0, 0) };
65 // Bonus for file distance of the two outermost pawns
66 const Score PawnsFileSpan = S(0, 15);
68 // Unsupported pawn penalty
69 const Score UnsupportedPawnPenalty = S(20, 10);
71 // Weakness of our pawn shelter in front of the king indexed by [rank]
72 const Value ShelterWeakness[RANK_NB] =
73 { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
75 // Danger of enemy pawns moving toward our king indexed by
76 // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
77 const Value StormDanger[][RANK_NB] = {
78 { V( 0), V(64), V(128), V(51), V(26) },
79 { V(26), V(32), V( 96), V(38), V(20) },
80 { V( 0), V( 0), V(160), V(25), V(13) } };
82 // Max bonus for king safety. Corresponds to start position with all the pawns
83 // in front of the king and no enemy pawn on the horizon.
84 const Value MaxSafetyBonus = V(263);
90 Score evaluate(const Position& pos, Pawns::Entry* e) {
92 const Color Them = (Us == WHITE ? BLACK : WHITE);
93 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
94 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
95 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
97 Bitboard b, p, doubled;
100 bool passed, isolated, opposed, connected, backward, candidate, unsupported, lever;
101 Score value = SCORE_ZERO;
102 const Square* pl = pos.list<PAWN>(Us);
103 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
105 Bitboard ourPawns = pos.pieces(Us, PAWN);
106 Bitboard theirPawns = pos.pieces(Them, PAWN);
108 e->passedPawns[Us] = e->candidatePawns[Us] = 0;
109 e->kingSquares[Us] = SQ_NONE;
110 e->semiopenFiles[Us] = 0xFF;
111 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
112 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
113 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
115 // Loop through all pawns of the current color and score each pawn
116 while ((s = *pl++) != SQ_NONE)
118 assert(pos.piece_on(s) == make_piece(Us, PAWN));
122 // This file cannot be semi-open
123 e->semiopenFiles[Us] &= ~(1 << f);
126 p = rank_bb(s - pawn_push(Us));
128 // Our rank plus previous one
131 // Flag the pawn as passed, isolated, doubled,
132 // unsupported or connected (but not the backward one).
133 connected = ourPawns & adjacent_files_bb(f) & b;
134 unsupported = !(ourPawns & adjacent_files_bb(f) & p);
135 isolated = !(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];
141 // Test for backward pawn.
142 // If the pawn is passed, isolated, or connected it cannot be
143 // backward. If there are friendly pawns behind on adjacent files
144 // or if it can capture an enemy pawn it cannot be backward either.
145 if ( (passed | isolated | connected)
146 || (ourPawns & pawn_attack_span(Them, s))
147 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
151 // We now know that there are no friendly pawns beside or behind this
152 // pawn on adjacent files. We now check whether the pawn is
153 // backward by looking in the forward direction on the adjacent
154 // files, and picking the closest pawn there.
155 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
156 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
158 // If we have an enemy pawn in the same or next rank, the pawn is
159 // backward because it cannot advance without being captured.
160 backward = (b | shift_bb<Up>(b)) & theirPawns;
163 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
165 // A not-passed pawn is a candidate to become passed, if it is free to
166 // advance and if the number of friendly pawns beside or behind this
167 // pawn on adjacent files is higher than or equal to the number of
168 // enemy pawns in the forward direction on the adjacent files.
169 candidate = !(opposed | passed | backward | isolated)
170 && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
171 && popcount<Max15>(b) >= popcount<Max15>(pawn_attack_span(Us, s) & theirPawns);
173 // Passed pawns will be properly scored in evaluation because we need
174 // full attack info to evaluate passed pawns. Only the frontmost passed
175 // pawn on each file is considered a true passed pawn.
176 if (passed && !doubled)
177 e->passedPawns[Us] |= s;
181 value -= Isolated[opposed][f];
183 if (unsupported && !isolated)
184 value -= UnsupportedPawnPenalty;
187 value -= Doubled[f] / rank_distance(s, lsb(doubled));
190 value -= Backward[opposed][f];
193 value += Connected[f][relative_rank(Us, s)];
196 value += Lever[relative_rank(Us, s)];
200 value += CandidatePassed[relative_rank(Us, s)];
203 e->candidatePawns[Us] |= s;
207 b = e->semiopenFiles[Us] ^ 0xFF;
208 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
210 // In endgame it's better to have pawns on both wings. So give a bonus according
211 // to file distance between left and right outermost pawns.
212 value += PawnsFileSpan * e->pawnSpan[Us];
221 /// init() initializes some tables by formula instead of hard-coding their values
225 const int bonusByFile[] = { 1, 3, 3, 4, 4, 3, 3, 1 };
227 for (Rank r = RANK_1; r < RANK_8; ++r)
228 for (File f = FILE_A; f <= FILE_H; ++f)
230 int bonus = r * (r - 1) * (r - 2) + bonusByFile[f] * (r / 2 + 1);
231 Connected[f][r] = make_score(bonus, bonus);
236 /// probe() takes a position as input, computes a Entry object, and returns a
237 /// pointer to it. The result is also stored in a hash table, so we don't have
238 /// to recompute everything when the same pawn structure occurs again.
240 Entry* probe(const Position& pos, Table& entries) {
242 Key key = pos.pawn_key();
243 Entry* e = entries[key];
249 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
254 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
255 /// the king is on, as well as the two adjacent files.
258 Value Entry::shelter_storm(const Position& pos, Square ksq) {
260 const Color Them = (Us == WHITE ? BLACK : WHITE);
261 const Bitboard Edges = (FileABB | FileHBB) & (Rank2BB | Rank3BB);
263 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
264 Bitboard ourPawns = b & pos.pieces(Us);
265 Bitboard theirPawns = b & pos.pieces(Them);
266 Value safety = MaxSafetyBonus;
267 File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
269 for (File f = kf - File(1); f <= kf + File(1); ++f)
271 b = ourPawns & file_bb(f);
272 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
274 b = theirPawns & file_bb(f);
275 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
277 if ( (Edges & make_square(f, rkThem))
279 && relative_rank(Us, ksq) == rkThem - 1)
282 safety -= ShelterWeakness[rkUs]
283 + StormDanger[rkUs == RANK_1 ? 0 :
284 rkThem != rkUs + 1 ? 1 : 2][rkThem];
291 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
292 /// when king square changes, which is about 20% of total king_safety() calls.
295 Score Entry::do_king_safety(const Position& pos, Square ksq) {
297 kingSquares[Us] = ksq;
298 castlingRights[Us] = pos.can_castle(Us);
299 minKPdistance[Us] = 0;
301 Bitboard pawns = pos.pieces(Us, PAWN);
303 while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
305 if (relative_rank(Us, ksq) > RANK_4)
306 return make_score(0, -16 * minKPdistance[Us]);
308 Value bonus = shelter_storm<Us>(pos, ksq);
310 // If we can castle use the bonus after the castling if it is bigger
311 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
312 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
314 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
315 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
317 return make_score(bonus, -16 * minKPdistance[Us]);
320 // Explicit template instantiation
321 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
322 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);