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 // Bonus for file distance of the two outermost pawns
61 const Score PawnsFileSpan = S(0, 8);
63 // Unsupported pawn penalty
64 const Score UnsupportedPawnPenalty = S(20, 10);
66 // Weakness of our pawn shelter in front of the king indexed by [rank]
67 const Value ShelterWeakness[RANK_NB] =
68 { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
70 // Danger of enemy pawns moving toward our king indexed by
71 // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
72 const Value StormDanger[][RANK_NB] = {
73 { V( 0), V(64), V(128), V(51), V(26) },
74 { V(26), V(32), V( 96), V(38), V(20) },
75 { V( 0), V( 0), V(160), V(25), V(13) } };
77 // Max bonus for king safety. Corresponds to start position with all the pawns
78 // in front of the king and no enemy pawn on the horizon.
79 const Value MaxSafetyBonus = V(263);
85 Score evaluate(const Position& pos, Pawns::Entry* e) {
87 const Color Them = (Us == WHITE ? BLACK : WHITE);
88 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
89 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
90 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
92 Bitboard b, p, doubled, connected;
94 bool passed, isolated, opposed, phalanx, backward, unsupported, lever;
95 Score value = SCORE_ZERO;
96 const Square* pl = pos.list<PAWN>(Us);
97 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
99 Bitboard ourPawns = pos.pieces(Us , PAWN);
100 Bitboard theirPawns = pos.pieces(Them, PAWN);
102 e->passedPawns[Us] = 0;
103 e->kingSquares[Us] = SQ_NONE;
104 e->semiopenFiles[Us] = 0xFF;
105 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
106 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
107 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
109 // Loop through all pawns of the current color and score each pawn
110 while ((s = *pl++) != SQ_NONE)
112 assert(pos.piece_on(s) == make_piece(Us, PAWN));
116 // This file cannot be semi-open
117 e->semiopenFiles[Us] &= ~(1 << f);
120 p = rank_bb(s - pawn_push(Us));
122 // Flag the pawn as passed, isolated, doubled,
123 // unsupported or connected (but not the backward one).
124 connected = ourPawns & adjacent_files_bb(f) & (rank_bb(s) | p);
125 phalanx = connected & rank_bb(s);
126 unsupported = !(ourPawns & adjacent_files_bb(f) & p);
127 isolated = !(ourPawns & adjacent_files_bb(f));
128 doubled = ourPawns & forward_bb(Us, s);
129 opposed = theirPawns & forward_bb(Us, s);
130 passed = !(theirPawns & passed_pawn_mask(Us, s));
131 lever = theirPawns & pawnAttacksBB[s];
133 // Test for backward pawn.
134 // If the pawn is passed, isolated, or connected it cannot be
135 // backward. If there are friendly pawns behind on adjacent files
136 // or if it can capture an enemy pawn it cannot be backward either.
137 if ( (passed | isolated | connected)
138 || (ourPawns & pawn_attack_span(Them, s))
139 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
143 // We now know that there are no friendly pawns beside or behind this
144 // pawn on adjacent files. We now check whether the pawn is
145 // backward by looking in the forward direction on the adjacent
146 // files, and picking the closest pawn there.
147 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
148 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
150 // If we have an enemy pawn in the same or next rank, the pawn is
151 // backward because it cannot advance without being captured.
152 backward = (b | shift_bb<Up>(b)) & theirPawns;
155 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
157 // Passed pawns will be properly scored in evaluation because we need
158 // full attack info to evaluate passed pawns. Only the frontmost passed
159 // pawn on each file is considered a true passed pawn.
160 if (passed && !doubled)
161 e->passedPawns[Us] |= s;
165 value -= Isolated[opposed][f];
167 if (unsupported && !isolated)
168 value -= UnsupportedPawnPenalty;
171 value -= Doubled[f] / rank_distance(s, lsb(doubled));
174 value -= Backward[opposed][f];
177 value += Connected[opposed][phalanx][relative_rank(Us, s)];
180 value += Lever[relative_rank(Us, s)];
183 b = e->semiopenFiles[Us] ^ 0xFF;
184 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
186 // In endgame it's better to have pawns on both wings. So give a bonus according
187 // to file distance between left and right outermost pawns.
188 value += PawnsFileSpan * e->pawnSpan[Us];
197 /// init() initializes some tables used by evaluation. Instead of hard-coded
198 /// tables, when makes sense, we prefer to calculate them with a formula to
199 /// reduce independent parameters and to allow easier tuning and better insight.
203 static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
205 for (int opposed = 0; opposed <= 1; ++opposed)
206 for (int phalanx = 0; phalanx <= 1; ++phalanx)
207 for (Rank r = RANK_2; r < RANK_8; ++r)
209 int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
210 Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
215 /// probe() takes a position as input, computes a Entry object, and returns a
216 /// pointer to it. The result is also stored in a hash table, so we don't have
217 /// to recompute everything when the same pawn structure occurs again.
219 Entry* probe(const Position& pos, Table& entries) {
221 Key key = pos.pawn_key();
222 Entry* e = entries[key];
228 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
233 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
234 /// the king is on, as well as the two adjacent files.
237 Value Entry::shelter_storm(const Position& pos, Square ksq) {
239 const Color Them = (Us == WHITE ? BLACK : WHITE);
240 const Bitboard Edges = (FileABB | FileHBB) & (Rank2BB | Rank3BB);
242 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
243 Bitboard ourPawns = b & pos.pieces(Us);
244 Bitboard theirPawns = b & pos.pieces(Them);
245 Value safety = MaxSafetyBonus;
246 File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
248 for (File f = kf - File(1); f <= kf + File(1); ++f)
250 b = ourPawns & file_bb(f);
251 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
253 b = theirPawns & file_bb(f);
254 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
256 if ( (Edges & make_square(f, rkThem))
258 && relative_rank(Us, ksq) == rkThem - 1)
261 safety -= ShelterWeakness[rkUs]
262 + StormDanger[rkUs == RANK_1 ? 0 :
263 rkThem != rkUs + 1 ? 1 : 2][rkThem];
270 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
271 /// when king square changes, which is about 20% of total king_safety() calls.
274 Score Entry::do_king_safety(const Position& pos, Square ksq) {
276 kingSquares[Us] = ksq;
277 castlingRights[Us] = pos.can_castle(Us);
278 minKPdistance[Us] = 0;
280 Bitboard pawns = pos.pieces(Us, PAWN);
282 while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
284 if (relative_rank(Us, ksq) > RANK_4)
285 return make_score(0, -16 * minKPdistance[Us]);
287 Value bonus = shelter_storm<Us>(pos, ksq);
289 // If we can castle use the bonus after the castling if it is bigger
290 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
291 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
293 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
294 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
296 return make_score(bonus, -16 * minKPdistance[Us]);
299 // Explicit template instantiation
300 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
301 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);