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 indexed by [rank]
64 const Value ShelterWeakness[RANK_NB] =
65 { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
67 // Danger of enemy pawns moving toward our king indexed by
68 // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
69 const Value StormDanger[][RANK_NB] = {
70 { V( 0), V(64), V(128), V(51), V(26) },
71 { V(26), V(32), V( 96), V(38), V(20) },
72 { V( 0), V( 0), V(160), V(25), V(13) } };
74 // Max bonus for king safety. Corresponds to start position with all the pawns
75 // in front of the king and no enemy pawn on the horizon.
76 const Value MaxSafetyBonus = V(263);
82 Score evaluate(const Position& pos, Pawns::Entry* e) {
84 const Color Them = (Us == WHITE ? BLACK : WHITE);
85 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
86 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
87 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
89 Bitboard b, p, doubled, connected;
91 bool passed, isolated, opposed, phalanx, backward, unsupported, lever;
92 Score value = SCORE_ZERO;
93 const Square* pl = pos.list<PAWN>(Us);
94 const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
96 Bitboard ourPawns = pos.pieces(Us , PAWN);
97 Bitboard theirPawns = pos.pieces(Them, PAWN);
99 e->passedPawns[Us] = 0;
100 e->kingSquares[Us] = SQ_NONE;
101 e->semiopenFiles[Us] = 0xFF;
102 e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
103 e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
104 e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
106 // Loop through all pawns of the current color and score each pawn
107 while ((s = *pl++) != SQ_NONE)
109 assert(pos.piece_on(s) == make_piece(Us, PAWN));
113 // This file cannot be semi-open
114 e->semiopenFiles[Us] &= ~(1 << f);
117 p = rank_bb(s - pawn_push(Us));
119 // Flag the pawn as passed, isolated, doubled,
120 // unsupported or connected (but not the backward one).
121 connected = ourPawns & adjacent_files_bb(f) & (rank_bb(s) | p);
122 phalanx = connected & rank_bb(s);
123 unsupported = !(ourPawns & adjacent_files_bb(f) & p);
124 isolated = !(ourPawns & adjacent_files_bb(f));
125 doubled = ourPawns & forward_bb(Us, s);
126 opposed = theirPawns & forward_bb(Us, s);
127 passed = !(theirPawns & passed_pawn_mask(Us, s));
128 lever = theirPawns & pawnAttacksBB[s];
130 // Test for backward pawn.
131 // If the pawn is passed, isolated, or connected it cannot be
132 // backward. If there are friendly pawns behind on adjacent files
133 // or if it can capture an enemy pawn it cannot be backward either.
134 if ( (passed | isolated | connected)
135 || (ourPawns & pawn_attack_span(Them, s))
136 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
140 // We now know that there are no friendly pawns beside or behind this
141 // pawn on adjacent files. We now check whether the pawn is
142 // backward by looking in the forward direction on the adjacent
143 // files, and picking the closest pawn there.
144 b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
145 b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
147 // If we have an enemy pawn in the same or next rank, the pawn is
148 // backward because it cannot advance without being captured.
149 backward = (b | shift_bb<Up>(b)) & theirPawns;
152 assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
154 // Passed pawns will be properly scored in evaluation because we need
155 // full attack info to evaluate passed pawns. Only the frontmost passed
156 // pawn on each file is considered a true passed pawn.
157 if (passed && !doubled)
158 e->passedPawns[Us] |= s;
162 value -= Isolated[opposed][f];
164 if (unsupported && !isolated)
165 value -= UnsupportedPawnPenalty;
168 value -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
171 value -= Backward[opposed][f];
174 value += Connected[opposed][phalanx][relative_rank(Us, s)];
177 value += Lever[relative_rank(Us, s)];
180 b = e->semiopenFiles[Us] ^ 0xFF;
181 e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
190 /// init() initializes some tables used by evaluation. Instead of hard-coded
191 /// tables, when makes sense, we prefer to calculate them with a formula to
192 /// reduce independent parameters and to allow easier tuning and better insight.
196 static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
198 for (int opposed = 0; opposed <= 1; ++opposed)
199 for (int phalanx = 0; phalanx <= 1; ++phalanx)
200 for (Rank r = RANK_2; r < RANK_8; ++r)
202 int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
203 Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
208 /// probe() takes a position as input, computes a Entry object, and returns a
209 /// pointer to it. The result is also stored in a hash table, so we don't have
210 /// to recompute everything when the same pawn structure occurs again.
212 Entry* probe(const Position& pos, Table& entries) {
214 Key key = pos.pawn_key();
215 Entry* e = entries[key];
221 e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
226 /// Entry::shelter_storm() calculates shelter and storm penalties for the file
227 /// the king is on, as well as the two adjacent files.
230 Value Entry::shelter_storm(const Position& pos, Square ksq) {
232 const Color Them = (Us == WHITE ? BLACK : WHITE);
233 const Bitboard Edges = (FileABB | FileHBB) & (Rank2BB | Rank3BB);
235 Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
236 Bitboard ourPawns = b & pos.pieces(Us);
237 Bitboard theirPawns = b & pos.pieces(Them);
238 Value safety = MaxSafetyBonus;
239 File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
241 for (File f = kf - File(1); f <= kf + File(1); ++f)
243 b = ourPawns & file_bb(f);
244 Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
246 b = theirPawns & file_bb(f);
247 Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
249 if ( (Edges & make_square(f, rkThem))
251 && relative_rank(Us, ksq) == rkThem - 1)
254 safety -= ShelterWeakness[rkUs]
255 + StormDanger[rkUs == RANK_1 ? 0 :
256 rkThem != rkUs + 1 ? 1 : 2][rkThem];
263 /// Entry::do_king_safety() calculates a bonus for king safety. It is called only
264 /// when king square changes, which is about 20% of total king_safety() calls.
267 Score Entry::do_king_safety(const Position& pos, Square ksq) {
269 kingSquares[Us] = ksq;
270 castlingRights[Us] = pos.can_castle(Us);
271 minKingPawnDistance[Us] = 0;
273 Bitboard pawns = pos.pieces(Us, PAWN);
275 while (!(DistanceRingsBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
277 if (relative_rank(Us, ksq) > RANK_4)
278 return make_score(0, -16 * minKingPawnDistance[Us]);
280 Value bonus = shelter_storm<Us>(pos, ksq);
282 // If we can castle use the bonus after the castling if it is bigger
283 if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
284 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
286 if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
287 bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
289 return make_score(bonus, -16 * minKingPawnDistance[Us]);
292 // Explicit template instantiation
293 template Score Entry::do_king_safety<WHITE>(const Position& pos, Square ksq);
294 template Score Entry::do_king_safety<BLACK>(const Position& pos, Square ksq);