2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
34 //// Local definitions
39 /// Constants and variables
41 #define S(mg, eg) make_score(mg, eg)
43 // Doubled pawn penalty by file
44 const Score DoubledPawnPenalty[8] = {
45 S(13, 43), S(20, 48), S(23, 48), S(23, 48),
46 S(23, 48), S(23, 48), S(20, 48), S(13, 43)
49 // Isolated pawn penalty by file
50 const Score IsolatedPawnPenalty[8] = {
51 S(25, 30), S(36, 35), S(40, 35), S(40, 35),
52 S(40, 35), S(40, 35), S(36, 35), S(25, 30)
55 // Backward pawn penalty by file
56 const Score BackwardPawnPenalty[8] = {
57 S(20, 28), S(29, 31), S(33, 31), S(33, 31),
58 S(33, 31), S(33, 31), S(29, 31), S(20, 28)
61 // Pawn chain membership bonus by file
62 const Score ChainBonus[8] = {
63 S(11,-1), S(13,-1), S(13,-1), S(14,-1),
64 S(14,-1), S(13,-1), S(13,-1), S(11,-1)
67 // Candidate passed pawn bonus by rank
68 const Score CandidateBonus[8] = {
69 S( 0, 0), S( 6, 13), S(6,13), S(14,29),
70 S(34,68), S(83,166), S(0, 0), S( 0, 0)
73 // Pawn storm tables for positions with opposite castling
74 const int QStormTable[64] = {
75 0, 0, 0, 0, 0, 0, 0, 0,
76 -22,-22,-22,-14,-6, 0, 0, 0,
77 -6,-10,-10,-10,-6, 0, 0, 0,
78 4, 12, 16, 12, 4, 0, 0, 0,
79 16, 23, 23, 16, 0, 0, 0, 0,
80 23, 31, 31, 23, 0, 0, 0, 0,
81 23, 31, 31, 23, 0, 0, 0, 0,
82 0, 0, 0, 0, 0, 0, 0, 0
85 const int KStormTable[64] = {
86 0, 0, 0, 0, 0, 0, 0, 0,
87 0, 0, 0,-10,-19,-28,-33,-33,
88 0, 0, 0,-10,-15,-19,-24,-24,
89 0, 0, 0, 0, 1, 1, 1, 1,
90 0, 0, 0, 0, 1, 10, 19, 19,
91 0, 0, 0, 0, 1, 19, 31, 27,
92 0, 0, 0, 0, 0, 22, 31, 22,
93 0, 0, 0, 0, 0, 0, 0, 0
96 // Pawn storm open file bonuses by file
97 const int16_t QStormOpenFileBonus[8] = { 31, 31, 18, 0, 0, 0, 0, 0 };
98 const int16_t KStormOpenFileBonus[8] = { 0, 0, 0, 0, 0, 26, 42, 26 };
100 // Pawn storm lever bonuses by file
101 const int StormLeverBonus[8] = { -8, -8, -13, 0, 0, -13, -8, -8 };
111 /// PawnInfoTable c'tor and d'tor instantiated one each thread
113 PawnInfoTable::PawnInfoTable() {
115 entries = new PawnInfo[PawnTableSize];
119 std::cerr << "Failed to allocate " << (PawnTableSize * sizeof(PawnInfo))
120 << " bytes for pawn hash table." << std::endl;
121 Application::exit_with_failure();
126 PawnInfoTable::~PawnInfoTable() {
132 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
133 /// a PawnInfo object, and returns a pointer to it. The result is also stored
134 /// in a hash table, so we don't have to recompute everything when the same
135 /// pawn structure occurs again.
137 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) const {
141 Key key = pos.get_pawn_key();
142 unsigned index = unsigned(key & (PawnTableSize - 1));
143 PawnInfo* pi = entries + index;
145 // If pi->key matches the position's pawn hash key, it means that we
146 // have analysed this pawn structure before, and we can simply return
147 // the information we found the last time instead of recomputing it.
151 // Clear the PawnInfo object, and set the key
152 memset(pi, 0, sizeof(PawnInfo));
153 pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
156 // Calculate pawn attacks
157 Bitboard whitePawns = pos.pieces(PAWN, WHITE);
158 Bitboard blackPawns = pos.pieces(PAWN, BLACK);
159 pi->pawnAttacks[WHITE] = ((whitePawns << 9) & ~FileABB) | ((whitePawns << 7) & ~FileHBB);
160 pi->pawnAttacks[BLACK] = ((blackPawns >> 7) & ~FileABB) | ((blackPawns >> 9) & ~FileHBB);
162 // Evaluate pawns for both colors
163 pi->value = evaluate_pawns<WHITE>(pos, whitePawns, blackPawns, pi)
164 - evaluate_pawns<BLACK>(pos, blackPawns, whitePawns, pi);
169 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
172 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
173 Bitboard theirPawns, PawnInfo* pi) const {
179 bool passed, isolated, doubled, opposed, chain, backward, candidate;
180 Score value = SCORE_ZERO;
181 const Square* ptr = pos.piece_list_begin(Us, PAWN);
183 // Initialize pawn storm scores by giving bonuses for open files
184 for (f = FILE_A; f <= FILE_H; f++)
185 if (!(ourPawns & file_bb(f)))
187 pi->ksStormValue[Us] += KStormOpenFileBonus[f];
188 pi->qsStormValue[Us] += QStormOpenFileBonus[f];
189 pi->halfOpenFiles[Us] |= (1 << f);
192 // Loop through all pawns of the current color and score each pawn
193 while ((s = *ptr++) != SQ_NONE)
198 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
200 // Calculate kingside and queenside pawn storm scores for both colors to be
201 // used when evaluating middle game positions with opposite side castling.
202 bonus = (f >= FILE_F ? evaluate_pawn_storm<Us, KingSide>(s, r, f, theirPawns) : 0);
203 pi->ksStormValue[Us] += KStormTable[relative_square(Us, s)] + bonus;
205 bonus = (f <= FILE_C ? evaluate_pawn_storm<Us, QueenSide>(s, r, f, theirPawns) : 0);
206 pi->qsStormValue[Us] += QStormTable[relative_square(Us, s)] + bonus;
208 // Our rank plus previous one. Used for chain detection.
209 b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
211 // Passed, isolated, doubled or member of a pawn
212 // chain (but not the backward one) ?
213 passed = !(theirPawns & passed_pawn_mask(Us, s));
214 doubled = ourPawns & squares_behind(Us, s);
215 opposed = theirPawns & squares_in_front_of(Us, s);
216 isolated = !(ourPawns & neighboring_files_bb(f));
217 chain = ourPawns & neighboring_files_bb(f) & b;
219 // Test for backward pawn
223 // If the pawn is passed, isolated, or member of a pawn chain
224 // it cannot be backward. If can capture an enemy pawn or if
225 // there are friendly pawns behind on neighboring files it cannot
226 // be backward either.
227 if ( !(passed | isolated | chain)
228 && !(ourPawns & attack_span_mask(opposite_color(Us), s))
229 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
231 // We now know that there are no friendly pawns beside or behind this
232 // pawn on neighboring files. We now check whether the pawn is
233 // backward by looking in the forward direction on the neighboring
234 // files, and seeing whether we meet a friendly or an enemy pawn first.
235 b = pos.attacks_from<PAWN>(s, Us);
237 // Note that we are sure to find something because pawn is not passed
238 // nor isolated, so loop is potentially infinite, but it isn't.
239 while (!(b & (ourPawns | theirPawns)))
240 Us == WHITE ? b <<= 8 : b >>= 8;
242 // The friendly pawn needs to be at least two ranks closer than the enemy
243 // pawn in order to help the potentially backward pawn advance.
244 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
247 assert(passed | opposed | (attack_span_mask(Us, s) & theirPawns));
249 // Test for candidate passed pawn
250 candidate = !(opposed | passed)
251 && (b = attack_span_mask(opposite_color(Us), s + pawn_push(Us)) & ourPawns) != EmptyBoardBB
252 && count_1s_max_15(b) >= count_1s_max_15(attack_span_mask(Us, s) & theirPawns);
254 // In order to prevent doubled passed pawns from receiving a too big
255 // bonus, only the frontmost passed pawn on each file is considered as
256 // a true passed pawn.
257 if (passed && (ourPawns & squares_in_front_of(Us, s)))
260 // Mark the pawn as passed. Pawn will be properly scored in evaluation
261 // because we need full attack info to evaluate passed pawns.
263 set_bit(&(pi->passedPawns[Us]), s);
268 value -= IsolatedPawnPenalty[f];
270 value -= IsolatedPawnPenalty[f] / 2;
273 value -= DoubledPawnPenalty[f];
277 value -= BackwardPawnPenalty[f];
279 value -= BackwardPawnPenalty[f] / 2;
282 value += ChainBonus[f];
285 value += CandidateBonus[relative_rank(Us, s)];
292 /// PawnInfoTable::evaluate_pawn_storm() evaluates each pawn which seems
293 /// to have good chances of creating an open file by exchanging itself
294 /// against an enemy pawn on an adjacent file.
296 template<Color Us, PawnInfoTable::SideType Side>
297 int PawnInfoTable::evaluate_pawn_storm(Square s, Rank r, File f, Bitboard theirPawns) const {
299 const Bitboard StormFilesBB = (Side == KingSide ? FileFBB | FileGBB | FileHBB
300 : FileABB | FileBBB | FileCBB);
301 const int K = (Side == KingSide ? 2 : 4);
302 const File RookFile = (Side == KingSide ? FILE_H : FILE_A);
304 Bitboard b = attack_span_mask(Us, s) & theirPawns & StormFilesBB;
309 // Give a bonus according to the distance of the nearest enemy pawn
310 Square s2 = pop_1st_bit(&b);
311 Rank r2 = square_rank(s2);
312 int v = StormLeverBonus[f] - K * rank_distance(r, r2);
314 // If enemy pawn has no pawn beside itself is particularly vulnerable.
315 // Big bonus, especially against a weakness on the rook file
316 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
317 v *= (square_file(s2) == RookFile ? 4 : 2);
325 /// PawnInfo::updateShelter calculates and caches king shelter. It is called
326 /// only when king square changes, about 20% of total king_shelter() calls.
327 Score PawnInfo::updateShelter(const Position& pos, Color c, Square ksq) {
330 unsigned r, k, shelter = 0;
332 if (relative_rank(c, ksq) <= RANK_4)
334 pawns = pos.pieces(PAWN, c) & this_and_neighboring_files_bb(ksq);
337 for (int i = 1; i < 4; i++)
340 shelter += BitCount8Bit[(pawns >> r) & 0xFF] * (128 >> i);
343 kingSquares[c] = ksq;
344 kingShelters[c] = make_score(shelter, 0);
345 return kingShelters[c];