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(unsigned numOfEntries) : size(numOfEntries) {
115 entries = new PawnInfo[size];
118 std::cerr << "Failed to allocate " << (numOfEntries * sizeof(PawnInfo))
119 << " bytes for pawn hash table." << std::endl;
120 Application::exit_with_failure();
125 PawnInfoTable::~PawnInfoTable() {
131 /// PawnInfo::clear() resets to zero the PawnInfo entry. Note that
132 /// kingSquares[] is initialized to SQ_NONE instead.
134 void PawnInfo::clear() {
136 memset(this, 0, sizeof(PawnInfo));
137 kingSquares[WHITE] = kingSquares[BLACK] = SQ_NONE;
141 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
142 /// a PawnInfo object, and returns a pointer to it. The result is also stored
143 /// in a hash table, so we don't have to recompute everything when the same
144 /// pawn structure occurs again.
146 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) const {
150 Key key = pos.get_pawn_key();
151 unsigned index = unsigned(key & (size - 1));
152 PawnInfo* pi = entries + index;
154 // If pi->key matches the position's pawn hash key, it means that we
155 // have analysed this pawn structure before, and we can simply return
156 // the information we found the last time instead of recomputing it.
160 // Clear the PawnInfo object, and set the key
164 // Calculate pawn attacks
165 Bitboard whitePawns = pos.pieces(PAWN, WHITE);
166 Bitboard blackPawns = pos.pieces(PAWN, BLACK);
167 pi->pawnAttacks[WHITE] = ((whitePawns << 9) & ~FileABB) | ((whitePawns << 7) & ~FileHBB);
168 pi->pawnAttacks[BLACK] = ((blackPawns >> 7) & ~FileABB) | ((blackPawns >> 9) & ~FileHBB);
170 // Evaluate pawns for both colors
171 pi->value = evaluate_pawns<WHITE>(pos, whitePawns, blackPawns, pi)
172 - evaluate_pawns<BLACK>(pos, blackPawns, whitePawns, pi);
177 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
180 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
181 Bitboard theirPawns, PawnInfo* pi) const {
187 bool passed, isolated, doubled, opposed, chain, backward, candidate;
188 Score value = make_score(0, 0);
189 const Square* ptr = pos.piece_list_begin(Us, PAWN);
191 // Initialize pawn storm scores by giving bonuses for open files
192 for (f = FILE_A; f <= FILE_H; f++)
193 if (!(ourPawns & file_bb(f)))
195 pi->ksStormValue[Us] += KStormOpenFileBonus[f];
196 pi->qsStormValue[Us] += QStormOpenFileBonus[f];
197 pi->halfOpenFiles[Us] |= (1 << f);
200 // Loop through all pawns of the current color and score each pawn
201 while ((s = *ptr++) != SQ_NONE)
206 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
208 // Calculate kingside and queenside pawn storm scores for both colors to be
209 // used when evaluating middle game positions with opposite side castling.
210 bonus = (f >= FILE_F ? evaluate_pawn_storm<Us, KingSide>(s, r, f, theirPawns) : 0);
211 pi->ksStormValue[Us] += KStormTable[relative_square(Us, s)] + bonus;
213 bonus = (f <= FILE_C ? evaluate_pawn_storm<Us, QueenSide>(s, r, f, theirPawns) : 0);
214 pi->qsStormValue[Us] += QStormTable[relative_square(Us, s)] + bonus;
216 // Our rank plus previous one. Used for chain detection.
217 b = rank_bb(r) | rank_bb(Us == WHITE ? r - 1 : r + 1);
219 // Passed, isolated, doubled or member of a pawn
220 // chain (but not the backward one) ?
221 passed = !(theirPawns & passed_pawn_mask(Us, s));
222 doubled = ourPawns & squares_behind(Us, s);
223 opposed = theirPawns & squares_in_front_of(Us, s);
224 isolated = !(ourPawns & neighboring_files_bb(f));
225 chain = ourPawns & neighboring_files_bb(f) & b;
227 // Test for backward pawn
231 // If the pawn is passed, isolated, or member of a pawn chain
232 // it cannot be backward. If can capture an enemy pawn or if
233 // there are friendly pawns behind on neighboring files it cannot
234 // be backward either.
235 if ( !(passed | isolated | chain)
236 && !(ourPawns & attack_span_mask(opposite_color(Us), s))
237 && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
239 // We now know that there are no friendly pawns beside or behind this
240 // pawn on neighboring files. We now check whether the pawn is
241 // backward by looking in the forward direction on the neighboring
242 // files, and seeing whether we meet a friendly or an enemy pawn first.
243 b = pos.attacks_from<PAWN>(s, Us);
245 // Note that we are sure to find something because pawn is not passed
246 // nor isolated, so loop is potentially infinite, but it isn't.
247 while (!(b & (ourPawns | theirPawns)))
248 Us == WHITE ? b <<= 8 : b >>= 8;
250 // The friendly pawn needs to be at least two ranks closer than the enemy
251 // pawn in order to help the potentially backward pawn advance.
252 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
255 assert(passed | opposed | (attack_span_mask(Us, s) & theirPawns));
257 // Test for candidate passed pawn
258 candidate = !(opposed | passed)
259 && (b = attack_span_mask(opposite_color(Us), s + pawn_push(Us)) & ourPawns) != EmptyBoardBB
260 && count_1s_max_15(b) >= count_1s_max_15(attack_span_mask(Us, s) & theirPawns);
262 // In order to prevent doubled passed pawns from receiving a too big
263 // bonus, only the frontmost passed pawn on each file is considered as
264 // a true passed pawn.
265 if (passed && (ourPawns & squares_in_front_of(Us, s)))
268 // Mark the pawn as passed. Pawn will be properly scored in evaluation
269 // because we need full attack info to evaluate passed pawns.
271 set_bit(&(pi->passedPawns), s);
276 value -= IsolatedPawnPenalty[f];
278 value -= IsolatedPawnPenalty[f] / 2;
281 value -= DoubledPawnPenalty[f];
285 value -= BackwardPawnPenalty[f];
287 value -= BackwardPawnPenalty[f] / 2;
290 value += ChainBonus[f];
293 value += CandidateBonus[relative_rank(Us, s)];
300 /// PawnInfoTable::evaluate_pawn_storm() evaluates each pawn which seems
301 /// to have good chances of creating an open file by exchanging itself
302 /// against an enemy pawn on an adjacent file.
304 template<Color Us, PawnInfoTable::SideType Side>
305 int PawnInfoTable::evaluate_pawn_storm(Square s, Rank r, File f, Bitboard theirPawns) const {
307 const Bitboard StormFilesBB = (Side == KingSide ? FileFBB | FileGBB | FileHBB
308 : FileABB | FileBBB | FileCBB);
309 const int K = (Side == KingSide ? 2 : 4);
310 const File RookFile = (Side == KingSide ? FILE_H : FILE_A);
312 Bitboard b = attack_span_mask(Us, s) & theirPawns & StormFilesBB;
317 // Give a bonus according to the distance of the nearest enemy pawn
318 Square s2 = pop_1st_bit(&b);
319 Rank r2 = square_rank(s2);
320 int v = StormLeverBonus[f] - K * rank_distance(r, r2);
322 // If enemy pawn has no pawn beside itself is particularly vulnerable.
323 // Big bonus, especially against a weakness on the rook file
324 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
325 v *= (square_file(s2) == RookFile ? 4 : 2);
333 /// PawnInfo::updateShelter calculates and caches king shelter. It is called
334 /// only when king square changes, about 20% of total get_king_shelter() calls.
335 int PawnInfo::updateShelter(const Position& pos, Color c, Square ksq) {
337 Bitboard pawns = pos.pieces(PAWN, c) & this_and_neighboring_files_bb(ksq);
338 unsigned shelter = 0;
339 unsigned r = ksq & (7 << 3);
341 for (int i = 1, k = (c ? -8 : 8); i < 4; i++)
344 shelter += BitCount8Bit[(pawns >> r) & 0xFF] * (128 >> i);
346 kingSquares[c] = ksq;
347 kingShelters[c] = shelter;