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 // UnpairedPawnsTable[] gives a score according to the number
74 // of panws that do not have an enemy pawn in front of them.
75 const int UnpairedPawnsTable[8] = { 32, 48, 64, 80, 96, 112, 128, 128 };
77 // Pawn storm tables for positions with opposite castling
78 const int QStormTable[64] = {
79 0, 0, 0, 0, 0, 0, 0, 0,
80 -22,-22,-22,-14,-6, 0, 0, 0,
81 -6,-10,-10,-10,-6, 0, 0, 0,
82 4, 12, 16, 12, 4, 0, 0, 0,
83 16, 23, 23, 16, 0, 0, 0, 0,
84 23, 31, 31, 23, 0, 0, 0, 0,
85 23, 31, 31, 23, 0, 0, 0, 0,
86 0, 0, 0, 0, 0, 0, 0, 0
89 const int KStormTable[64] = {
90 0, 0, 0, 0, 0, 0, 0, 0,
91 0, 0, 0,-10,-19,-28,-33,-33,
92 0, 0, 0,-10,-15,-19,-24,-24,
93 0, 0, 0, 0, 1, 1, 1, 1,
94 0, 0, 0, 0, 1, 10, 19, 19,
95 0, 0, 0, 0, 1, 19, 31, 27,
96 0, 0, 0, 0, 0, 22, 31, 22,
97 0, 0, 0, 0, 0, 0, 0, 0
100 // Pawn storm open file bonuses by file
101 const int16_t KStormOpenFileBonus[8] = { 31, 31, 18, 0, 0, 0, 0, 0 };
102 const int16_t QStormOpenFileBonus[8] = { 0, 0, 0, 0, 0, 26, 42, 26 };
104 // Pawn storm lever bonuses by file
105 const int StormLeverBonus[8] = { -8, -8, -13, 0, 0, -13, -8, -8 };
116 PawnInfoTable::PawnInfoTable(unsigned numOfEntries) {
119 entries = new PawnInfo[size];
122 std::cerr << "Failed to allocate " << (numOfEntries * sizeof(PawnInfo))
123 << " bytes for pawn hash table." << std::endl;
124 Application::exit_with_failure();
131 PawnInfoTable::~PawnInfoTable() {
136 /// PawnInfo::clear() resets to zero the PawnInfo entry. Note that
137 /// kingSquares[] is initialized to SQ_NONE instead.
139 void PawnInfo::clear() {
141 memset(this, 0, sizeof(PawnInfo));
142 kingSquares[WHITE] = kingSquares[BLACK] = SQ_NONE;
146 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
147 /// a PawnInfo object, and returns a pointer to it. The result is also
148 /// stored in a hash table, so we don't have to recompute everything when
149 /// the same pawn structure occurs again.
151 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) {
155 Key key = pos.get_pawn_key();
156 int index = int(key & (size - 1));
157 PawnInfo* pi = entries + index;
159 // If pi->key matches the position's pawn hash key, it means that we
160 // have analysed this pawn structure before, and we can simply return
161 // the information we found the last time instead of recomputing it.
165 // Clear the PawnInfo object, and set the key
169 // Calculate pawn attacks
170 Bitboard whitePawns = pos.pieces(PAWN, WHITE);
171 Bitboard blackPawns = pos.pieces(PAWN, BLACK);
172 pi->pawnAttacks[WHITE] = ((whitePawns << 9) & ~FileABB) | ((whitePawns << 7) & ~FileHBB);
173 pi->pawnAttacks[BLACK] = ((blackPawns >> 7) & ~FileABB) | ((blackPawns >> 9) & ~FileHBB);
175 // Evaluate pawns for both colors
176 pi->value = evaluate_pawns<WHITE>(pos, whitePawns, blackPawns, pi)
177 - evaluate_pawns<BLACK>(pos, blackPawns, whitePawns, pi);
182 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
185 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
186 Bitboard theirPawns, PawnInfo* pi) {
190 bool passed, isolated, doubled, opposed, chain, backward, candidate;
192 Score value = make_score(0, 0);
193 const Square* ptr = pos.piece_list_begin(Us, PAWN);
194 int unpairedPawnsNum = pos.piece_count(Us, PAWN);
196 // Initialize pawn storm scores by giving bonuses for open files
197 for (f = FILE_A; f <= FILE_H; f++)
198 if (!(ourPawns & file_bb(f)))
200 pi->ksStormValue[Us] += KStormOpenFileBonus[f];
201 pi->qsStormValue[Us] += QStormOpenFileBonus[f];
202 pi->halfOpenFiles[Us] |= (1 << f);
205 // Loop through all pawns of the current color and score each pawn
206 while ((s = *ptr++) != SQ_NONE)
211 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
213 // Passed, isolated or doubled pawn?
214 passed = !(theirPawns & passed_pawn_mask(Us, s));
215 isolated = !(ourPawns & neighboring_files_bb(s));
216 doubled = ourPawns & squares_behind(Us, s);
217 opposed = theirPawns & squares_in_front_of(Us, s);
219 // Decrease number of unpaired pawns
223 // We calculate kingside and queenside pawn storm
224 // scores for both colors. These are used when evaluating
225 // middle game positions with opposite side castling.
227 // Each pawn is given a base score given by a piece square table
228 // (KStormTable[] or QStormTable[]). Pawns which seem to have good
229 // chances of creating an open file by exchanging itself against an
230 // enemy pawn on an adjacent file gets an additional bonus.
232 // Kingside pawn storms
233 bonus = KStormTable[relative_square(Us, s)];
236 Bitboard b = outpost_mask(Us, s) & theirPawns & (FileFBB | FileGBB | FileHBB);
239 // Give a bonus according to the distance of the nearest enemy pawn
240 Square s2 = pop_1st_bit(&b);
241 int v = StormLeverBonus[f] - 2 * square_distance(s, s2);
243 // If enemy pawn has no pawn beside itself is particularly vulnerable.
244 // Big bonus, especially against a weakness on the rook file
245 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
246 v *= (square_file(s2) == FILE_H ? 4 : 2);
251 pi->ksStormValue[Us] += bonus;
253 // Queenside pawn storms
254 bonus = QStormTable[relative_square(Us, s)];
257 Bitboard b = outpost_mask(Us, s) & theirPawns & (FileABB | FileBBB | FileCBB);
260 // Give a bonus according to the distance of the nearest enemy pawn
261 Square s2 = pop_1st_bit(&b);
262 int v = StormLeverBonus[f] - 4 * square_distance(s, s2);
264 // If enemy pawn has no pawn beside itself is particularly vulnerable.
265 // Big bonus, especially against a weakness on the rook file
266 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
267 v *= (square_file(s2) == FILE_A ? 4 : 2);
272 pi->qsStormValue[Us] += bonus;
274 // Member of a pawn chain (but not the backward one)? We could speed up
275 // the test a little by introducing an array of masks indexed by color
276 // and square for doing the test, but because everything is hashed,
277 // it probably won't make any noticable difference.
279 & neighboring_files_bb(f)
280 & (rank_bb(r) | rank_bb(r - (Us == WHITE ? 1 : -1)));
282 // Test for backward pawn
284 // If the pawn is passed, isolated, or member of a pawn chain
285 // it cannot be backward. If can capture an enemy pawn or if
286 // there are friendly pawns behind on neighboring files it cannot
287 // be backward either.
288 if ( (passed | isolated | chain)
289 || (ourPawns & behind_bb(Us, r) & neighboring_files_bb(f))
290 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
294 // We now know that there are no friendly pawns beside or behind this
295 // pawn on neighboring files. We now check whether the pawn is
296 // backward by looking in the forward direction on the neighboring
297 // files, and seeing whether we meet a friendly or an enemy pawn first.
298 Bitboard b = pos.attacks_from<PAWN>(s, Us);
300 // Note that we are sure to find something because pawn is not passed
301 // nor isolated, so loop is potentially infinite, but it isn't.
302 while (!(b & (ourPawns | theirPawns)))
303 Us == WHITE ? b <<= 8 : b >>= 8;
305 // The friendly pawn needs to be at least two ranks closer than the enemy
306 // pawn in order to help the potentially backward pawn advance.
307 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
310 // Test for candidate passed pawn
313 && ( count_1s_max_15(neighboring_files_bb(f) & (behind_bb(Us, r) | rank_bb(r)) & ourPawns)
314 - count_1s_max_15(neighboring_files_bb(f) & in_front_bb(Us, r) & theirPawns)
317 // In order to prevent doubled passed pawns from receiving a too big
318 // bonus, only the frontmost passed pawn on each file is considered as
319 // a true passed pawn.
320 if (passed && (ourPawns & squares_in_front_of(Us, s)))
325 set_bit(&(pi->passedPawns), s);
329 value -= IsolatedPawnPenalty[f];
330 if (!(theirPawns & file_bb(f)))
331 value -= IsolatedPawnPenalty[f] / 2;
334 value -= DoubledPawnPenalty[f];
338 value -= BackwardPawnPenalty[f];
339 if (!(theirPawns & file_bb(f)))
340 value -= BackwardPawnPenalty[f] / 2;
343 value += ChainBonus[f];
346 value += CandidateBonus[relative_rank(Us, s)];
349 // Calculate a scale factor to be used to evaluate if position is drawish
350 pi->factor[Us] = UnpairedPawnsTable[unpairedPawnsNum];
356 /// PawnInfo::updateShelter calculates and caches king shelter. It is called
357 /// only when king square changes, about 20% of total get_king_shelter() calls.
358 int PawnInfo::updateShelter(const Position& pos, Color c, Square ksq) {
360 unsigned shelter = 0;
361 Bitboard pawns = pos.pieces(PAWN, c) & this_and_neighboring_files_bb(ksq);
362 unsigned r = ksq & (7 << 3);
363 for (int i = 1, k = (c ? -8 : 8); i < 4; i++)
366 shelter += BitCount8Bit[(pawns >> r) & 0xFF] * (128 >> i);
368 kingSquares[c] = ksq;
369 kingShelters[c] = shelter;