2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
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 // Doubled pawn penalty by file, middle game
42 const Value DoubledPawnMidgamePenalty[8] = {
43 Value(13), Value(20), Value(23), Value(23),
44 Value(23), Value(23), Value(20), Value(13)
47 // Doubled pawn penalty by file, endgame
48 const Value DoubledPawnEndgamePenalty[8] = {
49 Value(43), Value(48), Value(48), Value(48),
50 Value(48), Value(48), Value(48), Value(43)
53 // Isolated pawn penalty by file, middle game
54 const Value IsolatedPawnMidgamePenalty[8] = {
55 Value(25), Value(36), Value(40), Value(40),
56 Value(40), Value(40), Value(36), Value(25)
59 // Isolated pawn penalty by file, endgame
60 const Value IsolatedPawnEndgamePenalty[8] = {
61 Value(30), Value(35), Value(35), Value(35),
62 Value(35), Value(35), Value(35), Value(30)
65 // Backward pawn penalty by file, middle game
66 const Value BackwardPawnMidgamePenalty[8] = {
67 Value(20), Value(29), Value(33), Value(33),
68 Value(33), Value(33), Value(29), Value(20)
71 // Backward pawn penalty by file, endgame
72 const Value BackwardPawnEndgamePenalty[8] = {
73 Value(28), Value(31), Value(31), Value(31),
74 Value(31), Value(31), Value(31), Value(28)
77 // Pawn chain membership bonus by file, middle game
78 const Value ChainMidgameBonus[8] = {
79 Value(11), Value(13), Value(13), Value(14),
80 Value(14), Value(13), Value(13), Value(11)
83 // Pawn chain membership bonus by file, endgame
84 const Value ChainEndgameBonus[8] = {
85 Value(-1), Value(-1), Value(-1), Value(-1),
86 Value(-1), Value(-1), Value(-1), Value(-1)
89 // Candidate passed pawn bonus by rank, middle game
90 const Value CandidateMidgameBonus[8] = {
91 Value( 0), Value( 6), Value(6), Value(14),
92 Value(34), Value(83), Value(0), Value( 0)
95 // Candidate passed pawn bonus by rank, endgame
96 const Value CandidateEndgameBonus[8] = {
97 Value( 0), Value( 13), Value(13), Value(29),
98 Value(68), Value(166), Value( 0), Value( 0)
101 // Pawn storm tables for positions with opposite castling
102 const int QStormTable[64] = {
103 0, 0, 0, 0, 0, 0, 0, 0,
104 -22,-22,-22,-14,-6, 0, 0, 0,
105 -6,-10,-10,-10,-6, 0, 0, 0,
106 4, 12, 16, 12, 4, 0, 0, 0,
107 16, 23, 23, 16, 0, 0, 0, 0,
108 23, 31, 31, 23, 0, 0, 0, 0,
109 23, 31, 31, 23, 0, 0, 0, 0,
110 0, 0, 0, 0, 0, 0, 0, 0
113 const int KStormTable[64] = {
114 0, 0, 0, 0, 0, 0, 0, 0,
115 0, 0, 0,-10,-19,-28,-33,-33,
116 0, 0, 0,-10,-15,-19,-24,-24,
117 0, 0, 0, 0, 1, 1, 1, 1,
118 0, 0, 0, 0, 1, 10, 19, 19,
119 0, 0, 0, 0, 1, 19, 31, 27,
120 0, 0, 0, 0, 0, 22, 31, 22,
121 0, 0, 0, 0, 0, 0, 0, 0
124 // Pawn storm open file bonuses by file
125 const int16_t KStormOpenFileBonus[8] = { 31, 31, 18, 0, 0, 0, 0, 0 };
126 const int16_t QStormOpenFileBonus[8] = { 0, 0, 0, 0, 0, 26, 42, 26 };
128 // Pawn storm lever bonuses by file
129 const int StormLeverBonus[8] = { -8, -8, -13, 0, 0, -13, -8, -8 };
140 PawnInfoTable::PawnInfoTable(unsigned numOfEntries) {
143 entries = new PawnInfo[size];
146 std::cerr << "Failed to allocate " << (numOfEntries * sizeof(PawnInfo))
147 << " bytes for pawn hash table." << std::endl;
148 Application::exit_with_failure();
155 PawnInfoTable::~PawnInfoTable() {
160 /// PawnInfo::clear() resets to zero the PawnInfo entry. Note that
161 /// kingSquares[] is initialized to SQ_NONE instead.
163 void PawnInfo::clear() {
165 memset(this, 0, sizeof(PawnInfo));
166 kingSquares[WHITE] = kingSquares[BLACK] = SQ_NONE;
170 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
171 /// a PawnInfo object, and returns a pointer to it. The result is also
172 /// stored in a hash table, so we don't have to recompute everything when
173 /// the same pawn structure occurs again.
175 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) {
179 Key key = pos.get_pawn_key();
180 int index = int(key & (size - 1));
181 PawnInfo* pi = entries + index;
183 // If pi->key matches the position's pawn hash key, it means that we
184 // have analysed this pawn structure before, and we can simply return
185 // the information we found the last time instead of recomputing it.
189 // Clear the PawnInfo object, and set the key
193 Value mgValue[2] = {Value(0), Value(0)};
194 Value egValue[2] = {Value(0), Value(0)};
196 // Loop through the pawns for both colors
197 for (Color us = WHITE; us <= BLACK; us++)
199 Color them = opposite_color(us);
200 Bitboard ourPawns = pos.pawns(us);
201 Bitboard theirPawns = pos.pawns(them);
202 Bitboard pawns = ourPawns;
204 // Initialize pawn storm scores by giving bonuses for open files
205 for (File f = FILE_A; f <= FILE_H; f++)
206 if (!(pawns & file_bb(f)))
208 pi->ksStormValue[us] += KStormOpenFileBonus[f];
209 pi->qsStormValue[us] += QStormOpenFileBonus[f];
210 pi->halfOpenFiles[us] |= (1 << f);
213 // Loop through all pawns of the current color and score each pawn
216 Square s = pop_1st_bit(&pawns);
217 File f = square_file(s);
218 Rank r = square_rank(s);
220 assert(pos.piece_on(s) == piece_of_color_and_type(us, PAWN));
222 // Passed, isolated or doubled pawn?
223 bool passed = Position::pawn_is_passed(theirPawns, us, s);
224 bool isolated = Position::pawn_is_isolated(ourPawns, s);
225 bool doubled = Position::pawn_is_doubled(ourPawns, us, s);
227 // We calculate kingside and queenside pawn storm
228 // scores for both colors. These are used when evaluating
229 // middle game positions with opposite side castling.
231 // Each pawn is given a base score given by a piece square table
232 // (KStormTable[] or QStormTable[]). Pawns which seem to have good
233 // chances of creating an open file by exchanging itself against an
234 // enemy pawn on an adjacent file gets an additional bonus.
236 // Kingside pawn storms
237 int bonus = KStormTable[relative_square(us, s)];
240 Bitboard b = outpost_mask(us, s) & theirPawns & (FileFBB | FileGBB | FileHBB);
243 Square s2 = pop_1st_bit(&b);
244 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
246 // The enemy pawn has no pawn beside itself, which makes it
247 // particularly vulnerable. Big bonus, especially against a
248 // weakness on the rook file.
249 if (square_file(s2) == FILE_H)
250 bonus += 4*StormLeverBonus[f] - 8*square_distance(s, s2);
252 bonus += 2*StormLeverBonus[f] - 4*square_distance(s, s2);
254 // There is at least one enemy pawn beside the enemy pawn we look
255 // at, which means that the pawn has somewhat better chances of
256 // defending itself by advancing. Smaller bonus.
257 bonus += StormLeverBonus[f] - 2*square_distance(s, s2);
260 pi->ksStormValue[us] += bonus;
262 // Queenside pawn storms
263 bonus = QStormTable[relative_square(us, s)];
266 Bitboard b = outpost_mask(us, s) & theirPawns & (FileABB | FileBBB | FileCBB);
269 Square s2 = pop_1st_bit(&b);
270 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
272 // The enemy pawn has no pawn beside itself, which makes it
273 // particularly vulnerable. Big bonus, especially against a
274 // weakness on the rook file.
275 if (square_file(s2) == FILE_A)
276 bonus += 4*StormLeverBonus[f] - 16*square_distance(s, s2);
278 bonus += 2*StormLeverBonus[f] - 8*square_distance(s, s2);
280 // There is at least one enemy pawn beside the enemy pawn we look
281 // at, which means that the pawn has somewhat better chances of
282 // defending itself by advancing. Smaller bonus.
283 bonus += StormLeverBonus[f] - 4*square_distance(s, s2);
286 pi->qsStormValue[us] += bonus;
288 // Member of a pawn chain (but not the backward one)? We could speed up
289 // the test a little by introducing an array of masks indexed by color
290 // and square for doing the test, but because everything is hashed,
291 // it probably won't make any noticable difference.
292 bool chain = ourPawns
293 & neighboring_files_bb(f)
294 & (rank_bb(r) | rank_bb(r - (us == WHITE ? 1 : -1)));
296 // Test for backward pawn
298 // If the pawn is passed, isolated, or member of a pawn chain
299 // it cannot be backward. If can capture an enemy pawn or if
300 // there are friendly pawns behind on neighboring files it cannot
301 // be backward either.
306 || (pos.pawn_attacks(us, s) & theirPawns)
307 || (ourPawns & behind_bb(us, r) & neighboring_files_bb(f)))
311 // We now know that there are no friendly pawns beside or behind this
312 // pawn on neighboring files. We now check whether the pawn is
313 // backward by looking in the forward direction on the neighboring
314 // files, and seeing whether we meet a friendly or an enemy pawn first.
315 Bitboard b = pos.pawn_attacks(us, s);
318 for ( ; !(b & (ourPawns | theirPawns)); b <<= 8);
319 backward = (b | (b << 8)) & theirPawns;
323 for ( ; !(b & (ourPawns | theirPawns)); b >>= 8);
324 backward = (b | (b >> 8)) & theirPawns;
328 // Test for candidate passed pawn
331 && !(theirPawns & file_bb(f))
332 && ( count_1s_max_15(neighboring_files_bb(f) & (behind_bb(us, r) | rank_bb(r)) & ourPawns)
333 - count_1s_max_15(neighboring_files_bb(f) & in_front_bb(us, r) & theirPawns)
336 // In order to prevent doubled passed pawns from receiving a too big
337 // bonus, only the frontmost passed pawn on each file is considered as
338 // a true passed pawn.
339 if (passed && (ourPawns & squares_in_front_of(us, s)))
344 set_bit(&(pi->passedPawns), s);
348 mgValue[us] -= IsolatedPawnMidgamePenalty[f];
349 egValue[us] -= IsolatedPawnEndgamePenalty[f];
350 if (!(theirPawns & file_bb(f)))
352 mgValue[us] -= IsolatedPawnMidgamePenalty[f] / 2;
353 egValue[us] -= IsolatedPawnEndgamePenalty[f] / 2;
358 mgValue[us] -= DoubledPawnMidgamePenalty[f];
359 egValue[us] -= DoubledPawnEndgamePenalty[f];
363 mgValue[us] -= BackwardPawnMidgamePenalty[f];
364 egValue[us] -= BackwardPawnEndgamePenalty[f];
365 if (!(theirPawns & file_bb(f)))
367 mgValue[us] -= BackwardPawnMidgamePenalty[f] / 2;
368 egValue[us] -= BackwardPawnEndgamePenalty[f] / 2;
373 mgValue[us] += ChainMidgameBonus[f];
374 egValue[us] += ChainEndgameBonus[f];
378 mgValue[us] += CandidateMidgameBonus[relative_rank(us, s)];
379 egValue[us] += CandidateEndgameBonus[relative_rank(us, s)];
384 pi->mgValue = int16_t(mgValue[WHITE] - mgValue[BLACK]);
385 pi->egValue = int16_t(egValue[WHITE] - egValue[BLACK]);
390 /// PawnInfo::updateShelter calculates and caches king shelter. It is called
391 /// only when king square changes, about 20% of total get_king_shelter() calls.
392 int PawnInfo::updateShelter(const Position& pos, Color c, Square ksq) {
394 unsigned shelter = 0;
395 Bitboard pawns = pos.pawns(c) & this_and_neighboring_files_bb(ksq);
396 unsigned r = ksq & (7 << 3);
397 for (int i = 1, k = (c ? -8 : 8); i < 4; i++)
400 shelter += BitCount8Bit[(pawns >> r) & 0xFF] * (128 >> i);
402 kingSquares[c] = ksq;
403 kingShelters[c] = shelter;