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 // Calculate pawn attacks
194 Bitboard whitePawns = pos.pieces(PAWN, WHITE);
195 Bitboard blackPawns = pos.pieces(PAWN, BLACK);
196 pi->pawnAttacks[WHITE] = ((whitePawns << 9) & ~FileABB) | ((whitePawns << 7) & ~FileHBB);
197 pi->pawnAttacks[BLACK] = ((blackPawns >> 7) & ~FileABB) | ((blackPawns >> 9) & ~FileHBB);
199 // Evaluate pawns for both colors
200 Values whiteValues = evaluate_pawns<WHITE>(pos, whitePawns, blackPawns, pi);
201 Values blackValues = evaluate_pawns<BLACK>(pos, blackPawns, whitePawns, pi);
203 pi->mgValue = int16_t(whiteValues.first - blackValues.first);
204 pi->egValue = int16_t(whiteValues.second - blackValues.second);
209 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
212 PawnInfoTable::Values PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
213 Bitboard theirPawns, PawnInfo* pi) {
217 bool passed, isolated, doubled, chain, backward, candidate;
219 Value mgValue = Value(0);
220 Value egValue = Value(0);
221 Bitboard pawns = ourPawns;
223 // Initialize pawn storm scores by giving bonuses for open files
224 for (File f = FILE_A; f <= FILE_H; f++)
225 if (!(ourPawns & file_bb(f)))
227 pi->ksStormValue[Us] += KStormOpenFileBonus[f];
228 pi->qsStormValue[Us] += QStormOpenFileBonus[f];
229 pi->halfOpenFiles[Us] |= (1 << f);
232 // Loop through all pawns of the current color and score each pawn
235 s = pop_1st_bit(&pawns);
239 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
241 // Passed, isolated or doubled pawn?
242 passed = Position::pawn_is_passed(theirPawns, Us, s);
243 isolated = Position::pawn_is_isolated(ourPawns, s);
244 doubled = Position::pawn_is_doubled(ourPawns, Us, s);
246 // We calculate kingside and queenside pawn storm
247 // scores for both colors. These are used when evaluating
248 // middle game positions with opposite side castling.
250 // Each pawn is given a base score given by a piece square table
251 // (KStormTable[] or QStormTable[]). Pawns which seem to have good
252 // chances of creating an open file by exchanging itself against an
253 // enemy pawn on an adjacent file gets an additional bonus.
255 // Kingside pawn storms
256 bonus = KStormTable[relative_square(Us, s)];
259 Bitboard b = outpost_mask(Us, s) & theirPawns & (FileFBB | FileGBB | FileHBB);
262 Square s2 = pop_1st_bit(&b);
263 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
265 // The enemy pawn has no pawn beside itself, which makes it
266 // particularly vulnerable. Big bonus, especially against a
267 // weakness on the rook file.
268 if (square_file(s2) == FILE_H)
269 bonus += 4*StormLeverBonus[f] - 8*square_distance(s, s2);
271 bonus += 2*StormLeverBonus[f] - 4*square_distance(s, s2);
273 // There is at least one enemy pawn beside the enemy pawn we look
274 // at, which means that the pawn has somewhat better chances of
275 // defending itself by advancing. Smaller bonus.
276 bonus += StormLeverBonus[f] - 2*square_distance(s, s2);
279 pi->ksStormValue[Us] += bonus;
281 // Queenside pawn storms
282 bonus = QStormTable[relative_square(Us, s)];
285 Bitboard b = outpost_mask(Us, s) & theirPawns & (FileABB | FileBBB | FileCBB);
288 Square s2 = pop_1st_bit(&b);
289 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
291 // The enemy pawn has no pawn beside itself, which makes it
292 // particularly vulnerable. Big bonus, especially against a
293 // weakness on the rook file.
294 if (square_file(s2) == FILE_A)
295 bonus += 4*StormLeverBonus[f] - 16*square_distance(s, s2);
297 bonus += 2*StormLeverBonus[f] - 8*square_distance(s, s2);
299 // There is at least one enemy pawn beside the enemy pawn we look
300 // at, which means that the pawn has somewhat better chances of
301 // defending itself by advancing. Smaller bonus.
302 bonus += StormLeverBonus[f] - 4*square_distance(s, s2);
305 pi->qsStormValue[Us] += bonus;
307 // Member of a pawn chain (but not the backward one)? We could speed up
308 // the test a little by introducing an array of masks indexed by color
309 // and square for doing the test, but because everything is hashed,
310 // it probably won't make any noticable difference.
312 & neighboring_files_bb(f)
313 & (rank_bb(r) | rank_bb(r - (Us == WHITE ? 1 : -1)));
315 // Test for backward pawn
317 // If the pawn is passed, isolated, or member of a pawn chain
318 // it cannot be backward. If can capture an enemy pawn or if
319 // there are friendly pawns behind on neighboring files it cannot
320 // be backward either.
321 if ( (passed | isolated | chain)
322 || (ourPawns & behind_bb(Us, r) & neighboring_files_bb(f))
323 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
327 // We now know that there are no friendly pawns beside or behind this
328 // pawn on neighboring files. We now check whether the pawn is
329 // backward by looking in the forward direction on the neighboring
330 // files, and seeing whether we meet a friendly or an enemy pawn first.
331 Bitboard b = pos.attacks_from<PAWN>(s, Us);
333 // Note that we are sure to find something because pawn is not passed
334 // nor isolated, so loop is potentially infinite, but it isn't.
335 while (!(b & (ourPawns | theirPawns)))
336 Us == WHITE ? b <<= 8 : b >>= 8;
338 // The friendly pawn needs to be at least two ranks closer than the enemy
339 // pawn in order to help the potentially backward pawn advance.
340 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
343 // Test for candidate passed pawn
345 && !(theirPawns & file_bb(f))
346 && ( count_1s_max_15(neighboring_files_bb(f) & (behind_bb(Us, r) | rank_bb(r)) & ourPawns)
347 - count_1s_max_15(neighboring_files_bb(f) & in_front_bb(Us, r) & theirPawns)
350 // In order to prevent doubled passed pawns from receiving a too big
351 // bonus, only the frontmost passed pawn on each file is considered as
352 // a true passed pawn.
353 if (passed && (ourPawns & squares_in_front_of(Us, s)))
358 set_bit(&(pi->passedPawns), s);
362 mgValue -= IsolatedPawnMidgamePenalty[f];
363 egValue -= IsolatedPawnEndgamePenalty[f];
364 if (!(theirPawns & file_bb(f)))
366 mgValue -= IsolatedPawnMidgamePenalty[f] / 2;
367 egValue -= IsolatedPawnEndgamePenalty[f] / 2;
372 mgValue -= DoubledPawnMidgamePenalty[f];
373 egValue -= DoubledPawnEndgamePenalty[f];
377 mgValue -= BackwardPawnMidgamePenalty[f];
378 egValue -= BackwardPawnEndgamePenalty[f];
379 if (!(theirPawns & file_bb(f)))
381 mgValue -= BackwardPawnMidgamePenalty[f] / 2;
382 egValue -= BackwardPawnEndgamePenalty[f] / 2;
387 mgValue += ChainMidgameBonus[f];
388 egValue += ChainEndgameBonus[f];
392 mgValue += CandidateMidgameBonus[relative_rank(Us, s)];
393 egValue += CandidateEndgameBonus[relative_rank(Us, s)];
397 return Values(mgValue, egValue);
401 /// PawnInfo::updateShelter calculates and caches king shelter. It is called
402 /// only when king square changes, about 20% of total get_king_shelter() calls.
403 int PawnInfo::updateShelter(const Position& pos, Color c, Square ksq) {
405 unsigned shelter = 0;
406 Bitboard pawns = pos.pieces(PAWN, c) & this_and_neighboring_files_bb(ksq);
407 unsigned r = ksq & (7 << 3);
408 for (int i = 1, k = (c ? -8 : 8); i < 4; i++)
411 shelter += BitCount8Bit[(pawns >> r) & 0xFF] * (128 >> i);
413 kingSquares[c] = ksq;
414 kingShelters[c] = shelter;