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[16] = { 32, 48, 64, 80, 96, 112, 128, 128, 128 };
77 // PawnsQtyTable[] gives a score according to the number of panws
78 const int PawnsQtyTable[16] = { 16, 16, 16, 16, 16, 16, 16, 16, 16 };
80 // Pawn storm tables for positions with opposite castling
81 const int QStormTable[64] = {
82 0, 0, 0, 0, 0, 0, 0, 0,
83 -22,-22,-22,-14,-6, 0, 0, 0,
84 -6,-10,-10,-10,-6, 0, 0, 0,
85 4, 12, 16, 12, 4, 0, 0, 0,
86 16, 23, 23, 16, 0, 0, 0, 0,
87 23, 31, 31, 23, 0, 0, 0, 0,
88 23, 31, 31, 23, 0, 0, 0, 0,
89 0, 0, 0, 0, 0, 0, 0, 0
92 const int KStormTable[64] = {
93 0, 0, 0, 0, 0, 0, 0, 0,
94 0, 0, 0,-10,-19,-28,-33,-33,
95 0, 0, 0,-10,-15,-19,-24,-24,
96 0, 0, 0, 0, 1, 1, 1, 1,
97 0, 0, 0, 0, 1, 10, 19, 19,
98 0, 0, 0, 0, 1, 19, 31, 27,
99 0, 0, 0, 0, 0, 22, 31, 22,
100 0, 0, 0, 0, 0, 0, 0, 0
103 // Pawn storm open file bonuses by file
104 const int16_t KStormOpenFileBonus[8] = { 31, 31, 18, 0, 0, 0, 0, 0 };
105 const int16_t QStormOpenFileBonus[8] = { 0, 0, 0, 0, 0, 26, 42, 26 };
107 // Pawn storm lever bonuses by file
108 const int StormLeverBonus[8] = { -8, -8, -13, 0, 0, -13, -8, -8 };
119 PawnInfoTable::PawnInfoTable(unsigned numOfEntries) {
122 entries = new PawnInfo[size];
125 std::cerr << "Failed to allocate " << (numOfEntries * sizeof(PawnInfo))
126 << " bytes for pawn hash table." << std::endl;
127 Application::exit_with_failure();
134 PawnInfoTable::~PawnInfoTable() {
139 /// PawnInfo::clear() resets to zero the PawnInfo entry. Note that
140 /// kingSquares[] is initialized to SQ_NONE instead.
142 void PawnInfo::clear() {
144 memset(this, 0, sizeof(PawnInfo));
145 kingSquares[WHITE] = kingSquares[BLACK] = SQ_NONE;
149 /// PawnInfoTable::get_pawn_info() takes a position object as input, computes
150 /// a PawnInfo object, and returns a pointer to it. The result is also
151 /// stored in a hash table, so we don't have to recompute everything when
152 /// the same pawn structure occurs again.
154 PawnInfo* PawnInfoTable::get_pawn_info(const Position& pos) {
158 Key key = pos.get_pawn_key();
159 int index = int(key & (size - 1));
160 PawnInfo* pi = entries + index;
162 // If pi->key matches the position's pawn hash key, it means that we
163 // have analysed this pawn structure before, and we can simply return
164 // the information we found the last time instead of recomputing it.
168 // Clear the PawnInfo object, and set the key
172 // Calculate pawn attacks
173 Bitboard whitePawns = pos.pieces(PAWN, WHITE);
174 Bitboard blackPawns = pos.pieces(PAWN, BLACK);
175 pi->pawnAttacks[WHITE] = ((whitePawns << 9) & ~FileABB) | ((whitePawns << 7) & ~FileHBB);
176 pi->pawnAttacks[BLACK] = ((blackPawns >> 7) & ~FileABB) | ((blackPawns >> 9) & ~FileHBB);
178 // Evaluate pawns for both colors
179 pi->value = evaluate_pawns<WHITE>(pos, whitePawns, blackPawns, pi)
180 - evaluate_pawns<BLACK>(pos, blackPawns, whitePawns, pi);
185 /// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
188 Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
189 Bitboard theirPawns, PawnInfo* pi) {
193 bool passed, isolated, doubled, opposed, chain, backward, candidate;
195 Score value = make_score(0, 0);
196 const Square* ptr = pos.piece_list_begin(Us, PAWN);
197 int unpairedPawnsNum = pos.piece_count(Us, PAWN);
199 // Initialize pawn storm scores by giving bonuses for open files
200 for (f = FILE_A; f <= FILE_H; f++)
201 if (!(ourPawns & file_bb(f)))
203 pi->ksStormValue[Us] += KStormOpenFileBonus[f];
204 pi->qsStormValue[Us] += QStormOpenFileBonus[f];
205 pi->halfOpenFiles[Us] |= (1 << f);
208 // Loop through all pawns of the current color and score each pawn
209 while ((s = *ptr++) != SQ_NONE)
214 assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
216 // Passed, isolated or doubled pawn?
217 passed = !(theirPawns & passed_pawn_mask(Us, s));
218 isolated = !(ourPawns & neighboring_files_bb(s));
219 doubled = ourPawns & squares_behind(Us, s);
220 opposed = theirPawns & squares_in_front_of(Us, s);
222 // Decrease number of unpaired pawns
226 // We calculate kingside and queenside pawn storm
227 // scores for both colors. These are used when evaluating
228 // middle game positions with opposite side castling.
230 // Each pawn is given a base score given by a piece square table
231 // (KStormTable[] or QStormTable[]). Pawns which seem to have good
232 // chances of creating an open file by exchanging itself against an
233 // enemy pawn on an adjacent file gets an additional bonus.
235 // Kingside pawn storms
236 bonus = KStormTable[relative_square(Us, s)];
239 Bitboard b = outpost_mask(Us, s) & theirPawns & (FileFBB | FileGBB | FileHBB);
242 // Give a bonus according to the distance of the nearest enemy pawn
243 Square s2 = pop_1st_bit(&b);
244 int v = StormLeverBonus[f] - 2 * square_distance(s, s2);
246 // If enemy pawn has no pawn beside itself is particularly vulnerable.
247 // Big bonus, especially against a weakness on the rook file
248 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
249 v *= (square_file(s2) == FILE_H ? 4 : 2);
254 pi->ksStormValue[Us] += bonus;
256 // Queenside pawn storms
257 bonus = QStormTable[relative_square(Us, s)];
260 Bitboard b = outpost_mask(Us, s) & theirPawns & (FileABB | FileBBB | FileCBB);
263 // Give a bonus according to the distance of the nearest enemy pawn
264 Square s2 = pop_1st_bit(&b);
265 int v = StormLeverBonus[f] - 4 * square_distance(s, s2);
267 // If enemy pawn has no pawn beside itself is particularly vulnerable.
268 // Big bonus, especially against a weakness on the rook file
269 if (!(theirPawns & neighboring_files_bb(s2) & rank_bb(s2)))
270 v *= (square_file(s2) == FILE_A ? 4 : 2);
275 pi->qsStormValue[Us] += bonus;
277 // Member of a pawn chain (but not the backward one)? We could speed up
278 // the test a little by introducing an array of masks indexed by color
279 // and square for doing the test, but because everything is hashed,
280 // it probably won't make any noticable difference.
282 & neighboring_files_bb(f)
283 & (rank_bb(r) | rank_bb(r - (Us == WHITE ? 1 : -1)));
285 // Test for backward pawn
287 // If the pawn is passed, isolated, or member of a pawn chain
288 // it cannot be backward. If can capture an enemy pawn or if
289 // there are friendly pawns behind on neighboring files it cannot
290 // be backward either.
291 if ( (passed | isolated | chain)
292 || (ourPawns & behind_bb(Us, r) & neighboring_files_bb(f))
293 || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
297 // We now know that there are no friendly pawns beside or behind this
298 // pawn on neighboring files. We now check whether the pawn is
299 // backward by looking in the forward direction on the neighboring
300 // files, and seeing whether we meet a friendly or an enemy pawn first.
301 Bitboard b = pos.attacks_from<PAWN>(s, Us);
303 // Note that we are sure to find something because pawn is not passed
304 // nor isolated, so loop is potentially infinite, but it isn't.
305 while (!(b & (ourPawns | theirPawns)))
306 Us == WHITE ? b <<= 8 : b >>= 8;
308 // The friendly pawn needs to be at least two ranks closer than the enemy
309 // pawn in order to help the potentially backward pawn advance.
310 backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
313 // Test for candidate passed pawn
316 && ( count_1s_max_15(neighboring_files_bb(f) & (behind_bb(Us, r) | rank_bb(r)) & ourPawns)
317 - count_1s_max_15(neighboring_files_bb(f) & in_front_bb(Us, r) & theirPawns)
320 // In order to prevent doubled passed pawns from receiving a too big
321 // bonus, only the frontmost passed pawn on each file is considered as
322 // a true passed pawn.
323 if (passed && (ourPawns & squares_in_front_of(Us, s)))
328 set_bit(&(pi->passedPawns), s);
332 value -= IsolatedPawnPenalty[f];
333 if (!(theirPawns & file_bb(f)))
334 value -= IsolatedPawnPenalty[f] / 2;
337 value -= DoubledPawnPenalty[f];
341 value -= BackwardPawnPenalty[f];
342 if (!(theirPawns & file_bb(f)))
343 value -= BackwardPawnPenalty[f] / 2;
346 value += ChainBonus[f];
349 value += CandidateBonus[relative_rank(Us, s)];
352 // Calculate a scale factor to be used to evaluate if position is drawish
353 pi->factor[Us] = UnpairedPawnsTable[unpairedPawnsNum] * PawnsQtyTable[pos.piece_count(Us, PAWN)] / 16;
359 /// PawnInfo::updateShelter calculates and caches king shelter. It is called
360 /// only when king square changes, about 20% of total get_king_shelter() calls.
361 int PawnInfo::updateShelter(const Position& pos, Color c, Square ksq) {
363 unsigned shelter = 0;
364 Bitboard pawns = pos.pieces(PAWN, c) & this_and_neighboring_files_bb(ksq);
365 unsigned r = ksq & (7 << 3);
366 for (int i = 1, k = (c ? -8 : 8); i < 4; i++)
369 shelter += BitCount8Bit[(pawns >> r) & 0xFF] * (128 >> i);
371 kingSquares[c] = ksq;
372 kingShelters[c] = shelter;