2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
35 enum Tracing { NO_TRACE, TRACE };
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
41 Score scores[TERM_NB][COLOR_NB];
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
45 void add(int idx, Color c, Score s) {
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
60 std::ostream& operator<<(std::ostream& os, Term t) {
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
72 using namespace Trace;
76 constexpr Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
77 constexpr Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
78 constexpr Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
79 constexpr Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
81 constexpr Bitboard KingFlank[FILE_NB] = {
82 QueenSide ^ FileDBB, QueenSide, QueenSide,
83 CenterFiles, CenterFiles,
84 KingSide, KingSide, KingSide ^ FileEBB
87 // Threshold for lazy and space evaluation
88 constexpr Value LazyThreshold = Value(1500);
89 constexpr Value SpaceThreshold = Value(12222);
91 // KingAttackWeights[PieceType] contains king attack weights by piece type
92 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
94 // Penalties for enemy's safe checks
95 constexpr int QueenSafeCheck = 780;
96 constexpr int RookSafeCheck = 1080;
97 constexpr int BishopSafeCheck = 635;
98 constexpr int KnightSafeCheck = 790;
100 #define S(mg, eg) make_score(mg, eg)
102 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
103 // indexed by piece type and number of attacked squares in the mobility area.
104 constexpr Score MobilityBonus[][32] = {
105 { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knights
106 S( 22, 23), S( 28, 27), S( 33, 33) },
107 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
108 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
109 S( 91, 88), S( 98, 97) },
110 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
111 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
112 S( 46,166), S( 48,169), S( 58,171) },
113 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
114 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
115 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
116 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
117 S(106,184), S(109,191), S(113,206), S(116,212) }
120 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
121 // pieces if they occupy or can reach an outpost square, bigger if that
122 // square is supported by a pawn.
123 constexpr Score Outpost[][2] = {
124 { S(22, 6), S(36,12) }, // Knight
125 { S( 9, 2), S(15, 5) } // Bishop
128 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
129 // no (friendly) pawn on the rook file.
130 constexpr Score RookOnFile[] = { S(18, 7), S(44, 20) };
132 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
133 // which piece type attacks which one. Attacks on lesser pieces which are
134 // pawn-defended are not considered.
135 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
136 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
139 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
140 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(51, 38)
143 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
144 constexpr Score PassedRank[RANK_NB] = {
145 S(0, 0), S(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
148 // PassedFile[File] contains a bonus according to the file of a passed pawn
149 constexpr Score PassedFile[FILE_NB] = {
150 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
151 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
154 // Assorted bonuses and penalties
155 constexpr Score BishopPawns = S( 3, 7);
156 constexpr Score CloseEnemies = S( 8, 0);
157 constexpr Score CorneredBishop = S( 50, 50);
158 constexpr Score Hanging = S( 69, 36);
159 constexpr Score KingProtector = S( 7, 8);
160 constexpr Score KnightOnQueen = S( 16, 12);
161 constexpr Score LongDiagonalBishop = S( 45, 0);
162 constexpr Score MinorBehindPawn = S( 18, 3);
163 constexpr Score PawnlessFlank = S( 17, 95);
164 constexpr Score RestrictedPiece = S( 7, 7);
165 constexpr Score RookOnPawn = S( 10, 32);
166 constexpr Score SliderOnQueen = S( 59, 18);
167 constexpr Score ThreatByKing = S( 24, 89);
168 constexpr Score ThreatByPawnPush = S( 48, 39);
169 constexpr Score ThreatByRank = S( 13, 0);
170 constexpr Score ThreatBySafePawn = S(173, 94);
171 constexpr Score TrappedRook = S( 47, 4);
172 constexpr Score WeakQueen = S( 49, 15);
173 constexpr Score WeakUnopposedPawn = S( 12, 23);
177 // Evaluation class computes and stores attacks tables and other working data
182 Evaluation() = delete;
183 explicit Evaluation(const Position& p) : pos(p) {}
184 Evaluation& operator=(const Evaluation&) = delete;
188 template<Color Us> void initialize();
189 template<Color Us, PieceType Pt> Score pieces();
190 template<Color Us> Score king() const;
191 template<Color Us> Score threats() const;
192 template<Color Us> Score passed() const;
193 template<Color Us> Score space() const;
194 ScaleFactor scale_factor(Value eg) const;
195 Score initiative(Value eg) const;
200 Bitboard mobilityArea[COLOR_NB];
201 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
203 // attackedBy[color][piece type] is a bitboard representing all squares
204 // attacked by a given color and piece type. Special "piece types" which
205 // is also calculated is ALL_PIECES.
206 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
208 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
209 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
210 // pawn or squares attacked by 2 pawns are not explicitly added.
211 Bitboard attackedBy2[COLOR_NB];
213 // kingRing[color] are the squares adjacent to the king, plus (only for a
214 // king on its first rank) the squares two ranks in front. For instance,
215 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
217 Bitboard kingRing[COLOR_NB];
219 // kingAttackersCount[color] is the number of pieces of the given color
220 // which attack a square in the kingRing of the enemy king.
221 int kingAttackersCount[COLOR_NB];
223 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
224 // the given color which attack a square in the kingRing of the enemy king.
225 // The weights of the individual piece types are given by the elements in
226 // the KingAttackWeights array.
227 int kingAttackersWeight[COLOR_NB];
229 // kingAttacksCount[color] is the number of attacks by the given color to
230 // squares directly adjacent to the enemy king. Pieces which attack more
231 // than one square are counted multiple times. For instance, if there is
232 // a white knight on g5 and black's king is on g8, this white knight adds 2
233 // to kingAttacksCount[WHITE].
234 int kingAttacksCount[COLOR_NB];
238 // Evaluation::initialize() computes king and pawn attacks, and the king ring
239 // bitboard for a given color. This is done at the beginning of the evaluation.
240 template<Tracing T> template<Color Us>
241 void Evaluation<T>::initialize() {
243 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
244 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
245 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
246 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
248 // Find our pawns that are blocked or on the first two ranks
249 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
251 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
252 // are excluded from the mobility area.
253 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
255 // Initialise attackedBy bitboards for kings and pawns
256 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
257 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
258 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
259 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
261 // Init our king safety tables
262 kingRing[Us] = attackedBy[Us][KING];
263 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
264 kingRing[Us] |= shift<Up>(kingRing[Us]);
266 if (file_of(pos.square<KING>(Us)) == FILE_H)
267 kingRing[Us] |= shift<WEST>(kingRing[Us]);
269 else if (file_of(pos.square<KING>(Us)) == FILE_A)
270 kingRing[Us] |= shift<EAST>(kingRing[Us]);
272 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
273 kingRing[Us] &= ~double_pawn_attacks_bb<Us>(pos.pieces(Us, PAWN));
274 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
278 // Evaluation::pieces() scores pieces of a given color and type
279 template<Tracing T> template<Color Us, PieceType Pt>
280 Score Evaluation<T>::pieces() {
282 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
283 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
284 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
285 : Rank5BB | Rank4BB | Rank3BB);
286 const Square* pl = pos.squares<Pt>(Us);
290 Score score = SCORE_ZERO;
292 attackedBy[Us][Pt] = 0;
294 while ((s = *pl++) != SQ_NONE)
296 // Find attacked squares, including x-ray attacks for bishops and rooks
297 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
298 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
299 : pos.attacks_from<Pt>(s);
301 if (pos.blockers_for_king(Us) & s)
302 b &= LineBB[pos.square<KING>(Us)][s];
304 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
305 attackedBy[Us][Pt] |= b;
306 attackedBy[Us][ALL_PIECES] |= b;
308 if (b & kingRing[Them])
310 kingAttackersCount[Us]++;
311 kingAttackersWeight[Us] += KingAttackWeights[Pt];
312 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
315 int mob = popcount(b & mobilityArea[Us]);
317 mobility[Us] += MobilityBonus[Pt - 2][mob];
319 if (Pt == BISHOP || Pt == KNIGHT)
321 // Bonus if piece is on an outpost square or can reach one
322 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
324 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
326 else if (bb &= b & ~pos.pieces(Us))
327 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
329 // Knight and Bishop bonus for being right behind a pawn
330 if (shift<Down>(pos.pieces(PAWN)) & s)
331 score += MinorBehindPawn;
333 // Penalty if the piece is far from the king
334 score -= KingProtector * distance(s, pos.square<KING>(Us));
338 // Penalty according to number of pawns on the same color square as the
339 // bishop, bigger when the center files are blocked with pawns.
340 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
342 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
343 * (1 + popcount(blocked & CenterFiles));
345 // Bonus for bishop on a long diagonal which can "see" both center squares
346 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
347 score += LongDiagonalBishop;
350 // An important Chess960 pattern: A cornered bishop blocked by a friendly
351 // pawn diagonally in front of it is a very serious problem, especially
352 // when that pawn is also blocked.
355 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
357 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
358 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
359 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
360 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
367 // Bonus for aligning rook with enemy pawns on the same rank/file
368 if (relative_rank(Us, s) >= RANK_5)
369 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
371 // Bonus for rook on an open or semi-open file
372 if (pe->semiopen_file(Us, file_of(s)))
373 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
375 // Penalty when trapped by the king, even more if the king cannot castle
378 File kf = file_of(pos.square<KING>(Us));
379 if ((kf < FILE_E) == (file_of(s) < kf))
380 score -= TrappedRook * (1 + !pos.castling_rights(Us));
386 // Penalty if any relative pin or discovered attack against the queen
387 Bitboard queenPinners;
388 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
393 Trace::add(Pt, Us, score);
399 // Evaluation::king() assigns bonuses and penalties to a king of a given color
400 template<Tracing T> template<Color Us>
401 Score Evaluation<T>::king() const {
403 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
404 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
405 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
407 const Square ksq = pos.square<KING>(Us);
408 Bitboard kingFlank, weak, b, b1, b2, safe, unsafeChecks;
410 // King shelter and enemy pawns storm
411 Score score = pe->king_safety<Us>(pos);
413 // Find the squares that opponent attacks in our king flank, and the squares
414 // which are attacked twice in that flank.
415 kingFlank = KingFlank[file_of(ksq)];
416 b1 = attackedBy[Them][ALL_PIECES] & kingFlank & Camp;
417 b2 = b1 & attackedBy2[Them];
419 int tropism = popcount(b1) + popcount(b2);
421 // Main king safety evaluation
425 // Attacked squares defended at most once by our queen or king
426 weak = attackedBy[Them][ALL_PIECES]
428 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
430 // Analyse the safe enemy's checks which are possible on next move
431 safe = ~pos.pieces(Them);
432 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
434 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
435 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
437 // Enemy rooks checks
438 Bitboard RookCheck = b1
440 & attackedBy[Them][ROOK];
443 kingDanger += RookSafeCheck;
445 unsafeChecks |= b1 & attackedBy[Them][ROOK];
447 // Enemy queen safe checks: we count them only if they are from squares from
448 // which we can't give a rook check, because rook checks are more valuable.
449 Bitboard QueenCheck = (b1 | b2)
450 & attackedBy[Them][QUEEN]
452 & ~attackedBy[Us][QUEEN]
456 kingDanger += QueenSafeCheck;
458 // Enemy bishops checks: we count them only if they are from squares from
459 // which we can't give a queen check, because queen checks are more valuable.
460 Bitboard BishopCheck = b2
461 & attackedBy[Them][BISHOP]
466 kingDanger += BishopSafeCheck;
468 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
470 // Enemy knights checks
471 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
474 kingDanger += KnightSafeCheck;
478 // Unsafe or occupied checking squares will also be considered, as long as
479 // the square is in the attacker's mobility area.
480 unsafeChecks &= mobilityArea[Them];
482 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
483 + 69 * kingAttacksCount[Them]
484 + 185 * popcount(kingRing[Us] & weak)
485 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
486 + 5 * tropism * tropism / 16
487 - 873 * !pos.count<QUEEN>(Them)
488 - 6 * mg_value(score) / 8
489 + mg_value(mobility[Them] - mobility[Us])
492 // Transform the kingDanger units into a Score, and subtract it from the evaluation
494 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
496 // Penalty when our king is on a pawnless flank
497 if (!(pos.pieces(PAWN) & kingFlank))
498 score -= PawnlessFlank;
500 // King tropism bonus, to anticipate slow motion attacks on our king
501 score -= CloseEnemies * tropism;
504 Trace::add(KING, Us, score);
510 // Evaluation::threats() assigns bonuses according to the types of the
511 // attacking and the attacked pieces.
512 template<Tracing T> template<Color Us>
513 Score Evaluation<T>::threats() const {
515 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
516 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
517 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
519 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe, restricted;
520 Score score = SCORE_ZERO;
523 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
525 // Squares strongly protected by the enemy, either because they defend the
526 // square with a pawn, or because they defend the square twice and we don't.
527 stronglyProtected = attackedBy[Them][PAWN]
528 | (attackedBy2[Them] & ~attackedBy2[Us]);
530 // Non-pawn enemies, strongly protected
531 defended = nonPawnEnemies & stronglyProtected;
533 // Enemies not strongly protected and under our attack
534 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
536 // Safe or protected squares
537 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
539 // Bonus according to the kind of attacking pieces
542 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
545 Square s = pop_lsb(&b);
546 score += ThreatByMinor[type_of(pos.piece_on(s))];
547 if (type_of(pos.piece_on(s)) != PAWN)
548 score += ThreatByRank * (int)relative_rank(Them, s);
551 b = weak & attackedBy[Us][ROOK];
554 Square s = pop_lsb(&b);
555 score += ThreatByRook[type_of(pos.piece_on(s))];
556 if (type_of(pos.piece_on(s)) != PAWN)
557 score += ThreatByRank * (int)relative_rank(Them, s);
560 if (weak & attackedBy[Us][KING])
561 score += ThreatByKing;
563 b = ~attackedBy[Them][ALL_PIECES]
564 | (nonPawnEnemies & attackedBy2[Us]);
565 score += Hanging * popcount(weak & b);
568 // Bonus for restricting their piece moves
569 restricted = attackedBy[Them][ALL_PIECES]
571 & attackedBy[Us][ALL_PIECES];
572 score += RestrictedPiece * popcount(restricted);
574 // Bonus for enemy unopposed weak pawns
575 if (pos.pieces(Us, ROOK, QUEEN))
576 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
578 // Find squares where our pawns can push on the next move
579 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
580 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
582 // Keep only the squares which are relatively safe
583 b &= ~attackedBy[Them][PAWN] & safe;
585 // Bonus for safe pawn threats on the next move
586 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
587 score += ThreatByPawnPush * popcount(b);
589 // Our safe or protected pawns
590 b = pos.pieces(Us, PAWN) & safe;
592 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
593 score += ThreatBySafePawn * popcount(b);
595 // Bonus for threats on the next moves against enemy queen
596 if (pos.count<QUEEN>(Them) == 1)
598 Square s = pos.square<QUEEN>(Them);
599 safe = mobilityArea[Us] & ~stronglyProtected;
601 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
603 score += KnightOnQueen * popcount(b & safe);
605 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
606 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
608 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
612 Trace::add(THREAT, Us, score);
617 // Evaluation::passed() evaluates the passed pawns and candidate passed
618 // pawns of the given color.
620 template<Tracing T> template<Color Us>
621 Score Evaluation<T>::passed() const {
623 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
624 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
626 auto king_proximity = [&](Color c, Square s) {
627 return std::min(distance(pos.square<KING>(c), s), 5);
630 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
631 Score score = SCORE_ZERO;
633 b = pe->passed_pawns(Us);
637 Square s = pop_lsb(&b);
639 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
641 int r = relative_rank(Us, s);
643 Score bonus = PassedRank[r];
647 int w = (r-2) * (r-2) + 2;
648 Square blockSq = s + Up;
650 // Adjust bonus based on the king's proximity
651 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
652 - king_proximity(Us, blockSq) * 2) * w);
654 // If blockSq is not the queening square then consider also a second push
656 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
658 // If the pawn is free to advance, then increase the bonus
659 if (pos.empty(blockSq))
661 // If there is a rook or queen attacking/defending the pawn from behind,
662 // consider all the squaresToQueen. Otherwise consider only the squares
663 // in the pawn's path attacked or occupied by the enemy.
664 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
666 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
668 if (!(pos.pieces(Us) & bb))
669 defendedSquares &= attackedBy[Us][ALL_PIECES];
671 if (!(pos.pieces(Them) & bb))
672 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
674 // If there aren't any enemy attacks, assign a big bonus. Otherwise
675 // assign a smaller bonus if the block square isn't attacked.
676 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
678 // If the path to the queen is fully defended, assign a big bonus.
679 // Otherwise assign a smaller bonus if the block square is defended.
680 if (defendedSquares == squaresToQueen)
683 else if (defendedSquares & blockSq)
686 bonus += make_score(k * w, k * w);
690 // Scale down bonus for candidate passers which need more than one
691 // pawn push to become passed, or have a pawn in front of them.
692 if ( !pos.pawn_passed(Us, s + Up)
693 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
696 score += bonus + PassedFile[file_of(s)];
700 Trace::add(PASSED, Us, score);
706 // Evaluation::space() computes the space evaluation for a given side. The
707 // space evaluation is a simple bonus based on the number of safe squares
708 // available for minor pieces on the central four files on ranks 2--4. Safe
709 // squares one, two or three squares behind a friendly pawn are counted
710 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
711 // improve play on game opening.
713 template<Tracing T> template<Color Us>
714 Score Evaluation<T>::space() const {
716 if (pos.non_pawn_material() < SpaceThreshold)
719 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
720 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
721 constexpr Bitboard SpaceMask =
722 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
723 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
725 // Find the available squares for our pieces inside the area defined by SpaceMask
726 Bitboard safe = SpaceMask
727 & ~pos.pieces(Us, PAWN)
728 & ~attackedBy[Them][PAWN];
730 // Find all squares which are at most three squares behind some friendly pawn
731 Bitboard behind = pos.pieces(Us, PAWN);
732 behind |= shift<Down>(behind);
733 behind |= shift<Down>(shift<Down>(behind));
735 int bonus = popcount(safe) + popcount(behind & safe);
736 int weight = pos.count<ALL_PIECES>(Us)
737 - 2 * popcount(pe->semiopenFiles[WHITE] & pe->semiopenFiles[BLACK]);
739 Score score = make_score(bonus * weight * weight / 16, 0);
742 Trace::add(SPACE, Us, score);
748 // Evaluation::initiative() computes the initiative correction value
749 // for the position. It is a second order bonus/malus based on the
750 // known attacking/defending status of the players.
753 Score Evaluation<T>::initiative(Value eg) const {
755 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
756 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
758 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
759 && (pos.pieces(PAWN) & KingSide);
761 // Compute the initiative bonus for the attacking side
762 int complexity = 9 * pe->pawn_asymmetry()
763 + 11 * pos.count<PAWN>()
765 + 18 * pawnsOnBothFlanks
766 + 49 * !pos.non_pawn_material()
769 // Now apply the bonus: note that we find the attacking side by extracting
770 // the sign of the endgame value, and that we carefully cap the bonus so
771 // that the endgame score will never change sign after the bonus.
772 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
775 Trace::add(INITIATIVE, make_score(0, v));
777 return make_score(0, v);
781 // Evaluation::scale_factor() computes the scale factor for the winning side
784 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
786 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
787 int sf = me->scale_factor(pos, strongSide);
789 // If scale is not already specific, scale down the endgame via general heuristics
790 if (sf == SCALE_FACTOR_NORMAL)
792 if ( pos.opposite_bishops()
793 && pos.non_pawn_material(WHITE) == BishopValueMg
794 && pos.non_pawn_material(BLACK) == BishopValueMg)
795 sf = 8 + 4 * pe->pawn_asymmetry();
797 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
801 return ScaleFactor(sf);
805 // Evaluation::value() is the main function of the class. It computes the various
806 // parts of the evaluation and returns the value of the position from the point
807 // of view of the side to move.
810 Value Evaluation<T>::value() {
812 assert(!pos.checkers());
814 // Probe the material hash table
815 me = Material::probe(pos);
817 // If we have a specialized evaluation function for the current material
818 // configuration, call it and return.
819 if (me->specialized_eval_exists())
820 return me->evaluate(pos);
822 // Initialize score by reading the incrementally updated scores included in
823 // the position object (material + piece square tables) and the material
824 // imbalance. Score is computed internally from the white point of view.
825 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
827 // Probe the pawn hash table
828 pe = Pawns::probe(pos);
829 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
831 // Early exit if score is high
832 Value v = (mg_value(score) + eg_value(score)) / 2;
833 if (abs(v) > LazyThreshold)
834 return pos.side_to_move() == WHITE ? v : -v;
836 // Main evaluation begins here
841 // Pieces should be evaluated first (populate attack tables)
842 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
843 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
844 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
845 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
847 score += mobility[WHITE] - mobility[BLACK];
849 score += king< WHITE>() - king< BLACK>()
850 + threats<WHITE>() - threats<BLACK>()
851 + passed< WHITE>() - passed< BLACK>()
852 + space< WHITE>() - space< BLACK>();
854 score += initiative(eg_value(score));
856 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
857 ScaleFactor sf = scale_factor(eg_value(score));
858 v = mg_value(score) * int(me->game_phase())
859 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
861 v /= int(PHASE_MIDGAME);
863 // In case of tracing add all remaining individual evaluation terms
866 Trace::add(MATERIAL, pos.psq_score());
867 Trace::add(IMBALANCE, me->imbalance());
868 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
869 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
870 Trace::add(TOTAL, score);
873 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
880 /// evaluate() is the evaluator for the outer world. It returns a static
881 /// evaluation of the position from the point of view of the side to move.
883 Value Eval::evaluate(const Position& pos) {
884 return Evaluation<NO_TRACE>(pos).value();
888 /// trace() is like evaluate(), but instead of returning a value, it returns
889 /// a string (suitable for outputting to stdout) that contains the detailed
890 /// descriptions and values of each evaluation term. Useful for debugging.
892 std::string Eval::trace(const Position& pos) {
894 std::memset(scores, 0, sizeof(scores));
896 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
898 Value v = Evaluation<TRACE>(pos).value();
900 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
902 std::stringstream ss;
903 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
904 << " Term | White | Black | Total \n"
905 << " | MG EG | MG EG | MG EG \n"
906 << " ------------+-------------+-------------+------------\n"
907 << " Material | " << Term(MATERIAL)
908 << " Imbalance | " << Term(IMBALANCE)
909 << " Initiative | " << Term(INITIATIVE)
910 << " Pawns | " << Term(PAWN)
911 << " Knights | " << Term(KNIGHT)
912 << " Bishops | " << Term(BISHOP)
913 << " Rooks | " << Term(ROOK)
914 << " Queens | " << Term(QUEEN)
915 << " Mobility | " << Term(MOBILITY)
916 << " King safety | " << Term(KING)
917 << " Threats | " << Term(THREAT)
918 << " Passed | " << Term(PASSED)
919 << " Space | " << Term(SPACE)
920 << " ------------+-------------+-------------+------------\n"
921 << " Total | " << Term(TOTAL);
923 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";