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 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
121 // no (friendly) pawn on the rook file.
122 constexpr Score RookOnFile[] = { S(18, 7), S(44, 20) };
124 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
125 // which piece type attacks which one. Attacks on lesser pieces which are
126 // pawn-defended are not considered.
127 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
128 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
131 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
132 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(51, 38)
135 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
136 constexpr Score PassedRank[RANK_NB] = {
137 S(0, 0), S(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
140 // PassedFile[File] contains a bonus according to the file of a passed pawn
141 constexpr Score PassedFile[FILE_NB] = {
142 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
143 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
146 // Assorted bonuses and penalties
147 constexpr Score BishopPawns = S( 3, 7);
148 constexpr Score CorneredBishop = S( 50, 50);
149 constexpr Score FlankAttacks = S( 8, 0);
150 constexpr Score Hanging = S( 69, 36);
151 constexpr Score KingProtector = S( 7, 8);
152 constexpr Score KnightOnQueen = S( 16, 12);
153 constexpr Score LongDiagonalBishop = S( 45, 0);
154 constexpr Score MinorBehindPawn = S( 18, 3);
155 constexpr Score PawnlessFlank = S( 17, 95);
156 constexpr Score RestrictedPiece = S( 7, 7);
157 constexpr Score RookOnPawn = S( 10, 32);
158 constexpr Score SliderOnQueen = S( 59, 18);
159 constexpr Score ThreatByKing = S( 24, 89);
160 constexpr Score ThreatByPawnPush = S( 48, 39);
161 constexpr Score ThreatByRank = S( 13, 0);
162 constexpr Score ThreatBySafePawn = S(173, 94);
163 constexpr Score TrappedRook = S( 47, 4);
164 constexpr Score WeakQueen = S( 49, 15);
165 constexpr Score WeakUnopposedPawn = S( 12, 23);
166 constexpr Score Outpost = S( 9, 3);
170 // Evaluation class computes and stores attacks tables and other working data
175 Evaluation() = delete;
176 explicit Evaluation(const Position& p) : pos(p) {}
177 Evaluation& operator=(const Evaluation&) = delete;
181 template<Color Us> void initialize();
182 template<Color Us, PieceType Pt> Score pieces();
183 template<Color Us> Score king() const;
184 template<Color Us> Score threats() const;
185 template<Color Us> Score passed() const;
186 template<Color Us> Score space() const;
187 ScaleFactor scale_factor(Value eg) const;
188 Score initiative(Value eg) const;
193 Bitboard mobilityArea[COLOR_NB];
194 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
196 // attackedBy[color][piece type] is a bitboard representing all squares
197 // attacked by a given color and piece type. Special "piece types" which
198 // is also calculated is ALL_PIECES.
199 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
201 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
202 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
203 // pawn or squares attacked by 2 pawns are not explicitly added.
204 Bitboard attackedBy2[COLOR_NB];
206 // kingRing[color] are the squares adjacent to the king, plus (only for a
207 // king on its first rank) the squares two ranks in front. For instance,
208 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
210 Bitboard kingRing[COLOR_NB];
212 // kingAttackersCount[color] is the number of pieces of the given color
213 // which attack a square in the kingRing of the enemy king.
214 int kingAttackersCount[COLOR_NB];
216 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
217 // the given color which attack a square in the kingRing of the enemy king.
218 // The weights of the individual piece types are given by the elements in
219 // the KingAttackWeights array.
220 int kingAttackersWeight[COLOR_NB];
222 // kingAttacksCount[color] is the number of attacks by the given color to
223 // squares directly adjacent to the enemy king. Pieces which attack more
224 // than one square are counted multiple times. For instance, if there is
225 // a white knight on g5 and black's king is on g8, this white knight adds 2
226 // to kingAttacksCount[WHITE].
227 int kingAttacksCount[COLOR_NB];
231 // Evaluation::initialize() computes king and pawn attacks, and the king ring
232 // bitboard for a given color. This is done at the beginning of the evaluation.
233 template<Tracing T> template<Color Us>
234 void Evaluation<T>::initialize() {
236 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
237 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
238 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
239 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
241 const Square ksq = pos.square<KING>(Us);
243 // Find our pawns that are blocked or on the first two ranks
244 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
246 // Squares occupied by those pawns, by our king or queen or controlled by
247 // enemy pawns are excluded from the mobility area.
248 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
250 // Initialize attackedBy[] for king and pawns
251 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
252 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
253 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
254 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
256 // Init our king safety tables
257 kingRing[Us] = attackedBy[Us][KING];
258 if (relative_rank(Us, ksq) == RANK_1)
259 kingRing[Us] |= shift<Up>(kingRing[Us]);
261 if (file_of(ksq) == FILE_H)
262 kingRing[Us] |= shift<WEST>(kingRing[Us]);
264 else if (file_of(ksq) == FILE_A)
265 kingRing[Us] |= shift<EAST>(kingRing[Us]);
267 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
268 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
270 // Remove from kingRing[] the squares defended by two pawns
271 kingRing[Us] &= ~pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
275 // Evaluation::pieces() scores pieces of a given color and type
276 template<Tracing T> template<Color Us, PieceType Pt>
277 Score Evaluation<T>::pieces() {
279 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
280 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
281 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
282 : Rank5BB | Rank4BB | Rank3BB);
283 const Square* pl = pos.squares<Pt>(Us);
286 Score score = SCORE_ZERO;
288 attackedBy[Us][Pt] = 0;
290 for (Square s = *pl; s != SQ_NONE; s = *++pl)
292 // Find attacked squares, including x-ray attacks for bishops and rooks
293 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
294 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
295 : pos.attacks_from<Pt>(s);
297 if (pos.blockers_for_king(Us) & s)
298 b &= LineBB[pos.square<KING>(Us)][s];
300 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
301 attackedBy[Us][Pt] |= b;
302 attackedBy[Us][ALL_PIECES] |= b;
304 if (b & kingRing[Them])
306 kingAttackersCount[Us]++;
307 kingAttackersWeight[Us] += KingAttackWeights[Pt];
308 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
311 int mob = popcount(b & mobilityArea[Us]);
313 mobility[Us] += MobilityBonus[Pt - 2][mob];
315 if (Pt == BISHOP || Pt == KNIGHT)
317 // Bonus if piece is on an outpost square or can reach one
318 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
320 score += Outpost * (Pt == KNIGHT ? 4 : 2)
321 * (1 + bool(attackedBy[Us][PAWN] & s));
323 else if (bb &= b & ~pos.pieces(Us))
324 score += Outpost * (Pt == KNIGHT ? 2 : 1)
325 * (1 + bool(attackedBy[Us][PAWN] & bb));
327 // Knight and Bishop bonus for being right behind a pawn
328 if (shift<Down>(pos.pieces(PAWN)) & s)
329 score += MinorBehindPawn;
331 // Penalty if the piece is far from the king
332 score -= KingProtector * distance(s, pos.square<KING>(Us));
336 // Penalty according to number of pawns on the same color square as the
337 // bishop, bigger when the center files are blocked with pawns.
338 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
340 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
341 * (1 + popcount(blocked & CenterFiles));
343 // Bonus for bishop on a long diagonal which can "see" both center squares
344 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
345 score += LongDiagonalBishop;
348 // An important Chess960 pattern: A cornered bishop blocked by a friendly
349 // pawn diagonally in front of it is a very serious problem, especially
350 // when that pawn is also blocked.
353 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
355 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
356 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
357 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
358 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
365 // Bonus for aligning rook with enemy pawns on the same rank/file
366 if (relative_rank(Us, s) >= RANK_5)
367 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
369 // Bonus for rook on an open or semi-open file
370 if (pe->semiopen_file(Us, file_of(s)))
371 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
373 // Penalty when trapped by the king, even more if the king cannot castle
376 File kf = file_of(pos.square<KING>(Us));
377 if ((kf < FILE_E) == (file_of(s) < kf))
378 score -= TrappedRook * (1 + !pos.castling_rights(Us));
384 // Penalty if any relative pin or discovered attack against the queen
385 Bitboard queenPinners;
386 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
391 Trace::add(Pt, Us, score);
397 // Evaluation::king() assigns bonuses and penalties to a king of a given color
398 template<Tracing T> template<Color Us>
399 Score Evaluation<T>::king() const {
401 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
402 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
403 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
405 Bitboard weak, b, b1, b2, safe, unsafeChecks = 0;
407 const Square ksq = pos.square<KING>(Us);
409 // Init the score with king shelter and enemy pawns storm
410 Score score = pe->king_safety<Us>(pos);
412 // Attacked squares defended at most once by our queen or king
413 weak = attackedBy[Them][ALL_PIECES]
415 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
417 // Analyse the safe enemy's checks which are possible on next move
418 safe = ~pos.pieces(Them);
419 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
421 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
422 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
424 // Enemy rooks checks
425 Bitboard RookCheck = b1
427 & attackedBy[Them][ROOK];
430 kingDanger += RookSafeCheck;
432 unsafeChecks |= b1 & attackedBy[Them][ROOK];
434 // Enemy queen safe checks: we count them only if they are from squares from
435 // which we can't give a rook check, because rook checks are more valuable.
436 Bitboard QueenCheck = (b1 | b2)
437 & attackedBy[Them][QUEEN]
439 & ~attackedBy[Us][QUEEN]
443 kingDanger += QueenSafeCheck;
445 // Enemy bishops checks: we count them only if they are from squares from
446 // which we can't give a queen check, because queen checks are more valuable.
447 Bitboard BishopCheck = b2
448 & attackedBy[Them][BISHOP]
453 kingDanger += BishopSafeCheck;
455 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
457 // Enemy knights checks
458 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
461 kingDanger += KnightSafeCheck;
465 // Unsafe or occupied checking squares will also be considered, as long as
466 // the square is in the attacker's mobility area.
467 unsafeChecks &= mobilityArea[Them];
469 // Find the squares that opponent attacks in our king flank, and the squares
470 // which are attacked twice in that flank.
471 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
472 b2 = b1 & attackedBy2[Them];
474 int kingFlankAttacks = popcount(b1) + popcount(b2);
476 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
477 + 69 * kingAttacksCount[Them]
478 + 185 * popcount(kingRing[Us] & weak)
479 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
480 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
481 - 873 * !pos.count<QUEEN>(Them)
482 - 6 * mg_value(score) / 8
483 + mg_value(mobility[Them] - mobility[Us])
484 + 5 * kingFlankAttacks * kingFlankAttacks / 16
487 // Transform the kingDanger units into a Score, and subtract it from the evaluation
489 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
491 // Penalty when our king is on a pawnless flank
492 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
493 score -= PawnlessFlank;
495 // Penalty if king flank is under attack, potentially moving toward the king
496 score -= FlankAttacks * kingFlankAttacks;
499 Trace::add(KING, Us, score);
505 // Evaluation::threats() assigns bonuses according to the types of the
506 // attacking and the attacked pieces.
507 template<Tracing T> template<Color Us>
508 Score Evaluation<T>::threats() const {
510 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
511 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
512 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
514 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe, restricted;
515 Score score = SCORE_ZERO;
518 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
520 // Squares strongly protected by the enemy, either because they defend the
521 // square with a pawn, or because they defend the square twice and we don't.
522 stronglyProtected = attackedBy[Them][PAWN]
523 | (attackedBy2[Them] & ~attackedBy2[Us]);
525 // Non-pawn enemies, strongly protected
526 defended = nonPawnEnemies & stronglyProtected;
528 // Enemies not strongly protected and under our attack
529 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
531 // Safe or protected squares
532 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
534 // Bonus according to the kind of attacking pieces
537 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
540 Square s = pop_lsb(&b);
541 score += ThreatByMinor[type_of(pos.piece_on(s))];
542 if (type_of(pos.piece_on(s)) != PAWN)
543 score += ThreatByRank * (int)relative_rank(Them, s);
546 b = weak & attackedBy[Us][ROOK];
549 Square s = pop_lsb(&b);
550 score += ThreatByRook[type_of(pos.piece_on(s))];
551 if (type_of(pos.piece_on(s)) != PAWN)
552 score += ThreatByRank * (int)relative_rank(Them, s);
555 if (weak & attackedBy[Us][KING])
556 score += ThreatByKing;
558 b = ~attackedBy[Them][ALL_PIECES]
559 | (nonPawnEnemies & attackedBy2[Us]);
560 score += Hanging * popcount(weak & b);
563 // Bonus for restricting their piece moves
564 restricted = attackedBy[Them][ALL_PIECES]
566 & attackedBy[Us][ALL_PIECES];
567 score += RestrictedPiece * popcount(restricted);
569 // Bonus for enemy unopposed weak pawns
570 if (pos.pieces(Us, ROOK, QUEEN))
571 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
573 // Find squares where our pawns can push on the next move
574 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
575 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
577 // Keep only the squares which are relatively safe
578 b &= ~attackedBy[Them][PAWN] & safe;
580 // Bonus for safe pawn threats on the next move
581 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
582 score += ThreatByPawnPush * popcount(b);
584 // Our safe or protected pawns
585 b = pos.pieces(Us, PAWN) & safe;
587 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
588 score += ThreatBySafePawn * popcount(b);
590 // Bonus for threats on the next moves against enemy queen
591 if (pos.count<QUEEN>(Them) == 1)
593 Square s = pos.square<QUEEN>(Them);
594 safe = mobilityArea[Us] & ~stronglyProtected;
596 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
598 score += KnightOnQueen * popcount(b & safe);
600 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
601 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
603 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
607 Trace::add(THREAT, Us, score);
612 // Evaluation::passed() evaluates the passed pawns and candidate passed
613 // pawns of the given color.
615 template<Tracing T> template<Color Us>
616 Score Evaluation<T>::passed() const {
618 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
619 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
621 auto king_proximity = [&](Color c, Square s) {
622 return std::min(distance(pos.square<KING>(c), s), 5);
625 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
626 Score score = SCORE_ZERO;
628 b = pe->passed_pawns(Us);
632 Square s = pop_lsb(&b);
634 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
636 int r = relative_rank(Us, s);
638 Score bonus = PassedRank[r];
642 int w = (r-2) * (r-2) + 2;
643 Square blockSq = s + Up;
645 // Adjust bonus based on the king's proximity
646 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
647 - king_proximity(Us, blockSq) * 2) * w);
649 // If blockSq is not the queening square then consider also a second push
651 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
653 // If the pawn is free to advance, then increase the bonus
654 if (pos.empty(blockSq))
656 // If there is a rook or queen attacking/defending the pawn from behind,
657 // consider all the squaresToQueen. Otherwise consider only the squares
658 // in the pawn's path attacked or occupied by the enemy.
659 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
661 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
663 if (!(pos.pieces(Us) & bb))
664 defendedSquares &= attackedBy[Us][ALL_PIECES];
666 if (!(pos.pieces(Them) & bb))
667 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
669 // If there aren't any enemy attacks, assign a big bonus. Otherwise
670 // assign a smaller bonus if the block square isn't attacked.
671 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
673 // If the path to the queen is fully defended, assign a big bonus.
674 // Otherwise assign a smaller bonus if the block square is defended.
675 if (defendedSquares == squaresToQueen)
678 else if (defendedSquares & blockSq)
681 bonus += make_score(k * w, k * w);
685 // Scale down bonus for candidate passers which need more than one
686 // pawn push to become passed, or have a pawn in front of them.
687 if ( !pos.pawn_passed(Us, s + Up)
688 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
691 score += bonus + PassedFile[file_of(s)];
695 Trace::add(PASSED, Us, score);
701 // Evaluation::space() computes the space evaluation for a given side. The
702 // space evaluation is a simple bonus based on the number of safe squares
703 // available for minor pieces on the central four files on ranks 2--4. Safe
704 // squares one, two or three squares behind a friendly pawn are counted
705 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
706 // improve play on game opening.
708 template<Tracing T> template<Color Us>
709 Score Evaluation<T>::space() const {
711 if (pos.non_pawn_material() < SpaceThreshold)
714 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
715 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
716 constexpr Bitboard SpaceMask =
717 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
718 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
720 // Find the available squares for our pieces inside the area defined by SpaceMask
721 Bitboard safe = SpaceMask
722 & ~pos.pieces(Us, PAWN)
723 & ~attackedBy[Them][PAWN];
725 // Find all squares which are at most three squares behind some friendly pawn
726 Bitboard behind = pos.pieces(Us, PAWN);
727 behind |= shift<Down>(behind);
728 behind |= shift<Down>(shift<Down>(behind));
730 int bonus = popcount(safe) + popcount(behind & safe);
731 int weight = pos.count<ALL_PIECES>(Us)
732 - 2 * popcount(pe->semiopenFiles[WHITE] & pe->semiopenFiles[BLACK]);
734 Score score = make_score(bonus * weight * weight / 16, 0);
737 Trace::add(SPACE, Us, score);
743 // Evaluation::initiative() computes the initiative correction value
744 // for the position. It is a second order bonus/malus based on the
745 // known attacking/defending status of the players.
748 Score Evaluation<T>::initiative(Value eg) const {
750 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
751 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
753 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
754 && (pos.pieces(PAWN) & KingSide);
756 // Compute the initiative bonus for the attacking side
757 int complexity = 9 * pe->pawn_asymmetry()
758 + 11 * pos.count<PAWN>()
760 + 18 * pawnsOnBothFlanks
761 + 49 * !pos.non_pawn_material()
764 // Now apply the bonus: note that we find the attacking side by extracting
765 // the sign of the endgame value, and that we carefully cap the bonus so
766 // that the endgame score will never change sign after the bonus.
767 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
770 Trace::add(INITIATIVE, make_score(0, v));
772 return make_score(0, v);
776 // Evaluation::scale_factor() computes the scale factor for the winning side
779 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
781 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
782 int sf = me->scale_factor(pos, strongSide);
784 // If scale is not already specific, scale down the endgame via general heuristics
785 if (sf == SCALE_FACTOR_NORMAL)
787 if ( pos.opposite_bishops()
788 && pos.non_pawn_material(WHITE) == BishopValueMg
789 && pos.non_pawn_material(BLACK) == BishopValueMg)
790 sf = 8 + 4 * pe->pawn_asymmetry();
792 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
796 return ScaleFactor(sf);
800 // Evaluation::value() is the main function of the class. It computes the various
801 // parts of the evaluation and returns the value of the position from the point
802 // of view of the side to move.
805 Value Evaluation<T>::value() {
807 assert(!pos.checkers());
809 // Probe the material hash table
810 me = Material::probe(pos);
812 // If we have a specialized evaluation function for the current material
813 // configuration, call it and return.
814 if (me->specialized_eval_exists())
815 return me->evaluate(pos);
817 // Initialize score by reading the incrementally updated scores included in
818 // the position object (material + piece square tables) and the material
819 // imbalance. Score is computed internally from the white point of view.
820 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
822 // Probe the pawn hash table
823 pe = Pawns::probe(pos);
824 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
826 // Early exit if score is high
827 Value v = (mg_value(score) + eg_value(score)) / 2;
828 if (abs(v) > LazyThreshold)
829 return pos.side_to_move() == WHITE ? v : -v;
831 // Main evaluation begins here
836 // Pieces should be evaluated first (populate attack tables)
837 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
838 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
839 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
840 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
842 score += mobility[WHITE] - mobility[BLACK];
844 score += king< WHITE>() - king< BLACK>()
845 + threats<WHITE>() - threats<BLACK>()
846 + passed< WHITE>() - passed< BLACK>()
847 + space< WHITE>() - space< BLACK>();
849 score += initiative(eg_value(score));
851 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
852 ScaleFactor sf = scale_factor(eg_value(score));
853 v = mg_value(score) * int(me->game_phase())
854 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
858 // In case of tracing add all remaining individual evaluation terms
861 Trace::add(MATERIAL, pos.psq_score());
862 Trace::add(IMBALANCE, me->imbalance());
863 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
864 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
865 Trace::add(TOTAL, score);
868 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
875 /// evaluate() is the evaluator for the outer world. It returns a static
876 /// evaluation of the position from the point of view of the side to move.
878 Value Eval::evaluate(const Position& pos) {
879 return Evaluation<NO_TRACE>(pos).value();
883 /// trace() is like evaluate(), but instead of returning a value, it returns
884 /// a string (suitable for outputting to stdout) that contains the detailed
885 /// descriptions and values of each evaluation term. Useful for debugging.
887 std::string Eval::trace(const Position& pos) {
889 std::memset(scores, 0, sizeof(scores));
891 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
893 Value v = Evaluation<TRACE>(pos).value();
895 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
897 std::stringstream ss;
898 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
899 << " Term | White | Black | Total \n"
900 << " | MG EG | MG EG | MG EG \n"
901 << " ------------+-------------+-------------+------------\n"
902 << " Material | " << Term(MATERIAL)
903 << " Imbalance | " << Term(IMBALANCE)
904 << " Initiative | " << Term(INITIATIVE)
905 << " Pawns | " << Term(PAWN)
906 << " Knights | " << Term(KNIGHT)
907 << " Bishops | " << Term(BISHOP)
908 << " Rooks | " << Term(ROOK)
909 << " Queens | " << Term(QUEEN)
910 << " Mobility | " << Term(MOBILITY)
911 << " King safety | " << Term(KING)
912 << " Threats | " << Term(THREAT)
913 << " Passed | " << Term(PASSED)
914 << " Space | " << Term(SPACE)
915 << " ------------+-------------+-------------+------------\n"
916 << " Total | " << Term(TOTAL);
918 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";