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) 2015-2020 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, WINNABLE, 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 == WINNABLE || 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 // Threshold for lazy and space evaluation
77 constexpr Value LazyThreshold = Value(1400);
78 constexpr Value SpaceThreshold = Value(12222);
80 // KingAttackWeights[PieceType] contains king attack weights by piece type
81 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
83 // SafeCheck[PieceType][single/multiple] contains safe check bonus by piece type,
84 // higher if multiple safe checks are possible for that piece type.
85 constexpr int SafeCheck[][2] = {
86 {}, {}, {792, 1283}, {645, 967}, {1084, 1897}, {772, 1119}
89 #define S(mg, eg) make_score(mg, eg)
91 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
92 // indexed by piece type and number of attacked squares in the mobility area.
93 constexpr Score MobilityBonus[][32] = {
94 { S(-62,-81), S(-53,-56), S(-12,-31), S( -4,-16), S( 3, 5), S( 13, 11), // Knight
95 S( 22, 17), S( 28, 20), S( 33, 25) },
96 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishop
97 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
98 S( 91, 88), S( 98, 97) },
99 { S(-60,-78), S(-20,-17), S( 2, 23), S( 3, 39), S( 3, 70), S( 11, 99), // Rook
100 S( 22,103), S( 31,121), S( 40,134), S( 40,139), S( 41,158), S( 48,164),
101 S( 57,168), S( 57,169), S( 62,172) },
102 { S(-30,-48), S(-12,-30), S( -8, -7), S( -9, 19), S( 20, 40), S( 23, 55), // Queen
103 S( 23, 59), S( 35, 75), S( 38, 78), S( 53, 96), S( 64, 96), S( 65,100),
104 S( 65,121), S( 66,127), S( 67,131), S( 67,133), S( 72,136), S( 72,141),
105 S( 77,147), S( 79,150), S( 93,151), S(108,168), S(108,168), S(108,171),
106 S(110,182), S(114,182), S(114,192), S(116,219) }
109 // KingProtector[knight/bishop] contains penalty for each distance unit to own king
110 constexpr Score KingProtector[] = { S(8, 9), S(6, 9) };
112 // Outpost[knight/bishop] contains bonuses for each knight or bishop occupying a
113 // pawn protected square on rank 4 to 6 which is also safe from a pawn attack.
114 constexpr Score Outpost[] = { S(56, 36), S(30, 23) };
116 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
117 constexpr Score PassedRank[RANK_NB] = {
118 S(0, 0), S(10, 28), S(17, 33), S(15, 41), S(62, 72), S(168, 177), S(276, 260)
121 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
122 // no (friendly) pawn on the rook file.
123 constexpr Score RookOnFile[] = { S(19, 7), S(48, 29) };
125 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
126 // which piece type attacks which one. Attacks on lesser pieces which are
127 // pawn-defended are not considered.
128 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
129 S(0, 0), S(5, 32), S(57, 41), S(77, 56), S(88, 119), S(79, 161)
132 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
133 S(0, 0), S(3, 46), S(37, 68), S(42, 60), S(0, 38), S(58, 41)
136 // Assorted bonuses and penalties
137 constexpr Score BishopOnKingRing = S( 24, 0);
138 constexpr Score BishopPawns = S( 3, 7);
139 constexpr Score BishopXRayPawns = S( 4, 5);
140 constexpr Score CorneredBishop = S( 50, 50);
141 constexpr Score FlankAttacks = S( 8, 0);
142 constexpr Score Hanging = S( 69, 36);
143 constexpr Score KnightOnQueen = S( 16, 11);
144 constexpr Score LongDiagonalBishop = S( 45, 0);
145 constexpr Score MinorBehindPawn = S( 18, 3);
146 constexpr Score PassedFile = S( 11, 8);
147 constexpr Score PawnlessFlank = S( 17, 95);
148 constexpr Score QueenInfiltration = S( -2, 14);
149 constexpr Score ReachableOutpost = S( 31, 22);
150 constexpr Score RestrictedPiece = S( 7, 7);
151 constexpr Score RookOnKingRing = S( 16, 0);
152 constexpr Score RookOnQueenFile = S( 6, 11);
153 constexpr Score SliderOnQueen = S( 60, 18);
154 constexpr Score ThreatByKing = S( 24, 89);
155 constexpr Score ThreatByPawnPush = S( 48, 39);
156 constexpr Score ThreatBySafePawn = S(173, 94);
157 constexpr Score TrappedRook = S( 55, 13);
158 constexpr Score WeakQueenProtection = S( 14, 0);
159 constexpr Score WeakQueen = S( 56, 15);
164 // Evaluation class computes and stores attacks tables and other working data
169 Evaluation() = delete;
170 explicit Evaluation(const Position& p) : pos(p) {}
171 Evaluation& operator=(const Evaluation&) = delete;
175 template<Color Us> void initialize();
176 template<Color Us, PieceType Pt> Score pieces();
177 template<Color Us> Score king() const;
178 template<Color Us> Score threats() const;
179 template<Color Us> Score passed() const;
180 template<Color Us> Score space() const;
181 Value winnable(Score score) const;
186 Bitboard mobilityArea[COLOR_NB];
187 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
189 // attackedBy[color][piece type] is a bitboard representing all squares
190 // attacked by a given color and piece type. Special "piece types" which
191 // is also calculated is ALL_PIECES.
192 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
194 // attackedBy2[color] are the squares attacked by at least 2 units of a given
195 // color, including x-rays. But diagonal x-rays through pawns are not computed.
196 Bitboard attackedBy2[COLOR_NB];
198 // kingRing[color] are the squares adjacent to the king plus some other
199 // very near squares, depending on king position.
200 Bitboard kingRing[COLOR_NB];
202 // kingAttackersCount[color] is the number of pieces of the given color
203 // which attack a square in the kingRing of the enemy king.
204 int kingAttackersCount[COLOR_NB];
206 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
207 // the given color which attack a square in the kingRing of the enemy king.
208 // The weights of the individual piece types are given by the elements in
209 // the KingAttackWeights array.
210 int kingAttackersWeight[COLOR_NB];
212 // kingAttacksCount[color] is the number of attacks by the given color to
213 // squares directly adjacent to the enemy king. Pieces which attack more
214 // than one square are counted multiple times. For instance, if there is
215 // a white knight on g5 and black's king is on g8, this white knight adds 2
216 // to kingAttacksCount[WHITE].
217 int kingAttacksCount[COLOR_NB];
221 // Evaluation::initialize() computes king and pawn attacks, and the king ring
222 // bitboard for a given color. This is done at the beginning of the evaluation.
224 template<Tracing T> template<Color Us>
225 void Evaluation<T>::initialize() {
227 constexpr Color Them = ~Us;
228 constexpr Direction Up = pawn_push(Us);
229 constexpr Direction Down = -Up;
230 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
232 const Square ksq = pos.square<KING>(Us);
234 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
236 // Find our pawns that are blocked or on the first two ranks
237 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
239 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
240 // or controlled by enemy pawns are excluded from the mobility area.
241 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
243 // Initialize attackedBy[] for king and pawns
244 attackedBy[Us][KING] = attacks_bb<KING>(ksq);
245 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
246 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
247 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
249 // Init our king safety tables
250 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
251 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
252 kingRing[Us] = attacks_bb<KING>(s) | s;
254 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
255 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
257 // Remove from kingRing[] the squares defended by two pawns
258 kingRing[Us] &= ~dblAttackByPawn;
262 // Evaluation::pieces() scores pieces of a given color and type
264 template<Tracing T> template<Color Us, PieceType Pt>
265 Score Evaluation<T>::pieces() {
267 constexpr Color Them = ~Us;
268 constexpr Direction Down = -pawn_push(Us);
269 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
270 : Rank5BB | Rank4BB | Rank3BB);
271 const Square* pl = pos.squares<Pt>(Us);
274 Score score = SCORE_ZERO;
276 attackedBy[Us][Pt] = 0;
278 for (Square s = *pl; s != SQ_NONE; s = *++pl)
280 // Find attacked squares, including x-ray attacks for bishops and rooks
281 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
282 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
283 : attacks_bb<Pt>(s, pos.pieces());
285 if (pos.blockers_for_king(Us) & s)
286 b &= line_bb(pos.square<KING>(Us), s);
288 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
289 attackedBy[Us][Pt] |= b;
290 attackedBy[Us][ALL_PIECES] |= b;
292 if (b & kingRing[Them])
294 kingAttackersCount[Us]++;
295 kingAttackersWeight[Us] += KingAttackWeights[Pt];
296 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
299 else if (Pt == ROOK && (file_bb(s) & kingRing[Them]))
300 score += RookOnKingRing;
302 else if (Pt == BISHOP && (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & kingRing[Them]))
303 score += BishopOnKingRing;
305 int mob = popcount(b & mobilityArea[Us]);
307 mobility[Us] += MobilityBonus[Pt - 2][mob];
309 if (Pt == BISHOP || Pt == KNIGHT)
311 // Bonus if piece is on an outpost square or can reach one
312 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
314 score += Outpost[Pt == BISHOP];
315 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
316 score += ReachableOutpost;
318 // Bonus for a knight or bishop shielded by pawn
319 if (shift<Down>(pos.pieces(PAWN)) & s)
320 score += MinorBehindPawn;
322 // Penalty if the piece is far from the king
323 score -= KingProtector[Pt == BISHOP] * distance(pos.square<KING>(Us), s);
327 // Penalty according to the number of our pawns on the same color square as the
328 // bishop, bigger when the center files are blocked with pawns and smaller
329 // when the bishop is outside the pawn chain.
330 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
332 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
333 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
335 // Penalty for all enemy pawns x-rayed
336 score -= BishopXRayPawns * popcount(attacks_bb<BISHOP>(s) & pos.pieces(Them, PAWN));
338 // Bonus for bishop on a long diagonal which can "see" both center squares
339 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
340 score += LongDiagonalBishop;
342 // An important Chess960 pattern: a cornered bishop blocked by a friendly
343 // pawn diagonally in front of it is a very serious problem, especially
344 // when that pawn is also blocked.
345 if ( pos.is_chess960()
346 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
348 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
349 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
350 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
351 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
359 // Bonus for rook on the same file as a queen
360 if (file_bb(s) & pos.pieces(QUEEN))
361 score += RookOnQueenFile;
363 // Bonus for rook on an open or semi-open file
364 if (pos.is_on_semiopen_file(Us, s))
365 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
367 // Penalty when trapped by the king, even more if the king cannot castle
370 File kf = file_of(pos.square<KING>(Us));
371 if ((kf < FILE_E) == (file_of(s) < kf))
372 score -= TrappedRook * (1 + !pos.castling_rights(Us));
378 // Penalty if any relative pin or discovered attack against the queen
379 Bitboard queenPinners;
380 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
383 // Bonus for queen on weak square in enemy camp
384 if (relative_rank(Us, s) > RANK_4 && (~pe->pawn_attacks_span(Them) & s))
385 score += QueenInfiltration;
389 Trace::add(Pt, Us, score);
395 // Evaluation::king() assigns bonuses and penalties to a king of a given color
397 template<Tracing T> template<Color Us>
398 Score Evaluation<T>::king() const {
400 constexpr Color Them = ~Us;
401 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
402 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
404 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
405 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
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 rookChecks = b1 & attackedBy[Them][ROOK] & safe;
427 kingDanger += SafeCheck[ROOK][more_than_one(rookChecks)];
429 unsafeChecks |= b1 & attackedBy[Them][ROOK];
431 // Enemy queen safe checks: count them only if the checks are from squares from
432 // which opponent cannot give a rook check, because rook checks are more valuable.
433 queenChecks = (b1 | b2) & attackedBy[Them][QUEEN] & safe
434 & ~(attackedBy[Us][QUEEN] | rookChecks);
436 kingDanger += SafeCheck[QUEEN][more_than_one(queenChecks)];
438 // Enemy bishops checks: count them only if they are from squares from which
439 // opponent cannot give a queen check, because queen checks are more valuable.
440 bishopChecks = b2 & attackedBy[Them][BISHOP] & safe
443 kingDanger += SafeCheck[BISHOP][more_than_one(bishopChecks)];
446 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
448 // Enemy knights checks
449 knightChecks = attacks_bb<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
450 if (knightChecks & safe)
451 kingDanger += SafeCheck[KNIGHT][more_than_one(knightChecks & safe)];
453 unsafeChecks |= knightChecks;
455 // Find the squares that opponent attacks in our king flank, the squares
456 // which they attack twice in that flank, and the squares that we defend.
457 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
458 b2 = b1 & attackedBy2[Them];
459 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
461 int kingFlankAttack = popcount(b1) + popcount(b2);
462 int kingFlankDefense = popcount(b3);
464 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
465 + 185 * popcount(kingRing[Us] & weak)
466 + 148 * popcount(unsafeChecks)
467 + 98 * popcount(pos.blockers_for_king(Us))
468 + 69 * kingAttacksCount[Them]
469 + 3 * kingFlankAttack * kingFlankAttack / 8
470 + mg_value(mobility[Them] - mobility[Us])
471 - 873 * !pos.count<QUEEN>(Them)
472 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
473 - 6 * mg_value(score) / 8
474 - 4 * kingFlankDefense
477 // Transform the kingDanger units into a Score, and subtract it from the evaluation
478 if (kingDanger > 100)
479 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
481 // Penalty when our king is on a pawnless flank
482 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
483 score -= PawnlessFlank;
485 // Penalty if king flank is under attack, potentially moving toward the king
486 score -= FlankAttacks * kingFlankAttack;
489 Trace::add(KING, Us, score);
495 // Evaluation::threats() assigns bonuses according to the types of the
496 // attacking and the attacked pieces.
498 template<Tracing T> template<Color Us>
499 Score Evaluation<T>::threats() const {
501 constexpr Color Them = ~Us;
502 constexpr Direction Up = pawn_push(Us);
503 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
505 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
506 Score score = SCORE_ZERO;
509 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
511 // Squares strongly protected by the enemy, either because they defend the
512 // square with a pawn, or because they defend the square twice and we don't.
513 stronglyProtected = attackedBy[Them][PAWN]
514 | (attackedBy2[Them] & ~attackedBy2[Us]);
516 // Non-pawn enemies, strongly protected
517 defended = nonPawnEnemies & stronglyProtected;
519 // Enemies not strongly protected and under our attack
520 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
522 // Bonus according to the kind of attacking pieces
525 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
527 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
529 b = weak & attackedBy[Us][ROOK];
531 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
533 if (weak & attackedBy[Us][KING])
534 score += ThreatByKing;
536 b = ~attackedBy[Them][ALL_PIECES]
537 | (nonPawnEnemies & attackedBy2[Us]);
538 score += Hanging * popcount(weak & b);
540 // Additional bonus if weak piece is only protected by a queen
541 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
544 // Bonus for restricting their piece moves
545 b = attackedBy[Them][ALL_PIECES]
547 & attackedBy[Us][ALL_PIECES];
548 score += RestrictedPiece * popcount(b);
550 // Protected or unattacked squares
551 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
553 // Bonus for attacking enemy pieces with our relatively safe pawns
554 b = pos.pieces(Us, PAWN) & safe;
555 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
556 score += ThreatBySafePawn * popcount(b);
558 // Find squares where our pawns can push on the next move
559 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
560 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
562 // Keep only the squares which are relatively safe
563 b &= ~attackedBy[Them][PAWN] & safe;
565 // Bonus for safe pawn threats on the next move
566 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
567 score += ThreatByPawnPush * popcount(b);
569 // Bonus for threats on the next moves against enemy queen
570 if (pos.count<QUEEN>(Them) == 1)
572 Square s = pos.square<QUEEN>(Them);
573 safe = mobilityArea[Us] & ~stronglyProtected;
575 b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
577 score += KnightOnQueen * popcount(b & safe);
579 b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
580 | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
582 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
586 Trace::add(THREAT, Us, score);
591 // Evaluation::passed() evaluates the passed pawns and candidate passed
592 // pawns of the given color.
594 template<Tracing T> template<Color Us>
595 Score Evaluation<T>::passed() const {
597 constexpr Color Them = ~Us;
598 constexpr Direction Up = pawn_push(Us);
599 constexpr Direction Down = -Up;
601 auto king_proximity = [&](Color c, Square s) {
602 return std::min(distance(pos.square<KING>(c), s), 5);
605 Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
606 Score score = SCORE_ZERO;
608 b = pe->passed_pawns(Us);
610 blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
613 helpers = shift<Up>(pos.pieces(Us, PAWN))
615 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
617 // Remove blocked candidate passers that don't have help to pass
619 | shift<WEST>(helpers)
620 | shift<EAST>(helpers);
625 Square s = pop_lsb(&b);
627 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
629 int r = relative_rank(Us, s);
631 Score bonus = PassedRank[r];
636 Square blockSq = s + Up;
638 // Adjust bonus based on the king's proximity
639 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
640 - king_proximity(Us, blockSq) * 2) * w);
642 // If blockSq is not the queening square then consider also a second push
644 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
646 // If the pawn is free to advance, then increase the bonus
647 if (pos.empty(blockSq))
649 squaresToQueen = forward_file_bb(Us, s);
650 unsafeSquares = passed_pawn_span(Us, s);
652 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
654 if (!(pos.pieces(Them) & bb))
655 unsafeSquares &= attackedBy[Them][ALL_PIECES];
657 // If there are no enemy attacks on passed pawn span, assign a big bonus.
658 // Otherwise assign a smaller bonus if the path to queen is not attacked
659 // and even smaller bonus if it is attacked but block square is not.
660 int k = !unsafeSquares ? 35 :
661 !(unsafeSquares & squaresToQueen) ? 20 :
662 !(unsafeSquares & blockSq) ? 9 :
665 // Assign a larger bonus if the block square is defended
666 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
669 bonus += make_score(k * w, k * w);
673 score += bonus - PassedFile * edge_distance(file_of(s));
677 Trace::add(PASSED, Us, score);
683 // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
684 // play in the opening. It is based on the number of safe squares on the 4 central files
685 // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
686 // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
688 template<Tracing T> template<Color Us>
689 Score Evaluation<T>::space() const {
691 // Early exit if, for example, both queens or 6 minor pieces have been exchanged
692 if (pos.non_pawn_material() < SpaceThreshold)
695 constexpr Color Them = ~Us;
696 constexpr Direction Down = -pawn_push(Us);
697 constexpr Bitboard SpaceMask =
698 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
699 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
701 // Find the available squares for our pieces inside the area defined by SpaceMask
702 Bitboard safe = SpaceMask
703 & ~pos.pieces(Us, PAWN)
704 & ~attackedBy[Them][PAWN];
706 // Find all squares which are at most three squares behind some friendly pawn
707 Bitboard behind = pos.pieces(Us, PAWN);
708 behind |= shift<Down>(behind);
709 behind |= shift<Down+Down>(behind);
711 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
712 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
713 Score score = make_score(bonus * weight * weight / 16, 0);
716 Trace::add(SPACE, Us, score);
722 // Evaluation::winnable() adjusts the mg and eg score components based on the
723 // known attacking/defending status of the players. A single value is derived
724 // by interpolation from the mg and eg values and returned.
727 Value Evaluation<T>::winnable(Score score) const {
729 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
730 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
732 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
733 && (pos.pieces(PAWN) & KingSide);
735 bool almostUnwinnable = outflanking < 0
736 && !pawnsOnBothFlanks;
738 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
739 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
741 // Compute the initiative bonus for the attacking side
742 int complexity = 9 * pe->passed_count()
743 + 12 * pos.count<PAWN>()
745 + 21 * pawnsOnBothFlanks
747 + 51 * !pos.non_pawn_material()
748 - 43 * almostUnwinnable
751 Value mg = mg_value(score);
752 Value eg = eg_value(score);
754 // Now apply the bonus: note that we find the attacking side by extracting the
755 // sign of the midgame or endgame values, and that we carefully cap the bonus
756 // so that the midgame and endgame scores do not change sign after the bonus.
757 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
758 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
763 // Compute the scale factor for the winning side
764 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
765 int sf = me->scale_factor(pos, strongSide);
767 // If scale is not already specific, scale down the endgame via general heuristics
768 if (sf == SCALE_FACTOR_NORMAL)
770 if (pos.opposite_bishops())
772 if ( pos.non_pawn_material(WHITE) == BishopValueMg
773 && pos.non_pawn_material(BLACK) == BishopValueMg)
774 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
776 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
778 else if ( pos.non_pawn_material(WHITE) == RookValueMg
779 && pos.non_pawn_material(BLACK) == RookValueMg
780 && pos.count<PAWN>(strongSide) - pos.count<PAWN>(~strongSide) <= 1
781 && bool(KingSide & pos.pieces(strongSide, PAWN)) != bool(QueenSide & pos.pieces(strongSide, PAWN))
782 && (attacks_bb<KING>(pos.square<KING>(~strongSide)) & pos.pieces(~strongSide, PAWN)))
784 else if (pos.count<QUEEN>() == 1)
785 sf = 37 + 3 * (pos.count<QUEEN>(WHITE) == 1 ? pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK)
786 : pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE));
788 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
791 // Interpolate between the middlegame and (scaled by 'sf') endgame score
792 v = mg * int(me->game_phase())
793 + eg * int(PHASE_MIDGAME - me->game_phase()) * ScaleFactor(sf) / SCALE_FACTOR_NORMAL;
798 Trace::add(WINNABLE, make_score(u, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL - eg_value(score)));
799 Trace::add(TOTAL, make_score(mg, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL));
806 // Evaluation::value() is the main function of the class. It computes the various
807 // parts of the evaluation and returns the value of the position from the point
808 // of view of the side to move.
811 Value Evaluation<T>::value() {
813 assert(!pos.checkers());
815 // Probe the material hash table
816 me = Material::probe(pos);
818 // If we have a specialized evaluation function for the current material
819 // configuration, call it and return.
820 if (me->specialized_eval_exists())
821 return me->evaluate(pos);
823 // Initialize score by reading the incrementally updated scores included in
824 // the position object (material + piece square tables) and the material
825 // imbalance. Score is computed internally from the white point of view.
826 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
828 // Probe the pawn hash table
829 pe = Pawns::probe(pos);
830 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
832 // Early exit if score is high
833 Value v = (mg_value(score) + eg_value(score)) / 2;
834 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
835 return pos.side_to_move() == WHITE ? v : -v;
837 // Main evaluation begins here
841 // Pieces evaluated first (also populates attackedBy, attackedBy2).
842 // Note that the order of evaluation of the terms is left unspecified.
843 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
844 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
845 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
846 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
848 score += mobility[WHITE] - mobility[BLACK];
850 // More complex interactions that require fully populated attack bitboards
851 score += king< WHITE>() - king< BLACK>()
852 + threats<WHITE>() - threats<BLACK>()
853 + passed< WHITE>() - passed< BLACK>()
854 + space< WHITE>() - space< BLACK>();
856 // Derive single value from mg and eg parts of score
859 // In case of tracing add all remaining individual evaluation terms
862 Trace::add(MATERIAL, pos.psq_score());
863 Trace::add(IMBALANCE, me->imbalance());
864 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
865 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
871 // Side to move point of view
872 v = (pos.side_to_move() == WHITE ? v : -v) + Tempo;
874 // Damp down the evaluation linearly when shuffling
875 v = v * (100 - pos.rule50_count()) / 100;
883 /// evaluate() is the evaluator for the outer world. It returns a static
884 /// evaluation of the position from the point of view of the side to move.
886 Value Eval::evaluate(const Position& pos) {
887 return Evaluation<NO_TRACE>(pos).value();
891 /// trace() is like evaluate(), but instead of returning a value, it returns
892 /// a string (suitable for outputting to stdout) that contains the detailed
893 /// descriptions and values of each evaluation term. Useful for debugging.
895 std::string Eval::trace(const Position& pos) {
898 return "Total evaluation: none (in check)";
900 std::memset(scores, 0, sizeof(scores));
902 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
904 Value v = Evaluation<TRACE>(pos).value();
906 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
908 std::stringstream ss;
909 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
910 << " Term | White | Black | Total \n"
911 << " | MG EG | MG EG | MG EG \n"
912 << " ------------+-------------+-------------+------------\n"
913 << " Material | " << Term(MATERIAL)
914 << " Imbalance | " << Term(IMBALANCE)
915 << " Pawns | " << Term(PAWN)
916 << " Knights | " << Term(KNIGHT)
917 << " Bishops | " << Term(BISHOP)
918 << " Rooks | " << Term(ROOK)
919 << " Queens | " << Term(QUEEN)
920 << " Mobility | " << Term(MOBILITY)
921 << " King safety | " << Term(KING)
922 << " Threats | " << Term(THREAT)
923 << " Passed | " << Term(PASSED)
924 << " Space | " << Term(SPACE)
925 << " Winnable | " << Term(WINNABLE)
926 << " ------------+-------------+-------------+------------\n"
927 << " Total | " << Term(TOTAL);
929 ss << "\nFinal evaluation: " << to_cp(v) << " (white side)\n";