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, 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 // 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 // Penalties for enemy's safe checks
84 constexpr int QueenSafeCheck = 772;
85 constexpr int RookSafeCheck = 1084;
86 constexpr int BishopSafeCheck = 645;
87 constexpr int KnightSafeCheck = 792;
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 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
110 // no (friendly) pawn on the rook file.
111 constexpr Score RookOnFile[] = { S(19, 7), S(48, 29) };
113 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
114 // which piece type attacks which one. Attacks on lesser pieces which are
115 // pawn-defended are not considered.
116 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
117 S(0, 0), S(5, 32), S(57, 41), S(77, 56), S(88, 119), S(79, 161)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(3, 46), S(37, 68), S(42, 60), S(0, 38), S(58, 41)
124 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
125 constexpr Score PassedRank[RANK_NB] = {
126 S(0, 0), S(10, 28), S(17, 33), S(15, 41), S(62, 72), S(168, 177), S(276, 260)
129 // Assorted bonuses and penalties
130 constexpr Score BishopPawns = S( 3, 7);
131 constexpr Score BishopOnKingRing = S( 24, 0);
132 constexpr Score BishopXRayPawns = S( 4, 5);
133 constexpr Score CorneredBishop = S( 50, 50);
134 constexpr Score FlankAttacks = S( 8, 0);
135 constexpr Score Hanging = S( 69, 36);
136 constexpr Score BishopKingProtector = S( 6, 9);
137 constexpr Score KnightKingProtector = S( 8, 9);
138 constexpr Score KnightOnQueen = S( 16, 11);
139 constexpr Score LongDiagonalBishop = S( 45, 0);
140 constexpr Score MinorBehindPawn = S( 18, 3);
141 constexpr Score KnightOutpost = S( 56, 36);
142 constexpr Score BishopOutpost = S( 30, 23);
143 constexpr Score ReachableOutpost = S( 31, 22);
144 constexpr Score PassedFile = S( 11, 8);
145 constexpr Score PawnlessFlank = S( 17, 95);
146 constexpr Score RestrictedPiece = S( 7, 7);
147 constexpr Score RookOnKingRing = S( 16, 0);
148 constexpr Score RookOnQueenFile = S( 5, 9);
149 constexpr Score SliderOnQueen = S( 59, 18);
150 constexpr Score ThreatByKing = S( 24, 89);
151 constexpr Score ThreatByPawnPush = S( 48, 39);
152 constexpr Score ThreatBySafePawn = S(173, 94);
153 constexpr Score TrappedRook = S( 55, 13);
154 constexpr Score WeakQueen = S( 51, 14);
155 constexpr Score WeakQueenProtection = S( 15, 0);
159 // Evaluation class computes and stores attacks tables and other working data
164 Evaluation() = delete;
165 explicit Evaluation(const Position& p) : pos(p) {}
166 Evaluation& operator=(const Evaluation&) = delete;
170 template<Color Us> void initialize();
171 template<Color Us, PieceType Pt> Score pieces();
172 template<Color Us> Score king() const;
173 template<Color Us> Score threats() const;
174 template<Color Us> Score passed() const;
175 template<Color Us> Score space() const;
176 ScaleFactor scale_factor(Value eg) const;
177 Score initiative(Score score) const;
182 Bitboard mobilityArea[COLOR_NB];
183 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
185 // attackedBy[color][piece type] is a bitboard representing all squares
186 // attacked by a given color and piece type. Special "piece types" which
187 // is also calculated is ALL_PIECES.
188 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
190 // attackedBy2[color] are the squares attacked by at least 2 units of a given
191 // color, including x-rays. But diagonal x-rays through pawns are not computed.
192 Bitboard attackedBy2[COLOR_NB];
194 // kingRing[color] are the squares adjacent to the king plus some other
195 // very near squares, depending on king position.
196 Bitboard kingRing[COLOR_NB];
198 // kingAttackersCount[color] is the number of pieces of the given color
199 // which attack a square in the kingRing of the enemy king.
200 int kingAttackersCount[COLOR_NB];
202 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
203 // the given color which attack a square in the kingRing of the enemy king.
204 // The weights of the individual piece types are given by the elements in
205 // the KingAttackWeights array.
206 int kingAttackersWeight[COLOR_NB];
208 // kingAttacksCount[color] is the number of attacks by the given color to
209 // squares directly adjacent to the enemy king. Pieces which attack more
210 // than one square are counted multiple times. For instance, if there is
211 // a white knight on g5 and black's king is on g8, this white knight adds 2
212 // to kingAttacksCount[WHITE].
213 int kingAttacksCount[COLOR_NB];
217 // Evaluation::initialize() computes king and pawn attacks, and the king ring
218 // bitboard for a given color. This is done at the beginning of the evaluation.
219 template<Tracing T> template<Color Us>
220 void Evaluation<T>::initialize() {
222 constexpr Color Them = ~Us;
223 constexpr Direction Up = pawn_push(Us);
224 constexpr Direction Down = -Up;
225 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
227 const Square ksq = pos.square<KING>(Us);
229 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
231 // Find our pawns that are blocked or on the first two ranks
232 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
234 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
235 // or controlled by enemy pawns are excluded from the mobility area.
236 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
238 // Initialize attackedBy[] for king and pawns
239 attackedBy[Us][KING] = attacks_bb<KING>(ksq);
240 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
241 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
242 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
244 // Init our king safety tables
245 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
246 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
247 kingRing[Us] = attacks_bb<KING>(s) | s;
249 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
250 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
252 // Remove from kingRing[] the squares defended by two pawns
253 kingRing[Us] &= ~dblAttackByPawn;
257 // Evaluation::pieces() scores pieces of a given color and type
258 template<Tracing T> template<Color Us, PieceType Pt>
259 Score Evaluation<T>::pieces() {
261 constexpr Color Them = ~Us;
262 constexpr Direction Down = -pawn_push(Us);
263 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
264 : Rank5BB | Rank4BB | Rank3BB);
265 const Square* pl = pos.squares<Pt>(Us);
268 Score score = SCORE_ZERO;
270 attackedBy[Us][Pt] = 0;
272 for (Square s = *pl; s != SQ_NONE; s = *++pl)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
277 : attacks_bb<Pt>(s, pos.pieces());
279 if (pos.blockers_for_king(Us) & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
282 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
283 attackedBy[Us][Pt] |= b;
284 attackedBy[Us][ALL_PIECES] |= b;
286 if (b & kingRing[Them])
288 kingAttackersCount[Us]++;
289 kingAttackersWeight[Us] += KingAttackWeights[Pt];
290 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
293 else if (Pt == ROOK && (file_bb(s) & kingRing[Them]))
294 score += RookOnKingRing;
296 else if (Pt == BISHOP && (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & kingRing[Them]))
297 score += BishopOnKingRing;
299 int mob = popcount(b & mobilityArea[Us]);
301 mobility[Us] += MobilityBonus[Pt - 2][mob];
303 if (Pt == BISHOP || Pt == KNIGHT)
305 // Bonus if piece is on an outpost square or can reach one
306 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
308 score += (Pt == KNIGHT) ? KnightOutpost : BishopOutpost;
309 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
310 score += ReachableOutpost;
312 // Bonus for a knight or bishop shielded by pawn
313 if (shift<Down>(pos.pieces(PAWN)) & s)
314 score += MinorBehindPawn;
316 // Penalty if the piece is far from the king
317 score -= (Pt == KNIGHT ? KnightKingProtector
318 : BishopKingProtector) * distance(pos.square<KING>(Us), s);
322 // Penalty according to the number of our pawns on the same color square as the
323 // bishop, bigger when the center files are blocked with pawns and smaller
324 // when the bishop is outside the pawn chain.
325 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
327 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
328 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
330 // Penalty for all enemy pawns x-rayed
331 score -= BishopXRayPawns * popcount(attacks_bb<BISHOP>(s) & pos.pieces(Them, PAWN));
333 // Bonus for bishop on a long diagonal which can "see" both center squares
334 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
335 score += LongDiagonalBishop;
337 // An important Chess960 pattern: a cornered bishop blocked by a friendly
338 // pawn diagonally in front of it is a very serious problem, especially
339 // when that pawn is also blocked.
340 if ( pos.is_chess960()
341 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
343 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
344 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
345 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
346 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
354 // Bonus for rook on the same file as a queen
355 if (file_bb(s) & pos.pieces(QUEEN))
356 score += RookOnQueenFile;
358 // Bonus for rook on an open or semi-open file
359 if (pos.is_on_semiopen_file(Us, s))
360 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
362 // Penalty when trapped by the king, even more if the king cannot castle
365 File kf = file_of(pos.square<KING>(Us));
366 if ((kf < FILE_E) == (file_of(s) < kf))
367 score -= TrappedRook * (1 + !pos.castling_rights(Us));
373 // Penalty if any relative pin or discovered attack against the queen
374 Bitboard queenPinners;
375 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
380 Trace::add(Pt, Us, score);
386 // Evaluation::king() assigns bonuses and penalties to a king of a given color
387 template<Tracing T> template<Color Us>
388 Score Evaluation<T>::king() const {
390 constexpr Color Them = ~Us;
391 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
392 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
394 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
395 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
397 const Square ksq = pos.square<KING>(Us);
399 // Init the score with king shelter and enemy pawns storm
400 Score score = pe->king_safety<Us>(pos);
402 // Attacked squares defended at most once by our queen or king
403 weak = attackedBy[Them][ALL_PIECES]
405 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
407 // Analyse the safe enemy's checks which are possible on next move
408 safe = ~pos.pieces(Them);
409 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
411 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
412 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
414 // Enemy rooks checks
415 rookChecks = b1 & safe & attackedBy[Them][ROOK];
417 kingDanger += more_than_one(rookChecks) ? RookSafeCheck * 175/100
420 unsafeChecks |= b1 & attackedBy[Them][ROOK];
422 // Enemy queen safe checks: we count them only if they are from squares from
423 // which we can't give a rook check, because rook checks are more valuable.
424 queenChecks = (b1 | b2)
425 & attackedBy[Them][QUEEN]
427 & ~attackedBy[Us][QUEEN]
430 kingDanger += more_than_one(queenChecks) ? QueenSafeCheck * 145/100
433 // Enemy bishops checks: we count them only if they are from squares from
434 // which we can't give a queen check, because queen checks are more valuable.
436 & attackedBy[Them][BISHOP]
440 kingDanger += more_than_one(bishopChecks) ? BishopSafeCheck * 3/2
443 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
445 // Enemy knights checks
446 knightChecks = attacks_bb<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
447 if (knightChecks & safe)
448 kingDanger += more_than_one(knightChecks & safe) ? KnightSafeCheck * 162/100
451 unsafeChecks |= knightChecks;
453 // Find the squares that opponent attacks in our king flank, the squares
454 // which they attack twice in that flank, and the squares that we defend.
455 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
456 b2 = b1 & attackedBy2[Them];
457 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
459 int kingFlankAttack = popcount(b1) + popcount(b2);
460 int kingFlankDefense = popcount(b3);
462 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
463 + 185 * popcount(kingRing[Us] & weak)
464 + 148 * popcount(unsafeChecks)
465 + 98 * popcount(pos.blockers_for_king(Us))
466 + 69 * kingAttacksCount[Them]
467 + 3 * kingFlankAttack * kingFlankAttack / 8
468 + mg_value(mobility[Them] - mobility[Us])
469 - 873 * !pos.count<QUEEN>(Them)
470 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
471 - 6 * mg_value(score) / 8
472 - 4 * kingFlankDefense
475 // Transform the kingDanger units into a Score, and subtract it from the evaluation
476 if (kingDanger > 100)
477 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
479 // Penalty when our king is on a pawnless flank
480 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
481 score -= PawnlessFlank;
483 // Penalty if king flank is under attack, potentially moving toward the king
484 score -= FlankAttacks * kingFlankAttack;
487 Trace::add(KING, Us, score);
493 // Evaluation::threats() assigns bonuses according to the types of the
494 // attacking and the attacked pieces.
495 template<Tracing T> template<Color Us>
496 Score Evaluation<T>::threats() const {
498 constexpr Color Them = ~Us;
499 constexpr Direction Up = pawn_push(Us);
500 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
502 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
503 Score score = SCORE_ZERO;
506 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
508 // Squares strongly protected by the enemy, either because they defend the
509 // square with a pawn, or because they defend the square twice and we don't.
510 stronglyProtected = attackedBy[Them][PAWN]
511 | (attackedBy2[Them] & ~attackedBy2[Us]);
513 // Non-pawn enemies, strongly protected
514 defended = nonPawnEnemies & stronglyProtected;
516 // Enemies not strongly protected and under our attack
517 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
519 // Bonus according to the kind of attacking pieces
522 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
524 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
526 b = weak & attackedBy[Us][ROOK];
528 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
530 if (weak & attackedBy[Us][KING])
531 score += ThreatByKing;
533 b = ~attackedBy[Them][ALL_PIECES]
534 | (nonPawnEnemies & attackedBy2[Us]);
535 score += Hanging * popcount(weak & b);
537 // Additional bonus if weak piece is only protected by a queen
538 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
541 // Bonus for restricting their piece moves
542 b = attackedBy[Them][ALL_PIECES]
544 & attackedBy[Us][ALL_PIECES];
545 score += RestrictedPiece * popcount(b);
547 // Protected or unattacked squares
548 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
550 // Bonus for attacking enemy pieces with our relatively safe pawns
551 b = pos.pieces(Us, PAWN) & safe;
552 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
553 score += ThreatBySafePawn * popcount(b);
555 // Find squares where our pawns can push on the next move
556 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
557 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
559 // Keep only the squares which are relatively safe
560 b &= ~attackedBy[Them][PAWN] & safe;
562 // Bonus for safe pawn threats on the next move
563 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
564 score += ThreatByPawnPush * popcount(b);
566 // Bonus for threats on the next moves against enemy queen
567 if (pos.count<QUEEN>(Them) == 1)
569 Square s = pos.square<QUEEN>(Them);
570 safe = mobilityArea[Us] & ~stronglyProtected;
572 b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
574 score += KnightOnQueen * popcount(b & safe);
576 b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
577 | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
579 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
583 Trace::add(THREAT, Us, score);
588 // Evaluation::passed() evaluates the passed pawns and candidate passed
589 // pawns of the given color.
591 template<Tracing T> template<Color Us>
592 Score Evaluation<T>::passed() const {
594 constexpr Color Them = ~Us;
595 constexpr Direction Up = pawn_push(Us);
596 constexpr Direction Down = -Up;
598 auto king_proximity = [&](Color c, Square s) {
599 return std::min(distance(pos.square<KING>(c), s), 5);
602 Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
603 Score score = SCORE_ZERO;
605 b = pe->passed_pawns(Us);
607 blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
610 helpers = shift<Up>(pos.pieces(Us, PAWN))
612 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
614 // Remove blocked candidate passers that don't have help to pass
616 | shift<WEST>(helpers)
617 | shift<EAST>(helpers);
622 Square s = pop_lsb(&b);
624 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
626 int r = relative_rank(Us, s);
628 Score bonus = PassedRank[r];
633 Square blockSq = s + Up;
635 // Adjust bonus based on the king's proximity
636 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
637 - king_proximity(Us, blockSq) * 2) * w);
639 // If blockSq is not the queening square then consider also a second push
641 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
643 // If the pawn is free to advance, then increase the bonus
644 if (pos.empty(blockSq))
646 squaresToQueen = forward_file_bb(Us, s);
647 unsafeSquares = passed_pawn_span(Us, s);
649 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
651 if (!(pos.pieces(Them) & bb))
652 unsafeSquares &= attackedBy[Them][ALL_PIECES];
654 // If there are no enemy attacks on passed pawn span, assign a big bonus.
655 // Otherwise assign a smaller bonus if the path to queen is not attacked
656 // and even smaller bonus if it is attacked but block square is not.
657 int k = !unsafeSquares ? 35 :
658 !(unsafeSquares & squaresToQueen) ? 20 :
659 !(unsafeSquares & blockSq) ? 9 :
662 // Assign a larger bonus if the block square is defended
663 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
666 bonus += make_score(k * w, k * w);
670 score += bonus - PassedFile * edge_distance(file_of(s));
674 Trace::add(PASSED, Us, score);
680 // Evaluation::space() computes the space evaluation for a given side. The
681 // space evaluation is a simple bonus based on the number of safe squares
682 // available for minor pieces on the central four files on ranks 2--4. Safe
683 // squares one, two or three squares behind a friendly pawn are counted
684 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
685 // improve play on game opening.
687 template<Tracing T> template<Color Us>
688 Score Evaluation<T>::space() const {
690 if (pos.non_pawn_material() < SpaceThreshold)
693 constexpr Color Them = ~Us;
694 constexpr Direction Down = -pawn_push(Us);
695 constexpr Bitboard SpaceMask =
696 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
697 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
699 // Find the available squares for our pieces inside the area defined by SpaceMask
700 Bitboard safe = SpaceMask
701 & ~pos.pieces(Us, PAWN)
702 & ~attackedBy[Them][PAWN];
704 // Find all squares which are at most three squares behind some friendly pawn
705 Bitboard behind = pos.pieces(Us, PAWN);
706 behind |= shift<Down>(behind);
707 behind |= shift<Down+Down>(behind);
709 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
710 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
711 Score score = make_score(bonus * weight * weight / 16, 0);
714 Trace::add(SPACE, Us, score);
720 // Evaluation::initiative() computes the initiative correction value
721 // for the position. It is a second order bonus/malus based on the
722 // known attacking/defending status of the players.
725 Score Evaluation<T>::initiative(Score score) const {
727 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
728 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
730 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
731 && (pos.pieces(PAWN) & KingSide);
733 bool almostUnwinnable = outflanking < 0
734 && !pawnsOnBothFlanks;
736 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
737 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
739 // Compute the initiative bonus for the attacking side
740 int complexity = 9 * pe->passed_count()
741 + 12 * pos.count<PAWN>()
743 + 21 * pawnsOnBothFlanks
745 + 51 * !pos.non_pawn_material()
746 - 43 * almostUnwinnable
747 - 2 * pos.rule50_count()
750 Value mg = mg_value(score);
751 Value eg = eg_value(score);
753 // Now apply the bonus: note that we find the attacking side by extracting the
754 // sign of the midgame or endgame values, and that we carefully cap the bonus
755 // so that the midgame and endgame scores do not change sign after the bonus.
756 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
757 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
760 Trace::add(INITIATIVE, make_score(u, v));
762 return make_score(u, v);
766 // Evaluation::scale_factor() computes the scale factor for the winning side
769 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
771 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
772 int sf = me->scale_factor(pos, strongSide);
774 // If scale is not already specific, scale down the endgame via general heuristics
775 if (sf == SCALE_FACTOR_NORMAL)
777 if (pos.opposite_bishops())
779 if ( pos.non_pawn_material(WHITE) == BishopValueMg
780 && pos.non_pawn_material(BLACK) == BishopValueMg)
781 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
783 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
786 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
789 return ScaleFactor(sf);
793 // Evaluation::value() is the main function of the class. It computes the various
794 // parts of the evaluation and returns the value of the position from the point
795 // of view of the side to move.
798 Value Evaluation<T>::value() {
800 assert(!pos.checkers());
802 // Probe the material hash table
803 me = Material::probe(pos);
805 // If we have a specialized evaluation function for the current material
806 // configuration, call it and return.
807 if (me->specialized_eval_exists())
808 return me->evaluate(pos);
810 // Initialize score by reading the incrementally updated scores included in
811 // the position object (material + piece square tables) and the material
812 // imbalance. Score is computed internally from the white point of view.
813 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
815 // Probe the pawn hash table
816 pe = Pawns::probe(pos);
817 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
819 // Early exit if score is high
820 Value v = (mg_value(score) + eg_value(score)) / 2;
821 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
822 return pos.side_to_move() == WHITE ? v : -v;
824 // Main evaluation begins here
829 // Pieces evaluated first (also populates attackedBy, attackedBy2).
830 // Note that the order of evaluation of the terms is left unspecified
831 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
832 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
833 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
834 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
836 score += mobility[WHITE] - mobility[BLACK];
838 // More complex interactions that require fully populated attack bitboards
839 score += king< WHITE>() - king< BLACK>()
840 + threats<WHITE>() - threats<BLACK>()
841 + passed< WHITE>() - passed< BLACK>()
842 + space< WHITE>() - space< BLACK>();
844 score += initiative(score);
846 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
847 ScaleFactor sf = scale_factor(eg_value(score));
848 v = mg_value(score) * int(me->game_phase())
849 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
853 // In case of tracing add all remaining individual evaluation terms
856 Trace::add(MATERIAL, pos.psq_score());
857 Trace::add(IMBALANCE, me->imbalance());
858 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
859 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
860 Trace::add(TOTAL, score);
863 // Side to move point of view
864 return (pos.side_to_move() == WHITE ? v : -v) + Tempo;
870 /// evaluate() is the evaluator for the outer world. It returns a static
871 /// evaluation of the position from the point of view of the side to move.
873 Value Eval::evaluate(const Position& pos) {
874 return Evaluation<NO_TRACE>(pos).value();
878 /// trace() is like evaluate(), but instead of returning a value, it returns
879 /// a string (suitable for outputting to stdout) that contains the detailed
880 /// descriptions and values of each evaluation term. Useful for debugging.
882 std::string Eval::trace(const Position& pos) {
885 return "Total evaluation: none (in check)";
887 std::memset(scores, 0, sizeof(scores));
889 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
891 Value v = Evaluation<TRACE>(pos).value();
893 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
895 std::stringstream ss;
896 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
897 << " Term | White | Black | Total \n"
898 << " | MG EG | MG EG | MG EG \n"
899 << " ------------+-------------+-------------+------------\n"
900 << " Material | " << Term(MATERIAL)
901 << " Imbalance | " << Term(IMBALANCE)
902 << " Pawns | " << Term(PAWN)
903 << " Knights | " << Term(KNIGHT)
904 << " Bishops | " << Term(BISHOP)
905 << " Rooks | " << Term(ROOK)
906 << " Queens | " << Term(QUEEN)
907 << " Mobility | " << Term(MOBILITY)
908 << " King safety | " << Term(KING)
909 << " Threats | " << Term(THREAT)
910 << " Passed | " << Term(PASSED)
911 << " Space | " << Term(SPACE)
912 << " Initiative | " << Term(INITIATIVE)
913 << " ------------+-------------+-------------+------------\n"
914 << " Total | " << Term(TOTAL);
916 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";