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 // 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 Value winnable(Score score) const;
181 Bitboard mobilityArea[COLOR_NB];
182 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
184 // attackedBy[color][piece type] is a bitboard representing all squares
185 // attacked by a given color and piece type. Special "piece types" which
186 // is also calculated is ALL_PIECES.
187 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
189 // attackedBy2[color] are the squares attacked by at least 2 units of a given
190 // color, including x-rays. But diagonal x-rays through pawns are not computed.
191 Bitboard attackedBy2[COLOR_NB];
193 // kingRing[color] are the squares adjacent to the king plus some other
194 // very near squares, depending on king position.
195 Bitboard kingRing[COLOR_NB];
197 // kingAttackersCount[color] is the number of pieces of the given color
198 // which attack a square in the kingRing of the enemy king.
199 int kingAttackersCount[COLOR_NB];
201 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
202 // the given color which attack a square in the kingRing of the enemy king.
203 // The weights of the individual piece types are given by the elements in
204 // the KingAttackWeights array.
205 int kingAttackersWeight[COLOR_NB];
207 // kingAttacksCount[color] is the number of attacks by the given color to
208 // squares directly adjacent to the enemy king. Pieces which attack more
209 // than one square are counted multiple times. For instance, if there is
210 // a white knight on g5 and black's king is on g8, this white knight adds 2
211 // to kingAttacksCount[WHITE].
212 int kingAttacksCount[COLOR_NB];
216 // Evaluation::initialize() computes king and pawn attacks, and the king ring
217 // bitboard for a given color. This is done at the beginning of the evaluation.
218 template<Tracing T> template<Color Us>
219 void Evaluation<T>::initialize() {
221 constexpr Color Them = ~Us;
222 constexpr Direction Up = pawn_push(Us);
223 constexpr Direction Down = -Up;
224 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
226 const Square ksq = pos.square<KING>(Us);
228 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
230 // Find our pawns that are blocked or on the first two ranks
231 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
233 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
234 // or controlled by enemy pawns are excluded from the mobility area.
235 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
237 // Initialize attackedBy[] for king and pawns
238 attackedBy[Us][KING] = attacks_bb<KING>(ksq);
239 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
240 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
241 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
243 // Init our king safety tables
244 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
245 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
246 kingRing[Us] = attacks_bb<KING>(s) | s;
248 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
249 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
251 // Remove from kingRing[] the squares defended by two pawns
252 kingRing[Us] &= ~dblAttackByPawn;
256 // Evaluation::pieces() scores pieces of a given color and type
257 template<Tracing T> template<Color Us, PieceType Pt>
258 Score Evaluation<T>::pieces() {
260 constexpr Color Them = ~Us;
261 constexpr Direction Down = -pawn_push(Us);
262 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
263 : Rank5BB | Rank4BB | Rank3BB);
264 const Square* pl = pos.squares<Pt>(Us);
267 Score score = SCORE_ZERO;
269 attackedBy[Us][Pt] = 0;
271 for (Square s = *pl; s != SQ_NONE; s = *++pl)
273 // Find attacked squares, including x-ray attacks for bishops and rooks
274 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
275 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
276 : attacks_bb<Pt>(s, pos.pieces());
278 if (pos.blockers_for_king(Us) & s)
279 b &= line_bb(pos.square<KING>(Us), s);
281 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
282 attackedBy[Us][Pt] |= b;
283 attackedBy[Us][ALL_PIECES] |= b;
285 if (b & kingRing[Them])
287 kingAttackersCount[Us]++;
288 kingAttackersWeight[Us] += KingAttackWeights[Pt];
289 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
292 else if (Pt == ROOK && (file_bb(s) & kingRing[Them]))
293 score += RookOnKingRing;
295 else if (Pt == BISHOP && (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & kingRing[Them]))
296 score += BishopOnKingRing;
298 int mob = popcount(b & mobilityArea[Us]);
300 mobility[Us] += MobilityBonus[Pt - 2][mob];
302 if (Pt == BISHOP || Pt == KNIGHT)
304 // Bonus if piece is on an outpost square or can reach one
305 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
307 score += (Pt == KNIGHT) ? KnightOutpost : BishopOutpost;
308 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
309 score += ReachableOutpost;
311 // Bonus for a knight or bishop shielded by pawn
312 if (shift<Down>(pos.pieces(PAWN)) & s)
313 score += MinorBehindPawn;
315 // Penalty if the piece is far from the king
316 score -= (Pt == KNIGHT ? KnightKingProtector
317 : BishopKingProtector) * distance(pos.square<KING>(Us), s);
321 // Penalty according to the number of our pawns on the same color square as the
322 // bishop, bigger when the center files are blocked with pawns and smaller
323 // when the bishop is outside the pawn chain.
324 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
326 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
327 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
329 // Penalty for all enemy pawns x-rayed
330 score -= BishopXRayPawns * popcount(attacks_bb<BISHOP>(s) & pos.pieces(Them, PAWN));
332 // Bonus for bishop on a long diagonal which can "see" both center squares
333 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
334 score += LongDiagonalBishop;
336 // An important Chess960 pattern: a cornered bishop blocked by a friendly
337 // pawn diagonally in front of it is a very serious problem, especially
338 // when that pawn is also blocked.
339 if ( pos.is_chess960()
340 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
342 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
343 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
344 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
345 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
353 // Bonus for rook on the same file as a queen
354 if (file_bb(s) & pos.pieces(QUEEN))
355 score += RookOnQueenFile;
357 // Bonus for rook on an open or semi-open file
358 if (pos.is_on_semiopen_file(Us, s))
359 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
361 // Penalty when trapped by the king, even more if the king cannot castle
364 File kf = file_of(pos.square<KING>(Us));
365 if ((kf < FILE_E) == (file_of(s) < kf))
366 score -= TrappedRook * (1 + !pos.castling_rights(Us));
372 // Penalty if any relative pin or discovered attack against the queen
373 Bitboard queenPinners;
374 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
379 Trace::add(Pt, Us, score);
385 // Evaluation::king() assigns bonuses and penalties to a king of a given color
386 template<Tracing T> template<Color Us>
387 Score Evaluation<T>::king() const {
389 constexpr Color Them = ~Us;
390 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
391 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
393 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
394 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
396 const Square ksq = pos.square<KING>(Us);
398 // Init the score with king shelter and enemy pawns storm
399 Score score = pe->king_safety<Us>(pos);
401 // Attacked squares defended at most once by our queen or king
402 weak = attackedBy[Them][ALL_PIECES]
404 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
406 // Analyse the safe enemy's checks which are possible on next move
407 safe = ~pos.pieces(Them);
408 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
410 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
411 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
413 // Enemy rooks checks
414 rookChecks = b1 & safe & attackedBy[Them][ROOK];
416 kingDanger += more_than_one(rookChecks) ? RookSafeCheck * 175/100
419 unsafeChecks |= b1 & attackedBy[Them][ROOK];
421 // Enemy queen safe checks: we count them only if they are from squares from
422 // which we can't give a rook check, because rook checks are more valuable.
423 queenChecks = (b1 | b2)
424 & attackedBy[Them][QUEEN]
426 & ~attackedBy[Us][QUEEN]
429 kingDanger += more_than_one(queenChecks) ? QueenSafeCheck * 145/100
432 // Enemy bishops checks: we count them only if they are from squares from
433 // which we can't give a queen check, because queen checks are more valuable.
435 & attackedBy[Them][BISHOP]
439 kingDanger += more_than_one(bishopChecks) ? BishopSafeCheck * 3/2
442 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
444 // Enemy knights checks
445 knightChecks = attacks_bb<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
446 if (knightChecks & safe)
447 kingDanger += more_than_one(knightChecks & safe) ? KnightSafeCheck * 162/100
450 unsafeChecks |= knightChecks;
452 // Find the squares that opponent attacks in our king flank, the squares
453 // which they attack twice in that flank, and the squares that we defend.
454 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
455 b2 = b1 & attackedBy2[Them];
456 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
458 int kingFlankAttack = popcount(b1) + popcount(b2);
459 int kingFlankDefense = popcount(b3);
461 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
462 + 185 * popcount(kingRing[Us] & weak)
463 + 148 * popcount(unsafeChecks)
464 + 98 * popcount(pos.blockers_for_king(Us))
465 + 69 * kingAttacksCount[Them]
466 + 3 * kingFlankAttack * kingFlankAttack / 8
467 + mg_value(mobility[Them] - mobility[Us])
468 - 873 * !pos.count<QUEEN>(Them)
469 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
470 - 6 * mg_value(score) / 8
471 - 4 * kingFlankDefense
474 // Transform the kingDanger units into a Score, and subtract it from the evaluation
475 if (kingDanger > 100)
476 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
478 // Penalty when our king is on a pawnless flank
479 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
480 score -= PawnlessFlank;
482 // Penalty if king flank is under attack, potentially moving toward the king
483 score -= FlankAttacks * kingFlankAttack;
486 Trace::add(KING, Us, score);
492 // Evaluation::threats() assigns bonuses according to the types of the
493 // attacking and the attacked pieces.
494 template<Tracing T> template<Color Us>
495 Score Evaluation<T>::threats() const {
497 constexpr Color Them = ~Us;
498 constexpr Direction Up = pawn_push(Us);
499 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
501 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
502 Score score = SCORE_ZERO;
505 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
507 // Squares strongly protected by the enemy, either because they defend the
508 // square with a pawn, or because they defend the square twice and we don't.
509 stronglyProtected = attackedBy[Them][PAWN]
510 | (attackedBy2[Them] & ~attackedBy2[Us]);
512 // Non-pawn enemies, strongly protected
513 defended = nonPawnEnemies & stronglyProtected;
515 // Enemies not strongly protected and under our attack
516 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
518 // Bonus according to the kind of attacking pieces
521 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
523 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
525 b = weak & attackedBy[Us][ROOK];
527 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
529 if (weak & attackedBy[Us][KING])
530 score += ThreatByKing;
532 b = ~attackedBy[Them][ALL_PIECES]
533 | (nonPawnEnemies & attackedBy2[Us]);
534 score += Hanging * popcount(weak & b);
536 // Additional bonus if weak piece is only protected by a queen
537 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
540 // Bonus for restricting their piece moves
541 b = attackedBy[Them][ALL_PIECES]
543 & attackedBy[Us][ALL_PIECES];
544 score += RestrictedPiece * popcount(b);
546 // Protected or unattacked squares
547 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
549 // Bonus for attacking enemy pieces with our relatively safe pawns
550 b = pos.pieces(Us, PAWN) & safe;
551 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
552 score += ThreatBySafePawn * popcount(b);
554 // Find squares where our pawns can push on the next move
555 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
556 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
558 // Keep only the squares which are relatively safe
559 b &= ~attackedBy[Them][PAWN] & safe;
561 // Bonus for safe pawn threats on the next move
562 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
563 score += ThreatByPawnPush * popcount(b);
565 // Bonus for threats on the next moves against enemy queen
566 if (pos.count<QUEEN>(Them) == 1)
568 Square s = pos.square<QUEEN>(Them);
569 safe = mobilityArea[Us] & ~stronglyProtected;
571 b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
573 score += KnightOnQueen * popcount(b & safe);
575 b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
576 | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
578 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
582 Trace::add(THREAT, Us, score);
587 // Evaluation::passed() evaluates the passed pawns and candidate passed
588 // pawns of the given color.
590 template<Tracing T> template<Color Us>
591 Score Evaluation<T>::passed() const {
593 constexpr Color Them = ~Us;
594 constexpr Direction Up = pawn_push(Us);
595 constexpr Direction Down = -Up;
597 auto king_proximity = [&](Color c, Square s) {
598 return std::min(distance(pos.square<KING>(c), s), 5);
601 Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
602 Score score = SCORE_ZERO;
604 b = pe->passed_pawns(Us);
606 blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
609 helpers = shift<Up>(pos.pieces(Us, PAWN))
611 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
613 // Remove blocked candidate passers that don't have help to pass
615 | shift<WEST>(helpers)
616 | shift<EAST>(helpers);
621 Square s = pop_lsb(&b);
623 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
625 int r = relative_rank(Us, s);
627 Score bonus = PassedRank[r];
632 Square blockSq = s + Up;
634 // Adjust bonus based on the king's proximity
635 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
636 - king_proximity(Us, blockSq) * 2) * w);
638 // If blockSq is not the queening square then consider also a second push
640 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
642 // If the pawn is free to advance, then increase the bonus
643 if (pos.empty(blockSq))
645 squaresToQueen = forward_file_bb(Us, s);
646 unsafeSquares = passed_pawn_span(Us, s);
648 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
650 if (!(pos.pieces(Them) & bb))
651 unsafeSquares &= attackedBy[Them][ALL_PIECES];
653 // If there are no enemy attacks on passed pawn span, assign a big bonus.
654 // Otherwise assign a smaller bonus if the path to queen is not attacked
655 // and even smaller bonus if it is attacked but block square is not.
656 int k = !unsafeSquares ? 35 :
657 !(unsafeSquares & squaresToQueen) ? 20 :
658 !(unsafeSquares & blockSq) ? 9 :
661 // Assign a larger bonus if the block square is defended
662 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
665 bonus += make_score(k * w, k * w);
669 score += bonus - PassedFile * edge_distance(file_of(s));
673 Trace::add(PASSED, Us, score);
679 // Evaluation::space() computes the space evaluation for a given side. The
680 // space evaluation is a simple bonus based on the number of safe squares
681 // available for minor pieces on the central four files on ranks 2--4. Safe
682 // squares one, two or three squares behind a friendly pawn are counted
683 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
684 // improve play on game opening.
686 template<Tracing T> template<Color Us>
687 Score Evaluation<T>::space() const {
689 if (pos.non_pawn_material() < SpaceThreshold)
692 constexpr Color Them = ~Us;
693 constexpr Direction Down = -pawn_push(Us);
694 constexpr Bitboard SpaceMask =
695 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
696 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
698 // Find the available squares for our pieces inside the area defined by SpaceMask
699 Bitboard safe = SpaceMask
700 & ~pos.pieces(Us, PAWN)
701 & ~attackedBy[Them][PAWN];
703 // Find all squares which are at most three squares behind some friendly pawn
704 Bitboard behind = pos.pieces(Us, PAWN);
705 behind |= shift<Down>(behind);
706 behind |= shift<Down+Down>(behind);
708 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
709 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
710 Score score = make_score(bonus * weight * weight / 16, 0);
713 Trace::add(SPACE, Us, score);
719 // Evaluation::winnable() adjusts the mg and eg score components based on the
720 // known attacking/defending status of the players.
721 // A single value is derived from the mg and eg values and returned.
724 Value Evaluation<T>::winnable(Score score) const {
726 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
727 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
729 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
730 && (pos.pieces(PAWN) & KingSide);
732 bool almostUnwinnable = outflanking < 0
733 && !pawnsOnBothFlanks;
735 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
736 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
738 // Compute the initiative bonus for the attacking side
739 int complexity = 9 * pe->passed_count()
740 + 12 * pos.count<PAWN>()
742 + 21 * pawnsOnBothFlanks
744 + 51 * !pos.non_pawn_material()
745 - 43 * almostUnwinnable
746 - 2 * pos.rule50_count()
749 Value mg = mg_value(score);
750 Value eg = eg_value(score);
752 // Now apply the bonus: note that we find the attacking side by extracting the
753 // sign of the midgame or endgame values, and that we carefully cap the bonus
754 // so that the midgame and endgame scores do not change sign after the bonus.
755 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
756 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
761 // Compute the scale factor for the winning side
763 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
764 int sf = me->scale_factor(pos, strongSide);
766 // If scale is not already specific, scale down the endgame via general heuristics
767 if (sf == SCALE_FACTOR_NORMAL)
769 if (pos.opposite_bishops())
771 if ( pos.non_pawn_material(WHITE) == BishopValueMg
772 && pos.non_pawn_material(BLACK) == BishopValueMg)
773 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
775 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
778 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
781 // Interpolate between the middlegame and (scaled by 'sf') endgame score
782 v = mg * int(me->game_phase())
783 + eg * int(PHASE_MIDGAME - me->game_phase()) * ScaleFactor(sf) / SCALE_FACTOR_NORMAL;
788 Trace::add(WINNABLE, make_score(u, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL - eg_value(score)));
789 Trace::add(TOTAL, make_score(mg, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL));
796 // Evaluation::value() is the main function of the class. It computes the various
797 // parts of the evaluation and returns the value of the position from the point
798 // of view of the side to move.
801 Value Evaluation<T>::value() {
803 assert(!pos.checkers());
805 // Probe the material hash table
806 me = Material::probe(pos);
808 // If we have a specialized evaluation function for the current material
809 // configuration, call it and return.
810 if (me->specialized_eval_exists())
811 return me->evaluate(pos);
813 // Initialize score by reading the incrementally updated scores included in
814 // the position object (material + piece square tables) and the material
815 // imbalance. Score is computed internally from the white point of view.
816 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
818 // Probe the pawn hash table
819 pe = Pawns::probe(pos);
820 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
822 // Early exit if score is high
823 Value v = (mg_value(score) + eg_value(score)) / 2;
824 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
825 return pos.side_to_move() == WHITE ? v : -v;
827 // Main evaluation begins here
832 // Pieces evaluated first (also populates attackedBy, attackedBy2).
833 // Note that the order of evaluation of the terms is left unspecified
834 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
835 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
836 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
837 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
839 score += mobility[WHITE] - mobility[BLACK];
841 // More complex interactions that require fully populated attack bitboards
842 score += king< WHITE>() - king< BLACK>()
843 + threats<WHITE>() - threats<BLACK>()
844 + passed< WHITE>() - passed< BLACK>()
845 + space< WHITE>() - space< BLACK>();
847 // Derive single value from mg and eg parts of score
850 // In case of tracing add all remaining individual evaluation terms
853 Trace::add(MATERIAL, pos.psq_score());
854 Trace::add(IMBALANCE, me->imbalance());
855 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
856 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
859 // Side to move point of view
860 return (pos.side_to_move() == WHITE ? v : -v) + Tempo;
866 /// evaluate() is the evaluator for the outer world. It returns a static
867 /// evaluation of the position from the point of view of the side to move.
869 Value Eval::evaluate(const Position& pos) {
870 return Evaluation<NO_TRACE>(pos).value();
874 /// trace() is like evaluate(), but instead of returning a value, it returns
875 /// a string (suitable for outputting to stdout) that contains the detailed
876 /// descriptions and values of each evaluation term. Useful for debugging.
878 std::string Eval::trace(const Position& pos) {
881 return "Total evaluation: none (in check)";
883 std::memset(scores, 0, sizeof(scores));
885 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
887 Value v = Evaluation<TRACE>(pos).value();
889 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
891 std::stringstream ss;
892 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
893 << " Term | White | Black | Total \n"
894 << " | MG EG | MG EG | MG EG \n"
895 << " ------------+-------------+-------------+------------\n"
896 << " Material | " << Term(MATERIAL)
897 << " Imbalance | " << Term(IMBALANCE)
898 << " Pawns | " << Term(PAWN)
899 << " Knights | " << Term(KNIGHT)
900 << " Bishops | " << Term(BISHOP)
901 << " Rooks | " << Term(ROOK)
902 << " Queens | " << Term(QUEEN)
903 << " Mobility | " << Term(MOBILITY)
904 << " King safety | " << Term(KING)
905 << " Threats | " << Term(THREAT)
906 << " Passed | " << Term(PASSED)
907 << " Space | " << Term(SPACE)
908 << " Winnable | " << Term(WINNABLE)
909 << " ------------+-------------+-------------+------------\n"
910 << " Total | " << Term(TOTAL);
912 ss << "\nFinal evaluation: " << to_cp(v) << " (white side)\n";