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 LazyThreshold1 = Value(1400);
78 constexpr Value LazyThreshold2 = Value(1300);
79 constexpr Value SpaceThreshold = Value(12222);
81 // KingAttackWeights[PieceType] contains king attack weights by piece type
82 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
84 // SafeCheck[PieceType][single/multiple] contains safe check bonus by piece type,
85 // higher if multiple safe checks are possible for that piece type.
86 constexpr int SafeCheck[][2] = {
87 {}, {}, {792, 1283}, {645, 967}, {1084, 1897}, {772, 1119}
90 #define S(mg, eg) make_score(mg, eg)
92 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
93 // indexed by piece type and number of attacked squares in the mobility area.
94 constexpr Score MobilityBonus[][32] = {
95 { S(-62,-81), S(-53,-56), S(-12,-31), S( -4,-16), S( 3, 5), S( 13, 11), // Knight
96 S( 22, 17), S( 28, 20), S( 33, 25) },
97 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishop
98 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
99 S( 91, 88), S( 98, 97) },
100 { S(-60,-78), S(-20,-17), S( 2, 23), S( 3, 39), S( 3, 70), S( 11, 99), // Rook
101 S( 22,103), S( 31,121), S( 40,134), S( 40,139), S( 41,158), S( 48,164),
102 S( 57,168), S( 57,169), S( 62,172) },
103 { S(-30,-48), S(-12,-30), S( -8, -7), S( -9, 19), S( 20, 40), S( 23, 55), // Queen
104 S( 23, 59), S( 35, 75), S( 38, 78), S( 53, 96), S( 64, 96), S( 65,100),
105 S( 65,121), S( 66,127), S( 67,131), S( 67,133), S( 72,136), S( 72,141),
106 S( 77,147), S( 79,150), S( 93,151), S(108,168), S(108,168), S(108,171),
107 S(110,182), S(114,182), S(114,192), S(116,219) }
110 // KingProtector[knight/bishop] contains penalty for each distance unit to own king
111 constexpr Score KingProtector[] = { S(8, 9), S(6, 9) };
113 // Outpost[knight/bishop] contains bonuses for each knight or bishop occupying a
114 // pawn protected square on rank 4 to 6 which is also safe from a pawn attack.
115 constexpr Score Outpost[] = { S(56, 36), S(30, 23) };
117 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
118 constexpr Score PassedRank[RANK_NB] = {
119 S(0, 0), S(10, 28), S(17, 33), S(15, 41), S(62, 72), S(168, 177), S(276, 260)
122 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
123 // no (friendly) pawn on the rook file.
124 constexpr Score RookOnFile[] = { S(19, 7), S(48, 29) };
126 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
127 // which piece type attacks which one. Attacks on lesser pieces which are
128 // pawn-defended are not considered.
129 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
130 S(0, 0), S(5, 32), S(57, 41), S(77, 56), S(88, 119), S(79, 161)
133 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
134 S(0, 0), S(3, 46), S(37, 68), S(42, 60), S(0, 38), S(58, 41)
137 // Assorted bonuses and penalties
138 constexpr Score BadOutpost = S( -7, 36);
139 constexpr Score BishopOnKingRing = S( 24, 0);
140 constexpr Score BishopPawns = S( 3, 7);
141 constexpr Score BishopXRayPawns = S( 4, 5);
142 constexpr Score CorneredBishop = S( 50, 50);
143 constexpr Score FlankAttacks = S( 8, 0);
144 constexpr Score Hanging = S( 69, 36);
145 constexpr Score KnightOnQueen = S( 16, 11);
146 constexpr Score LongDiagonalBishop = S( 45, 0);
147 constexpr Score MinorBehindPawn = S( 18, 3);
148 constexpr Score PassedFile = S( 11, 8);
149 constexpr Score PawnlessFlank = S( 17, 95);
150 constexpr Score QueenInfiltration = S( -2, 14);
151 constexpr Score ReachableOutpost = S( 31, 22);
152 constexpr Score RestrictedPiece = S( 7, 7);
153 constexpr Score RookOnKingRing = S( 16, 0);
154 constexpr Score RookOnQueenFile = S( 6, 11);
155 constexpr Score SliderOnQueen = S( 60, 18);
156 constexpr Score ThreatByKing = S( 24, 89);
157 constexpr Score ThreatByPawnPush = S( 48, 39);
158 constexpr Score ThreatBySafePawn = S(173, 94);
159 constexpr Score TrappedRook = S( 55, 13);
160 constexpr Score WeakQueenProtection = S( 14, 0);
161 constexpr Score WeakQueen = S( 56, 15);
166 // Evaluation class computes and stores attacks tables and other working data
171 Evaluation() = delete;
172 explicit Evaluation(const Position& p) : pos(p) {}
173 Evaluation& operator=(const Evaluation&) = delete;
177 template<Color Us> void initialize();
178 template<Color Us, PieceType Pt> Score pieces();
179 template<Color Us> Score king() const;
180 template<Color Us> Score threats() const;
181 template<Color Us> Score passed() const;
182 template<Color Us> Score space() const;
183 Value winnable(Score score) const;
188 Bitboard mobilityArea[COLOR_NB];
189 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
191 // attackedBy[color][piece type] is a bitboard representing all squares
192 // attacked by a given color and piece type. Special "piece types" which
193 // is also calculated is ALL_PIECES.
194 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
196 // attackedBy2[color] are the squares attacked by at least 2 units of a given
197 // color, including x-rays. But diagonal x-rays through pawns are not computed.
198 Bitboard attackedBy2[COLOR_NB];
200 // kingRing[color] are the squares adjacent to the king plus some other
201 // very near squares, depending on king position.
202 Bitboard kingRing[COLOR_NB];
204 // kingAttackersCount[color] is the number of pieces of the given color
205 // which attack a square in the kingRing of the enemy king.
206 int kingAttackersCount[COLOR_NB];
208 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
209 // the given color which attack a square in the kingRing of the enemy king.
210 // The weights of the individual piece types are given by the elements in
211 // the KingAttackWeights array.
212 int kingAttackersWeight[COLOR_NB];
214 // kingAttacksCount[color] is the number of attacks by the given color to
215 // squares directly adjacent to the enemy king. Pieces which attack more
216 // than one square are counted multiple times. For instance, if there is
217 // a white knight on g5 and black's king is on g8, this white knight adds 2
218 // to kingAttacksCount[WHITE].
219 int kingAttacksCount[COLOR_NB];
223 // Evaluation::initialize() computes king and pawn attacks, and the king ring
224 // bitboard for a given color. This is done at the beginning of the evaluation.
226 template<Tracing T> template<Color Us>
227 void Evaluation<T>::initialize() {
229 constexpr Color Them = ~Us;
230 constexpr Direction Up = pawn_push(Us);
231 constexpr Direction Down = -Up;
232 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
234 const Square ksq = pos.square<KING>(Us);
236 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
238 // Find our pawns that are blocked or on the first two ranks
239 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
241 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
242 // or controlled by enemy pawns are excluded from the mobility area.
243 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
245 // Initialize attackedBy[] for king and pawns
246 attackedBy[Us][KING] = attacks_bb<KING>(ksq);
247 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
248 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
249 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
251 // Init our king safety tables
252 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
253 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
254 kingRing[Us] = attacks_bb<KING>(s) | s;
256 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
257 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
259 // Remove from kingRing[] the squares defended by two pawns
260 kingRing[Us] &= ~dblAttackByPawn;
264 // Evaluation::pieces() scores pieces of a given color and type
266 template<Tracing T> template<Color Us, PieceType Pt>
267 Score Evaluation<T>::pieces() {
269 constexpr Color Them = ~Us;
270 constexpr Direction Down = -pawn_push(Us);
271 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
272 : Rank5BB | Rank4BB | Rank3BB);
273 const Square* pl = pos.squares<Pt>(Us);
276 Score score = SCORE_ZERO;
278 attackedBy[Us][Pt] = 0;
280 for (Square s = *pl; s != SQ_NONE; s = *++pl)
282 // Find attacked squares, including x-ray attacks for bishops and rooks
283 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
284 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
285 : attacks_bb<Pt>(s, pos.pieces());
287 if (pos.blockers_for_king(Us) & s)
288 b &= line_bb(pos.square<KING>(Us), s);
290 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
291 attackedBy[Us][Pt] |= b;
292 attackedBy[Us][ALL_PIECES] |= b;
294 if (b & kingRing[Them])
296 kingAttackersCount[Us]++;
297 kingAttackersWeight[Us] += KingAttackWeights[Pt];
298 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
301 else if (Pt == ROOK && (file_bb(s) & kingRing[Them]))
302 score += RookOnKingRing;
304 else if (Pt == BISHOP && (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & kingRing[Them]))
305 score += BishopOnKingRing;
307 int mob = popcount(b & mobilityArea[Us]);
309 mobility[Us] += MobilityBonus[Pt - 2][mob];
311 if (Pt == BISHOP || Pt == KNIGHT)
313 // Bonus if the piece is on an outpost square or can reach one
314 // Reduced bonus for knights (BadOutpost) if few relevant targets
315 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
316 Bitboard targets = pos.pieces(Them) & ~pos.pieces(PAWN);
319 && bb & s & ~CenterFiles // on a side outpost
320 && !(b & targets) // no relevant attacks
321 && (!more_than_one(targets & (s & QueenSide ? QueenSide : KingSide))))
324 score += Outpost[Pt == BISHOP];
325 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
326 score += ReachableOutpost;
328 // Bonus for a knight or bishop shielded by pawn
329 if (shift<Down>(pos.pieces(PAWN)) & s)
330 score += MinorBehindPawn;
332 // Penalty if the piece is far from the king
333 score -= KingProtector[Pt == BISHOP] * distance(pos.square<KING>(Us), s);
337 // Penalty according to the number of our pawns on the same color square as the
338 // bishop, bigger when the center files are blocked with pawns and smaller
339 // when the bishop is outside the pawn chain.
340 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
342 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
343 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
345 // Penalty for all enemy pawns x-rayed
346 score -= BishopXRayPawns * popcount(attacks_bb<BISHOP>(s) & pos.pieces(Them, PAWN));
348 // Bonus for bishop on a long diagonal which can "see" both center squares
349 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
350 score += LongDiagonalBishop;
352 // An important Chess960 pattern: a cornered bishop blocked by a friendly
353 // pawn diagonally in front of it is a very serious problem, especially
354 // when that pawn is also blocked.
355 if ( pos.is_chess960()
356 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
358 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
359 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
360 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
361 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
369 // Bonus for rook on the same file as a queen
370 if (file_bb(s) & pos.pieces(QUEEN))
371 score += RookOnQueenFile;
373 // Bonus for rook on an open or semi-open file
374 if (pos.is_on_semiopen_file(Us, s))
375 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
377 // Penalty when trapped by the king, even more if the king cannot castle
380 File kf = file_of(pos.square<KING>(Us));
381 if ((kf < FILE_E) == (file_of(s) < kf))
382 score -= TrappedRook * (1 + !pos.castling_rights(Us));
388 // Penalty if any relative pin or discovered attack against the queen
389 Bitboard queenPinners;
390 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
393 // Bonus for queen on weak square in enemy camp
394 if (relative_rank(Us, s) > RANK_4 && (~pe->pawn_attacks_span(Them) & s))
395 score += QueenInfiltration;
399 Trace::add(Pt, Us, score);
405 // Evaluation::king() assigns bonuses and penalties to a king of a given color
407 template<Tracing T> template<Color Us>
408 Score Evaluation<T>::king() const {
410 constexpr Color Them = ~Us;
411 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
412 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
414 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
415 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
417 const Square ksq = pos.square<KING>(Us);
419 // Init the score with king shelter and enemy pawns storm
420 Score score = pe->king_safety<Us>(pos);
422 // Attacked squares defended at most once by our queen or king
423 weak = attackedBy[Them][ALL_PIECES]
425 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
427 // Analyse the safe enemy's checks which are possible on next move
428 safe = ~pos.pieces(Them);
429 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
431 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
432 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
434 // Enemy rooks checks
435 rookChecks = b1 & attackedBy[Them][ROOK] & safe;
437 kingDanger += SafeCheck[ROOK][more_than_one(rookChecks)];
439 unsafeChecks |= b1 & attackedBy[Them][ROOK];
441 // Enemy queen safe checks: count them only if the checks are from squares from
442 // which opponent cannot give a rook check, because rook checks are more valuable.
443 queenChecks = (b1 | b2) & attackedBy[Them][QUEEN] & safe
444 & ~(attackedBy[Us][QUEEN] | rookChecks);
446 kingDanger += SafeCheck[QUEEN][more_than_one(queenChecks)];
448 // Enemy bishops checks: count them only if they are from squares from which
449 // opponent cannot give a queen check, because queen checks are more valuable.
450 bishopChecks = b2 & attackedBy[Them][BISHOP] & safe
453 kingDanger += SafeCheck[BISHOP][more_than_one(bishopChecks)];
456 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
458 // Enemy knights checks
459 knightChecks = attacks_bb<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
460 if (knightChecks & safe)
461 kingDanger += SafeCheck[KNIGHT][more_than_one(knightChecks & safe)];
463 unsafeChecks |= knightChecks;
465 // Find the squares that opponent attacks in our king flank, the squares
466 // which they attack twice in that flank, and the squares that we defend.
467 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
468 b2 = b1 & attackedBy2[Them];
469 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
471 int kingFlankAttack = popcount(b1) + popcount(b2);
472 int kingFlankDefense = popcount(b3);
474 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
475 + 185 * popcount(kingRing[Us] & weak)
476 + 148 * popcount(unsafeChecks)
477 + 98 * popcount(pos.blockers_for_king(Us))
478 + 69 * kingAttacksCount[Them]
479 + 3 * kingFlankAttack * kingFlankAttack / 8
480 + mg_value(mobility[Them] - mobility[Us])
481 - 873 * !pos.count<QUEEN>(Them)
482 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
483 - 6 * mg_value(score) / 8
484 - 4 * kingFlankDefense
487 // Transform the kingDanger units into a Score, and subtract it from the evaluation
488 if (kingDanger > 100)
489 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
491 // Penalty when our king is on a pawnless flank
492 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
493 score -= PawnlessFlank;
495 // Penalty if king flank is under attack, potentially moving toward the king
496 score -= FlankAttacks * kingFlankAttack;
499 Trace::add(KING, Us, score);
505 // Evaluation::threats() assigns bonuses according to the types of the
506 // attacking and the attacked pieces.
508 template<Tracing T> template<Color Us>
509 Score Evaluation<T>::threats() const {
511 constexpr Color Them = ~Us;
512 constexpr Direction Up = pawn_push(Us);
513 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
515 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
516 Score score = SCORE_ZERO;
519 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
521 // Squares strongly protected by the enemy, either because they defend the
522 // square with a pawn, or because they defend the square twice and we don't.
523 stronglyProtected = attackedBy[Them][PAWN]
524 | (attackedBy2[Them] & ~attackedBy2[Us]);
526 // Non-pawn enemies, strongly protected
527 defended = nonPawnEnemies & stronglyProtected;
529 // Enemies not strongly protected and under our attack
530 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
532 // Bonus according to the kind of attacking pieces
535 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
537 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
539 b = weak & attackedBy[Us][ROOK];
541 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
543 if (weak & attackedBy[Us][KING])
544 score += ThreatByKing;
546 b = ~attackedBy[Them][ALL_PIECES]
547 | (nonPawnEnemies & attackedBy2[Us]);
548 score += Hanging * popcount(weak & b);
550 // Additional bonus if weak piece is only protected by a queen
551 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
554 // Bonus for restricting their piece moves
555 b = attackedBy[Them][ALL_PIECES]
557 & attackedBy[Us][ALL_PIECES];
558 score += RestrictedPiece * popcount(b);
560 // Protected or unattacked squares
561 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
563 // Bonus for attacking enemy pieces with our relatively safe pawns
564 b = pos.pieces(Us, PAWN) & safe;
565 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
566 score += ThreatBySafePawn * popcount(b);
568 // Find squares where our pawns can push on the next move
569 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
570 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
572 // Keep only the squares which are relatively safe
573 b &= ~attackedBy[Them][PAWN] & safe;
575 // Bonus for safe pawn threats on the next move
576 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
577 score += ThreatByPawnPush * popcount(b);
579 // Bonus for threats on the next moves against enemy queen
580 if (pos.count<QUEEN>(Them) == 1)
582 bool queenImbalance = pos.count<QUEEN>() == 1;
584 Square s = pos.square<QUEEN>(Them);
585 safe = mobilityArea[Us]
586 & ~pos.pieces(Us, PAWN)
587 & ~stronglyProtected;
589 b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
591 score += KnightOnQueen * popcount(b & safe) * (1 + queenImbalance);
593 b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
594 | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
596 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]) * (1 + queenImbalance);
600 Trace::add(THREAT, Us, score);
605 // Evaluation::passed() evaluates the passed pawns and candidate passed
606 // pawns of the given color.
608 template<Tracing T> template<Color Us>
609 Score Evaluation<T>::passed() const {
611 constexpr Color Them = ~Us;
612 constexpr Direction Up = pawn_push(Us);
613 constexpr Direction Down = -Up;
615 auto king_proximity = [&](Color c, Square s) {
616 return std::min(distance(pos.square<KING>(c), s), 5);
619 Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
620 Score score = SCORE_ZERO;
622 b = pe->passed_pawns(Us);
624 blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
627 helpers = shift<Up>(pos.pieces(Us, PAWN))
629 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
631 // Remove blocked candidate passers that don't have help to pass
633 | shift<WEST>(helpers)
634 | shift<EAST>(helpers);
639 Square s = pop_lsb(&b);
641 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
643 int r = relative_rank(Us, s);
645 Score bonus = PassedRank[r];
650 Square blockSq = s + Up;
652 // Adjust bonus based on the king's proximity
653 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
654 - king_proximity(Us, blockSq) * 2) * w);
656 // If blockSq is not the queening square then consider also a second push
658 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
660 // If the pawn is free to advance, then increase the bonus
661 if (pos.empty(blockSq))
663 squaresToQueen = forward_file_bb(Us, s);
664 unsafeSquares = passed_pawn_span(Us, s);
666 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
668 if (!(pos.pieces(Them) & bb))
669 unsafeSquares &= attackedBy[Them][ALL_PIECES];
671 // If there are no enemy attacks on passed pawn span, assign a big bonus.
672 // Otherwise assign a smaller bonus if the path to queen is not attacked
673 // and even smaller bonus if it is attacked but block square is not.
674 int k = !unsafeSquares ? 35 :
675 !(unsafeSquares & squaresToQueen) ? 20 :
676 !(unsafeSquares & blockSq) ? 9 :
679 // Assign a larger bonus if the block square is defended
680 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
683 bonus += make_score(k * w, k * w);
687 score += bonus - PassedFile * edge_distance(file_of(s));
691 Trace::add(PASSED, Us, score);
697 // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
698 // play in the opening. It is based on the number of safe squares on the 4 central files
699 // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
700 // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
702 template<Tracing T> template<Color Us>
703 Score Evaluation<T>::space() const {
705 // Early exit if, for example, both queens or 6 minor pieces have been exchanged
706 if (pos.non_pawn_material() < SpaceThreshold)
709 constexpr Color Them = ~Us;
710 constexpr Direction Down = -pawn_push(Us);
711 constexpr Bitboard SpaceMask =
712 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
713 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
715 // Find the available squares for our pieces inside the area defined by SpaceMask
716 Bitboard safe = SpaceMask
717 & ~pos.pieces(Us, PAWN)
718 & ~attackedBy[Them][PAWN];
720 // Find all squares which are at most three squares behind some friendly pawn
721 Bitboard behind = pos.pieces(Us, PAWN);
722 behind |= shift<Down>(behind);
723 behind |= shift<Down+Down>(behind);
725 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
726 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
727 Score score = make_score(bonus * weight * weight / 16, 0);
730 Trace::add(SPACE, Us, score);
736 // Evaluation::winnable() adjusts the midgame and endgame score components, based on
737 // the known attacking/defending status of the players. The final value is derived
738 // by interpolation from the midgame and endgame values.
741 Value Evaluation<T>::winnable(Score score) const {
743 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
744 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
746 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
747 && (pos.pieces(PAWN) & KingSide);
749 bool almostUnwinnable = outflanking < 0
750 && !pawnsOnBothFlanks;
752 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
753 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
755 // Compute the initiative bonus for the attacking side
756 int complexity = 9 * pe->passed_count()
757 + 12 * pos.count<PAWN>()
759 + 21 * pawnsOnBothFlanks
761 + 51 * !pos.non_pawn_material()
762 - 43 * almostUnwinnable
765 Value mg = mg_value(score);
766 Value eg = eg_value(score);
768 // Now apply the bonus: note that we find the attacking side by extracting the
769 // sign of the midgame or endgame values, and that we carefully cap the bonus
770 // so that the midgame and endgame scores do not change sign after the bonus.
771 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
772 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
777 // Compute the scale factor for the winning side
778 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
779 int sf = me->scale_factor(pos, strongSide);
781 // If scale factor is not already specific, scale down via general heuristics
782 if (sf == SCALE_FACTOR_NORMAL)
784 if (pos.opposite_bishops())
786 if ( pos.non_pawn_material(WHITE) == BishopValueMg
787 && pos.non_pawn_material(BLACK) == BishopValueMg)
788 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
790 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
792 else if ( pos.non_pawn_material(WHITE) == RookValueMg
793 && pos.non_pawn_material(BLACK) == RookValueMg
794 && pos.count<PAWN>(strongSide) - pos.count<PAWN>(~strongSide) <= 1
795 && bool(KingSide & pos.pieces(strongSide, PAWN)) != bool(QueenSide & pos.pieces(strongSide, PAWN))
796 && (attacks_bb<KING>(pos.square<KING>(~strongSide)) & pos.pieces(~strongSide, PAWN)))
798 else if (pos.count<QUEEN>() == 1)
799 sf = 37 + 3 * (pos.count<QUEEN>(WHITE) == 1 ? pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK)
800 : pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE));
802 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
805 // Interpolate between the middlegame and (scaled by 'sf') endgame score
806 v = mg * int(me->game_phase())
807 + eg * int(PHASE_MIDGAME - me->game_phase()) * ScaleFactor(sf) / SCALE_FACTOR_NORMAL;
812 Trace::add(WINNABLE, make_score(u, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL - eg_value(score)));
813 Trace::add(TOTAL, make_score(mg, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL));
820 // Evaluation::value() is the main function of the class. It computes the various
821 // parts of the evaluation and returns the value of the position from the point
822 // of view of the side to move.
825 Value Evaluation<T>::value() {
827 assert(!pos.checkers());
829 // Probe the material hash table
830 me = Material::probe(pos);
832 // If we have a specialized evaluation function for the current material
833 // configuration, call it and return.
834 if (me->specialized_eval_exists())
835 return me->evaluate(pos);
837 // Initialize score by reading the incrementally updated scores included in
838 // the position object (material + piece square tables) and the material
839 // imbalance. Score is computed internally from the white point of view.
840 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
842 // Probe the pawn hash table
843 pe = Pawns::probe(pos);
844 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
846 // Early exit if score is high
847 auto lazy_skip = [&](Value lazyThreshold) {
848 return abs(mg_value(score) + eg_value(score)) / 2 > lazyThreshold + pos.non_pawn_material() / 64;
851 if (lazy_skip(LazyThreshold1))
854 // Main evaluation begins here
858 // Pieces evaluated first (also populates attackedBy, attackedBy2).
859 // Note that the order of evaluation of the terms is left unspecified.
860 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
861 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
862 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
863 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
865 score += mobility[WHITE] - mobility[BLACK];
867 // More complex interactions that require fully populated attack bitboards
868 score += king< WHITE>() - king< BLACK>()
869 + passed< WHITE>() - passed< BLACK>();
871 if (lazy_skip(LazyThreshold2))
874 score += threats<WHITE>() - threats<BLACK>()
875 + space< WHITE>() - space< BLACK>();
878 // Derive single value from mg and eg parts of score
879 Value v = winnable(score);
881 // In case of tracing add all remaining individual evaluation terms
884 Trace::add(MATERIAL, pos.psq_score());
885 Trace::add(IMBALANCE, me->imbalance());
886 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
887 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
893 // Side to move point of view
894 v = (pos.side_to_move() == WHITE ? v : -v) + Tempo;
896 // Damp down the evaluation linearly when shuffling
897 v = v * (100 - pos.rule50_count()) / 100;
905 /// evaluate() is the evaluator for the outer world. It returns a static
906 /// evaluation of the position from the point of view of the side to move.
908 Value Eval::evaluate(const Position& pos) {
909 return Evaluation<NO_TRACE>(pos).value();
913 /// trace() is like evaluate(), but instead of returning a value, it returns
914 /// a string (suitable for outputting to stdout) that contains the detailed
915 /// descriptions and values of each evaluation term. Useful for debugging.
917 std::string Eval::trace(const Position& pos) {
920 return "Total evaluation: none (in check)";
922 std::memset(scores, 0, sizeof(scores));
924 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
926 Value v = Evaluation<TRACE>(pos).value();
928 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
930 std::stringstream ss;
931 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
932 << " Term | White | Black | Total \n"
933 << " | MG EG | MG EG | MG EG \n"
934 << " ------------+-------------+-------------+------------\n"
935 << " Material | " << Term(MATERIAL)
936 << " Imbalance | " << Term(IMBALANCE)
937 << " Pawns | " << Term(PAWN)
938 << " Knights | " << Term(KNIGHT)
939 << " Bishops | " << Term(BISHOP)
940 << " Rooks | " << Term(ROOK)
941 << " Queens | " << Term(QUEEN)
942 << " Mobility | " << Term(MOBILITY)
943 << " King safety | " << Term(KING)
944 << " Threats | " << Term(THREAT)
945 << " Passed | " << Term(PASSED)
946 << " Space | " << Term(SPACE)
947 << " Winnable | " << Term(WINNABLE)
948 << " ------------+-------------+-------------+------------\n"
949 << " Total | " << Term(TOTAL);
951 ss << "\nFinal evaluation: " << to_cp(v) << " (white side)\n";