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 piece is on an outpost square or can reach one
314 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
316 && bb & s & ~CenterFiles
317 && !(b & pos.pieces(Them) & ~pos.pieces(PAWN))
318 && !conditional_more_than_two(
319 pos.pieces(Them) & ~pos.pieces(PAWN) & (s & QueenSide ? QueenSide : KingSide)))
322 score += Outpost[Pt == BISHOP];
323 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
324 score += ReachableOutpost;
326 // Bonus for a knight or bishop shielded by pawn
327 if (shift<Down>(pos.pieces(PAWN)) & s)
328 score += MinorBehindPawn;
330 // Penalty if the piece is far from the king
331 score -= KingProtector[Pt == BISHOP] * distance(pos.square<KING>(Us), s);
335 // Penalty according to the number of our pawns on the same color square as the
336 // bishop, bigger when the center files are blocked with pawns and smaller
337 // when the bishop is outside the pawn chain.
338 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
340 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
341 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
343 // Penalty for all enemy pawns x-rayed
344 score -= BishopXRayPawns * popcount(attacks_bb<BISHOP>(s) & pos.pieces(Them, PAWN));
346 // Bonus for bishop on a long diagonal which can "see" both center squares
347 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
348 score += LongDiagonalBishop;
350 // An important Chess960 pattern: a cornered bishop blocked by a friendly
351 // pawn diagonally in front of it is a very serious problem, especially
352 // when that pawn is also blocked.
353 if ( pos.is_chess960()
354 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
356 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
357 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
358 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
359 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
367 // Bonus for rook on the same file as a queen
368 if (file_bb(s) & pos.pieces(QUEEN))
369 score += RookOnQueenFile;
371 // Bonus for rook on an open or semi-open file
372 if (pos.is_on_semiopen_file(Us, s))
373 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
375 // Penalty when trapped by the king, even more if the king cannot castle
378 File kf = file_of(pos.square<KING>(Us));
379 if ((kf < FILE_E) == (file_of(s) < kf))
380 score -= TrappedRook * (1 + !pos.castling_rights(Us));
386 // Penalty if any relative pin or discovered attack against the queen
387 Bitboard queenPinners;
388 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
391 // Bonus for queen on weak square in enemy camp
392 if (relative_rank(Us, s) > RANK_4 && (~pe->pawn_attacks_span(Them) & s))
393 score += QueenInfiltration;
397 Trace::add(Pt, Us, score);
403 // Evaluation::king() assigns bonuses and penalties to a king of a given color
405 template<Tracing T> template<Color Us>
406 Score Evaluation<T>::king() const {
408 constexpr Color Them = ~Us;
409 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
410 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
412 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
413 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
415 const Square ksq = pos.square<KING>(Us);
417 // Init the score with king shelter and enemy pawns storm
418 Score score = pe->king_safety<Us>(pos);
420 // Attacked squares defended at most once by our queen or king
421 weak = attackedBy[Them][ALL_PIECES]
423 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
425 // Analyse the safe enemy's checks which are possible on next move
426 safe = ~pos.pieces(Them);
427 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
429 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
430 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
432 // Enemy rooks checks
433 rookChecks = b1 & attackedBy[Them][ROOK] & safe;
435 kingDanger += SafeCheck[ROOK][more_than_one(rookChecks)];
437 unsafeChecks |= b1 & attackedBy[Them][ROOK];
439 // Enemy queen safe checks: count them only if the checks are from squares from
440 // which opponent cannot give a rook check, because rook checks are more valuable.
441 queenChecks = (b1 | b2) & attackedBy[Them][QUEEN] & safe
442 & ~(attackedBy[Us][QUEEN] | rookChecks);
444 kingDanger += SafeCheck[QUEEN][more_than_one(queenChecks)];
446 // Enemy bishops checks: count them only if they are from squares from which
447 // opponent cannot give a queen check, because queen checks are more valuable.
448 bishopChecks = b2 & attackedBy[Them][BISHOP] & safe
451 kingDanger += SafeCheck[BISHOP][more_than_one(bishopChecks)];
454 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
456 // Enemy knights checks
457 knightChecks = attacks_bb<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
458 if (knightChecks & safe)
459 kingDanger += SafeCheck[KNIGHT][more_than_one(knightChecks & safe)];
461 unsafeChecks |= knightChecks;
463 // Find the squares that opponent attacks in our king flank, the squares
464 // which they attack twice in that flank, and the squares that we defend.
465 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
466 b2 = b1 & attackedBy2[Them];
467 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
469 int kingFlankAttack = popcount(b1) + popcount(b2);
470 int kingFlankDefense = popcount(b3);
472 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
473 + 185 * popcount(kingRing[Us] & weak)
474 + 148 * popcount(unsafeChecks)
475 + 98 * popcount(pos.blockers_for_king(Us))
476 + 69 * kingAttacksCount[Them]
477 + 3 * kingFlankAttack * kingFlankAttack / 8
478 + mg_value(mobility[Them] - mobility[Us])
479 - 873 * !pos.count<QUEEN>(Them)
480 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
481 - 6 * mg_value(score) / 8
482 - 4 * kingFlankDefense
485 // Transform the kingDanger units into a Score, and subtract it from the evaluation
486 if (kingDanger > 100)
487 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
489 // Penalty when our king is on a pawnless flank
490 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
491 score -= PawnlessFlank;
493 // Penalty if king flank is under attack, potentially moving toward the king
494 score -= FlankAttacks * kingFlankAttack;
497 Trace::add(KING, Us, score);
503 // Evaluation::threats() assigns bonuses according to the types of the
504 // attacking and the attacked pieces.
506 template<Tracing T> template<Color Us>
507 Score Evaluation<T>::threats() const {
509 constexpr Color Them = ~Us;
510 constexpr Direction Up = pawn_push(Us);
511 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
513 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
514 Score score = SCORE_ZERO;
517 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
519 // Squares strongly protected by the enemy, either because they defend the
520 // square with a pawn, or because they defend the square twice and we don't.
521 stronglyProtected = attackedBy[Them][PAWN]
522 | (attackedBy2[Them] & ~attackedBy2[Us]);
524 // Non-pawn enemies, strongly protected
525 defended = nonPawnEnemies & stronglyProtected;
527 // Enemies not strongly protected and under our attack
528 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
530 // Bonus according to the kind of attacking pieces
533 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
535 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
537 b = weak & attackedBy[Us][ROOK];
539 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
541 if (weak & attackedBy[Us][KING])
542 score += ThreatByKing;
544 b = ~attackedBy[Them][ALL_PIECES]
545 | (nonPawnEnemies & attackedBy2[Us]);
546 score += Hanging * popcount(weak & b);
548 // Additional bonus if weak piece is only protected by a queen
549 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
552 // Bonus for restricting their piece moves
553 b = attackedBy[Them][ALL_PIECES]
555 & attackedBy[Us][ALL_PIECES];
556 score += RestrictedPiece * popcount(b);
558 // Protected or unattacked squares
559 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
561 // Bonus for attacking enemy pieces with our relatively safe pawns
562 b = pos.pieces(Us, PAWN) & safe;
563 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
564 score += ThreatBySafePawn * popcount(b);
566 // Find squares where our pawns can push on the next move
567 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
568 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
570 // Keep only the squares which are relatively safe
571 b &= ~attackedBy[Them][PAWN] & safe;
573 // Bonus for safe pawn threats on the next move
574 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
575 score += ThreatByPawnPush * popcount(b);
577 // Bonus for threats on the next moves against enemy queen
578 if (pos.count<QUEEN>(Them) == 1)
580 Square s = pos.square<QUEEN>(Them);
581 safe = mobilityArea[Us] & ~stronglyProtected;
583 b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
585 score += KnightOnQueen * popcount(b & safe);
587 b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
588 | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
590 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
594 Trace::add(THREAT, Us, score);
599 // Evaluation::passed() evaluates the passed pawns and candidate passed
600 // pawns of the given color.
602 template<Tracing T> template<Color Us>
603 Score Evaluation<T>::passed() const {
605 constexpr Color Them = ~Us;
606 constexpr Direction Up = pawn_push(Us);
607 constexpr Direction Down = -Up;
609 auto king_proximity = [&](Color c, Square s) {
610 return std::min(distance(pos.square<KING>(c), s), 5);
613 Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
614 Score score = SCORE_ZERO;
616 b = pe->passed_pawns(Us);
618 blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
621 helpers = shift<Up>(pos.pieces(Us, PAWN))
623 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
625 // Remove blocked candidate passers that don't have help to pass
627 | shift<WEST>(helpers)
628 | shift<EAST>(helpers);
633 Square s = pop_lsb(&b);
635 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
637 int r = relative_rank(Us, s);
639 Score bonus = PassedRank[r];
644 Square blockSq = s + Up;
646 // Adjust bonus based on the king's proximity
647 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
648 - king_proximity(Us, blockSq) * 2) * w);
650 // If blockSq is not the queening square then consider also a second push
652 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
654 // If the pawn is free to advance, then increase the bonus
655 if (pos.empty(blockSq))
657 squaresToQueen = forward_file_bb(Us, s);
658 unsafeSquares = passed_pawn_span(Us, s);
660 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
662 if (!(pos.pieces(Them) & bb))
663 unsafeSquares &= attackedBy[Them][ALL_PIECES];
665 // If there are no enemy attacks on passed pawn span, assign a big bonus.
666 // Otherwise assign a smaller bonus if the path to queen is not attacked
667 // and even smaller bonus if it is attacked but block square is not.
668 int k = !unsafeSquares ? 35 :
669 !(unsafeSquares & squaresToQueen) ? 20 :
670 !(unsafeSquares & blockSq) ? 9 :
673 // Assign a larger bonus if the block square is defended
674 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
677 bonus += make_score(k * w, k * w);
681 score += bonus - PassedFile * edge_distance(file_of(s));
685 Trace::add(PASSED, Us, score);
691 // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
692 // play in the opening. It is based on the number of safe squares on the 4 central files
693 // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
694 // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
696 template<Tracing T> template<Color Us>
697 Score Evaluation<T>::space() const {
699 // Early exit if, for example, both queens or 6 minor pieces have been exchanged
700 if (pos.non_pawn_material() < SpaceThreshold)
703 constexpr Color Them = ~Us;
704 constexpr Direction Down = -pawn_push(Us);
705 constexpr Bitboard SpaceMask =
706 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
707 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
709 // Find the available squares for our pieces inside the area defined by SpaceMask
710 Bitboard safe = SpaceMask
711 & ~pos.pieces(Us, PAWN)
712 & ~attackedBy[Them][PAWN];
714 // Find all squares which are at most three squares behind some friendly pawn
715 Bitboard behind = pos.pieces(Us, PAWN);
716 behind |= shift<Down>(behind);
717 behind |= shift<Down+Down>(behind);
719 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
720 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
721 Score score = make_score(bonus * weight * weight / 16, 0);
724 Trace::add(SPACE, Us, score);
730 // Evaluation::winnable() adjusts the midgame and endgame score components, based on
731 // the known attacking/defending status of the players. The final value is derived
732 // by interpolation from the midgame and endgame values.
735 Value Evaluation<T>::winnable(Score score) const {
737 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
738 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
740 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
741 && (pos.pieces(PAWN) & KingSide);
743 bool almostUnwinnable = outflanking < 0
744 && !pawnsOnBothFlanks;
746 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
747 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
749 // Compute the initiative bonus for the attacking side
750 int complexity = 9 * pe->passed_count()
751 + 12 * pos.count<PAWN>()
753 + 21 * pawnsOnBothFlanks
755 + 51 * !pos.non_pawn_material()
756 - 43 * almostUnwinnable
759 Value mg = mg_value(score);
760 Value eg = eg_value(score);
762 // Now apply the bonus: note that we find the attacking side by extracting the
763 // sign of the midgame or endgame values, and that we carefully cap the bonus
764 // so that the midgame and endgame scores do not change sign after the bonus.
765 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
766 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
771 // Compute the scale factor for the winning side
772 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
773 int sf = me->scale_factor(pos, strongSide);
775 // If scale factor is not already specific, scale down via general heuristics
776 if (sf == SCALE_FACTOR_NORMAL)
778 if (pos.opposite_bishops())
780 if ( pos.non_pawn_material(WHITE) == BishopValueMg
781 && pos.non_pawn_material(BLACK) == BishopValueMg)
782 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
784 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
786 else if ( pos.non_pawn_material(WHITE) == RookValueMg
787 && pos.non_pawn_material(BLACK) == RookValueMg
788 && pos.count<PAWN>(strongSide) - pos.count<PAWN>(~strongSide) <= 1
789 && bool(KingSide & pos.pieces(strongSide, PAWN)) != bool(QueenSide & pos.pieces(strongSide, PAWN))
790 && (attacks_bb<KING>(pos.square<KING>(~strongSide)) & pos.pieces(~strongSide, PAWN)))
792 else if (pos.count<QUEEN>() == 1)
793 sf = 37 + 3 * (pos.count<QUEEN>(WHITE) == 1 ? pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK)
794 : pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE));
796 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
799 // Interpolate between the middlegame and (scaled by 'sf') endgame score
800 v = mg * int(me->game_phase())
801 + eg * int(PHASE_MIDGAME - me->game_phase()) * ScaleFactor(sf) / SCALE_FACTOR_NORMAL;
806 Trace::add(WINNABLE, make_score(u, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL - eg_value(score)));
807 Trace::add(TOTAL, make_score(mg, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL));
814 // Evaluation::value() is the main function of the class. It computes the various
815 // parts of the evaluation and returns the value of the position from the point
816 // of view of the side to move.
819 Value Evaluation<T>::value() {
821 assert(!pos.checkers());
823 // Probe the material hash table
824 me = Material::probe(pos);
826 // If we have a specialized evaluation function for the current material
827 // configuration, call it and return.
828 if (me->specialized_eval_exists())
829 return me->evaluate(pos);
831 // Initialize score by reading the incrementally updated scores included in
832 // the position object (material + piece square tables) and the material
833 // imbalance. Score is computed internally from the white point of view.
834 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
836 // Probe the pawn hash table
837 pe = Pawns::probe(pos);
838 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
840 // Early exit if score is high
841 auto lazy_skip = [&](Value lazyThreshold) {
842 return abs(mg_value(score) + eg_value(score)) / 2 > lazyThreshold + pos.non_pawn_material() / 64;
845 if (lazy_skip(LazyThreshold1))
848 // Main evaluation begins here
852 // Pieces evaluated first (also populates attackedBy, attackedBy2).
853 // Note that the order of evaluation of the terms is left unspecified.
854 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
855 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
856 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
857 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
859 score += mobility[WHITE] - mobility[BLACK];
861 // More complex interactions that require fully populated attack bitboards
862 score += king< WHITE>() - king< BLACK>()
863 + passed< WHITE>() - passed< BLACK>();
865 if (lazy_skip(LazyThreshold2))
868 score += threats<WHITE>() - threats<BLACK>()
869 + space< WHITE>() - space< BLACK>();
872 // Derive single value from mg and eg parts of score
873 Value v = winnable(score);
875 // In case of tracing add all remaining individual evaluation terms
878 Trace::add(MATERIAL, pos.psq_score());
879 Trace::add(IMBALANCE, me->imbalance());
880 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
881 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
887 // Side to move point of view
888 v = (pos.side_to_move() == WHITE ? v : -v) + Tempo;
890 // Damp down the evaluation linearly when shuffling
891 v = v * (100 - pos.rule50_count()) / 100;
899 /// evaluate() is the evaluator for the outer world. It returns a static
900 /// evaluation of the position from the point of view of the side to move.
902 Value Eval::evaluate(const Position& pos) {
903 return Evaluation<NO_TRACE>(pos).value();
907 /// trace() is like evaluate(), but instead of returning a value, it returns
908 /// a string (suitable for outputting to stdout) that contains the detailed
909 /// descriptions and values of each evaluation term. Useful for debugging.
911 std::string Eval::trace(const Position& pos) {
914 return "Total evaluation: none (in check)";
916 std::memset(scores, 0, sizeof(scores));
918 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
920 Value v = Evaluation<TRACE>(pos).value();
922 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
924 std::stringstream ss;
925 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
926 << " Term | White | Black | Total \n"
927 << " | MG EG | MG EG | MG EG \n"
928 << " ------------+-------------+-------------+------------\n"
929 << " Material | " << Term(MATERIAL)
930 << " Imbalance | " << Term(IMBALANCE)
931 << " Pawns | " << Term(PAWN)
932 << " Knights | " << Term(KNIGHT)
933 << " Bishops | " << Term(BISHOP)
934 << " Rooks | " << Term(ROOK)
935 << " Queens | " << Term(QUEEN)
936 << " Mobility | " << Term(MOBILITY)
937 << " King safety | " << Term(KING)
938 << " Threats | " << Term(THREAT)
939 << " Passed | " << Term(PASSED)
940 << " Space | " << Term(SPACE)
941 << " Winnable | " << Term(WINNABLE)
942 << " ------------+-------------+-------------+------------\n"
943 << " Total | " << Term(TOTAL);
945 ss << "\nFinal evaluation: " << to_cp(v) << " (white side)\n";