2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
35 enum Tracing { NO_TRACE, TRACE };
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
41 Score scores[TERM_NB][COLOR_NB];
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
45 void add(int idx, Color c, Score s) {
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
60 std::ostream& operator<<(std::ostream& os, Term t) {
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
72 using namespace Trace;
76 // Threshold for lazy and space evaluation
77 constexpr Value LazyThreshold = Value(1400);
78 constexpr Value SpaceThreshold = Value(12222);
80 // KingAttackWeights[PieceType] contains king attack weights by piece type
81 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
83 // Penalties for enemy's safe checks
84 constexpr int QueenSafeCheck = 772;
85 constexpr int RookSafeCheck = 1084;
86 constexpr int BishopSafeCheck = 645;
87 constexpr int KnightSafeCheck = 792;
89 #define S(mg, eg) make_score(mg, eg)
91 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
92 // indexed by piece type and number of attacked squares in the mobility area.
93 constexpr Score MobilityBonus[][32] = {
94 { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knight
95 S( 22, 23), S( 28, 27), S( 33, 33) },
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(-34,-36), S(-15,-21), S(-10, -1), S(-10, 22), S( 20, 41), S( 23, 56), // 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 BishopXRayPawns = S( 4, 5);
132 constexpr Score CorneredBishop = S( 50, 50);
133 constexpr Score FlankAttacks = S( 8, 0);
134 constexpr Score Hanging = S( 69, 36);
135 constexpr Score BishopKingProtector = S( 6, 9);
136 constexpr Score KnightKingProtector = S( 8, 9);
137 constexpr Score KnightOnQueen = S( 16, 11);
138 constexpr Score LongDiagonalBishop = S( 45, 0);
139 constexpr Score MinorBehindPawn = S( 18, 3);
140 constexpr Score KnightOutpost = S( 56, 36);
141 constexpr Score BishopOutpost = S( 30, 23);
142 constexpr Score ReachableOutpost = S( 31, 22);
143 constexpr Score PassedFile = S( 11, 8);
144 constexpr Score PawnlessFlank = S( 17, 95);
145 constexpr Score RestrictedPiece = S( 7, 7);
146 constexpr Score RookOnQueenFile = S( 5, 9);
147 constexpr Score SliderOnQueen = S( 59, 18);
148 constexpr Score ThreatByKing = S( 24, 89);
149 constexpr Score ThreatByPawnPush = S( 48, 39);
150 constexpr Score ThreatBySafePawn = S(173, 94);
151 constexpr Score TrappedRook = S( 55, 13);
152 constexpr Score WeakQueen = S( 51, 14);
153 constexpr Score WeakQueenProtection = S( 15, 0);
157 // Evaluation class computes and stores attacks tables and other working data
162 Evaluation() = delete;
163 explicit Evaluation(const Position& p) : pos(p) {}
164 Evaluation& operator=(const Evaluation&) = delete;
168 template<Color Us> void initialize();
169 template<Color Us, PieceType Pt> Score pieces();
170 template<Color Us> Score king() const;
171 template<Color Us> Score threats() const;
172 template<Color Us> Score passed() const;
173 template<Color Us> Score space() const;
174 ScaleFactor scale_factor(Value eg) const;
175 Score initiative(Score score) const;
180 Bitboard mobilityArea[COLOR_NB];
181 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
183 // attackedBy[color][piece type] is a bitboard representing all squares
184 // attacked by a given color and piece type. Special "piece types" which
185 // is also calculated is ALL_PIECES.
186 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
188 // attackedBy2[color] are the squares attacked by at least 2 units of a given
189 // color, including x-rays. But diagonal x-rays through pawns are not computed.
190 Bitboard attackedBy2[COLOR_NB];
192 // kingRing[color] are the squares adjacent to the king plus some other
193 // very near squares, depending on king position.
194 Bitboard kingRing[COLOR_NB];
196 // kingAttackersCount[color] is the number of pieces of the given color
197 // which attack a square in the kingRing of the enemy king.
198 int kingAttackersCount[COLOR_NB];
200 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
201 // the given color which attack a square in the kingRing of the enemy king.
202 // The weights of the individual piece types are given by the elements in
203 // the KingAttackWeights array.
204 int kingAttackersWeight[COLOR_NB];
206 // kingAttacksCount[color] is the number of attacks by the given color to
207 // squares directly adjacent to the enemy king. Pieces which attack more
208 // than one square are counted multiple times. For instance, if there is
209 // a white knight on g5 and black's king is on g8, this white knight adds 2
210 // to kingAttacksCount[WHITE].
211 int kingAttacksCount[COLOR_NB];
215 // Evaluation::initialize() computes king and pawn attacks, and the king ring
216 // bitboard for a given color. This is done at the beginning of the evaluation.
217 template<Tracing T> template<Color Us>
218 void Evaluation<T>::initialize() {
220 constexpr Color Them = ~Us;
221 constexpr Direction Up = pawn_push(Us);
222 constexpr Direction Down = -Up;
223 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
225 const Square ksq = pos.square<KING>(Us);
227 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
229 // Find our pawns that are blocked or on the first two ranks
230 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
232 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
233 // or controlled by enemy pawns are excluded from the mobility area.
234 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
236 // Initialize attackedBy[] for king and pawns
237 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
238 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
239 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
240 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
242 // Init our king safety tables
243 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
244 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
245 kingRing[Us] = PseudoAttacks[KING][s] | s;
247 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
248 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
250 // Remove from kingRing[] the squares defended by two pawns
251 kingRing[Us] &= ~dblAttackByPawn;
255 // Evaluation::pieces() scores pieces of a given color and type
256 template<Tracing T> template<Color Us, PieceType Pt>
257 Score Evaluation<T>::pieces() {
259 constexpr Color Them = ~Us;
260 constexpr Direction Down = -pawn_push(Us);
261 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
262 : Rank5BB | Rank4BB | Rank3BB);
263 const Square* pl = pos.squares<Pt>(Us);
266 Score score = SCORE_ZERO;
268 attackedBy[Us][Pt] = 0;
270 for (Square s = *pl; s != SQ_NONE; s = *++pl)
272 // Find attacked squares, including x-ray attacks for bishops and rooks
273 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
274 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
275 : pos.attacks_from<Pt>(s);
277 if (pos.blockers_for_king(Us) & s)
278 b &= LineBB[pos.square<KING>(Us)][s];
280 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
281 attackedBy[Us][Pt] |= b;
282 attackedBy[Us][ALL_PIECES] |= b;
284 if (b & kingRing[Them])
286 kingAttackersCount[Us]++;
287 kingAttackersWeight[Us] += KingAttackWeights[Pt];
288 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
291 int mob = popcount(b & mobilityArea[Us]);
293 mobility[Us] += MobilityBonus[Pt - 2][mob];
295 if (Pt == BISHOP || Pt == KNIGHT)
297 // Bonus if piece is on an outpost square or can reach one
298 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
300 score += (Pt == KNIGHT) ? KnightOutpost : BishopOutpost;
301 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
302 score += ReachableOutpost;
304 // Bonus for a knight or bishop shielded by pawn
305 if (shift<Down>(pos.pieces(PAWN)) & s)
306 score += MinorBehindPawn;
308 // Penalty if the piece is far from the king
309 score -= (Pt == KNIGHT ? KnightKingProtector
310 : BishopKingProtector) * distance(pos.square<KING>(Us), s);
314 // Penalty according to number of pawns on the same color square as the
315 // bishop, bigger when the center files are blocked with pawns and smaller
316 // when the bishop is outside the pawn chain.
317 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
319 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
320 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
322 // Penalty for all enemy pawns x-rayed
323 score -= BishopXRayPawns * popcount(PseudoAttacks[BISHOP][s] & pos.pieces(Them, PAWN));
325 // Bonus for bishop on a long diagonal which can "see" both center squares
326 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
327 score += LongDiagonalBishop;
329 // An important Chess960 pattern: a cornered bishop blocked by a friendly
330 // pawn diagonally in front of it is a very serious problem, especially
331 // when that pawn is also blocked.
332 if ( pos.is_chess960()
333 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
335 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
336 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
337 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
338 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
346 // Bonus for rook on the same file as a queen
347 if (file_bb(s) & pos.pieces(QUEEN))
348 score += RookOnQueenFile;
350 // Bonus for rook on an open or semi-open file
351 if (pos.is_on_semiopen_file(Us, s))
352 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
354 // Penalty when trapped by the king, even more if the king cannot castle
357 File kf = file_of(pos.square<KING>(Us));
358 if ((kf < FILE_E) == (file_of(s) < kf))
359 score -= TrappedRook * (1 + !pos.castling_rights(Us));
365 // Penalty if any relative pin or discovered attack against the queen
366 Bitboard queenPinners;
367 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
372 Trace::add(Pt, Us, score);
378 // Evaluation::king() assigns bonuses and penalties to a king of a given color
379 template<Tracing T> template<Color Us>
380 Score Evaluation<T>::king() const {
382 constexpr Color Them = ~Us;
383 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
384 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
386 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
387 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
389 const Square ksq = pos.square<KING>(Us);
391 // Init the score with king shelter and enemy pawns storm
392 Score score = pe->king_safety<Us>(pos);
394 // Attacked squares defended at most once by our queen or king
395 weak = attackedBy[Them][ALL_PIECES]
397 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
399 // Analyse the safe enemy's checks which are possible on next move
400 safe = ~pos.pieces(Them);
401 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
403 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
404 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
406 // Enemy rooks checks
407 rookChecks = b1 & safe & attackedBy[Them][ROOK];
409 kingDanger += more_than_one(rookChecks) ? RookSafeCheck * 175/100
412 unsafeChecks |= b1 & attackedBy[Them][ROOK];
414 // Enemy queen safe checks: we count them only if they are from squares from
415 // which we can't give a rook check, because rook checks are more valuable.
416 queenChecks = (b1 | b2)
417 & attackedBy[Them][QUEEN]
419 & ~attackedBy[Us][QUEEN]
422 kingDanger += more_than_one(queenChecks) ? QueenSafeCheck * 145/100
425 // Enemy bishops checks: we count them only if they are from squares from
426 // which we can't give a queen check, because queen checks are more valuable.
428 & attackedBy[Them][BISHOP]
432 kingDanger += more_than_one(bishopChecks) ? BishopSafeCheck * 3/2
435 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
437 // Enemy knights checks
438 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
439 if (knightChecks & safe)
440 kingDanger += more_than_one(knightChecks & safe) ? KnightSafeCheck * 162/100
443 unsafeChecks |= knightChecks;
445 // Find the squares that opponent attacks in our king flank, the squares
446 // which they attack twice in that flank, and the squares that we defend.
447 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
448 b2 = b1 & attackedBy2[Them];
449 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
451 int kingFlankAttack = popcount(b1) + popcount(b2);
452 int kingFlankDefense = popcount(b3);
454 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
455 + 185 * popcount(kingRing[Us] & weak)
456 + 148 * popcount(unsafeChecks)
457 + 98 * popcount(pos.blockers_for_king(Us))
458 + 69 * kingAttacksCount[Them]
459 + 3 * kingFlankAttack * kingFlankAttack / 8
460 + mg_value(mobility[Them] - mobility[Us])
461 - 873 * !pos.count<QUEEN>(Them)
462 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
463 - 6 * mg_value(score) / 8
464 - 4 * kingFlankDefense
467 // Transform the kingDanger units into a Score, and subtract it from the evaluation
468 if (kingDanger > 100)
469 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
471 // Penalty when our king is on a pawnless flank
472 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
473 score -= PawnlessFlank;
475 // Penalty if king flank is under attack, potentially moving toward the king
476 score -= FlankAttacks * kingFlankAttack;
479 Trace::add(KING, Us, score);
485 // Evaluation::threats() assigns bonuses according to the types of the
486 // attacking and the attacked pieces.
487 template<Tracing T> template<Color Us>
488 Score Evaluation<T>::threats() const {
490 constexpr Color Them = ~Us;
491 constexpr Direction Up = pawn_push(Us);
492 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
494 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
495 Score score = SCORE_ZERO;
498 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
500 // Squares strongly protected by the enemy, either because they defend the
501 // square with a pawn, or because they defend the square twice and we don't.
502 stronglyProtected = attackedBy[Them][PAWN]
503 | (attackedBy2[Them] & ~attackedBy2[Us]);
505 // Non-pawn enemies, strongly protected
506 defended = nonPawnEnemies & stronglyProtected;
508 // Enemies not strongly protected and under our attack
509 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
511 // Bonus according to the kind of attacking pieces
514 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
516 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
518 b = weak & attackedBy[Us][ROOK];
520 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
522 if (weak & attackedBy[Us][KING])
523 score += ThreatByKing;
525 b = ~attackedBy[Them][ALL_PIECES]
526 | (nonPawnEnemies & attackedBy2[Us]);
527 score += Hanging * popcount(weak & b);
529 // Additional bonus if weak piece is only protected by a queen
530 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
533 // Bonus for restricting their piece moves
534 b = attackedBy[Them][ALL_PIECES]
536 & attackedBy[Us][ALL_PIECES];
537 score += RestrictedPiece * popcount(b);
539 // Protected or unattacked squares
540 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
542 // Bonus for attacking enemy pieces with our relatively safe pawns
543 b = pos.pieces(Us, PAWN) & safe;
544 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
545 score += ThreatBySafePawn * popcount(b);
547 // Find squares where our pawns can push on the next move
548 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
549 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
551 // Keep only the squares which are relatively safe
552 b &= ~attackedBy[Them][PAWN] & safe;
554 // Bonus for safe pawn threats on the next move
555 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
556 score += ThreatByPawnPush * popcount(b);
558 // Bonus for threats on the next moves against enemy queen
559 if (pos.count<QUEEN>(Them) == 1)
561 Square s = pos.square<QUEEN>(Them);
562 safe = mobilityArea[Us] & ~stronglyProtected;
564 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
566 score += KnightOnQueen * popcount(b & safe);
568 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
569 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
571 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
575 Trace::add(THREAT, Us, score);
580 // Evaluation::passed() evaluates the passed pawns and candidate passed
581 // pawns of the given color.
583 template<Tracing T> template<Color Us>
584 Score Evaluation<T>::passed() const {
586 constexpr Color Them = ~Us;
587 constexpr Direction Up = pawn_push(Us);
588 constexpr Direction Down = -Up;
590 auto king_proximity = [&](Color c, Square s) {
591 return std::min(distance(pos.square<KING>(c), s), 5);
594 Bitboard b, bb, squaresToQueen, unsafeSquares, candidatePassers, leverable;
595 Score score = SCORE_ZERO;
597 b = pe->passed_pawns(Us);
599 candidatePassers = b & shift<Down>(pos.pieces(Them, PAWN));
600 if (candidatePassers)
602 // Can we lever the blocker of a candidate passer?
603 leverable = shift<Up>(pos.pieces(Us, PAWN))
605 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES])
606 & (~(attackedBy[Them][KNIGHT] | attackedBy[Them][BISHOP])
607 | (attackedBy[Us ][KNIGHT] | attackedBy[Us ][BISHOP]));
609 // Remove candidate otherwise
610 b &= ~candidatePassers
611 | shift<WEST>(leverable)
612 | shift<EAST>(leverable);
617 Square s = pop_lsb(&b);
619 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
621 int r = relative_rank(Us, s);
623 Score bonus = PassedRank[r];
628 Square blockSq = s + Up;
630 // Adjust bonus based on the king's proximity
631 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
632 - king_proximity(Us, blockSq) * 2) * w);
634 // If blockSq is not the queening square then consider also a second push
636 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
638 // If the pawn is free to advance, then increase the bonus
639 if (pos.empty(blockSq))
641 squaresToQueen = forward_file_bb(Us, s);
642 unsafeSquares = passed_pawn_span(Us, s);
644 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
646 if (!(pos.pieces(Them) & bb))
647 unsafeSquares &= attackedBy[Them][ALL_PIECES];
649 // If there are no enemy attacks on passed pawn span, assign a big bonus.
650 // Otherwise assign a smaller bonus if the path to queen is not attacked
651 // and even smaller bonus if it is attacked but block square is not.
652 int k = !unsafeSquares ? 35 :
653 !(unsafeSquares & squaresToQueen) ? 20 :
654 !(unsafeSquares & blockSq) ? 9 :
657 // Assign a larger bonus if the block square is defended
658 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
661 bonus += make_score(k * w, k * w);
665 score += bonus - PassedFile * edge_distance(file_of(s));
669 Trace::add(PASSED, Us, score);
675 // Evaluation::space() computes the space evaluation for a given side. The
676 // space evaluation is a simple bonus based on the number of safe squares
677 // available for minor pieces on the central four files on ranks 2--4. Safe
678 // squares one, two or three squares behind a friendly pawn are counted
679 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
680 // improve play on game opening.
682 template<Tracing T> template<Color Us>
683 Score Evaluation<T>::space() const {
685 if (pos.non_pawn_material() < SpaceThreshold)
688 constexpr Color Them = ~Us;
689 constexpr Direction Down = -pawn_push(Us);
690 constexpr Bitboard SpaceMask =
691 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
692 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
694 // Find the available squares for our pieces inside the area defined by SpaceMask
695 Bitboard safe = SpaceMask
696 & ~pos.pieces(Us, PAWN)
697 & ~attackedBy[Them][PAWN];
699 // Find all squares which are at most three squares behind some friendly pawn
700 Bitboard behind = pos.pieces(Us, PAWN);
701 behind |= shift<Down>(behind);
702 behind |= shift<Down+Down>(behind);
704 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
705 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
706 Score score = make_score(bonus * weight * weight / 16, 0);
709 Trace::add(SPACE, Us, score);
715 // Evaluation::initiative() computes the initiative correction value
716 // for the position. It is a second order bonus/malus based on the
717 // known attacking/defending status of the players.
720 Score Evaluation<T>::initiative(Score score) const {
722 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
723 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
725 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
726 && (pos.pieces(PAWN) & KingSide);
728 bool almostUnwinnable = outflanking < 0
729 && !pawnsOnBothFlanks;
731 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
732 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
734 // Compute the initiative bonus for the attacking side
735 int complexity = 9 * pe->passed_count()
736 + 11 * pos.count<PAWN>()
738 + 21 * pawnsOnBothFlanks
740 + 51 * !pos.non_pawn_material()
741 - 43 * almostUnwinnable
744 Value mg = mg_value(score);
745 Value eg = eg_value(score);
747 // Now apply the bonus: note that we find the attacking side by extracting the
748 // sign of the midgame or endgame values, and that we carefully cap the bonus
749 // so that the midgame and endgame scores do not change sign after the bonus.
750 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
751 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
754 Trace::add(INITIATIVE, make_score(u, v));
756 return make_score(u, v);
760 // Evaluation::scale_factor() computes the scale factor for the winning side
763 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
765 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
766 int sf = me->scale_factor(pos, strongSide);
768 // If scale is not already specific, scale down the endgame via general heuristics
769 if (sf == SCALE_FACTOR_NORMAL)
771 if (pos.opposite_bishops())
773 if ( pos.non_pawn_material(WHITE) == BishopValueMg
774 && pos.non_pawn_material(BLACK) == BishopValueMg)
775 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
777 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
780 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
782 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
785 return ScaleFactor(sf);
789 // Evaluation::value() is the main function of the class. It computes the various
790 // parts of the evaluation and returns the value of the position from the point
791 // of view of the side to move.
794 Value Evaluation<T>::value() {
796 assert(!pos.checkers());
798 // Probe the material hash table
799 me = Material::probe(pos);
801 // If we have a specialized evaluation function for the current material
802 // configuration, call it and return.
803 if (me->specialized_eval_exists())
804 return me->evaluate(pos);
806 // Initialize score by reading the incrementally updated scores included in
807 // the position object (material + piece square tables) and the material
808 // imbalance. Score is computed internally from the white point of view.
809 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
811 // Probe the pawn hash table
812 pe = Pawns::probe(pos);
813 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
815 // Early exit if score is high
816 Value v = (mg_value(score) + eg_value(score)) / 2;
817 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
818 return pos.side_to_move() == WHITE ? v : -v;
820 // Main evaluation begins here
825 // Pieces evaluated first (also populates attackedBy, attackedBy2).
826 // Note that the order of evaluation of the terms is left unspecified
827 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
828 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
829 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
830 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
832 score += mobility[WHITE] - mobility[BLACK];
834 // More complex interactions that require fully populated attack bitboards
835 score += king< WHITE>() - king< BLACK>()
836 + threats<WHITE>() - threats<BLACK>()
837 + passed< WHITE>() - passed< BLACK>()
838 + space< WHITE>() - space< BLACK>();
840 score += initiative(score);
842 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
843 ScaleFactor sf = scale_factor(eg_value(score));
844 v = mg_value(score) * int(me->game_phase())
845 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
849 // In case of tracing add all remaining individual evaluation terms
852 Trace::add(MATERIAL, pos.psq_score());
853 Trace::add(IMBALANCE, me->imbalance());
854 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
855 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
856 Trace::add(TOTAL, score);
859 return (pos.side_to_move() == WHITE ? v : -v) + Tempo; // Side to move point of view
865 /// evaluate() is the evaluator for the outer world. It returns a static
866 /// evaluation of the position from the point of view of the side to move.
868 Value Eval::evaluate(const Position& pos) {
869 return Evaluation<NO_TRACE>(pos).value();
873 /// trace() is like evaluate(), but instead of returning a value, it returns
874 /// a string (suitable for outputting to stdout) that contains the detailed
875 /// descriptions and values of each evaluation term. Useful for debugging.
877 std::string Eval::trace(const Position& pos) {
880 return "Total evaluation: none (in check)";
882 std::memset(scores, 0, sizeof(scores));
884 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
886 Value v = Evaluation<TRACE>(pos).value();
888 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
890 std::stringstream ss;
891 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
892 << " Term | White | Black | Total \n"
893 << " | MG EG | MG EG | MG EG \n"
894 << " ------------+-------------+-------------+------------\n"
895 << " Material | " << Term(MATERIAL)
896 << " Imbalance | " << Term(IMBALANCE)
897 << " Pawns | " << Term(PAWN)
898 << " Knights | " << Term(KNIGHT)
899 << " Bishops | " << Term(BISHOP)
900 << " Rooks | " << Term(ROOK)
901 << " Queens | " << Term(QUEEN)
902 << " Mobility | " << Term(MOBILITY)
903 << " King safety | " << Term(KING)
904 << " Threats | " << Term(THREAT)
905 << " Passed | " << Term(PASSED)
906 << " Space | " << Term(SPACE)
907 << " Initiative | " << Term(INITIATIVE)
908 << " ------------+-------------+-------------+------------\n"
909 << " Total | " << Term(TOTAL);
911 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";