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) 2015-2019 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/>.
22 #include <cstring> // For std::memset
34 enum Tracing { NO_TRACE, TRACE };
36 enum Term { // The first 8 entries are reserved for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
40 Score scores[TERM_NB][COLOR_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
48 void add(int idx, Score w, Score b = SCORE_ZERO) {
49 scores[idx][WHITE] = w;
50 scores[idx][BLACK] = b;
53 std::ostream& operator<<(std::ostream& os, Score s) {
54 os << std::setw(5) << to_cp(mg_value(s)) << " "
55 << std::setw(5) << to_cp(eg_value(s));
59 std::ostream& operator<<(std::ostream& os, Term t) {
61 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
62 os << " ---- ----" << " | " << " ---- ----";
64 os << scores[t][WHITE] << " | " << scores[t][BLACK];
66 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
71 using namespace Trace;
75 // Threshold for lazy and space evaluation
76 constexpr Value LazyThreshold = Value(1500);
77 constexpr Value SpaceThreshold = Value(12222);
79 // KingAttackWeights[PieceType] contains king attack weights by piece type
80 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
82 // Penalties for enemy's safe checks
83 constexpr int QueenSafeCheck = 780;
84 constexpr int RookSafeCheck = 1080;
85 constexpr int BishopSafeCheck = 635;
86 constexpr int KnightSafeCheck = 790;
88 #define S(mg, eg) make_score(mg, eg)
90 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
91 // indexed by piece type and number of attacked squares in the mobility area.
92 constexpr Score MobilityBonus[][32] = {
93 { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knights
94 S( 22, 23), S( 28, 27), S( 33, 33) },
95 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
96 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
97 S( 91, 88), S( 98, 97) },
98 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
99 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
100 S( 46,166), S( 48,169), S( 58,171) },
101 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
102 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
103 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
104 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
105 S(106,184), S(109,191), S(113,206), S(116,212) }
108 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
109 // no (friendly) pawn on the rook file.
110 constexpr Score RookOnFile[] = { S(18, 7), S(44, 20) };
112 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
113 // which piece type attacks which one. Attacks on lesser pieces which are
114 // pawn-defended are not considered.
115 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
116 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
119 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
120 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(51, 38)
123 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
124 constexpr Score PassedRank[RANK_NB] = {
125 S(0, 0), S(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
128 // PassedFile[File] contains a bonus according to the file of a passed pawn
129 constexpr Score PassedFile[FILE_NB] = {
130 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
131 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
134 // Assorted bonuses and penalties
135 constexpr Score BishopPawns = S( 3, 7);
136 constexpr Score CorneredBishop = S( 50, 50);
137 constexpr Score FlankAttacks = S( 8, 0);
138 constexpr Score Hanging = S( 69, 36);
139 constexpr Score KingProtector = S( 7, 8);
140 constexpr Score KnightOnQueen = S( 16, 12);
141 constexpr Score LongDiagonalBishop = S( 45, 0);
142 constexpr Score MinorBehindPawn = S( 18, 3);
143 constexpr Score Outpost = S( 9, 3);
144 constexpr Score PawnlessFlank = S( 17, 95);
145 constexpr Score RestrictedPiece = S( 7, 7);
146 constexpr Score RookOnPawn = S( 10, 32);
147 constexpr Score SliderOnQueen = S( 59, 18);
148 constexpr Score ThreatByKing = S( 24, 89);
149 constexpr Score ThreatByPawnPush = S( 48, 39);
150 constexpr Score ThreatByRank = S( 13, 0);
151 constexpr Score ThreatBySafePawn = S(173, 94);
152 constexpr Score TrappedRook = S( 47, 4);
153 constexpr Score WeakQueen = S( 49, 15);
154 constexpr Score WeakUnopposedPawn = S( 12, 23);
158 // Evaluation class computes and stores attacks tables and other working data
163 Evaluation() = delete;
164 explicit Evaluation(const Position& p) : pos(p) {}
165 Evaluation& operator=(const Evaluation&) = delete;
169 template<Color Us> void initialize();
170 template<Color Us, PieceType Pt> Score pieces();
171 template<Color Us> Score king() const;
172 template<Color Us> Score threats() const;
173 template<Color Us> Score passed() const;
174 template<Color Us> Score space() const;
175 ScaleFactor scale_factor(Value eg) const;
176 Score initiative(Value eg) const;
181 Bitboard mobilityArea[COLOR_NB];
182 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
184 // attackedBy[color][piece type] is a bitboard representing all squares
185 // attacked by a given color and piece type. Special "piece types" which
186 // is also calculated is ALL_PIECES.
187 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
189 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
190 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
191 // pawn or squares attacked by 2 pawns are not explicitly added.
192 Bitboard attackedBy2[COLOR_NB];
194 // kingRing[color] are the squares adjacent to the king, plus (only for a
195 // king on its first rank) the squares two ranks in front. For instance,
196 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
198 Bitboard kingRing[COLOR_NB];
200 // kingAttackersCount[color] is the number of pieces of the given color
201 // which attack a square in the kingRing of the enemy king.
202 int kingAttackersCount[COLOR_NB];
204 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
205 // the given color which attack a square in the kingRing of the enemy king.
206 // The weights of the individual piece types are given by the elements in
207 // the KingAttackWeights array.
208 int kingAttackersWeight[COLOR_NB];
210 // kingAttacksCount[color] is the number of attacks by the given color to
211 // squares directly adjacent to the enemy king. Pieces which attack more
212 // than one square are counted multiple times. For instance, if there is
213 // a white knight on g5 and black's king is on g8, this white knight adds 2
214 // to kingAttacksCount[WHITE].
215 int kingAttacksCount[COLOR_NB];
219 // Evaluation::initialize() computes king and pawn attacks, and the king ring
220 // bitboard for a given color. This is done at the beginning of the evaluation.
221 template<Tracing T> template<Color Us>
222 void Evaluation<T>::initialize() {
224 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
225 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
226 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
227 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
229 const Square ksq = pos.square<KING>(Us);
231 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
233 // Find our pawns that are blocked or on the first two ranks
234 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
236 // Squares occupied by those pawns, by our king or queen or controlled by
237 // enemy pawns are excluded from the mobility area.
238 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
240 // Initialize attackedBy[] for king and pawns
241 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
242 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
243 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
244 attackedBy2[Us] = (attackedBy[Us][KING] & attackedBy[Us][PAWN])
247 // Init our king safety tables
248 kingRing[Us] = attackedBy[Us][KING];
249 if (relative_rank(Us, ksq) == RANK_1)
250 kingRing[Us] |= shift<Up>(kingRing[Us]);
252 if (file_of(ksq) == FILE_H)
253 kingRing[Us] |= shift<WEST>(kingRing[Us]);
255 else if (file_of(ksq) == FILE_A)
256 kingRing[Us] |= shift<EAST>(kingRing[Us]);
258 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
259 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
261 // Remove from kingRing[] the squares defended by two pawns
262 kingRing[Us] &= ~dblAttackByPawn;
266 // Evaluation::pieces() scores pieces of a given color and type
267 template<Tracing T> template<Color Us, PieceType Pt>
268 Score Evaluation<T>::pieces() {
270 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
271 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
272 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
273 : Rank5BB | Rank4BB | Rank3BB);
274 const Square* pl = pos.squares<Pt>(Us);
277 Score score = SCORE_ZERO;
279 attackedBy[Us][Pt] = 0;
281 for (Square s = *pl; s != SQ_NONE; s = *++pl)
283 // Find attacked squares, including x-ray attacks for bishops and rooks
284 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
285 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
286 : pos.attacks_from<Pt>(s);
288 if (pos.blockers_for_king(Us) & s)
289 b &= LineBB[pos.square<KING>(Us)][s];
291 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
292 attackedBy[Us][Pt] |= b;
293 attackedBy[Us][ALL_PIECES] |= b;
295 if (b & kingRing[Them])
297 kingAttackersCount[Us]++;
298 kingAttackersWeight[Us] += KingAttackWeights[Pt];
299 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
302 int mob = popcount(b & mobilityArea[Us]);
304 mobility[Us] += MobilityBonus[Pt - 2][mob];
306 if (Pt == BISHOP || Pt == KNIGHT)
308 // Bonus if piece is on an outpost square or can reach one
309 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
311 score += Outpost * (Pt == KNIGHT ? 4 : 2)
312 * (1 + bool(attackedBy[Us][PAWN] & s));
314 else if (bb &= b & ~pos.pieces(Us))
315 score += Outpost * (Pt == KNIGHT ? 2 : 1)
316 * (1 + bool(attackedBy[Us][PAWN] & bb));
318 // Knight and Bishop bonus for being right behind a pawn
319 if (shift<Down>(pos.pieces(PAWN)) & s)
320 score += MinorBehindPawn;
322 // Penalty if the piece is far from the king
323 score -= KingProtector * distance(s, pos.square<KING>(Us));
327 // Penalty according to number of pawns on the same color square as the
328 // bishop, bigger when the center files are blocked with pawns.
329 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
331 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
332 * (1 + popcount(blocked & CenterFiles));
334 // Bonus for bishop on a long diagonal which can "see" both center squares
335 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
336 score += LongDiagonalBishop;
339 // An important Chess960 pattern: A cornered bishop blocked by a friendly
340 // pawn diagonally in front of it is a very serious problem, especially
341 // when that pawn is also blocked.
344 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
346 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
347 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
348 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
349 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
356 // Bonus for aligning rook with enemy pawns on the same rank/file
357 if (relative_rank(Us, s) >= RANK_5)
358 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
360 // Bonus for rook on an open or semi-open file
361 if (pos.semiopen_file(Us, file_of(s)))
362 score += RookOnFile[bool(pos.semiopen_file(Them, file_of(s)))];
364 // Penalty when trapped by the king, even more if the king cannot castle
367 File kf = file_of(pos.square<KING>(Us));
368 if ((kf < FILE_E) == (file_of(s) < kf))
369 score -= TrappedRook * (1 + !pos.castling_rights(Us));
375 // Penalty if any relative pin or discovered attack against the queen
376 Bitboard queenPinners;
377 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
382 Trace::add(Pt, Us, score);
388 // Evaluation::king() assigns bonuses and penalties to a king of a given color
389 template<Tracing T> template<Color Us>
390 Score Evaluation<T>::king() const {
392 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
393 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
394 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
396 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
397 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
399 const Square ksq = pos.square<KING>(Us);
401 // Init the score with king shelter and enemy pawns storm
402 Score score = pe->king_safety<Us>(pos);
404 // Attacked squares defended at most once by our queen or king
405 weak = attackedBy[Them][ALL_PIECES]
407 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
409 // Analyse the safe enemy's checks which are possible on next move
410 safe = ~pos.pieces(Them);
411 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
413 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
414 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
416 // Enemy rooks checks
417 rookChecks = b1 & safe & attackedBy[Them][ROOK];
420 kingDanger += RookSafeCheck;
422 unsafeChecks |= b1 & attackedBy[Them][ROOK];
424 // Enemy queen safe checks: we count them only if they are from squares from
425 // which we can't give a rook check, because rook checks are more valuable.
426 queenChecks = (b1 | b2)
427 & attackedBy[Them][QUEEN]
429 & ~attackedBy[Us][QUEEN]
433 kingDanger += QueenSafeCheck;
435 // Enemy bishops checks: we count them only if they are from squares from
436 // which we can't give a queen check, because queen checks are more valuable.
438 & attackedBy[Them][BISHOP]
443 kingDanger += BishopSafeCheck;
445 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
447 // Enemy knights checks
448 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
450 if (knightChecks & safe)
451 kingDanger += KnightSafeCheck;
453 unsafeChecks |= knightChecks;
455 // Unsafe or occupied checking squares will also be considered, as long as
456 // the square is in the attacker's mobility area.
457 unsafeChecks &= mobilityArea[Them];
459 // Find the squares that opponent attacks in our king flank, and the squares
460 // which are attacked twice in that flank.
461 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
462 b2 = b1 & attackedBy2[Them];
464 int kingFlankAttacks = popcount(b1) + popcount(b2);
466 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
467 + 69 * kingAttacksCount[Them]
468 + 185 * popcount(kingRing[Us] & weak)
469 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
470 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
471 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
472 - 873 * !pos.count<QUEEN>(Them)
473 - 6 * mg_value(score) / 8
474 + mg_value(mobility[Them] - mobility[Us])
475 + 5 * kingFlankAttacks * kingFlankAttacks / 16
478 // Transform the kingDanger units into a Score, and subtract it from the evaluation
479 if (kingDanger > 100)
480 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
482 // Penalty when our king is on a pawnless flank
483 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
484 score -= PawnlessFlank;
486 // Penalty if king flank is under attack, potentially moving toward the king
487 score -= FlankAttacks * kingFlankAttacks;
490 Trace::add(KING, Us, score);
496 // Evaluation::threats() assigns bonuses according to the types of the
497 // attacking and the attacked pieces.
498 template<Tracing T> template<Color Us>
499 Score Evaluation<T>::threats() const {
501 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
502 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
503 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
505 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
506 Score score = SCORE_ZERO;
509 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
511 // Squares strongly protected by the enemy, either because they defend the
512 // square with a pawn, or because they defend the square twice and we don't.
513 stronglyProtected = attackedBy[Them][PAWN]
514 | (attackedBy2[Them] & ~attackedBy2[Us]);
516 // Non-pawn enemies, strongly protected
517 defended = nonPawnEnemies & stronglyProtected;
519 // Enemies not strongly protected and under our attack
520 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
522 // Safe or protected squares
523 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
525 // Bonus according to the kind of attacking pieces
528 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
531 Square s = pop_lsb(&b);
532 score += ThreatByMinor[type_of(pos.piece_on(s))];
533 if (type_of(pos.piece_on(s)) != PAWN)
534 score += ThreatByRank * (int)relative_rank(Them, s);
537 b = weak & attackedBy[Us][ROOK];
540 Square s = pop_lsb(&b);
541 score += ThreatByRook[type_of(pos.piece_on(s))];
542 if (type_of(pos.piece_on(s)) != PAWN)
543 score += ThreatByRank * (int)relative_rank(Them, s);
546 if (weak & attackedBy[Us][KING])
547 score += ThreatByKing;
549 b = ~attackedBy[Them][ALL_PIECES]
550 | (nonPawnEnemies & attackedBy2[Us]);
551 score += Hanging * popcount(weak & b);
554 // Bonus for restricting their piece moves
555 b = attackedBy[Them][ALL_PIECES]
557 & attackedBy[Us][ALL_PIECES];
559 score += RestrictedPiece * popcount(b);
561 // Bonus for enemy unopposed weak pawns
562 if (pos.pieces(Us, ROOK, QUEEN))
563 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
565 // Find squares where our pawns can push on the next move
566 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
567 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
569 // Keep only the squares which are relatively safe
570 b &= ~attackedBy[Them][PAWN] & safe;
572 // Bonus for safe pawn threats on the next move
573 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
574 score += ThreatByPawnPush * popcount(b);
576 // Our safe or protected pawns
577 b = pos.pieces(Us, PAWN) & safe;
579 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
580 score += ThreatBySafePawn * popcount(b);
582 // Bonus for threats on the next moves against enemy queen
583 if (pos.count<QUEEN>(Them) == 1)
585 Square s = pos.square<QUEEN>(Them);
586 safe = mobilityArea[Us] & ~stronglyProtected;
588 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
590 score += KnightOnQueen * popcount(b & safe);
592 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
593 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
595 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
599 Trace::add(THREAT, Us, score);
604 // Evaluation::passed() evaluates the passed pawns and candidate passed
605 // pawns of the given color.
607 template<Tracing T> template<Color Us>
608 Score Evaluation<T>::passed() const {
610 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
611 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
613 auto king_proximity = [&](Color c, Square s) {
614 return std::min(distance(pos.square<KING>(c), s), 5);
617 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
618 Score score = SCORE_ZERO;
620 b = pe->passed_pawns(Us);
624 Square s = pop_lsb(&b);
626 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
628 int r = relative_rank(Us, s);
630 Score bonus = PassedRank[r];
634 int w = (r-2) * (r-2) + 2;
635 Square blockSq = s + Up;
637 // Adjust bonus based on the king's proximity
638 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
639 - king_proximity(Us, blockSq) * 2) * w);
641 // If blockSq is not the queening square then consider also a second push
643 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
645 // If the pawn is free to advance, then increase the bonus
646 if (pos.empty(blockSq))
648 // If there is a rook or queen attacking/defending the pawn from behind,
649 // consider all the squaresToQueen. Otherwise consider only the squares
650 // in the pawn's path attacked or occupied by the enemy.
651 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
653 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
655 if (!(pos.pieces(Us) & bb))
656 defendedSquares &= attackedBy[Us][ALL_PIECES];
658 if (!(pos.pieces(Them) & bb))
659 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
661 // If there aren't any enemy attacks, assign a big bonus. Otherwise
662 // assign a smaller bonus if the block square isn't attacked.
663 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
665 // If the path to the queen is fully defended, assign a big bonus.
666 // Otherwise assign a smaller bonus if the block square is defended.
667 if (defendedSquares == squaresToQueen)
670 else if (defendedSquares & blockSq)
673 bonus += make_score(k * w, k * w);
677 // Scale down bonus for candidate passers which need more than one
678 // pawn push to become passed, or have a pawn in front of them.
679 if ( !pos.pawn_passed(Us, s + Up)
680 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
683 score += bonus + PassedFile[file_of(s)];
687 Trace::add(PASSED, Us, score);
693 // Evaluation::space() computes the space evaluation for a given side. The
694 // space evaluation is a simple bonus based on the number of safe squares
695 // available for minor pieces on the central four files on ranks 2--4. Safe
696 // squares one, two or three squares behind a friendly pawn are counted
697 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
698 // improve play on game opening.
700 template<Tracing T> template<Color Us>
701 Score Evaluation<T>::space() const {
703 if (pos.non_pawn_material() < SpaceThreshold)
706 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
707 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
708 constexpr Bitboard SpaceMask =
709 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
710 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
712 // Find the available squares for our pieces inside the area defined by SpaceMask
713 Bitboard safe = SpaceMask
714 & ~pos.pieces(Us, PAWN)
715 & ~attackedBy[Them][PAWN];
717 // Find all squares which are at most three squares behind some friendly pawn
718 Bitboard behind = pos.pieces(Us, PAWN);
719 behind |= shift<Down>(behind);
720 behind |= shift<Down>(shift<Down>(behind));
722 int bonus = popcount(safe) + popcount(behind & safe);
723 int weight = pos.count<ALL_PIECES>(Us)
724 - (16 - pos.count<PAWN>()) / 4;
726 Score score = make_score(bonus * weight * weight / 16, 0);
729 Trace::add(SPACE, Us, score);
735 // Evaluation::initiative() computes the initiative correction value
736 // for the position. It is a second order bonus/malus based on the
737 // known attacking/defending status of the players.
740 Score Evaluation<T>::initiative(Value eg) const {
742 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
743 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
745 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
746 && (pos.pieces(PAWN) & KingSide);
748 // Compute the initiative bonus for the attacking side
749 int complexity = 9 * pe->passed_count()
750 + 11 * pos.count<PAWN>()
752 + 18 * pawnsOnBothFlanks
753 + 49 * !pos.non_pawn_material()
756 // Now apply the bonus: note that we find the attacking side by extracting
757 // the sign of the endgame value, and that we carefully cap the bonus so
758 // that the endgame score will never change sign after the bonus.
759 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
762 Trace::add(INITIATIVE, make_score(0, v));
764 return make_score(0, v);
768 // Evaluation::scale_factor() computes the scale factor for the winning side
771 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
773 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
774 int sf = me->scale_factor(pos, strongSide);
776 // If scale is not already specific, scale down the endgame via general heuristics
777 if (sf == SCALE_FACTOR_NORMAL)
779 if ( pos.opposite_bishops()
780 && pos.non_pawn_material(WHITE) == BishopValueMg
781 && pos.non_pawn_material(BLACK) == BishopValueMg)
782 sf = 16 + 4 * pe->passed_count();
784 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
788 return ScaleFactor(sf);
792 // Evaluation::value() is the main function of the class. It computes the various
793 // parts of the evaluation and returns the value of the position from the point
794 // of view of the side to move.
797 Value Evaluation<T>::value() {
799 assert(!pos.checkers());
801 // Probe the material hash table
802 me = Material::probe(pos);
804 // If we have a specialized evaluation function for the current material
805 // configuration, call it and return.
806 if (me->specialized_eval_exists())
807 return me->evaluate(pos);
809 // Initialize score by reading the incrementally updated scores included in
810 // the position object (material + piece square tables) and the material
811 // imbalance. Score is computed internally from the white point of view.
812 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
814 // Probe the pawn hash table
815 pe = Pawns::probe(pos);
816 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
818 // Early exit if score is high
819 Value v = (mg_value(score) + eg_value(score)) / 2;
820 if (abs(v) > LazyThreshold)
821 return pos.side_to_move() == WHITE ? v : -v;
823 // Main evaluation begins here
828 // Pieces should be evaluated first (populate attack tables)
829 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
830 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
831 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
832 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
834 score += mobility[WHITE] - mobility[BLACK];
836 score += king< WHITE>() - king< BLACK>()
837 + threats<WHITE>() - threats<BLACK>()
838 + passed< WHITE>() - passed< BLACK>()
839 + space< WHITE>() - space< BLACK>();
841 score += initiative(eg_value(score));
843 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
844 ScaleFactor sf = scale_factor(eg_value(score));
845 v = mg_value(score) * int(me->game_phase())
846 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
850 // In case of tracing add all remaining individual evaluation terms
853 Trace::add(MATERIAL, pos.psq_score());
854 Trace::add(IMBALANCE, me->imbalance());
855 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
856 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
857 Trace::add(TOTAL, score);
860 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
867 /// evaluate() is the evaluator for the outer world. It returns a static
868 /// evaluation of the position from the point of view of the side to move.
870 Value Eval::evaluate(const Position& pos) {
871 return Evaluation<NO_TRACE>(pos).value();
875 /// trace() is like evaluate(), but instead of returning a value, it returns
876 /// a string (suitable for outputting to stdout) that contains the detailed
877 /// descriptions and values of each evaluation term. Useful for debugging.
879 std::string Eval::trace(const Position& pos) {
881 std::memset(scores, 0, sizeof(scores));
883 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
885 Value v = Evaluation<TRACE>(pos).value();
887 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
889 std::stringstream ss;
890 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
891 << " Term | White | Black | Total \n"
892 << " | MG EG | MG EG | MG EG \n"
893 << " ------------+-------------+-------------+------------\n"
894 << " Material | " << Term(MATERIAL)
895 << " Imbalance | " << Term(IMBALANCE)
896 << " Pawns | " << Term(PAWN)
897 << " Knights | " << Term(KNIGHT)
898 << " Bishops | " << Term(BISHOP)
899 << " Rooks | " << Term(ROOK)
900 << " Queens | " << Term(QUEEN)
901 << " Mobility | " << Term(MOBILITY)
902 << " King safety | " << Term(KING)
903 << " Threats | " << Term(THREAT)
904 << " Passed | " << Term(PASSED)
905 << " Space | " << Term(SPACE)
906 << " Initiative | " << Term(INITIATIVE)
907 << " ------------+-------------+-------------+------------\n"
908 << " Total | " << Term(TOTAL);
910 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";