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 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
471 - 873 * !pos.count<QUEEN>(Them)
472 - 6 * mg_value(score) / 8
473 + mg_value(mobility[Them] - mobility[Us])
474 + 5 * kingFlankAttacks * kingFlankAttacks / 16
477 // Transform the kingDanger units into a Score, and subtract it from the evaluation
478 if (kingDanger > 100)
479 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
481 // Penalty when our king is on a pawnless flank
482 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
483 score -= PawnlessFlank;
485 // Penalty if king flank is under attack, potentially moving toward the king
486 score -= FlankAttacks * kingFlankAttacks;
489 Trace::add(KING, Us, score);
495 // Evaluation::threats() assigns bonuses according to the types of the
496 // attacking and the attacked pieces.
497 template<Tracing T> template<Color Us>
498 Score Evaluation<T>::threats() const {
500 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
501 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
502 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
504 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
505 Score score = SCORE_ZERO;
508 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
510 // Squares strongly protected by the enemy, either because they defend the
511 // square with a pawn, or because they defend the square twice and we don't.
512 stronglyProtected = attackedBy[Them][PAWN]
513 | (attackedBy2[Them] & ~attackedBy2[Us]);
515 // Non-pawn enemies, strongly protected
516 defended = nonPawnEnemies & stronglyProtected;
518 // Enemies not strongly protected and under our attack
519 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
521 // Safe or protected squares
522 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
524 // Bonus according to the kind of attacking pieces
527 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
530 Square s = pop_lsb(&b);
531 score += ThreatByMinor[type_of(pos.piece_on(s))];
532 if (type_of(pos.piece_on(s)) != PAWN)
533 score += ThreatByRank * (int)relative_rank(Them, s);
536 b = weak & attackedBy[Us][ROOK];
539 Square s = pop_lsb(&b);
540 score += ThreatByRook[type_of(pos.piece_on(s))];
541 if (type_of(pos.piece_on(s)) != PAWN)
542 score += ThreatByRank * (int)relative_rank(Them, s);
545 if (weak & attackedBy[Us][KING])
546 score += ThreatByKing;
548 b = ~attackedBy[Them][ALL_PIECES]
549 | (nonPawnEnemies & attackedBy2[Us]);
550 score += Hanging * popcount(weak & b);
553 // Bonus for restricting their piece moves
554 b = attackedBy[Them][ALL_PIECES]
556 & attackedBy[Us][ALL_PIECES];
558 score += RestrictedPiece * popcount(b);
560 // Bonus for enemy unopposed weak pawns
561 if (pos.pieces(Us, ROOK, QUEEN))
562 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
564 // Find squares where our pawns can push on the next move
565 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
566 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
568 // Keep only the squares which are relatively safe
569 b &= ~attackedBy[Them][PAWN] & safe;
571 // Bonus for safe pawn threats on the next move
572 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
573 score += ThreatByPawnPush * popcount(b);
575 // Our safe or protected pawns
576 b = pos.pieces(Us, PAWN) & safe;
578 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
579 score += ThreatBySafePawn * popcount(b);
581 // Bonus for threats on the next moves against enemy queen
582 if (pos.count<QUEEN>(Them) == 1)
584 Square s = pos.square<QUEEN>(Them);
585 safe = mobilityArea[Us] & ~stronglyProtected;
587 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
589 score += KnightOnQueen * popcount(b & safe);
591 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
592 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
594 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
598 Trace::add(THREAT, Us, score);
603 // Evaluation::passed() evaluates the passed pawns and candidate passed
604 // pawns of the given color.
606 template<Tracing T> template<Color Us>
607 Score Evaluation<T>::passed() const {
609 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
610 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
612 auto king_proximity = [&](Color c, Square s) {
613 return std::min(distance(pos.square<KING>(c), s), 5);
616 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
617 Score score = SCORE_ZERO;
619 b = pe->passed_pawns(Us);
623 Square s = pop_lsb(&b);
625 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
627 int r = relative_rank(Us, s);
629 Score bonus = PassedRank[r];
633 int w = (r-2) * (r-2) + 2;
634 Square blockSq = s + Up;
636 // Adjust bonus based on the king's proximity
637 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
638 - king_proximity(Us, blockSq) * 2) * w);
640 // If blockSq is not the queening square then consider also a second push
642 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
644 // If the pawn is free to advance, then increase the bonus
645 if (pos.empty(blockSq))
647 // If there is a rook or queen attacking/defending the pawn from behind,
648 // consider all the squaresToQueen. Otherwise consider only the squares
649 // in the pawn's path attacked or occupied by the enemy.
650 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
652 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
654 if (!(pos.pieces(Us) & bb))
655 defendedSquares &= attackedBy[Us][ALL_PIECES];
657 if (!(pos.pieces(Them) & bb))
658 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
660 // If there aren't any enemy attacks, assign a big bonus. Otherwise
661 // assign a smaller bonus if the block square isn't attacked.
662 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
664 // If the path to the queen is fully defended, assign a big bonus.
665 // Otherwise assign a smaller bonus if the block square is defended.
666 if (defendedSquares == squaresToQueen)
669 else if (defendedSquares & blockSq)
672 bonus += make_score(k * w, k * w);
676 // Scale down bonus for candidate passers which need more than one
677 // pawn push to become passed, or have a pawn in front of them.
678 if ( !pos.pawn_passed(Us, s + Up)
679 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
682 score += bonus + PassedFile[file_of(s)];
686 Trace::add(PASSED, Us, score);
692 // Evaluation::space() computes the space evaluation for a given side. The
693 // space evaluation is a simple bonus based on the number of safe squares
694 // available for minor pieces on the central four files on ranks 2--4. Safe
695 // squares one, two or three squares behind a friendly pawn are counted
696 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
697 // improve play on game opening.
699 template<Tracing T> template<Color Us>
700 Score Evaluation<T>::space() const {
702 if (pos.non_pawn_material() < SpaceThreshold)
705 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
706 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
707 constexpr Bitboard SpaceMask =
708 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
709 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
711 // Find the available squares for our pieces inside the area defined by SpaceMask
712 Bitboard safe = SpaceMask
713 & ~pos.pieces(Us, PAWN)
714 & ~attackedBy[Them][PAWN];
716 // Find all squares which are at most three squares behind some friendly pawn
717 Bitboard behind = pos.pieces(Us, PAWN);
718 behind |= shift<Down>(behind);
719 behind |= shift<Down>(shift<Down>(behind));
721 int bonus = popcount(safe) + popcount(behind & safe);
722 int weight = pos.count<ALL_PIECES>(Us)
723 - (16 - pos.count<PAWN>()) / 4;
725 Score score = make_score(bonus * weight * weight / 16, 0);
728 Trace::add(SPACE, Us, score);
734 // Evaluation::initiative() computes the initiative correction value
735 // for the position. It is a second order bonus/malus based on the
736 // known attacking/defending status of the players.
739 Score Evaluation<T>::initiative(Value eg) const {
741 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
742 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
744 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
745 && (pos.pieces(PAWN) & KingSide);
747 // Compute the initiative bonus for the attacking side
748 int complexity = 9 * pe->passed_count()
749 + 11 * pos.count<PAWN>()
751 + 18 * pawnsOnBothFlanks
752 + 49 * !pos.non_pawn_material()
755 // Now apply the bonus: note that we find the attacking side by extracting
756 // the sign of the endgame value, and that we carefully cap the bonus so
757 // that the endgame score will never change sign after the bonus.
758 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
761 Trace::add(INITIATIVE, make_score(0, v));
763 return make_score(0, v);
767 // Evaluation::scale_factor() computes the scale factor for the winning side
770 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
772 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
773 int sf = me->scale_factor(pos, strongSide);
775 // If scale is not already specific, scale down the endgame via general heuristics
776 if (sf == SCALE_FACTOR_NORMAL)
778 if ( pos.opposite_bishops()
779 && pos.non_pawn_material(WHITE) == BishopValueMg
780 && pos.non_pawn_material(BLACK) == BishopValueMg)
781 sf = 16 + 4 * pe->passed_count();
783 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
787 return ScaleFactor(sf);
791 // Evaluation::value() is the main function of the class. It computes the various
792 // parts of the evaluation and returns the value of the position from the point
793 // of view of the side to move.
796 Value Evaluation<T>::value() {
798 assert(!pos.checkers());
800 // Probe the material hash table
801 me = Material::probe(pos);
803 // If we have a specialized evaluation function for the current material
804 // configuration, call it and return.
805 if (me->specialized_eval_exists())
806 return me->evaluate(pos);
808 // Initialize score by reading the incrementally updated scores included in
809 // the position object (material + piece square tables) and the material
810 // imbalance. Score is computed internally from the white point of view.
811 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
813 // Probe the pawn hash table
814 pe = Pawns::probe(pos);
815 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
817 // Early exit if score is high
818 Value v = (mg_value(score) + eg_value(score)) / 2;
819 if (abs(v) > LazyThreshold)
820 return pos.side_to_move() == WHITE ? v : -v;
822 // Main evaluation begins here
827 // Pieces should be evaluated first (populate attack tables)
828 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
829 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
830 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
831 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
833 score += mobility[WHITE] - mobility[BLACK];
835 score += king< WHITE>() - king< BLACK>()
836 + threats<WHITE>() - threats<BLACK>()
837 + passed< WHITE>() - passed< BLACK>()
838 + space< WHITE>() - space< BLACK>();
840 score += initiative(eg_value(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) // Side to move point of view
866 /// evaluate() is the evaluator for the outer world. It returns a static
867 /// evaluation of the position from the point of view of the side to move.
869 Value Eval::evaluate(const Position& pos) {
870 return Evaluation<NO_TRACE>(pos).value();
874 /// trace() is like evaluate(), but instead of returning a value, it returns
875 /// a string (suitable for outputting to stdout) that contains the detailed
876 /// descriptions and values of each evaluation term. Useful for debugging.
878 std::string Eval::trace(const Position& pos) {
880 std::memset(scores, 0, sizeof(scores));
882 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
884 Value v = Evaluation<TRACE>(pos).value();
886 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
888 std::stringstream ss;
889 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
890 << " Term | White | Black | Total \n"
891 << " | MG EG | MG EG | MG EG \n"
892 << " ------------+-------------+-------------+------------\n"
893 << " Material | " << Term(MATERIAL)
894 << " Imbalance | " << Term(IMBALANCE)
895 << " Pawns | " << Term(PAWN)
896 << " Knights | " << Term(KNIGHT)
897 << " Bishops | " << Term(BISHOP)
898 << " Rooks | " << Term(ROOK)
899 << " Queens | " << Term(QUEEN)
900 << " Mobility | " << Term(MOBILITY)
901 << " King safety | " << Term(KING)
902 << " Threats | " << Term(THREAT)
903 << " Passed | " << Term(PASSED)
904 << " Space | " << Term(SPACE)
905 << " Initiative | " << Term(INITIATIVE)
906 << " ------------+-------------+-------------+------------\n"
907 << " Total | " << Term(TOTAL);
909 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";