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 = 780;
85 constexpr int RookSafeCheck = 1080;
86 constexpr int BishopSafeCheck = 635;
87 constexpr int KnightSafeCheck = 790;
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), // Knights
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), // Bishops
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(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
100 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
101 S( 46,166), S( 48,169), S( 58,171) },
102 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
103 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
104 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
105 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
106 S(106,184), S(109,191), S(113,206), S(116,212) }
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(21, 4), S(47, 25) };
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(2, 44), S(36, 71), S(36, 61), S(0, 38), S(51, 38)
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 CorneredBishop = S( 50, 50);
132 constexpr Score FlankAttacks = S( 8, 0);
133 constexpr Score Hanging = S( 69, 36);
134 constexpr Score KingProtector = S( 7, 8);
135 constexpr Score KnightOnQueen = S( 16, 12);
136 constexpr Score LongDiagonalBishop = S( 45, 0);
137 constexpr Score MinorBehindPawn = S( 18, 3);
138 constexpr Score Outpost = S( 30, 21);
139 constexpr Score PassedFile = S( 11, 8);
140 constexpr Score PawnlessFlank = S( 17, 95);
141 constexpr Score RestrictedPiece = S( 7, 7);
142 constexpr Score RookOnQueenFile = S( 7, 6);
143 constexpr Score SliderOnQueen = S( 59, 18);
144 constexpr Score ThreatByKing = S( 24, 89);
145 constexpr Score ThreatByPawnPush = S( 48, 39);
146 constexpr Score ThreatBySafePawn = S(173, 94);
147 constexpr Score TrappedRook = S( 52, 10);
148 constexpr Score WeakQueen = S( 49, 15);
149 constexpr Score WeakQueenProtection = S( 14, 0);
153 // Evaluation class computes and stores attacks tables and other working data
158 Evaluation() = delete;
159 explicit Evaluation(const Position& p) : pos(p) {}
160 Evaluation& operator=(const Evaluation&) = delete;
164 template<Color Us> void initialize();
165 template<Color Us, PieceType Pt> Score pieces();
166 template<Color Us> Score king() const;
167 template<Color Us> Score threats() const;
168 template<Color Us> Score passed() const;
169 template<Color Us> Score space() const;
170 ScaleFactor scale_factor(Value eg) const;
171 Score initiative(Score score) const;
176 Bitboard mobilityArea[COLOR_NB];
177 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
179 // attackedBy[color][piece type] is a bitboard representing all squares
180 // attacked by a given color and piece type. Special "piece types" which
181 // is also calculated is ALL_PIECES.
182 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
184 // attackedBy2[color] are the squares attacked by at least 2 units of a given
185 // color, including x-rays. But diagonal x-rays through pawns are not computed.
186 Bitboard attackedBy2[COLOR_NB];
188 // kingRing[color] are the squares adjacent to the king plus some other
189 // very near squares, depending on king position.
190 Bitboard kingRing[COLOR_NB];
192 // kingAttackersCount[color] is the number of pieces of the given color
193 // which attack a square in the kingRing of the enemy king.
194 int kingAttackersCount[COLOR_NB];
196 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
197 // the given color which attack a square in the kingRing of the enemy king.
198 // The weights of the individual piece types are given by the elements in
199 // the KingAttackWeights array.
200 int kingAttackersWeight[COLOR_NB];
202 // kingAttacksCount[color] is the number of attacks by the given color to
203 // squares directly adjacent to the enemy king. Pieces which attack more
204 // than one square are counted multiple times. For instance, if there is
205 // a white knight on g5 and black's king is on g8, this white knight adds 2
206 // to kingAttacksCount[WHITE].
207 int kingAttacksCount[COLOR_NB];
211 // Evaluation::initialize() computes king and pawn attacks, and the king ring
212 // bitboard for a given color. This is done at the beginning of the evaluation.
213 template<Tracing T> template<Color Us>
214 void Evaluation<T>::initialize() {
216 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
217 constexpr Direction Up = pawn_push(Us);
218 constexpr Direction Down = -Up;
219 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
221 const Square ksq = pos.square<KING>(Us);
223 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
225 // Find our pawns that are blocked or on the first two ranks
226 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
228 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
229 // or controlled by enemy pawns are excluded from the mobility area.
230 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
232 // Initialize attackedBy[] for king and pawns
233 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
234 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
235 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
236 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
238 // Init our king safety tables
239 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
240 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
241 kingRing[Us] = PseudoAttacks[KING][s] | s;
243 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
244 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
246 // Remove from kingRing[] the squares defended by two pawns
247 kingRing[Us] &= ~dblAttackByPawn;
251 // Evaluation::pieces() scores pieces of a given color and type
252 template<Tracing T> template<Color Us, PieceType Pt>
253 Score Evaluation<T>::pieces() {
255 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
256 constexpr Direction Down = -pawn_push(Us);
257 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
258 : Rank5BB | Rank4BB | Rank3BB);
259 const Square* pl = pos.squares<Pt>(Us);
262 Score score = SCORE_ZERO;
264 attackedBy[Us][Pt] = 0;
266 for (Square s = *pl; s != SQ_NONE; s = *++pl)
268 // Find attacked squares, including x-ray attacks for bishops and rooks
269 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
270 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
271 : pos.attacks_from<Pt>(s);
273 if (pos.blockers_for_king(Us) & s)
274 b &= LineBB[pos.square<KING>(Us)][s];
276 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
277 attackedBy[Us][Pt] |= b;
278 attackedBy[Us][ALL_PIECES] |= b;
280 if (b & kingRing[Them])
282 kingAttackersCount[Us]++;
283 kingAttackersWeight[Us] += KingAttackWeights[Pt];
284 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
287 int mob = popcount(b & mobilityArea[Us]);
289 mobility[Us] += MobilityBonus[Pt - 2][mob];
291 if (Pt == BISHOP || Pt == KNIGHT)
293 // Bonus if piece is on an outpost square or can reach one
294 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
296 score += Outpost * (Pt == KNIGHT ? 2 : 1);
298 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
301 // Knight and Bishop bonus for being right behind a pawn
302 if (shift<Down>(pos.pieces(PAWN)) & s)
303 score += MinorBehindPawn;
305 // Penalty if the piece is far from the king
306 score -= KingProtector * distance(s, pos.square<KING>(Us));
310 // Penalty according to number of pawns on the same color square as the
311 // bishop, bigger when the center files are blocked with pawns and smaller
312 // when the bishop is outside the pawn chain.
313 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
315 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
316 * (!bool(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
318 // Bonus for bishop on a long diagonal which can "see" both center squares
319 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
320 score += LongDiagonalBishop;
322 // An important Chess960 pattern: a cornered bishop blocked by a friendly
323 // pawn diagonally in front of it is a very serious problem, especially
324 // when that pawn is also blocked.
325 if ( pos.is_chess960()
326 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
328 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
329 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
330 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
331 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
339 // Bonus for rook on the same file as a queen
340 if (file_bb(s) & pos.pieces(QUEEN))
341 score += RookOnQueenFile;
343 // Bonus for rook on an open or semi-open file
344 if (pos.is_on_semiopen_file(Us, s))
345 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
347 // Penalty when trapped by the king, even more if the king cannot castle
350 File kf = file_of(pos.square<KING>(Us));
351 if ((kf < FILE_E) == (file_of(s) < kf))
352 score -= TrappedRook * (1 + !pos.castling_rights(Us));
358 // Penalty if any relative pin or discovered attack against the queen
359 Bitboard queenPinners;
360 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
365 Trace::add(Pt, Us, score);
371 // Evaluation::king() assigns bonuses and penalties to a king of a given color
372 template<Tracing T> template<Color Us>
373 Score Evaluation<T>::king() const {
375 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
376 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
377 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
379 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
380 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
382 const Square ksq = pos.square<KING>(Us);
384 // Init the score with king shelter and enemy pawns storm
385 Score score = pe->king_safety<Us>(pos);
387 // Attacked squares defended at most once by our queen or king
388 weak = attackedBy[Them][ALL_PIECES]
390 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
392 // Analyse the safe enemy's checks which are possible on next move
393 safe = ~pos.pieces(Them);
394 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
396 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
397 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
399 // Enemy rooks checks
400 rookChecks = b1 & safe & attackedBy[Them][ROOK];
403 kingDanger += RookSafeCheck;
405 unsafeChecks |= b1 & attackedBy[Them][ROOK];
407 // Enemy queen safe checks: we count them only if they are from squares from
408 // which we can't give a rook check, because rook checks are more valuable.
409 queenChecks = (b1 | b2)
410 & attackedBy[Them][QUEEN]
412 & ~attackedBy[Us][QUEEN]
416 kingDanger += QueenSafeCheck;
418 // Enemy bishops checks: we count them only if they are from squares from
419 // which we can't give a queen check, because queen checks are more valuable.
421 & attackedBy[Them][BISHOP]
426 kingDanger += BishopSafeCheck;
428 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
430 // Enemy knights checks
431 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
433 if (knightChecks & safe)
434 kingDanger += KnightSafeCheck;
436 unsafeChecks |= knightChecks;
438 // Find the squares that opponent attacks in our king flank, the squares
439 // which they attack twice in that flank, and the squares that we defend.
440 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
441 b2 = b1 & attackedBy2[Them];
442 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
444 int kingFlankAttack = popcount(b1) + popcount(b2);
445 int kingFlankDefense = popcount(b3);
447 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
448 + 185 * popcount(kingRing[Us] & weak)
449 + 148 * popcount(unsafeChecks)
450 + 98 * popcount(pos.blockers_for_king(Us))
451 + 69 * kingAttacksCount[Them]
452 + 3 * kingFlankAttack * kingFlankAttack / 8
453 + mg_value(mobility[Them] - mobility[Us])
454 - 873 * !pos.count<QUEEN>(Them)
455 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
456 - 6 * mg_value(score) / 8
457 - 4 * kingFlankDefense
460 // Transform the kingDanger units into a Score, and subtract it from the evaluation
461 if (kingDanger > 100)
462 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
464 // Penalty when our king is on a pawnless flank
465 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
466 score -= PawnlessFlank;
468 // Penalty if king flank is under attack, potentially moving toward the king
469 score -= FlankAttacks * kingFlankAttack;
472 Trace::add(KING, Us, score);
478 // Evaluation::threats() assigns bonuses according to the types of the
479 // attacking and the attacked pieces.
480 template<Tracing T> template<Color Us>
481 Score Evaluation<T>::threats() const {
483 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
484 constexpr Direction Up = pawn_push(Us);
485 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
487 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
488 Score score = SCORE_ZERO;
491 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
493 // Squares strongly protected by the enemy, either because they defend the
494 // square with a pawn, or because they defend the square twice and we don't.
495 stronglyProtected = attackedBy[Them][PAWN]
496 | (attackedBy2[Them] & ~attackedBy2[Us]);
498 // Non-pawn enemies, strongly protected
499 defended = nonPawnEnemies & stronglyProtected;
501 // Enemies not strongly protected and under our attack
502 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
504 // Bonus according to the kind of attacking pieces
507 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
509 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
511 b = weak & attackedBy[Us][ROOK];
513 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
515 if (weak & attackedBy[Us][KING])
516 score += ThreatByKing;
518 b = ~attackedBy[Them][ALL_PIECES]
519 | (nonPawnEnemies & attackedBy2[Us]);
520 score += Hanging * popcount(weak & b);
522 // Additional bonus if weak piece is only protected by a queen
523 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
526 // Bonus for restricting their piece moves
527 b = attackedBy[Them][ALL_PIECES]
529 & attackedBy[Us][ALL_PIECES];
530 score += RestrictedPiece * popcount(b);
532 // Protected or unattacked squares
533 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
535 // Bonus for attacking enemy pieces with our relatively safe pawns
536 b = pos.pieces(Us, PAWN) & safe;
537 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
538 score += ThreatBySafePawn * popcount(b);
540 // Find squares where our pawns can push on the next move
541 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
542 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
544 // Keep only the squares which are relatively safe
545 b &= ~attackedBy[Them][PAWN] & safe;
547 // Bonus for safe pawn threats on the next move
548 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
549 score += ThreatByPawnPush * popcount(b);
551 // Bonus for threats on the next moves against enemy queen
552 if (pos.count<QUEEN>(Them) == 1)
554 Square s = pos.square<QUEEN>(Them);
555 safe = mobilityArea[Us] & ~stronglyProtected;
557 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
559 score += KnightOnQueen * popcount(b & safe);
561 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
562 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
564 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
568 Trace::add(THREAT, Us, score);
573 // Evaluation::passed() evaluates the passed pawns and candidate passed
574 // pawns of the given color.
576 template<Tracing T> template<Color Us>
577 Score Evaluation<T>::passed() const {
579 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
580 constexpr Direction Up = pawn_push(Us);
582 auto king_proximity = [&](Color c, Square s) {
583 return std::min(distance(pos.square<KING>(c), s), 5);
586 Bitboard b, bb, squaresToQueen, unsafeSquares;
587 Score score = SCORE_ZERO;
589 b = pe->passed_pawns(Us);
593 Square s = pop_lsb(&b);
595 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
597 int r = relative_rank(Us, s);
599 Score bonus = PassedRank[r];
604 Square blockSq = s + Up;
606 // Adjust bonus based on the king's proximity
607 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
608 - king_proximity(Us, blockSq) * 2) * w);
610 // If blockSq is not the queening square then consider also a second push
612 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
614 // If the pawn is free to advance, then increase the bonus
615 if (pos.empty(blockSq))
617 squaresToQueen = forward_file_bb(Us, s);
618 unsafeSquares = passed_pawn_span(Us, s);
620 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
622 if (!(pos.pieces(Them) & bb))
623 unsafeSquares &= attackedBy[Them][ALL_PIECES];
625 // If there are no enemy attacks on passed pawn span, assign a big bonus.
626 // Otherwise assign a smaller bonus if the path to queen is not attacked
627 // and even smaller bonus if it is attacked but block square is not.
628 int k = !unsafeSquares ? 35 :
629 !(unsafeSquares & squaresToQueen) ? 20 :
630 !(unsafeSquares & blockSq) ? 9 :
633 // Assign a larger bonus if the block square is defended
634 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
637 bonus += make_score(k * w, k * w);
641 // Scale down bonus for candidate passers which need more than one
642 // pawn push to become passed, or have a pawn in front of them.
643 if ( !pos.pawn_passed(Us, s + Up)
644 || (pos.pieces(PAWN) & (s + Up)))
647 score += bonus - PassedFile * edge_distance(file_of(s));
651 Trace::add(PASSED, Us, score);
657 // Evaluation::space() computes the space evaluation for a given side. The
658 // space evaluation is a simple bonus based on the number of safe squares
659 // available for minor pieces on the central four files on ranks 2--4. Safe
660 // squares one, two or three squares behind a friendly pawn are counted
661 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
662 // improve play on game opening.
664 template<Tracing T> template<Color Us>
665 Score Evaluation<T>::space() const {
667 if (pos.non_pawn_material() < SpaceThreshold)
670 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
671 constexpr Direction Down = -pawn_push(Us);
672 constexpr Bitboard SpaceMask =
673 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
674 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
676 // Find the available squares for our pieces inside the area defined by SpaceMask
677 Bitboard safe = SpaceMask
678 & ~pos.pieces(Us, PAWN)
679 & ~attackedBy[Them][PAWN];
681 // Find all squares which are at most three squares behind some friendly pawn
682 Bitboard behind = pos.pieces(Us, PAWN);
683 behind |= shift<Down>(behind);
684 behind |= shift<Down+Down>(behind);
686 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
687 int weight = pos.count<ALL_PIECES>(Us) - 1;
688 Score score = make_score(bonus * weight * weight / 16, 0);
691 Trace::add(SPACE, Us, score);
697 // Evaluation::initiative() computes the initiative correction value
698 // for the position. It is a second order bonus/malus based on the
699 // known attacking/defending status of the players.
702 Score Evaluation<T>::initiative(Score score) const {
704 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
705 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
707 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
708 && (pos.pieces(PAWN) & KingSide);
710 bool almostUnwinnable = outflanking < 0
711 && !pawnsOnBothFlanks;
713 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
714 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
716 // Compute the initiative bonus for the attacking side
717 int complexity = 9 * pe->passed_count()
718 + 11 * pos.count<PAWN>()
720 + 21 * pawnsOnBothFlanks
722 + 51 * !pos.non_pawn_material()
723 - 43 * almostUnwinnable
726 Value mg = mg_value(score);
727 Value eg = eg_value(score);
729 // Now apply the bonus: note that we find the attacking side by extracting the
730 // sign of the midgame or endgame values, and that we carefully cap the bonus
731 // so that the midgame and endgame scores do not change sign after the bonus.
732 int u = ((mg > 0) - (mg < 0)) * std::max(std::min(complexity + 50, 0), -abs(mg));
733 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
736 Trace::add(INITIATIVE, make_score(u, v));
738 return make_score(u, v);
742 // Evaluation::scale_factor() computes the scale factor for the winning side
745 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
747 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
748 int sf = me->scale_factor(pos, strongSide);
750 // If scale is not already specific, scale down the endgame via general heuristics
751 if (sf == SCALE_FACTOR_NORMAL)
753 if ( pos.opposite_bishops()
754 && pos.non_pawn_material() == 2 * BishopValueMg)
757 sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
759 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
762 return ScaleFactor(sf);
766 // Evaluation::value() is the main function of the class. It computes the various
767 // parts of the evaluation and returns the value of the position from the point
768 // of view of the side to move.
771 Value Evaluation<T>::value() {
773 assert(!pos.checkers());
775 // Probe the material hash table
776 me = Material::probe(pos);
778 // If we have a specialized evaluation function for the current material
779 // configuration, call it and return.
780 if (me->specialized_eval_exists())
781 return me->evaluate(pos);
783 // Initialize score by reading the incrementally updated scores included in
784 // the position object (material + piece square tables) and the material
785 // imbalance. Score is computed internally from the white point of view.
786 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
788 // Probe the pawn hash table
789 pe = Pawns::probe(pos);
790 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
792 // Early exit if score is high
793 Value v = (mg_value(score) + eg_value(score)) / 2;
794 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
795 return pos.side_to_move() == WHITE ? v : -v;
797 // Main evaluation begins here
802 // Pieces should be evaluated first (populate attack tables)
803 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
804 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
805 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
806 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
808 score += mobility[WHITE] - mobility[BLACK];
810 score += king< WHITE>() - king< BLACK>()
811 + threats<WHITE>() - threats<BLACK>()
812 + passed< WHITE>() - passed< BLACK>()
813 + space< WHITE>() - space< BLACK>();
815 score += initiative(score);
817 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
818 ScaleFactor sf = scale_factor(eg_value(score));
819 v = mg_value(score) * int(me->game_phase())
820 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
824 // In case of tracing add all remaining individual evaluation terms
827 Trace::add(MATERIAL, pos.psq_score());
828 Trace::add(IMBALANCE, me->imbalance());
829 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
830 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
831 Trace::add(TOTAL, score);
834 return (pos.side_to_move() == WHITE ? v : -v) + Tempo; // Side to move point of view
840 /// evaluate() is the evaluator for the outer world. It returns a static
841 /// evaluation of the position from the point of view of the side to move.
843 Value Eval::evaluate(const Position& pos) {
844 return Evaluation<NO_TRACE>(pos).value();
848 /// trace() is like evaluate(), but instead of returning a value, it returns
849 /// a string (suitable for outputting to stdout) that contains the detailed
850 /// descriptions and values of each evaluation term. Useful for debugging.
852 std::string Eval::trace(const Position& pos) {
855 return "Total evaluation: none (in check)";
857 std::memset(scores, 0, sizeof(scores));
859 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
861 Value v = Evaluation<TRACE>(pos).value();
863 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
865 std::stringstream ss;
866 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
867 << " Term | White | Black | Total \n"
868 << " | MG EG | MG EG | MG EG \n"
869 << " ------------+-------------+-------------+------------\n"
870 << " Material | " << Term(MATERIAL)
871 << " Imbalance | " << Term(IMBALANCE)
872 << " Pawns | " << Term(PAWN)
873 << " Knights | " << Term(KNIGHT)
874 << " Bishops | " << Term(BISHOP)
875 << " Rooks | " << Term(ROOK)
876 << " Queens | " << Term(QUEEN)
877 << " Mobility | " << Term(MOBILITY)
878 << " King safety | " << Term(KING)
879 << " Threats | " << Term(THREAT)
880 << " Passed | " << Term(PASSED)
881 << " Space | " << Term(SPACE)
882 << " Initiative | " << Term(INITIATIVE)
883 << " ------------+-------------+-------------+------------\n"
884 << " Total | " << Term(TOTAL);
886 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";