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/>.
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, 77, 55, 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(18, 7), S(44, 20) };
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(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(0, 24), S(38, 71), S(38, 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(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
129 // PassedFile[File] contains a bonus according to the file of a passed pawn
130 constexpr Score PassedFile[FILE_NB] = {
131 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
132 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
135 // Assorted bonuses and penalties
136 constexpr Score BishopPawns = S( 3, 7);
137 constexpr Score CorneredBishop = S( 50, 50);
138 constexpr Score FlankAttacks = S( 8, 0);
139 constexpr Score Hanging = S( 69, 36);
140 constexpr Score KingProtector = S( 7, 8);
141 constexpr Score KnightOnQueen = S( 16, 12);
142 constexpr Score LongDiagonalBishop = S( 45, 0);
143 constexpr Score MinorBehindPawn = S( 18, 3);
144 constexpr Score Outpost = S( 36, 12);
145 constexpr Score PawnlessFlank = S( 17, 95);
146 constexpr Score RestrictedPiece = S( 7, 7);
147 constexpr Score RookOnPawn = S( 10, 32);
148 constexpr Score SliderOnQueen = S( 59, 18);
149 constexpr Score ThreatByKing = S( 24, 89);
150 constexpr Score ThreatByPawnPush = S( 48, 39);
151 constexpr Score ThreatByRank = S( 13, 0);
152 constexpr Score ThreatBySafePawn = S(173, 94);
153 constexpr Score TrappedRook = S( 47, 4);
154 constexpr Score WeakQueen = S( 49, 15);
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 at least 2 units of a given
190 // color, including x-rays. But diagonal x-rays through pawns are not computed.
191 Bitboard attackedBy2[COLOR_NB];
193 // kingRing[color] are the squares adjacent to the king plus some other
194 // very near squares, depending on king position.
195 Bitboard kingRing[COLOR_NB];
197 // kingAttackersCount[color] is the number of pieces of the given color
198 // which attack a square in the kingRing of the enemy king.
199 int kingAttackersCount[COLOR_NB];
201 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
202 // the given color which attack a square in the kingRing of the enemy king.
203 // The weights of the individual piece types are given by the elements in
204 // the KingAttackWeights array.
205 int kingAttackersWeight[COLOR_NB];
207 // kingAttacksCount[color] is the number of attacks by the given color to
208 // squares directly adjacent to the enemy king. Pieces which attack more
209 // than one square are counted multiple times. For instance, if there is
210 // a white knight on g5 and black's king is on g8, this white knight adds 2
211 // to kingAttacksCount[WHITE].
212 int kingAttacksCount[COLOR_NB];
216 // Evaluation::initialize() computes king and pawn attacks, and the king ring
217 // bitboard for a given color. This is done at the beginning of the evaluation.
218 template<Tracing T> template<Color Us>
219 void Evaluation<T>::initialize() {
221 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
222 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
223 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
224 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
226 const Square ksq = pos.square<KING>(Us);
228 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
230 // Find our pawns that are blocked or on the first two ranks
231 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
233 // Squares occupied by those pawns, by our king or queen or controlled by
234 // enemy pawns are excluded from the mobility area.
235 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
237 // Initialize attackedBy[] for king and pawns
238 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
239 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
240 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
241 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
243 // Init our king safety tables
244 kingRing[Us] = attackedBy[Us][KING];
245 if (relative_rank(Us, ksq) == RANK_1)
246 kingRing[Us] |= shift<Up>(kingRing[Us]);
248 if (file_of(ksq) == FILE_H)
249 kingRing[Us] |= shift<WEST>(kingRing[Us]);
251 else if (file_of(ksq) == FILE_A)
252 kingRing[Us] |= shift<EAST>(kingRing[Us]);
254 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
255 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
257 // Remove from kingRing[] the squares defended by two pawns
258 kingRing[Us] &= ~dblAttackByPawn;
262 // Evaluation::pieces() scores pieces of a given color and type
263 template<Tracing T> template<Color Us, PieceType Pt>
264 Score Evaluation<T>::pieces() {
266 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
267 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
268 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
269 : Rank5BB | Rank4BB | Rank3BB);
270 const Square* pl = pos.squares<Pt>(Us);
273 Score score = SCORE_ZERO;
275 attackedBy[Us][Pt] = 0;
277 for (Square s = *pl; s != SQ_NONE; s = *++pl)
279 // Find attacked squares, including x-ray attacks for bishops and rooks
280 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
281 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
282 : pos.attacks_from<Pt>(s);
284 if (pos.blockers_for_king(Us) & s)
285 b &= LineBB[pos.square<KING>(Us)][s];
287 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
288 attackedBy[Us][Pt] |= b;
289 attackedBy[Us][ALL_PIECES] |= b;
291 if (b & kingRing[Them])
293 kingAttackersCount[Us]++;
294 kingAttackersWeight[Us] += KingAttackWeights[Pt];
295 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
298 int mob = popcount(b & mobilityArea[Us]);
300 mobility[Us] += MobilityBonus[Pt - 2][mob];
302 if (Pt == BISHOP || Pt == KNIGHT)
304 // Bonus if piece is on an outpost square or can reach one
305 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
307 score += Outpost * (Pt == KNIGHT ? 2 : 1);
309 else if (bb & b & ~pos.pieces(Us))
310 score += Outpost / (Pt == KNIGHT ? 1 : 2);
312 // Knight and Bishop bonus for being right behind a pawn
313 if (shift<Down>(pos.pieces(PAWN)) & s)
314 score += MinorBehindPawn;
316 // Penalty if the piece is far from the king
317 score -= KingProtector * distance(s, pos.square<KING>(Us));
321 // Penalty according to number of pawns on the same color square as the
322 // bishop, bigger when the center files are blocked with pawns.
323 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
325 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
326 * (1 + popcount(blocked & CenterFiles));
328 // Bonus for bishop on a long diagonal which can "see" both center squares
329 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
330 score += LongDiagonalBishop;
333 // An important Chess960 pattern: A cornered bishop blocked by a friendly
334 // pawn diagonally in front of it is a very serious problem, especially
335 // when that pawn is also blocked.
338 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
340 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
341 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
342 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
343 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
350 // Bonus for aligning rook with enemy pawns on the same rank/file
351 if (relative_rank(Us, s) >= RANK_5)
352 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
354 // Bonus for rook on an open or semi-open file
355 if (pos.is_on_semiopen_file(Us, s))
356 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, s))];
358 // Penalty when trapped by the king, even more if the king cannot castle
361 File kf = file_of(pos.square<KING>(Us));
362 if ((kf < FILE_E) == (file_of(s) < kf))
363 score -= TrappedRook * (1 + !pos.castling_rights(Us));
369 // Penalty if any relative pin or discovered attack against the queen
370 Bitboard queenPinners;
371 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
376 Trace::add(Pt, Us, score);
382 // Evaluation::king() assigns bonuses and penalties to a king of a given color
383 template<Tracing T> template<Color Us>
384 Score Evaluation<T>::king() const {
386 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
387 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
388 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
390 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
391 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
393 const Square ksq = pos.square<KING>(Us);
395 // Init the score with king shelter and enemy pawns storm
396 Score score = pe->king_safety<Us>(pos);
398 // Attacked squares defended at most once by our queen or king
399 weak = attackedBy[Them][ALL_PIECES]
401 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
403 // Analyse the safe enemy's checks which are possible on next move
404 safe = ~pos.pieces(Them);
405 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
407 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
408 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
410 // Enemy rooks checks
411 rookChecks = b1 & safe & attackedBy[Them][ROOK];
414 kingDanger += RookSafeCheck;
416 unsafeChecks |= b1 & attackedBy[Them][ROOK];
418 // Enemy queen safe checks: we count them only if they are from squares from
419 // which we can't give a rook check, because rook checks are more valuable.
420 queenChecks = (b1 | b2)
421 & attackedBy[Them][QUEEN]
423 & ~attackedBy[Us][QUEEN]
427 kingDanger += QueenSafeCheck;
429 // Enemy bishops checks: we count them only if they are from squares from
430 // which we can't give a queen check, because queen checks are more valuable.
432 & attackedBy[Them][BISHOP]
437 kingDanger += BishopSafeCheck;
439 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
441 // Enemy knights checks
442 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
444 if (knightChecks & safe)
445 kingDanger += KnightSafeCheck;
447 unsafeChecks |= knightChecks;
449 // Unsafe or occupied checking squares will also be considered, as long as
450 // the square is in the attacker's mobility area.
451 unsafeChecks &= mobilityArea[Them];
453 // Find the squares that opponent attacks in our king flank, and the squares
454 // which are attacked twice in that flank.
455 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
456 b2 = b1 & attackedBy2[Them];
458 int kingFlankAttacks = popcount(b1) + popcount(b2);
460 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
461 + 69 * kingAttacksCount[Them]
462 + 185 * popcount(kingRing[Us] & weak)
463 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
464 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
465 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
466 - 873 * !pos.count<QUEEN>(Them)
467 - 6 * mg_value(score) / 8
468 + mg_value(mobility[Them] - mobility[Us])
469 + 5 * kingFlankAttacks * kingFlankAttacks / 16
472 // Transform the kingDanger units into a Score, and subtract it from the evaluation
473 if (kingDanger > 100)
474 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
476 // Penalty when our king is on a pawnless flank
477 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
478 score -= PawnlessFlank;
480 // Penalty if king flank is under attack, potentially moving toward the king
481 score -= FlankAttacks * kingFlankAttacks;
484 Trace::add(KING, Us, score);
490 // Evaluation::threats() assigns bonuses according to the types of the
491 // attacking and the attacked pieces.
492 template<Tracing T> template<Color Us>
493 Score Evaluation<T>::threats() const {
495 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
496 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
497 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
499 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
500 Score score = SCORE_ZERO;
503 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
505 // Squares strongly protected by the enemy, either because they defend the
506 // square with a pawn, or because they defend the square twice and we don't.
507 stronglyProtected = attackedBy[Them][PAWN]
508 | (attackedBy2[Them] & ~attackedBy2[Us]);
510 // Non-pawn enemies, strongly protected
511 defended = nonPawnEnemies & stronglyProtected;
513 // Enemies not strongly protected and under our attack
514 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
516 // Safe or protected squares
517 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
519 // Bonus according to the kind of attacking pieces
522 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
525 Square s = pop_lsb(&b);
526 score += ThreatByMinor[type_of(pos.piece_on(s))];
527 if (type_of(pos.piece_on(s)) != PAWN)
528 score += ThreatByRank * (int)relative_rank(Them, s);
531 b = weak & attackedBy[Us][ROOK];
534 Square s = pop_lsb(&b);
535 score += ThreatByRook[type_of(pos.piece_on(s))];
536 if (type_of(pos.piece_on(s)) != PAWN)
537 score += ThreatByRank * (int)relative_rank(Them, s);
540 if (weak & attackedBy[Us][KING])
541 score += ThreatByKing;
543 b = ~attackedBy[Them][ALL_PIECES]
544 | (nonPawnEnemies & attackedBy2[Us]);
545 score += Hanging * popcount(weak & b);
548 // Bonus for restricting their piece moves
549 b = attackedBy[Them][ALL_PIECES]
551 & attackedBy[Us][ALL_PIECES];
553 score += RestrictedPiece * popcount(b);
555 // Find squares where our pawns can push on the next move
556 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
557 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
559 // Keep only the squares which are relatively safe
560 b &= ~attackedBy[Them][PAWN] & safe;
562 // Bonus for safe pawn threats on the next move
563 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
564 score += ThreatByPawnPush * popcount(b);
566 // Our safe or protected pawns
567 b = pos.pieces(Us, PAWN) & safe;
569 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
570 score += ThreatBySafePawn * popcount(b);
572 // Bonus for threats on the next moves against enemy queen
573 if (pos.count<QUEEN>(Them) == 1)
575 Square s = pos.square<QUEEN>(Them);
576 safe = mobilityArea[Us] & ~stronglyProtected;
578 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
580 score += KnightOnQueen * popcount(b & safe);
582 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
583 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
585 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
589 Trace::add(THREAT, Us, score);
594 // Evaluation::passed() evaluates the passed pawns and candidate passed
595 // pawns of the given color.
597 template<Tracing T> template<Color Us>
598 Score Evaluation<T>::passed() const {
600 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
601 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
603 auto king_proximity = [&](Color c, Square s) {
604 return std::min(distance(pos.square<KING>(c), s), 5);
607 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
608 Bitboard wideUnsafeSquares;
609 Score score = SCORE_ZERO;
611 b = pe->passed_pawns(Us);
615 Square s = pop_lsb(&b);
617 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
619 int r = relative_rank(Us, s);
621 Score bonus = PassedRank[r];
625 int w = (r-2) * (r-2) + 2;
626 Square blockSq = s + Up;
628 // Adjust bonus based on the king's proximity
629 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
630 - king_proximity(Us, blockSq) * 2) * w);
632 // If blockSq is not the queening square then consider also a second push
634 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
636 // If the pawn is free to advance, then increase the bonus
637 if (pos.empty(blockSq))
639 // If there is a rook or queen attacking/defending the pawn from behind,
640 // consider all the squaresToQueen. Otherwise consider only the squares
641 // in the pawn's path attacked or occupied by the enemy.
642 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
643 wideUnsafeSquares = AllSquares;
645 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
647 if (!(pos.pieces(Us) & bb))
648 defendedSquares &= attackedBy[Us][ALL_PIECES];
650 if (!(pos.pieces(Them) & bb))
651 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
654 wideUnsafeSquares = (attackedBy[Them][ALL_PIECES] | pos.pieces(Them))
655 & (shift<WEST>(squaresToQueen) | shift<EAST>(squaresToQueen));
657 // If there aren't any enemy attacks, assign a big bonus. Otherwise
658 // assign a smaller bonus if the block square isn't attacked.
659 int k = !wideUnsafeSquares ? 35 : !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
661 // Assign a larger bonus if the block square is defended.
662 if (defendedSquares & blockSq)
665 bonus += make_score(k * w, k * w);
669 // Scale down bonus for candidate passers which need more than one
670 // pawn push to become passed, or have a pawn in front of them.
671 if ( !pos.pawn_passed(Us, s + Up)
672 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
675 score += bonus + PassedFile[file_of(s)];
679 Trace::add(PASSED, Us, score);
685 // Evaluation::space() computes the space evaluation for a given side. The
686 // space evaluation is a simple bonus based on the number of safe squares
687 // available for minor pieces on the central four files on ranks 2--4. Safe
688 // squares one, two or three squares behind a friendly pawn are counted
689 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
690 // improve play on game opening.
692 template<Tracing T> template<Color Us>
693 Score Evaluation<T>::space() const {
695 if (pos.non_pawn_material() < SpaceThreshold)
698 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
699 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
700 constexpr Bitboard SpaceMask =
701 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
702 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
704 // Find the available squares for our pieces inside the area defined by SpaceMask
705 Bitboard safe = SpaceMask
706 & ~pos.pieces(Us, PAWN)
707 & ~attackedBy[Them][PAWN];
709 // Find all squares which are at most three squares behind some friendly pawn
710 Bitboard behind = pos.pieces(Us, PAWN);
711 behind |= shift<Down>(behind);
712 behind |= shift<Down+Down>(behind);
714 int bonus = popcount(safe) + popcount(behind & safe);
715 int weight = pos.count<ALL_PIECES>(Us) - 1;
716 Score score = make_score(bonus * weight * weight / 16, 0);
719 Trace::add(SPACE, Us, score);
725 // Evaluation::initiative() computes the initiative correction value
726 // for the position. It is a second order bonus/malus based on the
727 // known attacking/defending status of the players.
730 Score Evaluation<T>::initiative(Value eg) const {
732 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
733 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
735 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
736 && (pos.pieces(PAWN) & KingSide);
738 // Compute the initiative bonus for the attacking side
739 int complexity = 9 * pe->passed_count()
740 + 11 * pos.count<PAWN>()
742 + 18 * pawnsOnBothFlanks
743 + 49 * !pos.non_pawn_material()
746 // Now apply the bonus: note that we find the attacking side by extracting
747 // the sign of the endgame value, and that we carefully cap the bonus so
748 // that the endgame score will never change sign after the bonus.
749 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
752 Trace::add(INITIATIVE, make_score(0, v));
754 return make_score(0, v);
758 // Evaluation::scale_factor() computes the scale factor for the winning side
761 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
763 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
764 int sf = me->scale_factor(pos, strongSide);
766 // If scale is not already specific, scale down the endgame via general heuristics
767 if (sf == SCALE_FACTOR_NORMAL)
769 if ( pos.opposite_bishops()
770 && pos.non_pawn_material() == 2 * BishopValueMg)
771 sf = 16 + 4 * pe->passed_count();
773 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
777 return ScaleFactor(sf);
781 // Evaluation::value() is the main function of the class. It computes the various
782 // parts of the evaluation and returns the value of the position from the point
783 // of view of the side to move.
786 Value Evaluation<T>::value() {
788 assert(!pos.checkers());
790 // Probe the material hash table
791 me = Material::probe(pos);
793 // If we have a specialized evaluation function for the current material
794 // configuration, call it and return.
795 if (me->specialized_eval_exists())
796 return me->evaluate(pos);
798 // Initialize score by reading the incrementally updated scores included in
799 // the position object (material + piece square tables) and the material
800 // imbalance. Score is computed internally from the white point of view.
801 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
803 // Probe the pawn hash table
804 pe = Pawns::probe(pos);
805 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
807 // Early exit if score is high
808 Value v = (mg_value(score) + eg_value(score)) / 2;
809 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
810 return pos.side_to_move() == WHITE ? v : -v;
812 // Main evaluation begins here
817 // Pieces should be evaluated first (populate attack tables)
818 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
819 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
820 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
821 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
823 score += mobility[WHITE] - mobility[BLACK];
825 score += king< WHITE>() - king< BLACK>()
826 + threats<WHITE>() - threats<BLACK>()
827 + passed< WHITE>() - passed< BLACK>()
828 + space< WHITE>() - space< BLACK>();
830 score += initiative(eg_value(score));
832 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
833 ScaleFactor sf = scale_factor(eg_value(score));
834 v = mg_value(score) * int(me->game_phase())
835 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
839 // In case of tracing add all remaining individual evaluation terms
842 Trace::add(MATERIAL, pos.psq_score());
843 Trace::add(IMBALANCE, me->imbalance());
844 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
845 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
846 Trace::add(TOTAL, score);
849 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
856 /// evaluate() is the evaluator for the outer world. It returns a static
857 /// evaluation of the position from the point of view of the side to move.
859 Value Eval::evaluate(const Position& pos) {
860 return Evaluation<NO_TRACE>(pos).value();
864 /// trace() is like evaluate(), but instead of returning a value, it returns
865 /// a string (suitable for outputting to stdout) that contains the detailed
866 /// descriptions and values of each evaluation term. Useful for debugging.
868 std::string Eval::trace(const Position& pos) {
870 std::memset(scores, 0, sizeof(scores));
872 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
874 Value v = Evaluation<TRACE>(pos).value();
876 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
878 std::stringstream ss;
879 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
880 << " Term | White | Black | Total \n"
881 << " | MG EG | MG EG | MG EG \n"
882 << " ------------+-------------+-------------+------------\n"
883 << " Material | " << Term(MATERIAL)
884 << " Imbalance | " << Term(IMBALANCE)
885 << " Pawns | " << Term(PAWN)
886 << " Knights | " << Term(KNIGHT)
887 << " Bishops | " << Term(BISHOP)
888 << " Rooks | " << Term(ROOK)
889 << " Queens | " << Term(QUEEN)
890 << " Mobility | " << Term(MOBILITY)
891 << " King safety | " << Term(KING)
892 << " Threats | " << Term(THREAT)
893 << " Passed | " << Term(PASSED)
894 << " Space | " << Term(SPACE)
895 << " Initiative | " << Term(INITIATIVE)
896 << " ------------+-------------+-------------+------------\n"
897 << " Total | " << Term(TOTAL);
899 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";