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) 2015-2017 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
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
78 Bitboard mobilityArea[COLOR_NB];
80 // attackedBy[color][piece type] is a bitboard representing all squares
81 // attacked by a given color and piece type (can be also ALL_PIECES).
82 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
84 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
85 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
86 // pawn or squares attacked by 2 pawns are not explicitly added.
87 Bitboard attackedBy2[COLOR_NB];
89 // kingRing[color] is the zone around the king which is considered
90 // by the king safety evaluation. This consists of the squares directly
91 // adjacent to the king, and (only for a king on its first rank) the
92 // squares two ranks in front of the king. For instance, if black's king
93 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
94 // f7, g7, h7, f6, g6 and h6.
95 Bitboard kingRing[COLOR_NB];
97 // kingAttackersCount[color] is the number of pieces of the given color
98 // which attack a square in the kingRing of the enemy king.
99 int kingAttackersCount[COLOR_NB];
101 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
102 // given color which attack a square in the kingRing of the enemy king. The
103 // weights of the individual piece types are given by the elements in the
104 // KingAttackWeights array.
105 int kingAttackersWeight[COLOR_NB];
107 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
108 // color to squares directly adjacent to the enemy king. Pieces which attack
109 // more than one square are counted multiple times. For instance, if there is
110 // a white knight on g5 and black's king is on g8, this white knight adds 2
111 // to kingAdjacentZoneAttacksCount[WHITE].
112 int kingAdjacentZoneAttacksCount[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
119 // indexed by piece type and number of attacked squares in the mobility area.
120 const Score MobilityBonus[][32] = {
121 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
122 S( 22, 26), S( 29, 29), S( 36, 29) },
123 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
124 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
125 S( 91, 88), S( 98, 97) },
126 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
127 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
128 S( 46,166), S( 48,169), S( 58,171) },
129 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
130 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
131 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
132 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
133 S(106,184), S(109,191), S(113,206), S(116,212) }
136 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
137 // pieces if they can reach an outpost square, bigger if that square is
138 // supported by a pawn. If the minor piece occupies an outpost square
139 // then score is doubled.
140 const Score Outpost[][2] = {
141 { S(22, 6), S(33, 9) }, // Knight
142 { S( 9, 2), S(14, 4) } // Bishop
145 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
146 // friendly pawn on the rook file.
147 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
149 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
150 // which piece type attacks which one. Attacks on lesser pieces which are
151 // pawn-defended are not considered.
152 const Score ThreatByMinor[PIECE_TYPE_NB] = {
153 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
156 const Score ThreatByRook[PIECE_TYPE_NB] = {
157 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
160 // ThreatByKing[on one/on many] contains bonuses for king attacks on
161 // pawns or pieces which are not pawn-defended.
162 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
164 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
165 // We don't use a Score because we process the two components independently.
166 const Value Passed[][RANK_NB] = {
167 { V(5), V( 5), V(31), V(73), V(166), V(252) },
168 { V(7), V(14), V(38), V(73), V(166), V(252) }
171 // PassedFile[File] contains a bonus according to the file of a passed pawn
172 const Score PassedFile[FILE_NB] = {
173 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
174 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
177 // KingProtector[PieceType-2] contains a bonus according to distance from king
178 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
180 // Assorted bonuses and penalties used by evaluation
181 const Score MinorBehindPawn = S( 16, 0);
182 const Score BishopPawns = S( 8, 12);
183 const Score RookOnPawn = S( 8, 24);
184 const Score TrappedRook = S( 92, 0);
185 const Score WeakQueen = S( 50, 10);
186 const Score OtherCheck = S( 10, 10);
187 const Score CloseEnemies = S( 7, 0);
188 const Score PawnlessFlank = S( 20, 80);
189 const Score ThreatByHangingPawn = S( 71, 61);
190 const Score ThreatBySafePawn = S(182,175);
191 const Score ThreatByRank = S( 16, 3);
192 const Score Hanging = S( 48, 27);
193 const Score ThreatByPawnPush = S( 38, 22);
194 const Score HinderPassedPawn = S( 7, 0);
196 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
197 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
198 // happen in Chess960 games.
199 const Score TrappedBishopA1H1 = S(50, 50);
204 // KingAttackWeights[PieceType] contains king attack weights by piece type
205 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
207 // Penalties for enemy's safe checks
208 const int QueenCheck = 780;
209 const int RookCheck = 880;
210 const int BishopCheck = 435;
211 const int KnightCheck = 790;
213 // Threshold for lazy and space evaluation
214 const Value LazyThreshold = Value(1500);
215 const Value SpaceThreshold = Value(12222);
217 // eval_init() initializes king and attack bitboards for a given color
218 // adding pawn attacks. To be done at the beginning of the evaluation.
221 void eval_init(const Position& pos, EvalInfo& ei) {
223 const Color Them = (Us == WHITE ? BLACK : WHITE);
224 const Square Up = (Us == WHITE ? NORTH : SOUTH);
225 const Square Down = (Us == WHITE ? SOUTH : NORTH);
226 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
228 // Find our pawns on the first two ranks, and those which are blocked
229 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
231 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
232 // are excluded from the mobility area.
233 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
235 // Initialise the attack bitboards with the king and pawn information
236 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
237 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
239 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
240 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
242 // Init our king safety tables only if we are going to use them
243 if (pos.non_pawn_material(Them) >= QueenValueMg)
246 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
247 ei.kingRing[Us] |= shift<Up>(b);
249 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
250 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
253 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
257 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
260 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
261 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
263 const Color Them = (Us == WHITE ? BLACK : WHITE);
264 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
265 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
266 : Rank5BB | Rank4BB | Rank3BB);
267 const Square* pl = pos.squares<Pt>(Us);
271 Score score = SCORE_ZERO;
273 ei.attackedBy[Us][Pt] = 0;
275 while ((s = *pl++) != SQ_NONE)
277 // Find attacked squares, including x-ray attacks for bishops and rooks
278 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
279 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
280 : pos.attacks_from<Pt>(s);
282 if (pos.pinned_pieces(Us) & s)
283 b &= LineBB[pos.square<KING>(Us)][s];
285 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
286 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
288 if (b & ei.kingRing[Them])
290 ei.kingAttackersCount[Us]++;
291 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
292 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
295 int mob = popcount(b & ei.mobilityArea[Us]);
297 mobility[Us] += MobilityBonus[Pt - 2][mob];
299 // Bonus for this piece as a king protector
300 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
302 if (Pt == BISHOP || Pt == KNIGHT)
304 // Bonus for outpost squares
305 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
307 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
310 bb &= b & ~pos.pieces(Us);
312 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
315 // Bonus when behind a pawn
316 if ( relative_rank(Us, s) < RANK_5
317 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
318 score += MinorBehindPawn;
320 // Penalty for pawns on the same color square as the bishop
322 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
324 // An important Chess960 pattern: A cornered bishop blocked by a friendly
325 // pawn diagonally in front of it is a very serious problem, especially
326 // when that pawn is also blocked.
329 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
331 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
332 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
333 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
334 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
341 // Bonus for aligning with enemy pawns on the same rank/file
342 if (relative_rank(Us, s) >= RANK_5)
343 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
345 // Bonus when on an open or semi-open file
346 if (ei.pe->semiopen_file(Us, file_of(s)))
347 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
349 // Penalty when trapped by the king, even more if the king cannot castle
352 Square ksq = pos.square<KING>(Us);
354 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
355 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
356 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
362 // Penalty if any relative pin or discovered attack against the queen
364 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
370 Trace::add(Pt, Us, score);
372 // Recursively call evaluate_pieces() of next piece type until KING is excluded
373 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
377 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
379 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
382 // evaluate_king() assigns bonuses and penalties to a king of a given color
384 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
385 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
386 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
388 const Bitboard KingFlank[FILE_NB] = {
389 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
392 template<Color Us, bool DoTrace>
393 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
395 const Color Them = (Us == WHITE ? BLACK : WHITE);
396 const Square Up = (Us == WHITE ? NORTH : SOUTH);
397 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
398 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
400 const Square ksq = pos.square<KING>(Us);
401 Bitboard undefended, b, b1, b2, safe, other;
404 // King shelter and enemy pawns storm
405 Score score = ei.pe->king_safety<Us>(pos, ksq);
407 // Main king safety evaluation
408 if (ei.kingAttackersCount[Them])
410 // Find the attacked squares which are defended only by our king...
411 undefended = ei.attackedBy[Them][ALL_PIECES]
412 & ei.attackedBy[Us][KING]
413 & ~ei.attackedBy2[Us];
415 // ... and those which are not defended at all in the larger king ring
416 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
417 & ei.kingRing[Us] & ~pos.pieces(Them);
419 // Initialize the 'kingDanger' variable, which will be transformed
420 // later into a king danger score. The initial value is based on the
421 // number and types of the enemy's attacking pieces, the number of
422 // attacked and undefended squares around our king and the quality of
423 // the pawn shelter (current 'score' value).
424 kingDanger = ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]
425 + 102 * ei.kingAdjacentZoneAttacksCount[Them]
426 + 201 * popcount(undefended)
427 + 143 * (popcount(b) + !!pos.pinned_pieces(Us))
428 - 848 * !pos.count<QUEEN>(Them)
429 - 28 * mg_value(score) / 25 - 5;
431 // Analyse the safe enemy's checks which are possible on next move
432 safe = ~pos.pieces(Them);
433 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
435 b1 = pos.attacks_from<ROOK >(ksq);
436 b2 = pos.attacks_from<BISHOP>(ksq);
438 // Enemy queen safe checks
439 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
440 kingDanger += QueenCheck;
442 // For minors and rooks, also consider the square safe if attacked twice,
443 // and only defended by our queen.
444 safe |= ei.attackedBy2[Them]
445 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
446 & ei.attackedBy[Us][QUEEN];
448 // Some other potential checks are also analysed, even from squares
449 // currently occupied by the opponent own pieces, as long as the square
450 // is not attacked by our pawns, and is not occupied by a blocked pawn.
451 other = ~( ei.attackedBy[Us][PAWN]
452 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
454 // Enemy rooks safe and other checks
455 if (b1 & ei.attackedBy[Them][ROOK] & safe)
456 kingDanger += RookCheck;
458 else if (b1 & ei.attackedBy[Them][ROOK] & other)
461 // Enemy bishops safe and other checks
462 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
463 kingDanger += BishopCheck;
465 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
468 // Enemy knights safe and other checks
469 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
471 kingDanger += KnightCheck;
476 // Transform the kingDanger units into a Score, and substract it from the evaluation
478 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
481 // King tropism: firstly, find squares that opponent attacks in our king flank
482 File kf = file_of(ksq);
483 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
485 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
486 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
488 // Secondly, add the squares which are attacked twice in that flank and
489 // which are not defended by our pawns.
490 b = (Us == WHITE ? b << 4 : b >> 4)
491 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
493 score -= CloseEnemies * popcount(b);
495 // Penalty when our king is on a pawnless flank
496 if (!(pos.pieces(PAWN) & KingFlank[kf]))
497 score -= PawnlessFlank;
500 Trace::add(KING, Us, score);
506 // evaluate_threats() assigns bonuses according to the types of the attacking
507 // and the attacked pieces.
509 template<Color Us, bool DoTrace>
510 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
512 const Color Them = (Us == WHITE ? BLACK : WHITE);
513 const Square Up = (Us == WHITE ? NORTH : SOUTH);
514 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
515 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
516 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
517 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
519 Bitboard b, weak, defended, stronglyProtected, safeThreats;
520 Score score = SCORE_ZERO;
522 // Non-pawn enemies attacked by a pawn
523 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
527 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
528 | ei.attackedBy[Us][ALL_PIECES]);
530 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
532 score += ThreatBySafePawn * popcount(safeThreats);
534 if (weak ^ safeThreats)
535 score += ThreatByHangingPawn;
538 // Squares strongly protected by the opponent, either because they attack the
539 // square with a pawn, or because they attack the square twice and we don't.
540 stronglyProtected = ei.attackedBy[Them][PAWN]
541 | (ei.attackedBy2[Them] & ~ei.attackedBy2[Us]);
543 // Non-pawn enemies, strongly protected
544 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
547 // Enemies not strongly protected and under our attack
548 weak = pos.pieces(Them)
550 & ei.attackedBy[Us][ALL_PIECES];
552 // Add a bonus according to the kind of attacking pieces
555 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
558 Square s = pop_lsb(&b);
559 score += ThreatByMinor[type_of(pos.piece_on(s))];
560 if (type_of(pos.piece_on(s)) != PAWN)
561 score += ThreatByRank * (int)relative_rank(Them, s);
564 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
567 Square s = pop_lsb(&b);
568 score += ThreatByRook[type_of(pos.piece_on(s))];
569 if (type_of(pos.piece_on(s)) != PAWN)
570 score += ThreatByRank * (int)relative_rank(Them, s);
573 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
575 b = weak & ei.attackedBy[Us][KING];
577 score += ThreatByKing[more_than_one(b)];
580 // Bonus if some pawns can safely push and attack an enemy piece
581 b = pos.pieces(Us, PAWN) & ~TRank7BB;
582 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
585 & ~ei.attackedBy[Them][PAWN]
586 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
588 b = (shift<Left>(b) | shift<Right>(b))
590 & ~ei.attackedBy[Us][PAWN];
592 score += ThreatByPawnPush * popcount(b);
595 Trace::add(THREAT, Us, score);
601 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
602 // pawns of the given color.
604 template<Color Us, bool DoTrace>
605 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
607 const Color Them = (Us == WHITE ? BLACK : WHITE);
609 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
610 Score score = SCORE_ZERO;
612 b = ei.pe->passed_pawns(Us);
616 Square s = pop_lsb(&b);
618 assert(!(pos.pieces(Them, PAWN) & forward_bb(Us, s + pawn_push(Us))));
620 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
621 score -= HinderPassedPawn * popcount(bb);
623 int r = relative_rank(Us, s) - RANK_2;
624 int rr = r * (r - 1);
626 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
630 Square blockSq = s + pawn_push(Us);
632 // Adjust bonus based on the king's proximity
633 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
634 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
636 // If blockSq is not the queening square then consider also a second push
637 if (relative_rank(Us, blockSq) != RANK_8)
638 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
640 // If the pawn is free to advance, then increase the bonus
641 if (pos.empty(blockSq))
643 // If there is a rook or queen attacking/defending the pawn from behind,
644 // consider all the squaresToQueen. Otherwise consider only the squares
645 // in the pawn's path attacked or occupied by the enemy.
646 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
648 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
650 if (!(pos.pieces(Us) & bb))
651 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
653 if (!(pos.pieces(Them) & bb))
654 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
656 // If there aren't any enemy attacks, assign a big bonus. Otherwise
657 // assign a smaller bonus if the block square isn't attacked.
658 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
660 // If the path to the queen is fully defended, assign a big bonus.
661 // Otherwise assign a smaller bonus if the block square is defended.
662 if (defendedSquares == squaresToQueen)
665 else if (defendedSquares & blockSq)
668 mbonus += k * rr, ebonus += k * rr;
670 else if (pos.pieces(Us) & blockSq)
671 mbonus += rr + r * 2, ebonus += rr + r * 2;
674 // Scale down bonus for candidate passers which need more than one
675 // pawn push to become passed or have a pawn in front of them.
676 if (!pos.pawn_passed(Us, s + pawn_push(Us)) || (pos.pieces(PAWN) & forward_bb(Us, s)))
677 mbonus /= 2, ebonus /= 2;
679 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
683 Trace::add(PASSED, Us, score);
689 // evaluate_space() computes the space evaluation for a given side. The
690 // space evaluation is a simple bonus based on the number of safe squares
691 // available for minor pieces on the central four files on ranks 2--4. Safe
692 // squares one, two or three squares behind a friendly pawn are counted
693 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
694 // improve play on game opening.
696 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
698 const Color Them = (Us == WHITE ? BLACK : WHITE);
699 const Bitboard SpaceMask =
700 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
701 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
703 // Find the safe squares for our pieces inside the area defined by
704 // SpaceMask. A square is unsafe if it is attacked by an enemy
705 // pawn, or if it is undefended and attacked by an enemy piece.
706 Bitboard safe = SpaceMask
707 & ~pos.pieces(Us, PAWN)
708 & ~ei.attackedBy[Them][PAWN]
709 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
711 // Find all squares which are at most three squares behind some friendly pawn
712 Bitboard behind = pos.pieces(Us, PAWN);
713 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
714 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
716 // Since SpaceMask[Us] is fully on our half of the board...
717 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
719 // ...count safe + (behind & safe) with a single popcount.
720 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
721 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
723 return make_score(bonus * weight * weight / 16, 0);
727 // evaluate_initiative() computes the initiative correction value for the
728 // position, i.e., second order bonus/malus based on the known attacking/defending
729 // status of the players.
730 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
732 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
733 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
734 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
736 // Compute the initiative bonus for the attacking side
737 int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
739 // Now apply the bonus: note that we find the attacking side by extracting
740 // the sign of the endgame value, and that we carefully cap the bonus so
741 // that the endgame score will never change sign after the bonus.
742 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
744 return make_score(0, value);
748 // evaluate_scale_factor() computes the scale factor for the winning side
749 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
751 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
752 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
754 // If we don't already have an unusual scale factor, check for certain
755 // types of endgames, and use a lower scale for those.
756 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
758 if (pos.opposite_bishops())
760 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
761 // is almost a draw, in case of KBP vs KB, it is even more a draw.
762 if ( pos.non_pawn_material(WHITE) == BishopValueMg
763 && pos.non_pawn_material(BLACK) == BishopValueMg)
764 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
766 // Endgame with opposite-colored bishops, but also other pieces. Still
767 // a bit drawish, but not as drawish as with only the two bishops.
768 return ScaleFactor(46);
770 // Endings where weaker side can place his king in front of the opponent's
771 // pawns are drawish.
772 else if ( abs(eg) <= BishopValueEg
773 && pos.count<PAWN>(strongSide) <= 2
774 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
775 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
784 /// evaluate() is the main evaluation function. It returns a static evaluation
785 /// of the position from the point of view of the side to move.
787 template<bool DoTrace>
788 Value Eval::evaluate(const Position& pos) {
790 assert(!pos.checkers());
792 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
796 // Probe the material hash table
797 ei.me = Material::probe(pos);
799 // If we have a specialized evaluation function for the current material
800 // configuration, call it and return.
801 if (ei.me->specialized_eval_exists())
802 return ei.me->evaluate(pos);
804 // Initialize score by reading the incrementally updated scores included in
805 // the position object (material + piece square tables) and the material
806 // imbalance. Score is computed internally from the white point of view.
807 Score score = pos.psq_score() + ei.me->imbalance();
809 // Probe the pawn hash table
810 ei.pe = Pawns::probe(pos);
811 score += ei.pe->pawns_score();
813 // Early exit if score is high
814 v = (mg_value(score) + eg_value(score)) / 2;
815 if (abs(v) > LazyThreshold)
816 return pos.side_to_move() == WHITE ? v : -v;
818 // Initialize attack and king safety bitboards
819 eval_init<WHITE>(pos, ei);
820 eval_init<BLACK>(pos, ei);
822 // Evaluate all pieces but king and pawns
823 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
824 score += mobility[WHITE] - mobility[BLACK];
826 // Evaluate kings after all other pieces because we need full attack
827 // information when computing the king safety evaluation.
828 score += evaluate_king<WHITE, DoTrace>(pos, ei)
829 - evaluate_king<BLACK, DoTrace>(pos, ei);
831 // Evaluate tactical threats, we need full attack information including king
832 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
833 - evaluate_threats<BLACK, DoTrace>(pos, ei);
835 // Evaluate passed pawns, we need full attack information including king
836 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
837 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
839 // Evaluate space for both sides, only during opening
840 if (pos.non_pawn_material() >= SpaceThreshold)
841 score += evaluate_space<WHITE>(pos, ei)
842 - evaluate_space<BLACK>(pos, ei);
844 // Evaluate position potential for the winning side
845 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
847 // Evaluate scale factor for the winning side
848 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
850 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
851 v = mg_value(score) * int(ei.me->game_phase())
852 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
854 v /= int(PHASE_MIDGAME);
856 // In case of tracing add all remaining individual evaluation terms
859 Trace::add(MATERIAL, pos.psq_score());
860 Trace::add(IMBALANCE, ei.me->imbalance());
861 Trace::add(PAWN, ei.pe->pawns_score());
862 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
863 if (pos.non_pawn_material() >= SpaceThreshold)
864 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
865 , evaluate_space<BLACK>(pos, ei));
866 Trace::add(TOTAL, score);
869 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
872 // Explicit template instantiations
873 template Value Eval::evaluate<true >(const Position&);
874 template Value Eval::evaluate<false>(const Position&);
877 /// trace() is like evaluate(), but instead of returning a value, it returns
878 /// a string (suitable for outputting to stdout) that contains the detailed
879 /// descriptions and values of each evaluation term. Useful for debugging.
881 std::string Eval::trace(const Position& pos) {
883 std::memset(scores, 0, sizeof(scores));
885 Value v = evaluate<true>(pos);
886 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
888 std::stringstream ss;
889 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
890 << " Eval 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 << " Bishop | " << 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 pawns | " << Term(PASSED)
904 << " Space | " << Term(SPACE)
905 << "----------------+-------------+-------------+-------------\n"
906 << " Total | " << Term(TOTAL);
908 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";