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) >= RookValueMg + KnightValueMg)
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] > (1 - pos.count<QUEEN>(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 - 9 * mg_value(score) / 8
432 // Analyse the safe enemy's checks which are possible on next move
433 safe = ~pos.pieces(Them);
434 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
436 b1 = pos.attacks_from<ROOK >(ksq);
437 b2 = pos.attacks_from<BISHOP>(ksq);
439 // Enemy queen safe checks
440 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
441 kingDanger += QueenCheck;
443 // For minors and rooks, also consider the square safe if attacked twice,
444 // and only defended by our queen.
445 safe |= ei.attackedBy2[Them]
446 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
447 & ei.attackedBy[Us][QUEEN];
449 // Some other potential checks are also analysed, even from squares
450 // currently occupied by the opponent own pieces, as long as the square
451 // is not attacked by our pawns, and is not occupied by a blocked pawn.
452 other = ~( ei.attackedBy[Us][PAWN]
453 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
455 // Enemy rooks safe and other checks
456 if (b1 & ei.attackedBy[Them][ROOK] & safe)
457 kingDanger += RookCheck;
459 else if (b1 & ei.attackedBy[Them][ROOK] & other)
462 // Enemy bishops safe and other checks
463 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
464 kingDanger += BishopCheck;
466 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
469 // Enemy knights safe and other checks
470 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
472 kingDanger += KnightCheck;
477 // Transform the kingDanger units into a Score, and substract it from the evaluation
479 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
482 // King tropism: firstly, find squares that opponent attacks in our king flank
483 File kf = file_of(ksq);
484 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
486 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
487 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
489 // Secondly, add the squares which are attacked twice in that flank and
490 // which are not defended by our pawns.
491 b = (Us == WHITE ? b << 4 : b >> 4)
492 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
494 score -= CloseEnemies * popcount(b);
496 // Penalty when our king is on a pawnless flank
497 if (!(pos.pieces(PAWN) & KingFlank[kf]))
498 score -= PawnlessFlank;
501 Trace::add(KING, Us, score);
507 // evaluate_threats() assigns bonuses according to the types of the attacking
508 // and the attacked pieces.
510 template<Color Us, bool DoTrace>
511 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
513 const Color Them = (Us == WHITE ? BLACK : WHITE);
514 const Square Up = (Us == WHITE ? NORTH : SOUTH);
515 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
516 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
517 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
518 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
520 Bitboard b, weak, defended, stronglyProtected, safeThreats;
521 Score score = SCORE_ZERO;
523 // Non-pawn enemies attacked by a pawn
524 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
528 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
529 | ei.attackedBy[Us][ALL_PIECES]);
531 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
533 score += ThreatBySafePawn * popcount(safeThreats);
535 if (weak ^ safeThreats)
536 score += ThreatByHangingPawn;
539 // Squares strongly protected by the opponent, either because they attack the
540 // square with a pawn, or because they attack the square twice and we don't.
541 stronglyProtected = ei.attackedBy[Them][PAWN]
542 | (ei.attackedBy2[Them] & ~ei.attackedBy2[Us]);
544 // Non-pawn enemies, strongly protected
545 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
548 // Enemies not strongly protected and under our attack
549 weak = pos.pieces(Them)
551 & ei.attackedBy[Us][ALL_PIECES];
553 // Add a bonus according to the kind of attacking pieces
556 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
559 Square s = pop_lsb(&b);
560 score += ThreatByMinor[type_of(pos.piece_on(s))];
561 if (type_of(pos.piece_on(s)) != PAWN)
562 score += ThreatByRank * (int)relative_rank(Them, s);
565 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
568 Square s = pop_lsb(&b);
569 score += ThreatByRook[type_of(pos.piece_on(s))];
570 if (type_of(pos.piece_on(s)) != PAWN)
571 score += ThreatByRank * (int)relative_rank(Them, s);
574 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
576 b = weak & ei.attackedBy[Us][KING];
578 score += ThreatByKing[more_than_one(b)];
581 // Bonus if some pawns can safely push and attack an enemy piece
582 b = pos.pieces(Us, PAWN) & ~TRank7BB;
583 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
586 & ~ei.attackedBy[Them][PAWN]
587 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
589 b = (shift<Left>(b) | shift<Right>(b))
591 & ~ei.attackedBy[Us][PAWN];
593 score += ThreatByPawnPush * popcount(b);
596 Trace::add(THREAT, Us, score);
602 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
603 // pawns of the given color.
605 template<Color Us, bool DoTrace>
606 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
608 const Color Them = (Us == WHITE ? BLACK : WHITE);
610 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
611 Score score = SCORE_ZERO;
613 b = ei.pe->passed_pawns(Us);
617 Square s = pop_lsb(&b);
619 assert(!(pos.pieces(Them, PAWN) & forward_bb(Us, s + pawn_push(Us))));
621 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
622 score -= HinderPassedPawn * popcount(bb);
624 int r = relative_rank(Us, s) - RANK_2;
625 int rr = r * (r - 1);
627 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
631 Square blockSq = s + pawn_push(Us);
633 // Adjust bonus based on the king's proximity
634 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
635 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
637 // If blockSq is not the queening square then consider also a second push
638 if (relative_rank(Us, blockSq) != RANK_8)
639 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
641 // If the pawn is free to advance, then increase the bonus
642 if (pos.empty(blockSq))
644 // If there is a rook or queen attacking/defending the pawn from behind,
645 // consider all the squaresToQueen. Otherwise consider only the squares
646 // in the pawn's path attacked or occupied by the enemy.
647 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
649 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
651 if (!(pos.pieces(Us) & bb))
652 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
654 if (!(pos.pieces(Them) & bb))
655 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
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 = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
661 // If the path to the queen is fully defended, assign a big bonus.
662 // Otherwise assign a smaller bonus if the block square is defended.
663 if (defendedSquares == squaresToQueen)
666 else if (defendedSquares & blockSq)
669 mbonus += k * rr, ebonus += k * rr;
671 else if (pos.pieces(Us) & blockSq)
672 mbonus += rr + r * 2, ebonus += rr + r * 2;
675 // Scale down bonus for candidate passers which need more than one
676 // pawn push to become passed or have a pawn in front of them.
677 if (!pos.pawn_passed(Us, s + pawn_push(Us)) || (pos.pieces(PAWN) & forward_bb(Us, s)))
678 mbonus /= 2, ebonus /= 2;
680 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
684 Trace::add(PASSED, Us, score);
690 // evaluate_space() computes the space evaluation for a given side. The
691 // space evaluation is a simple bonus based on the number of safe squares
692 // available for minor pieces on the central four files on ranks 2--4. Safe
693 // squares one, two or three squares behind a friendly pawn are counted
694 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
695 // improve play on game opening.
697 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
699 const Color Them = (Us == WHITE ? BLACK : WHITE);
700 const Bitboard SpaceMask =
701 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
702 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
704 // Find the safe squares for our pieces inside the area defined by
705 // SpaceMask. A square is unsafe if it is attacked by an enemy
706 // pawn, or if it is undefended and attacked by an enemy piece.
707 Bitboard safe = SpaceMask
708 & ~pos.pieces(Us, PAWN)
709 & ~ei.attackedBy[Them][PAWN]
710 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
712 // Find all squares which are at most three squares behind some friendly pawn
713 Bitboard behind = pos.pieces(Us, PAWN);
714 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
715 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
717 // Since SpaceMask[Us] is fully on our half of the board...
718 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
720 // ...count safe + (behind & safe) with a single popcount.
721 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
722 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
724 return make_score(bonus * weight * weight / 16, 0);
728 // evaluate_initiative() computes the initiative correction value for the
729 // position, i.e., second order bonus/malus based on the known attacking/defending
730 // status of the players.
731 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
733 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
734 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
735 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
737 // Compute the initiative bonus for the attacking side
738 int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
740 // Now apply the bonus: note that we find the attacking side by extracting
741 // the sign of the endgame value, and that we carefully cap the bonus so
742 // that the endgame score will never change sign after the bonus.
743 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
745 return make_score(0, value);
749 // evaluate_scale_factor() computes the scale factor for the winning side
750 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
752 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
753 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
755 // If we don't already have an unusual scale factor, check for certain
756 // types of endgames, and use a lower scale for those.
757 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
759 if (pos.opposite_bishops())
761 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
762 // is almost a draw, in case of KBP vs KB, it is even more a draw.
763 if ( pos.non_pawn_material(WHITE) == BishopValueMg
764 && pos.non_pawn_material(BLACK) == BishopValueMg)
765 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
767 // Endgame with opposite-colored bishops, but also other pieces. Still
768 // a bit drawish, but not as drawish as with only the two bishops.
769 return ScaleFactor(46);
771 // Endings where weaker side can place his king in front of the opponent's
772 // pawns are drawish.
773 else if ( abs(eg) <= BishopValueEg
774 && pos.count<PAWN>(strongSide) <= 2
775 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
776 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
785 /// evaluate() is the main evaluation function. It returns a static evaluation
786 /// of the position from the point of view of the side to move.
788 template<bool DoTrace>
789 Value Eval::evaluate(const Position& pos) {
791 assert(!pos.checkers());
793 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
797 // Probe the material hash table
798 ei.me = Material::probe(pos);
800 // If we have a specialized evaluation function for the current material
801 // configuration, call it and return.
802 if (ei.me->specialized_eval_exists())
803 return ei.me->evaluate(pos);
805 // Initialize score by reading the incrementally updated scores included in
806 // the position object (material + piece square tables) and the material
807 // imbalance. Score is computed internally from the white point of view.
808 Score score = pos.psq_score() + ei.me->imbalance();
810 // Probe the pawn hash table
811 ei.pe = Pawns::probe(pos);
812 score += ei.pe->pawns_score();
814 // Early exit if score is high
815 v = (mg_value(score) + eg_value(score)) / 2;
816 if (abs(v) > LazyThreshold)
817 return pos.side_to_move() == WHITE ? v : -v;
819 // Initialize attack and king safety bitboards
820 eval_init<WHITE>(pos, ei);
821 eval_init<BLACK>(pos, ei);
823 // Evaluate all pieces but king and pawns
824 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
825 score += mobility[WHITE] - mobility[BLACK];
827 // Evaluate kings after all other pieces because we need full attack
828 // information when computing the king safety evaluation.
829 score += evaluate_king<WHITE, DoTrace>(pos, ei)
830 - evaluate_king<BLACK, DoTrace>(pos, ei);
832 // Evaluate tactical threats, we need full attack information including king
833 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
834 - evaluate_threats<BLACK, DoTrace>(pos, ei);
836 // Evaluate passed pawns, we need full attack information including king
837 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
838 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
840 // Evaluate space for both sides, only during opening
841 if (pos.non_pawn_material() >= SpaceThreshold)
842 score += evaluate_space<WHITE>(pos, ei)
843 - evaluate_space<BLACK>(pos, ei);
845 // Evaluate position potential for the winning side
846 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
848 // Evaluate scale factor for the winning side
849 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
851 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
852 v = mg_value(score) * int(ei.me->game_phase())
853 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
855 v /= int(PHASE_MIDGAME);
857 // In case of tracing add all remaining individual evaluation terms
860 Trace::add(MATERIAL, pos.psq_score());
861 Trace::add(IMBALANCE, ei.me->imbalance());
862 Trace::add(PAWN, ei.pe->pawns_score());
863 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
864 if (pos.non_pawn_material() >= SpaceThreshold)
865 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
866 , evaluate_space<BLACK>(pos, ei));
867 Trace::add(TOTAL, score);
870 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
873 // Explicit template instantiations
874 template Value Eval::evaluate<true >(const Position&);
875 template Value Eval::evaluate<false>(const Position&);
878 /// trace() is like evaluate(), but instead of returning a value, it returns
879 /// a string (suitable for outputting to stdout) that contains the detailed
880 /// descriptions and values of each evaluation term. Useful for debugging.
882 std::string Eval::trace(const Position& pos) {
884 std::memset(scores, 0, sizeof(scores));
886 Value v = evaluate<true>(pos);
887 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
889 std::stringstream ss;
890 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
891 << " Eval term | White | Black | Total \n"
892 << " | MG EG | MG EG | MG EG \n"
893 << "----------------+-------------+-------------+-------------\n"
894 << " Material | " << Term(MATERIAL)
895 << " Imbalance | " << Term(IMBALANCE)
896 << " Pawns | " << Term(PAWN)
897 << " Knights | " << Term(KNIGHT)
898 << " Bishops | " << Term(BISHOP)
899 << " Rooks | " << Term(ROOK)
900 << " Queens | " << Term(QUEEN)
901 << " Mobility | " << Term(MOBILITY)
902 << " King safety | " << Term(KING)
903 << " Threats | " << Term(THREAT)
904 << " Passed pawns | " << Term(PASSED)
905 << " Space | " << Term(SPACE)
906 << "----------------+-------------+-------------+-------------\n"
907 << " Total | " << Term(TOTAL);
909 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";