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.
76 // attackedBy[color][piece type] is a bitboard representing all squares
77 // attacked by a given color and piece type (can be also ALL_PIECES).
78 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
80 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
81 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
82 // pawn or squares attacked by 2 pawns are not explicitly added.
83 Bitboard attackedBy2[COLOR_NB];
85 // kingRing[color] is the zone around the king which is considered
86 // by the king safety evaluation. This consists of the squares directly
87 // adjacent to the king, and the three (or two, for a king on an edge file)
88 // squares two ranks in front of the king. For instance, if black's king
89 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
90 // f7, g7, h7, f6, g6 and h6.
91 Bitboard kingRing[COLOR_NB];
93 // kingAttackersCount[color] is the number of pieces of the given color
94 // which attack a square in the kingRing of the enemy king.
95 int kingAttackersCount[COLOR_NB];
97 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
98 // given color which attack a square in the kingRing of the enemy king. The
99 // weights of the individual piece types are given by the elements in the
100 // KingAttackWeights array.
101 int kingAttackersWeight[COLOR_NB];
103 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
104 // color to squares directly adjacent to the enemy king. Pieces which attack
105 // more than one square are counted multiple times. For instance, if there is
106 // a white knight on g5 and black's king is on g8, this white knight adds 2
107 // to kingAdjacentZoneAttacksCount[WHITE].
108 int kingAdjacentZoneAttacksCount[COLOR_NB];
110 Bitboard pinnedPieces[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
119 // game, indexed by piece type and number of attacked squares in the MobilityArea.
120 const Score MobilityBonus[][32] = {
122 { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
123 S( 22, 26), S( 30, 28), S( 36, 29) },
124 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
125 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
126 S( 92, 90), S( 97, 94) },
127 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
128 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
129 S( 43,165), S( 49,168), S( 59,169) },
130 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
131 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
132 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
133 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
134 S(118,174), S(119,177), S(123,191), S(128,199) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
138 // bishops outposts, bigger if outpost piece is supported by a pawn.
139 const Score Outpost[][2] = {
140 { S(43,11), S(65,20) }, // Knights
141 { S(20, 3), S(29, 8) } // Bishops
144 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
145 // knights and bishops which can reach an outpost square in one move, bigger
146 // if outpost square is supported by a pawn.
147 const Score ReachableOutpost[][2] = {
148 { S(21, 5), S(35, 8) }, // Knights
149 { S( 8, 0), S(14, 4) } // Bishops
152 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
153 // friendly pawn on the rook file.
154 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
156 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
157 // type is attacked by a pawn which is protected or is not attacked.
158 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
159 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
162 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
163 // which piece type attacks which one. Attacks on lesser pieces which are
164 // pawn-defended are not considered.
165 const Score ThreatByMinor[PIECE_TYPE_NB] = {
166 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
169 const Score ThreatByRook[PIECE_TYPE_NB] = {
170 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
173 // ThreatByKing[on one/on many] contains bonuses for king attacks on
174 // pawns or pieces which are not pawn-defended.
175 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
177 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
178 // We don't use a Score because we process the two components independently.
179 const Value Passed[][RANK_NB] = {
180 { V(5), V( 5), V(31), V(73), V(166), V(252) },
181 { V(7), V(14), V(38), V(73), V(166), V(252) }
184 // PassedFile[File] contains a bonus according to the file of a passed pawn
185 const Score PassedFile[FILE_NB] = {
186 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
187 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
190 // Assorted bonuses and penalties used by evaluation
191 const Score MinorBehindPawn = S(16, 0);
192 const Score BishopPawns = S( 8, 12);
193 const Score RookOnPawn = S( 8, 24);
194 const Score TrappedRook = S(92, 0);
195 const Score WeakQueen = S(50, 10);
196 const Score OtherCheck = S(10, 10);
197 const Score CloseEnemies = S( 7, 0);
198 const Score PawnlessFlank = S(20, 80);
199 const Score LooseEnemies = S( 0, 25);
200 const Score ThreatByHangingPawn = S(71, 61);
201 const Score ThreatByRank = S(16, 3);
202 const Score Hanging = S(48, 27);
203 const Score ThreatByPawnPush = S(38, 22);
204 const Score HinderPassedPawn = S( 7, 0);
206 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
207 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
208 // happen in Chess960 games.
209 const Score TrappedBishopA1H1 = S(50, 50);
214 // KingAttackWeights[PieceType] contains king attack weights by piece type
215 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
217 // Penalties for enemy's safe checks
218 const int QueenContactCheck = 997;
219 const int QueenCheck = 745;
220 const int RookCheck = 688;
221 const int BishopCheck = 588;
222 const int KnightCheck = 924;
224 // Threshold for lazy evaluation
225 const Value LazyEval = Value(1500);
227 // eval_init() initializes king and attack bitboards for a given color
228 // adding pawn attacks. To be done at the beginning of the evaluation.
231 void eval_init(const Position& pos, EvalInfo& ei) {
233 const Color Them = (Us == WHITE ? BLACK : WHITE);
234 const Square Down = (Us == WHITE ? SOUTH : NORTH);
236 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
237 Bitboard b = ei.attackedBy[Them][KING];
238 ei.attackedBy[Them][ALL_PIECES] |= b;
239 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
240 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
242 // Init king safety tables only if we are going to use them
243 if (pos.non_pawn_material(Us) >= QueenValueMg)
245 ei.kingRing[Them] = b | shift<Down>(b);
246 ei.kingAttackersCount[Us] = popcount(b & ei.attackedBy[Us][PAWN]);
247 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
250 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
254 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
257 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
258 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
259 const Bitboard* mobilityArea) {
260 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
261 const Color Them = (Us == WHITE ? BLACK : WHITE);
262 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
263 : Rank5BB | Rank4BB | Rank3BB);
264 const Square* pl = pos.squares<Pt>(Us);
268 Score score = SCORE_ZERO;
270 ei.attackedBy[Us][Pt] = 0;
272 while ((s = *pl++) != SQ_NONE)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
277 : pos.attacks_from<Pt>(s);
279 if (ei.pinnedPieces[Us] & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
282 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
283 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
285 if (b & ei.kingRing[Them])
287 ei.kingAttackersCount[Us]++;
288 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
289 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
293 b &= ~( ei.attackedBy[Them][KNIGHT]
294 | ei.attackedBy[Them][BISHOP]
295 | ei.attackedBy[Them][ROOK]);
297 int mob = popcount(b & mobilityArea[Us]);
299 mobility[Us] += MobilityBonus[Pt][mob];
301 if (Pt == BISHOP || Pt == KNIGHT)
303 // Bonus for outpost squares
304 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
306 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
309 bb &= b & ~pos.pieces(Us);
311 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
314 // Bonus when behind a pawn
315 if ( relative_rank(Us, s) < RANK_5
316 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
317 score += MinorBehindPawn;
319 // Penalty for pawns on the same color square as the bishop
321 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
323 // An important Chess960 pattern: A cornered bishop blocked by a friendly
324 // pawn diagonally in front of it is a very serious problem, especially
325 // when that pawn is also blocked.
328 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
330 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
331 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
332 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
333 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
340 // Bonus for aligning with enemy pawns on the same rank/file
341 if (relative_rank(Us, s) >= RANK_5)
342 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
344 // Bonus when on an open or semi-open file
345 if (ei.pi->semiopen_file(Us, file_of(s)))
346 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
348 // Penalize when trapped by the king, even more if the king cannot castle
351 Square ksq = pos.square<KING>(Us);
353 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
354 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
355 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
361 // Penalty if any relative pin or discovered attack against the queen
363 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
369 Trace::add(Pt, Us, score);
371 // Recursively call evaluate_pieces() of next piece type until KING is excluded
372 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
376 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
378 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
381 // evaluate_king() assigns bonuses and penalties to a king of a given color
383 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
385 const Bitboard KingFlank[FILE_NB] = {
386 CenterFiles >> 2, CenterFiles >> 2, CenterFiles >> 2, CenterFiles, CenterFiles,
387 CenterFiles << 2, CenterFiles << 2, CenterFiles << 2
390 template<Color Us, bool DoTrace>
391 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
393 const Color Them = (Us == WHITE ? BLACK : WHITE);
394 const Square Up = (Us == WHITE ? NORTH : SOUTH);
395 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
396 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
398 const Square ksq = pos.square<KING>(Us);
399 Bitboard undefended, b, b1, b2, safe, other;
402 // King shelter and enemy pawns storm
403 Score score = ei.pi->king_safety<Us>(pos, ksq);
405 // Main king safety evaluation
406 if (ei.kingAttackersCount[Them])
408 // Find the attacked squares which are defended only by the king...
409 undefended = ei.attackedBy[Them][ALL_PIECES]
410 & ei.attackedBy[Us][KING]
411 & ~ei.attackedBy2[Us];
413 // ... and those which are not defended at all in the larger king ring
414 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
415 & ei.kingRing[Us] & ~pos.pieces(Them);
417 // Initialize the 'kingDanger' variable, which will be transformed
418 // later into a king danger score. The initial value is based on the
419 // number and types of the enemy's attacking pieces, the number of
420 // attacked and undefended squares around our king and the quality of
421 // the pawn shelter (current 'score' value).
422 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
423 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
424 + 235 * popcount(undefended)
425 + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
426 - 717 * !pos.count<QUEEN>(Them)
427 - 7 * mg_value(score) / 5 - 5;
429 // Analyse the enemy's safe queen contact checks. Firstly, find the
430 // undefended squares around the king reachable by the enemy queen...
431 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
433 // ...and keep squares supported by another enemy piece
434 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
436 // Analyse the safe enemy's checks which are possible on next move...
437 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
439 // ... and some other potential checks, only requiring the square to be
440 // safe from pawn-attacks, and not being occupied by a blocked pawn.
441 other = ~( ei.attackedBy[Us][PAWN]
442 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
444 b1 = pos.attacks_from<ROOK >(ksq);
445 b2 = pos.attacks_from<BISHOP>(ksq);
447 // Enemy queen safe checks
448 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
449 kingDanger += QueenCheck;
451 // For other pieces, also consider the square safe if attacked twice,
452 // and only defended by a queen.
453 safe |= ei.attackedBy2[Them]
454 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
455 & ei.attackedBy[Us][QUEEN];
457 // Enemy rooks safe and other checks
458 if (b1 & ei.attackedBy[Them][ROOK] & safe)
459 kingDanger += RookCheck;
461 else if (b1 & ei.attackedBy[Them][ROOK] & other)
464 // Enemy bishops safe and other checks
465 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
466 kingDanger += BishopCheck;
468 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
471 // Enemy knights safe and other checks
472 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
474 kingDanger += KnightCheck;
479 // Compute the king danger score and subtract it from the evaluation
481 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
484 // King tropism: firstly, find squares that opponent attacks in our king flank
485 File kf = file_of(ksq);
486 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
488 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
489 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
491 // Secondly, add the squares which are attacked twice in that flank and
492 // which are not defended by our pawns.
493 b = (Us == WHITE ? b << 4 : b >> 4)
494 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
496 score -= CloseEnemies * popcount(b);
498 // Penalty when our king is on a pawnless flank
499 if (!(pos.pieces(PAWN) & KingFlank[kf]))
500 score -= PawnlessFlank;
503 Trace::add(KING, Us, score);
509 // evaluate_threats() assigns bonuses according to the types of the attacking
510 // and the attacked pieces.
512 template<Color Us, bool DoTrace>
513 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
515 const Color Them = (Us == WHITE ? BLACK : WHITE);
516 const Square Up = (Us == WHITE ? NORTH : SOUTH);
517 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
518 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
519 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
520 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
522 Bitboard b, weak, defended, safeThreats;
523 Score score = SCORE_ZERO;
525 // Small bonus if the opponent has loose pawns or pieces
526 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
527 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
528 score += LooseEnemies;
530 // Non-pawn enemies attacked by a pawn
531 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
535 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
536 | ei.attackedBy[Us][ALL_PIECES]);
538 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
540 if (weak ^ safeThreats)
541 score += ThreatByHangingPawn;
544 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
547 // Non-pawn enemies defended by a pawn
548 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
550 // Enemies not defended by a pawn and under our attack
551 weak = pos.pieces(Them)
552 & ~ei.attackedBy[Them][PAWN]
553 & ei.attackedBy[Us][ALL_PIECES];
555 // Add a bonus according to the kind of attacking pieces
558 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
561 Square s = pop_lsb(&b);
562 score += ThreatByMinor[type_of(pos.piece_on(s))];
563 if (type_of(pos.piece_on(s)) != PAWN)
564 score += ThreatByRank * (int)relative_rank(Them, s);
567 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
570 Square s = pop_lsb(&b);
571 score += ThreatByRook[type_of(pos.piece_on(s))];
572 if (type_of(pos.piece_on(s)) != PAWN)
573 score += ThreatByRank * (int)relative_rank(Them, s);
576 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
578 b = weak & ei.attackedBy[Us][KING];
580 score += ThreatByKing[more_than_one(b)];
583 // Bonus if some pawns can safely push and attack an enemy piece
584 b = pos.pieces(Us, PAWN) & ~TRank7BB;
585 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
588 & ~ei.attackedBy[Them][PAWN]
589 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
591 b = (shift<Left>(b) | shift<Right>(b))
593 & ~ei.attackedBy[Us][PAWN];
595 score += ThreatByPawnPush * popcount(b);
598 Trace::add(THREAT, Us, score);
604 // evaluate_passed_pawns() evaluates the passed pawns of the given color
606 template<Color Us, bool DoTrace>
607 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
609 const Color Them = (Us == WHITE ? BLACK : WHITE);
611 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
612 Score score = SCORE_ZERO;
614 b = ei.pi->passed_pawns(Us);
618 Square s = pop_lsb(&b);
620 assert(pos.pawn_passed(Us, s));
621 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
623 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
624 score -= HinderPassedPawn * popcount(bb);
626 int r = relative_rank(Us, s) - RANK_2;
627 int rr = r * (r - 1);
629 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
633 Square blockSq = s + pawn_push(Us);
635 // Adjust bonus based on the king's proximity
636 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
637 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
639 // If blockSq is not the queening square then consider also a second push
640 if (relative_rank(Us, blockSq) != RANK_8)
641 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
643 // If the pawn is free to advance, then increase the bonus
644 if (pos.empty(blockSq))
646 // If there is a rook or queen attacking/defending the pawn from behind,
647 // consider all the squaresToQueen. Otherwise consider only the squares
648 // in the pawn's path attacked or occupied by the enemy.
649 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
651 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
653 if (!(pos.pieces(Us) & bb))
654 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
656 if (!(pos.pieces(Them) & bb))
657 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
659 // If there aren't any enemy attacks, assign a big bonus. Otherwise
660 // assign a smaller bonus if the block square isn't attacked.
661 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
663 // If the path to the queen is fully defended, assign a big bonus.
664 // Otherwise assign a smaller bonus if the block square is defended.
665 if (defendedSquares == squaresToQueen)
668 else if (defendedSquares & blockSq)
671 mbonus += k * rr, ebonus += k * rr;
673 else if (pos.pieces(Us) & blockSq)
674 mbonus += rr + r * 2, ebonus += rr + r * 2;
677 // Assign a small bonus when the opponent has no pieces left
678 if (!pos.non_pawn_material(Them))
681 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
685 Trace::add(PASSED, Us, score);
687 // Add the scores to the middlegame and endgame eval
692 // evaluate_space() computes the space evaluation for a given side. The
693 // space evaluation is a simple bonus based on the number of safe squares
694 // available for minor pieces on the central four files on ranks 2--4. Safe
695 // squares one, two or three squares behind a friendly pawn are counted
696 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
697 // improve play on game opening.
699 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
701 const Color Them = (Us == WHITE ? BLACK : WHITE);
702 const Bitboard SpaceMask =
703 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
704 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
706 // Find the safe squares for our pieces inside the area defined by
707 // SpaceMask. A square is unsafe if it is attacked by an enemy
708 // pawn, or if it is undefended and attacked by an enemy piece.
709 Bitboard safe = SpaceMask
710 & ~pos.pieces(Us, PAWN)
711 & ~ei.attackedBy[Them][PAWN]
712 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
714 // Find all squares which are at most three squares behind some friendly pawn
715 Bitboard behind = pos.pieces(Us, PAWN);
716 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
717 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
719 // Since SpaceMask[Us] is fully on our half of the board...
720 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
722 // ...count safe + (behind & safe) with a single popcount
723 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
724 bonus = std::min(16, bonus);
725 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
727 return make_score(bonus * weight * weight / 18, 0);
731 // evaluate_initiative() computes the initiative correction value for the
732 // position, i.e., second order bonus/malus based on the known attacking/defending
733 // status of the players.
734 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
736 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
737 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
738 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
740 // Compute the initiative bonus for the attacking side
741 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
743 // Now apply the bonus: note that we find the attacking side by extracting
744 // the sign of the endgame value, and that we carefully cap the bonus so
745 // that the endgame score will never be divided by more than two.
746 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
748 return make_score(0, value);
752 // evaluate_scale_factor() computes the scale factor for the winning side
753 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
755 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
756 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
758 // If we don't already have an unusual scale factor, check for certain
759 // types of endgames, and use a lower scale for those.
760 if ( ei.me->game_phase() < PHASE_MIDGAME
761 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
763 if (pos.opposite_bishops())
765 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
766 // is almost a draw, in case of KBP vs KB, it is even more a draw.
767 if ( pos.non_pawn_material(WHITE) == BishopValueMg
768 && pos.non_pawn_material(BLACK) == BishopValueMg)
769 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
771 // Endgame with opposite-colored bishops, but also other pieces. Still
772 // a bit drawish, but not as drawish as with only the two bishops.
774 sf = ScaleFactor(46);
776 // Endings where weaker side can place his king in front of the opponent's
777 // pawns are drawish.
778 else if ( abs(eg) <= BishopValueEg
779 && pos.count<PAWN>(strongSide) <= 2
780 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
781 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
788 Value lazy_eval(Value mg, Value eg) {
790 if (mg > LazyEval && eg > LazyEval)
791 return LazyEval + ((mg + eg) / 2 - LazyEval) / 4;
793 else if (mg < -LazyEval && eg < -LazyEval)
794 return -LazyEval + ((mg + eg) / 2 + LazyEval) / 4;
802 /// evaluate() is the main evaluation function. It returns a static evaluation
803 /// of the position from the point of view of the side to move.
805 template<bool DoTrace>
806 Value Eval::evaluate(const Position& pos) {
808 assert(!pos.checkers());
810 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
813 // Probe the material hash table
814 ei.me = Material::probe(pos);
816 // If we have a specialized evaluation function for the current material
817 // configuration, call it and return.
818 if (ei.me->specialized_eval_exists())
819 return ei.me->evaluate(pos);
821 // Initialize score by reading the incrementally updated scores included in
822 // the position object (material + piece square tables) and the material
823 // imbalance. Score is computed internally from the white point of view.
824 Score score = pos.psq_score() + ei.me->imbalance();
826 // Probe the pawn hash table
827 ei.pi = Pawns::probe(pos);
828 score += ei.pi->pawns_score();
830 // We have taken into account all cheap evaluation terms.
831 // If score exceeds a threshold return a lazy evaluation.
832 Value lazy = lazy_eval(mg_value(score), eg_value(score));
834 return pos.side_to_move() == WHITE ? lazy : -lazy;
836 // Initialize attack and king safety bitboards
837 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
838 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
839 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
840 eval_init<WHITE>(pos, ei);
841 eval_init<BLACK>(pos, ei);
843 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
844 Bitboard blockedPawns[] = {
845 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
846 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
849 // Do not include in mobility area squares protected by enemy pawns, or occupied
850 // by our blocked pawns or king.
851 Bitboard mobilityArea[] = {
852 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
853 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
856 // Evaluate all pieces but king and pawns
857 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
858 score += mobility[WHITE] - mobility[BLACK];
860 // Evaluate kings after all other pieces because we need full attack
861 // information when computing the king safety evaluation.
862 score += evaluate_king<WHITE, DoTrace>(pos, ei)
863 - evaluate_king<BLACK, DoTrace>(pos, ei);
865 // Evaluate tactical threats, we need full attack information including king
866 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
867 - evaluate_threats<BLACK, DoTrace>(pos, ei);
869 // Evaluate passed pawns, we need full attack information including king
870 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
871 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
873 // Evaluate space for both sides, only during opening
874 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
875 score += evaluate_space<WHITE>(pos, ei)
876 - evaluate_space<BLACK>(pos, ei);
878 // Evaluate position potential for the winning side
879 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
881 // Evaluate scale factor for the winning side
882 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
884 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
885 Value v = mg_value(score) * int(ei.me->game_phase())
886 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
888 v /= int(PHASE_MIDGAME);
890 // In case of tracing add all remaining individual evaluation terms
893 Trace::add(MATERIAL, pos.psq_score());
894 Trace::add(IMBALANCE, ei.me->imbalance());
895 Trace::add(PAWN, ei.pi->pawns_score());
896 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
897 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
898 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
899 , evaluate_space<BLACK>(pos, ei));
900 Trace::add(TOTAL, score);
903 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
906 // Explicit template instantiations
907 template Value Eval::evaluate<true >(const Position&);
908 template Value Eval::evaluate<false>(const Position&);
911 /// trace() is like evaluate(), but instead of returning a value, it returns
912 /// a string (suitable for outputting to stdout) that contains the detailed
913 /// descriptions and values of each evaluation term. Useful for debugging.
915 std::string Eval::trace(const Position& pos) {
917 std::memset(scores, 0, sizeof(scores));
919 Value v = evaluate<true>(pos);
920 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
922 std::stringstream ss;
923 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
924 << " Eval term | White | Black | Total \n"
925 << " | MG EG | MG EG | MG EG \n"
926 << "----------------+-------------+-------------+-------------\n"
927 << " Material | " << Term(MATERIAL)
928 << " Imbalance | " << Term(IMBALANCE)
929 << " Pawns | " << Term(PAWN)
930 << " Knights | " << Term(KNIGHT)
931 << " Bishop | " << Term(BISHOP)
932 << " Rooks | " << Term(ROOK)
933 << " Queens | " << Term(QUEEN)
934 << " Mobility | " << Term(MOBILITY)
935 << " King safety | " << Term(KING)
936 << " Threats | " << Term(THREAT)
937 << " Passed pawns | " << Term(PASSED)
938 << " Space | " << Term(SPACE)
939 << "----------------+-------------+-------------+-------------\n"
940 << " Total | " << Term(TOTAL);
942 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";