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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
22 #include <cstring> // For std::memset
33 // Struct EvalInfo contains various information computed and collected
34 // by the evaluation functions.
37 // Pointers to material and pawn hash table entries
41 // attackedBy[color][piece type] is a bitboard representing all squares
42 // attacked by a given color and piece type, attackedBy[color][ALL_PIECES]
43 // contains all squares attacked by the given color.
44 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
46 // kingRing[color] is the zone around the king which is considered
47 // by the king safety evaluation. This consists of the squares directly
48 // adjacent to the king, and the three (or two, for a king on an edge file)
49 // squares two ranks in front of the king. For instance, if black's king
50 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
51 // f7, g7, h7, f6, g6 and h6.
52 Bitboard kingRing[COLOR_NB];
54 // kingAttackersCount[color] is the number of pieces of the given color
55 // which attack a square in the kingRing of the enemy king.
56 int kingAttackersCount[COLOR_NB];
58 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
59 // given color which attack a square in the kingRing of the enemy king. The
60 // weights of the individual piece types are given by the elements in the
61 // KingAttackWeights array.
62 int kingAttackersWeight[COLOR_NB];
64 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
65 // color to squares directly adjacent to the enemy king. Pieces which attack
66 // more than one square are counted multiple times. For instance, if there is
67 // a white knight on g5 and black's king is on g8, this white knight adds 2
68 // to kingAdjacentZoneAttacksCount[WHITE].
69 int kingAdjacentZoneAttacksCount[COLOR_NB];
71 Bitboard pinnedPieces[COLOR_NB];
76 enum Term { // First 8 entries are for PieceType
77 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERMS_NB
80 Score scores[COLOR_NB][TERMS_NB];
82 std::ostream& operator<<(std::ostream& os, Term idx);
84 double to_cp(Value v);
85 void write(int idx, Color c, Score s);
86 void write(int idx, Score w, Score b = SCORE_ZERO);
87 std::string do_trace(const Position& pos);
90 // Evaluation weights, indexed by evaluation term
91 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
92 const struct Weight { int mg, eg; } Weights[] = {
93 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {322, 0}
97 #define S(mg, eg) make_score(mg, eg)
99 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
100 // game, indexed by piece type and number of attacked squares not occupied by
102 const Score MobilityBonus[][32] = {
104 { S(-65,-50), S(-42,-30), S(-9,-10), S( 3, 0), S(15, 10), S(27, 20), // Knights
105 S( 37, 28), S( 42, 31), S(44, 33) },
106 { S(-52,-47), S(-28,-23), S( 6, 1), S(20, 15), S(34, 29), S(48, 43), // Bishops
107 S( 60, 55), S( 68, 63), S(74, 68), S(77, 72), S(80, 75), S(82, 77),
108 S( 84, 79), S( 86, 81) },
109 { S(-47,-53), S(-31,-26), S(-5, 0), S( 1, 16), S( 7, 32), S(13, 48), // Rooks
110 S( 18, 64), S( 22, 80), S(26, 96), S(29,109), S(31,115), S(33,119),
111 S( 35,122), S( 36,123), S(37,124) },
112 { S(-42,-40), S(-28,-23), S(-5, -7), S( 0, 0), S( 6, 10), S(11, 19), // Queens
113 S( 13, 29), S( 18, 38), S(20, 40), S(21, 41), S(22, 41), S(22, 41),
114 S( 22, 41), S( 23, 41), S(24, 41), S(25, 41), S(25, 41), S(25, 41),
115 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41), S(25, 41), S(25, 41),
116 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41) }
119 // Outpost[Bishop/Knight][Square] contains bonuses for knights and bishops
120 // outposts, indexed by piece type and square (from white's point of view).
121 const Value Outpost[][SQUARE_NB] = {
123 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
124 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
125 V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0),
126 V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0),
127 V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0),
128 V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0) },
130 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
131 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
132 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
133 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
134 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
135 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0) }
138 // Threat[defended/weak][minor/major attacking][attacked PieceType] contains
139 // bonuses according to which piece type attacks which one.
140 const Score Threat[][2][PIECE_TYPE_NB] = {
141 { { S(0, 0), S( 0, 0), S(19, 37), S(24, 37), S(44, 97), S(35,106) }, // Defended Minor
142 { S(0, 0), S( 0, 0), S( 9, 14), S( 9, 14), S( 7, 14), S(24, 48) } }, // Defended Major
143 { { S(0, 0), S( 0,32), S(33, 41), S(31, 50), S(41,100), S(35,104) }, // Weak Minor
144 { S(0, 0), S( 0,27), S(26, 57), S(26, 57), S(0 , 43), S(23, 51) } } // Weak Major
147 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
148 // type is attacked by an enemy pawn.
149 const Score ThreatenedByPawn[PIECE_TYPE_NB] = {
150 S(0, 0), S(0, 0), S(87, 118), S(84, 122), S(114, 203), S(121, 217)
153 // Assorted bonuses and penalties used by evaluation
154 const Score KingOnOne = S( 2, 58);
155 const Score KingOnMany = S( 6,125);
156 const Score RookOnPawn = S( 7, 27);
157 const Score RookOnOpenFile = S(43, 21);
158 const Score RookOnSemiOpenFile = S(19, 10);
159 const Score BishopPawns = S( 8, 12);
160 const Score MinorBehindPawn = S(16, 0);
161 const Score TrappedRook = S(92, 0);
162 const Score Unstoppable = S( 0, 20);
163 const Score Hanging = S(31, 26);
164 const Score PawnAttackThreat = S(20, 20);
165 const Score PawnSafePush = S( 5, 5);
167 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
168 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
169 // happen in Chess960 games.
170 const Score TrappedBishopA1H1 = S(50, 50);
175 // SpaceMask[Color] contains the area of the board which is considered
176 // by the space evaluation. In the middlegame, each side is given a bonus
177 // based on how many squares inside this area are safe and available for
178 // friendly minor pieces.
179 const Bitboard SpaceMask[COLOR_NB] = {
180 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
181 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
184 // King danger constants and variables. The king danger scores are looked-up
185 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
186 // of the enemy attack are added up into an integer, which is used as an
187 // index to KingDanger[].
189 // KingAttackWeights[PieceType] contains king attack weights by piece type
190 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
192 // Bonuses for enemy's safe checks
193 const int QueenContactCheck = 89;
194 const int RookContactCheck = 71;
195 const int QueenCheck = 50;
196 const int RookCheck = 37;
197 const int BishopCheck = 6;
198 const int KnightCheck = 14;
200 // KingDanger[attackUnits] contains the actual king danger weighted
201 // scores, indexed by a calculated integer number.
202 Score KingDanger[512];
204 // apply_weight() weighs score 's' by weight 'w' trying to prevent overflow
205 Score apply_weight(Score s, const Weight& w) {
206 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
210 // init_eval_info() initializes king bitboards for given color adding
211 // pawn attacks. To be done at the beginning of the evaluation.
214 void init_eval_info(const Position& pos, EvalInfo& ei) {
216 const Color Them = (Us == WHITE ? BLACK : WHITE);
217 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
219 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
220 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
221 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
223 // Init king safety tables only if we are going to use them
224 if (pos.non_pawn_material(Us) >= QueenValueMg)
226 ei.kingRing[Them] = b | shift_bb<Down>(b);
227 b &= ei.attackedBy[Us][PAWN];
228 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
229 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
232 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
236 // evaluate_outpost() evaluates bishop and knight outpost squares
238 template<PieceType Pt, Color Us>
239 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
241 const Color Them = (Us == WHITE ? BLACK : WHITE);
243 assert (Pt == BISHOP || Pt == KNIGHT);
245 // Initial bonus based on square
246 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
248 // Increase bonus if supported by pawn, especially if the opponent has
249 // no minor piece which can trade with the outpost piece.
250 if (bonus && (ei.attackedBy[Us][PAWN] & s))
252 if ( !pos.pieces(Them, KNIGHT)
253 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
254 bonus += bonus + bonus / 2;
259 return make_score(bonus * 2, bonus / 2);
263 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
265 template<PieceType Pt, Color Us, bool Trace>
266 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
270 Score score = SCORE_ZERO;
272 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
273 const Color Them = (Us == WHITE ? BLACK : WHITE);
274 const Square* pl = pos.list<Pt>(Us);
276 ei.attackedBy[Us][Pt] = 0;
278 while ((s = *pl++) != SQ_NONE)
280 // Find attacked squares, including x-ray attacks for bishops and rooks
281 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
282 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
283 : pos.attacks_from<Pt>(s);
285 if (ei.pinnedPieces[Us] & s)
286 b &= LineBB[pos.king_square(Us)][s];
288 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
290 if (b & ei.kingRing[Them])
292 ei.kingAttackersCount[Us]++;
293 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
294 Bitboard bb = b & ei.attackedBy[Them][KING];
296 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
300 b &= ~( ei.attackedBy[Them][KNIGHT]
301 | ei.attackedBy[Them][BISHOP]
302 | ei.attackedBy[Them][ROOK]);
304 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
305 : popcount<Full >(b & mobilityArea[Us]);
307 mobility[Us] += MobilityBonus[Pt][mob];
309 // Decrease score if we are attacked by an enemy pawn. The remaining part
310 // of threat evaluation must be done later when we have full attack info.
311 if (ei.attackedBy[Them][PAWN] & s)
312 score -= ThreatenedByPawn[Pt];
314 if (Pt == BISHOP || Pt == KNIGHT)
316 // Bonus for outpost square
317 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
318 score += evaluate_outpost<Pt, Us>(pos, ei, s);
320 // Bonus when behind a pawn
321 if ( relative_rank(Us, s) < RANK_5
322 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
323 score += MinorBehindPawn;
325 // Penalty for pawns on same color square of bishop
327 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
329 // An important Chess960 pattern: A cornered bishop blocked by a friendly
330 // pawn diagonally in front of it is a very serious problem, especially
331 // when that pawn is also blocked.
334 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
336 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
337 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
338 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
339 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
346 // Bonus for aligning with enemy pawns on the same rank/file
347 if (relative_rank(Us, s) >= RANK_5)
349 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
351 score += popcount<Max15>(alignedPawns) * RookOnPawn;
354 // Bonus when on an open or semi-open file
355 if (ei.pi->semiopen_file(Us, file_of(s)))
356 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
358 // Penalize when trapped by the king, even more if king cannot castle
359 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
361 Square ksq = pos.king_square(Us);
363 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
364 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
365 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
366 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
372 Tracing::write(Pt, Us, score);
374 // Recursively call evaluate_pieces() of next piece type until KING excluded
375 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
379 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
381 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
384 // evaluate_king() assigns bonuses and penalties to a king of a given color
386 template<Color Us, bool Trace>
387 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
389 const Color Them = (Us == WHITE ? BLACK : WHITE);
391 Bitboard undefended, b, b1, b2, safe;
393 const Square ksq = pos.king_square(Us);
395 // King shelter and enemy pawns storm
396 Score score = ei.pi->king_safety<Us>(pos, ksq);
398 // Main king safety evaluation
399 if (ei.kingAttackersCount[Them])
401 // Find the attacked squares around the king which have no defenders
402 // apart from the king itself
403 undefended = ei.attackedBy[Them][ALL_PIECES]
404 & ei.attackedBy[Us][KING]
405 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
406 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
407 | ei.attackedBy[Us][QUEEN]);
409 // Initialize the 'attackUnits' variable, which is used later on as an
410 // index into the KingDanger[] array. The initial value is based on the
411 // number and types of the enemy's attacking pieces, the number of
412 // attacked and undefended squares around our king and the quality of
413 // the pawn shelter (current 'score' value).
414 attackUnits = std::min(74, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
415 + 8 * ei.kingAdjacentZoneAttacksCount[Them]
416 + 25 * popcount<Max15>(undefended)
417 + 11 * (ei.pinnedPieces[Us] != 0)
418 - mg_value(score) / 8
419 - !pos.count<QUEEN>(Them) * 60;
421 // Analyse the enemy's safe queen contact checks. Firstly, find the
422 // undefended squares around the king reachable by the enemy queen...
423 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
426 // ...and then remove squares not supported by another enemy piece
427 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
428 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
431 attackUnits += QueenContactCheck * popcount<Max15>(b);
434 // Analyse the enemy's safe rook contact checks. Firstly, find the
435 // undefended squares around the king reachable by the enemy rooks...
436 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
438 // Consider only squares where the enemy's rook gives check
439 b &= PseudoAttacks[ROOK][ksq];
443 // ...and then remove squares not supported by another enemy piece
444 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
445 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
448 attackUnits += RookContactCheck * popcount<Max15>(b);
451 // Analyse the enemy's safe distance checks for sliders and knights
452 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
454 b1 = pos.attacks_from<ROOK >(ksq) & safe;
455 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
457 // Enemy queen safe checks
458 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
460 attackUnits += QueenCheck * popcount<Max15>(b);
462 // Enemy rooks safe checks
463 b = b1 & ei.attackedBy[Them][ROOK];
465 attackUnits += RookCheck * popcount<Max15>(b);
467 // Enemy bishops safe checks
468 b = b2 & ei.attackedBy[Them][BISHOP];
470 attackUnits += BishopCheck * popcount<Max15>(b);
472 // Enemy knights safe checks
473 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
475 attackUnits += KnightCheck * popcount<Max15>(b);
477 // Finally, extract the king danger score from the KingDanger[]
478 // array and subtract the score from evaluation.
479 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
483 Tracing::write(KING, Us, score);
489 // evaluate_threats() assigns bonuses according to the type of attacking piece
490 // and the type of attacked one.
492 template<Color Us, bool Trace>
493 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
495 const Color Them = (Us == WHITE ? BLACK : WHITE);
496 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
497 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
498 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
499 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
500 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
502 enum { Defended, Weak };
503 enum { Minor, Major };
505 Bitboard b, weak, defended;
506 Score score = SCORE_ZERO;
508 // Non-pawn enemies defended by a pawn
509 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
510 & ei.attackedBy[Them][PAWN];
512 // Add a bonus according to the kind of attacking pieces
515 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
517 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
519 b = defended & (ei.attackedBy[Us][ROOK]);
521 score += Threat[Defended][Major][type_of(pos.piece_on(pop_lsb(&b)))];
524 // Enemies not defended by a pawn and under our attack
525 weak = pos.pieces(Them)
526 & ~ei.attackedBy[Them][PAWN]
527 & ei.attackedBy[Us][ALL_PIECES];
529 // Add a bonus according to the kind of attacking pieces
532 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
534 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
536 b = weak & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
538 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
540 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
542 score += Hanging * popcount<Max15>(b);
544 b = weak & ei.attackedBy[Us][KING];
546 score += more_than_one(b) ? KingOnMany : KingOnOne;
549 // Add a small bonus for safe pawn pushes
550 b = pos.pieces(Us, PAWN) & ~TRank7BB;
551 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
554 & ~ei.attackedBy[Them][PAWN]
555 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
558 score += popcount<Full>(b) * PawnSafePush;
560 // Add another bonus if the pawn push attacks an enemy piece
561 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
563 & ~ei.attackedBy[Us][PAWN];
566 score += popcount<Max15>(b) * PawnAttackThreat;
569 Tracing::write(Tracing::THREAT, Us, score);
575 // evaluate_passed_pawns() evaluates the passed pawns of the given color
577 template<Color Us, bool Trace>
578 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
580 const Color Them = (Us == WHITE ? BLACK : WHITE);
582 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
583 Score score = SCORE_ZERO;
585 b = ei.pi->passed_pawns(Us);
589 Square s = pop_lsb(&b);
591 assert(pos.pawn_passed(Us, s));
593 int r = relative_rank(Us, s) - RANK_2;
594 int rr = r * (r - 1);
596 // Base bonus based on rank
597 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
601 Square blockSq = s + pawn_push(Us);
603 // Adjust bonus based on the king's proximity
604 ebonus += distance(pos.king_square(Them), blockSq) * 5 * rr
605 - distance(pos.king_square(Us ), blockSq) * 2 * rr;
607 // If blockSq is not the queening square then consider also a second push
608 if (relative_rank(Us, blockSq) != RANK_8)
609 ebonus -= distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
611 // If the pawn is free to advance, then increase the bonus
612 if (pos.empty(blockSq))
614 // If there is a rook or queen attacking/defending the pawn from behind,
615 // consider all the squaresToQueen. Otherwise consider only the squares
616 // in the pawn's path attacked or occupied by the enemy.
617 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
619 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
621 if (!(pos.pieces(Us) & bb))
622 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
624 if (!(pos.pieces(Them) & bb))
625 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
627 // If there aren't any enemy attacks, assign a big bonus. Otherwise
628 // assign a smaller bonus if the block square isn't attacked.
629 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
631 // If the path to queen is fully defended, assign a big bonus.
632 // Otherwise assign a smaller bonus if the block square is defended.
633 if (defendedSquares == squaresToQueen)
636 else if (defendedSquares & blockSq)
639 mbonus += k * rr, ebonus += k * rr;
641 else if (pos.pieces(Us) & blockSq)
642 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
645 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
646 ebonus += ebonus / 4;
648 score += make_score(mbonus, ebonus);
652 Tracing::write(Tracing::PASSED, Us, apply_weight(score, Weights[PassedPawns]));
654 // Add the scores to the middlegame and endgame eval
655 return apply_weight(score, Weights[PassedPawns]);
659 // evaluate_space() computes the space evaluation for a given side. The
660 // space evaluation is a simple bonus based on the number of safe squares
661 // available for minor pieces on the central four files on ranks 2--4. Safe
662 // squares one, two or three squares behind a friendly pawn are counted
663 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
664 // improve play on game opening.
666 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
668 const Color Them = (Us == WHITE ? BLACK : WHITE);
670 // Find the safe squares for our pieces inside the area defined by
671 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
672 // pawn, or if it is undefended and attacked by an enemy piece.
673 Bitboard safe = SpaceMask[Us]
674 & ~pos.pieces(Us, PAWN)
675 & ~ei.attackedBy[Them][PAWN]
676 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
678 // Find all squares which are at most three squares behind some friendly pawn
679 Bitboard behind = pos.pieces(Us, PAWN);
680 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
681 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
683 // Since SpaceMask[Us] is fully on our half of the board
684 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
686 // Count safe + (behind & safe) with a single popcount
687 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
688 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
689 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
691 return make_score(bonus * weight * weight, 0);
695 // do_evaluate() is the evaluation entry point, called directly from evaluate()
698 Value do_evaluate(const Position& pos) {
700 assert(!pos.checkers());
703 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
705 // Initialize score by reading the incrementally updated scores included
706 // in the position object (material + piece square tables).
707 // Score is computed from the point of view of white.
708 score = pos.psq_score();
710 // Probe the material hash table
711 ei.mi = Material::probe(pos);
712 score += ei.mi->imbalance();
714 // If we have a specialized evaluation function for the current material
715 // configuration, call it and return.
716 if (ei.mi->specialized_eval_exists())
717 return ei.mi->evaluate(pos);
719 // Probe the pawn hash table
720 ei.pi = Pawns::probe(pos);
721 score += apply_weight(ei.pi->pawns_score(), Weights[PawnStructure]);
723 // Initialize attack and king safety bitboards
724 init_eval_info<WHITE>(pos, ei);
725 init_eval_info<BLACK>(pos, ei);
727 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
728 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
730 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
731 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
732 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
734 // Evaluate pieces and mobility
735 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
736 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
738 // Evaluate kings after all other pieces because we need complete attack
739 // information when computing the king safety evaluation.
740 score += evaluate_king<WHITE, Trace>(pos, ei)
741 - evaluate_king<BLACK, Trace>(pos, ei);
743 // Evaluate tactical threats, we need full attack information including king
744 score += evaluate_threats<WHITE, Trace>(pos, ei)
745 - evaluate_threats<BLACK, Trace>(pos, ei);
747 // Evaluate passed pawns, we need full attack information including king
748 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
749 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
751 // If both sides have only pawns, score for potential unstoppable pawns
752 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
755 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
756 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
758 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
759 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
762 // Evaluate space for both sides, only during opening
763 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
765 Score s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
766 score += apply_weight(s, Weights[Space]);
769 // Scale winning side if position is more drawish than it appears
770 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
771 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
773 // If we don't already have an unusual scale factor, check for certain
774 // types of endgames, and use a lower scale for those.
775 if ( ei.mi->game_phase() < PHASE_MIDGAME
776 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
778 if (pos.opposite_bishops())
780 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
781 // is almost a draw, in case of KBP vs KB is even more a draw.
782 if ( pos.non_pawn_material(WHITE) == BishopValueMg
783 && pos.non_pawn_material(BLACK) == BishopValueMg)
784 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
786 // Endgame with opposite-colored bishops, but also other pieces. Still
787 // a bit drawish, but not as drawish as with only the two bishops.
789 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
791 // Endings where weaker side can place his king in front of the opponent's
792 // pawns are drawish.
793 else if ( abs(eg_value(score)) <= BishopValueEg
794 && ei.pi->pawn_span(strongSide) <= 1
795 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide)))
796 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
799 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
800 Value v = mg_value(score) * int(ei.mi->game_phase())
801 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
803 v /= int(PHASE_MIDGAME);
805 // In case of tracing add all single evaluation terms for both white and black
808 Tracing::write(Tracing::MATERIAL, pos.psq_score());
809 Tracing::write(Tracing::IMBALANCE, ei.mi->imbalance());
810 Tracing::write(PAWN, ei.pi->pawns_score());
811 Tracing::write(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
812 , apply_weight(mobility[BLACK], Weights[Mobility]));
813 Tracing::write(Tracing::SPACE, apply_weight(evaluate_space<WHITE>(pos, ei), Weights[Space])
814 , apply_weight(evaluate_space<BLACK>(pos, ei), Weights[Space]));
815 Tracing::write(Tracing::TOTAL, score);
818 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
824 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
826 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
828 void Tracing::write(int idx, Score w, Score b) {
829 scores[WHITE][idx] = w, scores[BLACK][idx] = b;
832 std::ostream& Tracing::operator<<(std::ostream& os, Term t) {
834 double wScore[] = { to_cp(mg_value(scores[WHITE][t])), to_cp(eg_value(scores[WHITE][t])) };
835 double bScore[] = { to_cp(mg_value(scores[BLACK][t])), to_cp(eg_value(scores[BLACK][t])) };
837 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
838 os << " --- --- | --- --- | ";
840 os << std::setw(5) << wScore[MG] << " " << std::setw(5) << wScore[EG] << " | "
841 << std::setw(5) << bScore[MG] << " " << std::setw(5) << bScore[EG] << " | ";
843 os << std::setw(5) << wScore[MG] - bScore[MG] << " "
844 << std::setw(5) << wScore[EG] - bScore[EG] << " \n";
849 std::string Tracing::do_trace(const Position& pos) {
851 std::memset(scores, 0, sizeof(scores));
853 Value v = do_evaluate<true>(pos);
854 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
856 std::stringstream ss;
857 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
858 << " Eval term | White | Black | Total \n"
859 << " | MG EG | MG EG | MG EG \n"
860 << "----------------+-------------+-------------+-------------\n"
861 << " Material | " << Term(MATERIAL)
862 << " Imbalance | " << Term(IMBALANCE)
863 << " Pawns | " << Term(PAWN)
864 << " Knights | " << Term(KNIGHT)
865 << " Bishop | " << Term(BISHOP)
866 << " Rooks | " << Term(ROOK)
867 << " Queens | " << Term(QUEEN)
868 << " Mobility | " << Term(MOBILITY)
869 << " King safety | " << Term(KING)
870 << " Threats | " << Term(THREAT)
871 << " Passed pawns | " << Term(PASSED)
872 << " Space | " << Term(SPACE)
873 << "----------------+-------------+-------------+-------------\n"
874 << " Total | " << Term(TOTAL);
876 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
886 /// evaluate() is the main evaluation function. It returns a static evaluation
887 /// of the position always from the point of view of the side to move.
889 Value evaluate(const Position& pos) {
890 return do_evaluate<false>(pos);
894 /// trace() is like evaluate(), but instead of returning a value, it returns
895 /// a string (suitable for outputting to stdout) that contains the detailed
896 /// descriptions and values of each evaluation term. It's mainly used for
898 std::string trace(const Position& pos) {
899 return Tracing::do_trace(pos);
903 /// init() computes evaluation weights, usually at startup
907 const int MaxSlope = 8700;
908 const int Peak = 1280000;
911 for (int i = 0; i < 400; ++i)
913 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
914 KingDanger[i] = apply_weight(make_score(t / 1000, 0), Weights[KingSafety]);