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 Terms { // First 8 entries are for PieceType
77 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERMS_NB
80 Score scores[COLOR_NB][TERMS_NB];
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 void print(std::stringstream& ss, const char* name, int idx);
88 std::string do_trace(const Position& pos);
91 // Evaluation weights, indexed by evaluation term
92 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
93 const struct Weight { int mg, eg; } Weights[] = {
94 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {322, 0}
98 #define S(mg, eg) make_score(mg, eg)
100 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
101 // game, indexed by piece type and number of attacked squares not occupied by
103 const Score MobilityBonus[][32] = {
105 { S(-65,-50), S(-42,-30), S(-9,-10), S( 3, 0), S(15, 10), S(27, 20), // Knights
106 S( 37, 28), S( 42, 31), S(44, 33) },
107 { S(-52,-47), S(-28,-23), S( 6, 1), S(20, 15), S(34, 29), S(48, 43), // Bishops
108 S( 60, 55), S( 68, 63), S(74, 68), S(77, 72), S(80, 75), S(82, 77),
109 S( 84, 79), S( 86, 81) },
110 { S(-47,-53), S(-31,-26), S(-5, 0), S( 1, 16), S( 7, 32), S(13, 48), // Rooks
111 S( 18, 64), S( 22, 80), S(26, 96), S(29,109), S(31,115), S(33,119),
112 S( 35,122), S( 36,123), S(37,124) },
113 { S(-42,-40), S(-28,-23), S(-5, -7), S( 0, 0), S( 6, 10), S(11, 19), // Queens
114 S( 13, 29), S( 18, 38), S(20, 40), S(21, 41), S(22, 41), S(22, 41),
115 S( 22, 41), S( 23, 41), S(24, 41), S(25, 41), S(25, 41), S(25, 41),
116 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41), S(25, 41), S(25, 41),
117 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41) }
120 // Outpost[PieceType][Square] contains bonuses for knights and bishops outposts,
121 // indexed by piece type and square (from white's point of view).
122 const Value Outpost[][SQUARE_NB] = {
124 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
125 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
126 V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0),
127 V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0),
128 V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0),
129 V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0) },
131 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
132 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
133 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
134 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
135 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
136 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0) }
139 // Threat[defended/weak][minor/major attacking][attacked PieceType] contains
140 // bonuses according to which piece type attacks which one.
141 const Score Threat[][2][PIECE_TYPE_NB] = {
142 { { S(0, 0), S( 0, 0), S(19, 37), S(24, 37), S(44, 97), S(35,106) }, // Defended Minor
143 { S(0, 0), S( 0, 0), S( 9, 14), S( 9, 14), S( 7, 14), S(24, 48) } }, // Defended Major
144 { { S(0, 0), S( 0,32), S(33, 41), S(31, 50), S(41,100), S(35,104) }, // Weak Minor
145 { S(0, 0), S( 0,27), S(26, 57), S(26, 57), S(0 , 43), S(23, 51) } } // Weak Major
148 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
149 // type is attacked by an enemy pawn.
150 const Score ThreatenedByPawn[] = {
151 S(0, 0), S(0, 0), S(87, 118), S(84, 122), S(114, 203), S(121, 217)
154 // Assorted bonuses and penalties used by evaluation
155 const Score KingOnOne = S( 2, 58);
156 const Score KingOnMany = S( 6,125);
157 const Score RookOnPawn = S( 7, 27);
158 const Score RookOnOpenFile = S(43, 21);
159 const Score RookOnSemiOpenFile = S(19, 10);
160 const Score BishopPawns = S( 8, 12);
161 const Score MinorBehindPawn = S(16, 0);
162 const Score TrappedRook = S(92, 0);
163 const Score Unstoppable = S( 0, 20);
164 const Score Hanging = S(31, 26);
165 const Score PawnAttackThreat = S(20, 20);
166 const Score PawnSafePush = S( 5, 5);
168 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
169 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
170 // happen in Chess960 games.
171 const Score TrappedBishopA1H1 = S(50, 50);
176 // SpaceMask[Color] contains the area of the board which is considered
177 // by the space evaluation. In the middlegame, each side is given a bonus
178 // based on how many squares inside this area are safe and available for
179 // friendly minor pieces.
180 const Bitboard SpaceMask[] = {
181 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
182 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
185 // King danger constants and variables. The king danger scores are looked-up
186 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
187 // of the enemy attack are added up into an integer, which is used as an
188 // index to KingDanger[].
190 // KingAttackWeights[PieceType] contains king attack weights by piece type
191 const int KingAttackWeights[] = { 0, 0, 7, 5, 4, 1 };
193 // Bonuses for enemy's safe checks
194 const int QueenContactCheck = 89;
195 const int RookContactCheck = 71;
196 const int QueenCheck = 50;
197 const int RookCheck = 37;
198 const int BishopCheck = 6;
199 const int KnightCheck = 14;
201 // KingDanger[attackUnits] contains the actual king danger weighted
202 // scores, indexed by a calculated integer number.
203 Score KingDanger[512];
205 // apply_weight() weighs score 's' by weight 'w' trying to prevent overflow
206 Score apply_weight(Score s, const Weight& w) {
207 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
211 // init_eval_info() initializes king bitboards for given color adding
212 // pawn attacks. To be done at the beginning of the evaluation.
215 void init_eval_info(const Position& pos, EvalInfo& ei) {
217 const Color Them = (Us == WHITE ? BLACK : WHITE);
218 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
220 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
222 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
223 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
225 // Init king safety tables only if we are going to use them
226 if (pos.non_pawn_material(Us) >= QueenValueMg)
228 ei.kingRing[Them] = b | shift_bb<Down>(b);
229 b &= ei.attackedBy[Us][PAWN];
230 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
231 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
234 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
238 // evaluate_outpost() evaluates bishop and knight outpost squares
240 template<PieceType Pt, Color Us>
241 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
243 const Color Them = (Us == WHITE ? BLACK : WHITE);
245 assert (Pt == BISHOP || Pt == KNIGHT);
247 // Initial bonus based on square
248 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
250 // Increase bonus if supported by pawn, especially if the opponent has
251 // no minor piece which can trade with the outpost piece.
252 if (bonus && (ei.attackedBy[Us][PAWN] & s))
254 if ( !pos.pieces(Them, KNIGHT)
255 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
256 bonus += bonus + bonus / 2;
261 return make_score(bonus * 2, bonus / 2);
265 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
267 template<PieceType Pt, Color Us, bool Trace>
268 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
272 Score score = SCORE_ZERO;
274 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
275 const Color Them = (Us == WHITE ? BLACK : WHITE);
276 const Square* pl = pos.list<Pt>(Us);
278 ei.attackedBy[Us][Pt] = 0;
280 while ((s = *pl++) != SQ_NONE)
282 // Find attacked squares, including x-ray attacks for bishops and rooks
283 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
284 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
285 : pos.attacks_from<Pt>(s);
287 if (ei.pinnedPieces[Us] & s)
288 b &= LineBB[pos.king_square(Us)][s];
290 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
292 if (b & ei.kingRing[Them])
294 ei.kingAttackersCount[Us]++;
295 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
296 Bitboard bb = b & ei.attackedBy[Them][KING];
298 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
302 b &= ~( ei.attackedBy[Them][KNIGHT]
303 | ei.attackedBy[Them][BISHOP]
304 | ei.attackedBy[Them][ROOK]);
306 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
307 : popcount<Full >(b & mobilityArea[Us]);
309 mobility[Us] += MobilityBonus[Pt][mob];
311 // Decrease score if we are attacked by an enemy pawn. The remaining part
312 // of threat evaluation must be done later when we have full attack info.
313 if (ei.attackedBy[Them][PAWN] & s)
314 score -= ThreatenedByPawn[Pt];
316 if (Pt == BISHOP || Pt == KNIGHT)
318 // Bonus for outpost square
319 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
320 score += evaluate_outpost<Pt, Us>(pos, ei, s);
322 // Bonus when behind a pawn
323 if ( relative_rank(Us, s) < RANK_5
324 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
325 score += MinorBehindPawn;
327 // Penalty for pawns on same color square of bishop
329 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
331 // An important Chess960 pattern: A cornered bishop blocked by a friendly
332 // pawn diagonally in front of it is a very serious problem, especially
333 // when that pawn is also blocked.
336 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
338 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
339 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
340 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
341 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
348 // Bonus for aligning with enemy pawns on the same rank/file
349 if (relative_rank(Us, s) >= RANK_5)
351 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
353 score += popcount<Max15>(alignedPawns) * RookOnPawn;
356 // Bonus when on an open or semi-open file
357 if (ei.pi->semiopen_file(Us, file_of(s)))
358 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
360 // Penalize when trapped by the king, even more if king cannot castle
361 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
363 Square ksq = pos.king_square(Us);
365 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
366 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
367 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
368 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
374 Tracing::write(Pt, Us, score);
376 // Recursively call evaluate_pieces() of next piece type until KING excluded
377 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
381 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
383 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
386 // evaluate_king() assigns bonuses and penalties to a king of a given color
388 template<Color Us, bool Trace>
389 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
391 const Color Them = (Us == WHITE ? BLACK : WHITE);
393 Bitboard undefended, b, b1, b2, safe;
395 const Square ksq = pos.king_square(Us);
397 // King shelter and enemy pawns storm
398 Score score = ei.pi->king_safety<Us>(pos, ksq);
400 // Main king safety evaluation
401 if (ei.kingAttackersCount[Them])
403 // Find the attacked squares around the king which have no defenders
404 // apart from the king itself
405 undefended = ei.attackedBy[Them][ALL_PIECES]
406 & ei.attackedBy[Us][KING]
407 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
408 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
409 | ei.attackedBy[Us][QUEEN]);
411 // Initialize the 'attackUnits' variable, which is used later on as an
412 // index into the KingDanger[] array. The initial value is based on the
413 // number and types of the enemy's attacking pieces, the number of
414 // attacked and undefended squares around our king and the quality of
415 // the pawn shelter (current 'score' value).
416 attackUnits = std::min(74, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
417 + 8 * ei.kingAdjacentZoneAttacksCount[Them]
418 + 25 * popcount<Max15>(undefended)
419 + 11 * (ei.pinnedPieces[Us] != 0)
420 - mg_value(score) / 8
421 - !pos.count<QUEEN>(Them) * 60;
423 // Analyse the enemy's safe queen contact checks. Firstly, find the
424 // undefended squares around the king reachable by the enemy queen...
425 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
428 // ...and then remove squares not supported by another enemy piece
429 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
430 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
433 attackUnits += QueenContactCheck * popcount<Max15>(b);
436 // Analyse the enemy's safe rook contact checks. Firstly, find the
437 // undefended squares around the king reachable by the enemy rooks...
438 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
440 // Consider only squares where the enemy's rook gives check
441 b &= PseudoAttacks[ROOK][ksq];
445 // ...and then remove squares not supported by another enemy piece
446 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
447 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
450 attackUnits += RookContactCheck * popcount<Max15>(b);
453 // Analyse the enemy's safe distance checks for sliders and knights
454 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
456 b1 = pos.attacks_from<ROOK >(ksq) & safe;
457 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
459 // Enemy queen safe checks
460 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
462 attackUnits += QueenCheck * popcount<Max15>(b);
464 // Enemy rooks safe checks
465 b = b1 & ei.attackedBy[Them][ROOK];
467 attackUnits += RookCheck * popcount<Max15>(b);
469 // Enemy bishops safe checks
470 b = b2 & ei.attackedBy[Them][BISHOP];
472 attackUnits += BishopCheck * popcount<Max15>(b);
474 // Enemy knights safe checks
475 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
477 attackUnits += KnightCheck * popcount<Max15>(b);
479 // Finally, extract the king danger score from the KingDanger[]
480 // array and subtract the score from evaluation.
481 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
485 Tracing::write(KING, Us, score);
491 // evaluate_threats() assigns bonuses according to the type of attacking piece
492 // and the type of attacked one.
494 template<Color Us, bool Trace>
495 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
497 const Color Them = (Us == WHITE ? BLACK : WHITE);
498 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
499 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
500 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
501 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
502 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
504 enum { Defended, Weak };
505 enum { Minor, Major };
507 Bitboard b, weak, defended;
508 Score score = SCORE_ZERO;
510 // Non-pawn enemies defended by a pawn
511 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
512 & ei.attackedBy[Them][PAWN];
514 // Add a bonus according to the kind of attacking pieces
517 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
519 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
521 b = defended & (ei.attackedBy[Us][ROOK]);
523 score += Threat[Defended][Major][type_of(pos.piece_on(pop_lsb(&b)))];
526 // Enemies not defended by a pawn and under our attack
527 weak = pos.pieces(Them)
528 & ~ei.attackedBy[Them][PAWN]
529 & ei.attackedBy[Us][ALL_PIECES];
531 // Add a bonus according to the kind of attacking pieces
534 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
536 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
538 b = weak & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
540 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
542 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
544 score += Hanging * popcount<Max15>(b);
546 b = weak & ei.attackedBy[Us][KING];
548 score += more_than_one(b) ? KingOnMany : KingOnOne;
551 // Add a small bonus for safe pawn pushes
552 b = pos.pieces(Us, PAWN) & ~TRank7BB;
553 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
556 & ~ei.attackedBy[Them][PAWN]
557 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
560 score += popcount<Full>(b) * PawnSafePush;
562 // Add another bonus if the pawn push attacks an enemy piece
563 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
565 & ~ei.attackedBy[Us][PAWN];
568 score += popcount<Max15>(b) * PawnAttackThreat;
571 Tracing::write(Tracing::THREAT, Us, score);
577 // evaluate_passed_pawns() evaluates the passed pawns of the given color
579 template<Color Us, bool Trace>
580 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
582 const Color Them = (Us == WHITE ? BLACK : WHITE);
584 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
585 Score score = SCORE_ZERO;
587 b = ei.pi->passed_pawns(Us);
591 Square s = pop_lsb(&b);
593 assert(pos.pawn_passed(Us, s));
595 int r = relative_rank(Us, s) - RANK_2;
596 int rr = r * (r - 1);
598 // Base bonus based on rank
599 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
603 Square blockSq = s + pawn_push(Us);
605 // Adjust bonus based on the king's proximity
606 ebonus += distance(pos.king_square(Them), blockSq) * 5 * rr
607 - distance(pos.king_square(Us ), blockSq) * 2 * rr;
609 // If blockSq is not the queening square then consider also a second push
610 if (relative_rank(Us, blockSq) != RANK_8)
611 ebonus -= distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
613 // If the pawn is free to advance, then increase the bonus
614 if (pos.empty(blockSq))
616 // If there is a rook or queen attacking/defending the pawn from behind,
617 // consider all the squaresToQueen. Otherwise consider only the squares
618 // in the pawn's path attacked or occupied by the enemy.
619 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
621 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
623 if (!(pos.pieces(Us) & bb))
624 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
626 if (!(pos.pieces(Them) & bb))
627 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
629 // If there aren't any enemy attacks, assign a big bonus. Otherwise
630 // assign a smaller bonus if the block square isn't attacked.
631 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
633 // If the path to queen is fully defended, assign a big bonus.
634 // Otherwise assign a smaller bonus if the block square is defended.
635 if (defendedSquares == squaresToQueen)
638 else if (defendedSquares & blockSq)
641 mbonus += k * rr, ebonus += k * rr;
643 else if (pos.pieces(Us) & blockSq)
644 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
647 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
648 ebonus += ebonus / 4;
650 score += make_score(mbonus, ebonus);
654 Tracing::write(Tracing::PASSED, Us, apply_weight(score, Weights[PassedPawns]));
656 // Add the scores to the middlegame and endgame eval
657 return apply_weight(score, Weights[PassedPawns]);
661 // evaluate_space() computes the space evaluation for a given side. The
662 // space evaluation is a simple bonus based on the number of safe squares
663 // available for minor pieces on the central four files on ranks 2--4. Safe
664 // squares one, two or three squares behind a friendly pawn are counted
665 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
666 // improve play on game opening.
668 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
670 const Color Them = (Us == WHITE ? BLACK : WHITE);
672 // Find the safe squares for our pieces inside the area defined by
673 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
674 // pawn, or if it is undefended and attacked by an enemy piece.
675 Bitboard safe = SpaceMask[Us]
676 & ~pos.pieces(Us, PAWN)
677 & ~ei.attackedBy[Them][PAWN]
678 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
680 // Find all squares which are at most three squares behind some friendly pawn
681 Bitboard behind = pos.pieces(Us, PAWN);
682 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
683 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
685 // Since SpaceMask[Us] is fully on our half of the board
686 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
688 // Count safe + (behind & safe) with a single popcount
689 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
690 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
691 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
693 return make_score(bonus * weight * weight, 0);
697 // do_evaluate() is the evaluation entry point, called directly from evaluate()
700 Value do_evaluate(const Position& pos) {
702 assert(!pos.checkers());
705 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
707 // Initialize score by reading the incrementally updated scores included
708 // in the position object (material + piece square tables).
709 // Score is computed from the point of view of white.
710 score = pos.psq_score();
712 // Probe the material hash table
713 ei.mi = Material::probe(pos);
714 score += ei.mi->imbalance();
716 // If we have a specialized evaluation function for the current material
717 // configuration, call it and return.
718 if (ei.mi->specialized_eval_exists())
719 return ei.mi->evaluate(pos);
721 // Probe the pawn hash table
722 ei.pi = Pawns::probe(pos);
723 score += apply_weight(ei.pi->pawns_score(), Weights[PawnStructure]);
725 // Initialize attack and king safety bitboards
726 init_eval_info<WHITE>(pos, ei);
727 init_eval_info<BLACK>(pos, ei);
729 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
730 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
732 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
733 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
734 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
736 // Evaluate pieces and mobility
737 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
738 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
740 // Evaluate kings after all other pieces because we need complete attack
741 // information when computing the king safety evaluation.
742 score += evaluate_king<WHITE, Trace>(pos, ei)
743 - evaluate_king<BLACK, Trace>(pos, ei);
745 // Evaluate tactical threats, we need full attack information including king
746 score += evaluate_threats<WHITE, Trace>(pos, ei)
747 - evaluate_threats<BLACK, Trace>(pos, ei);
749 // Evaluate passed pawns, we need full attack information including king
750 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
751 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
753 // If both sides have only pawns, score for potential unstoppable pawns
754 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
757 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
758 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
760 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
761 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
764 // Evaluate space for both sides, only during opening
765 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
767 Score s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
768 score += apply_weight(s, Weights[Space]);
771 // Scale winning side if position is more drawish than it appears
772 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
773 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
775 // If we don't already have an unusual scale factor, check for certain
776 // types of endgames, and use a lower scale for those.
777 if ( ei.mi->game_phase() < PHASE_MIDGAME
778 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
780 if (pos.opposite_bishops())
782 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
783 // is almost a draw, in case of KBP vs KB is even more a draw.
784 if ( pos.non_pawn_material(WHITE) == BishopValueMg
785 && pos.non_pawn_material(BLACK) == BishopValueMg)
786 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
788 // Endgame with opposite-colored bishops, but also other pieces. Still
789 // a bit drawish, but not as drawish as with only the two bishops.
791 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
793 // Endings where weaker side can place his king in front of the opponent's
794 // pawns are drawish.
795 else if ( abs(eg_value(score)) <= BishopValueEg
796 && ei.pi->pawn_span(strongSide) <= 1
797 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide)))
798 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
801 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
802 Value v = mg_value(score) * int(ei.mi->game_phase())
803 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
805 v /= int(PHASE_MIDGAME);
807 // In case of tracing add all single evaluation contributions for both white and black
810 Tracing::write(Tracing::MATERIAL, pos.psq_score());
811 Tracing::write(Tracing::IMBALANCE, ei.mi->imbalance());
812 Tracing::write(PAWN, ei.pi->pawns_score());
813 Tracing::write(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
814 , apply_weight(mobility[BLACK], Weights[Mobility]));
815 Tracing::write(Tracing::SPACE, apply_weight(evaluate_space<WHITE>(pos, ei), Weights[Space])
816 , apply_weight(evaluate_space<BLACK>(pos, ei), Weights[Space]));
817 Tracing::write(Tracing::TOTAL, score);
822 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
826 // Tracing function definitions
828 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
830 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
832 void Tracing::write(int idx, Score w, Score b) {
834 write(idx, WHITE, w);
835 write(idx, BLACK, b);
838 void Tracing::print(std::stringstream& ss, const char* name, int idx) {
840 Score wScore = scores[WHITE][idx];
841 Score bScore = scores[BLACK][idx];
844 case MATERIAL: case IMBALANCE: case PAWN: case TOTAL:
845 ss << std::setw(15) << name << " | --- --- | --- --- | "
846 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
847 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
850 ss << std::setw(15) << name << " | " << std::noshowpos
851 << std::setw(5) << to_cp(mg_value(wScore)) << " "
852 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
853 << std::setw(5) << to_cp(mg_value(bScore)) << " "
854 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
855 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
856 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
860 std::string Tracing::do_trace(const Position& pos) {
862 std::memset(scores, 0, sizeof(scores));
864 Value v = do_evaluate<true>(pos);
865 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
867 std::stringstream ss;
868 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
869 << " Eval term | White | Black | Total \n"
870 << " | MG EG | MG EG | MG EG \n"
871 << "----------------+-------------+-------------+-------------\n";
873 print(ss, "Material", MATERIAL);
874 print(ss, "Imbalance", IMBALANCE);
875 print(ss, "Pawns", PAWN);
876 print(ss, "Knights", KNIGHT);
877 print(ss, "Bishops", BISHOP);
878 print(ss, "Rooks", ROOK);
879 print(ss, "Queens", QUEEN);
880 print(ss, "Mobility", MOBILITY);
881 print(ss, "King safety", KING);
882 print(ss, "Threats", THREAT);
883 print(ss, "Passed pawns", PASSED);
884 print(ss, "Space", SPACE);
886 ss << "----------------+-------------+-------------+-------------\n";
887 print(ss, "Total", TOTAL);
889 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
899 /// evaluate() is the main evaluation function. It returns a static evaluation
900 /// of the position always from the point of view of the side to move.
902 Value evaluate(const Position& pos) {
903 return do_evaluate<false>(pos);
907 /// trace() is like evaluate(), but instead of returning a value, it returns
908 /// a string (suitable for outputting to stdout) that contains the detailed
909 /// descriptions and values of each evaluation term. It's mainly used for
911 std::string trace(const Position& pos) {
912 return Tracing::do_trace(pos);
916 /// init() computes evaluation weights, usually at startup
920 const int MaxSlope = 8700;
921 const int Peak = 1280000;
924 for (int i = 0; i < 400; ++i)
926 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
927 KingDanger[i] = apply_weight(make_score(t / 1000, 0), Weights[KingSafety]);