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 to squares
65 // directly adjacent to the king of the given color. Pieces which attack
66 // more than one square are counted multiple times. For instance, if black's
67 // king is on g8 and there's a white knight on g5, this knight adds
68 // 2 to kingAdjacentZoneAttacksCount[BLACK].
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);
166 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
167 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
168 // happen in Chess960 games.
169 const Score TrappedBishopA1H1 = S(50, 50);
174 // SpaceMask[Color] contains the area of the board which is considered
175 // by the space evaluation. In the middlegame, each side is given a bonus
176 // based on how many squares inside this area are safe and available for
177 // friendly minor pieces.
178 const Bitboard SpaceMask[COLOR_NB] = {
179 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
180 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
183 // King danger constants and variables. The king danger scores are looked-up
184 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
185 // of the enemy attack are added up into an integer, which is used as an
186 // index to KingDanger[].
188 // KingAttackWeights[PieceType] contains king attack weights by piece type
189 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
191 // Bonuses for enemy's safe checks
192 const int QueenContactCheck = 89;
193 const int RookContactCheck = 71;
194 const int QueenCheck = 50;
195 const int RookCheck = 37;
196 const int BishopCheck = 6;
197 const int KnightCheck = 14;
199 // KingDanger[attackUnits] contains the actual king danger weighted
200 // scores, indexed by a calculated integer number.
201 Score KingDanger[512];
203 // apply_weight() weighs score 's' by weight 'w' trying to prevent overflow
204 Score apply_weight(Score s, const Weight& w) {
205 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
209 // init_eval_info() initializes king bitboards for given color adding
210 // pawn attacks. To be done at the beginning of the evaluation.
213 void init_eval_info(const Position& pos, EvalInfo& ei) {
215 const Color Them = (Us == WHITE ? BLACK : WHITE);
216 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
218 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
219 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
220 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
222 // Init king safety tables only if we are going to use them
223 if (pos.non_pawn_material(Us) >= QueenValueMg)
225 ei.kingRing[Them] = b | shift_bb<Down>(b);
226 b &= ei.attackedBy[Us][PAWN];
227 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
228 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
231 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
235 // evaluate_outpost() evaluates bishop and knight outpost squares
237 template<PieceType Pt, Color Us>
238 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
240 const Color Them = (Us == WHITE ? BLACK : WHITE);
242 assert (Pt == BISHOP || Pt == KNIGHT);
244 // Initial bonus based on square
245 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
247 // Increase bonus if supported by pawn, especially if the opponent has
248 // no minor piece which can trade with the outpost piece.
249 if (bonus && (ei.attackedBy[Us][PAWN] & s))
251 if ( !pos.pieces(Them, KNIGHT)
252 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
253 bonus += bonus + bonus / 2;
258 return make_score(bonus * 2, bonus / 2);
262 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
264 template<PieceType Pt, Color Us, bool Trace>
265 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
269 Score score = SCORE_ZERO;
271 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
272 const Color Them = (Us == WHITE ? BLACK : WHITE);
273 const Square* pl = pos.list<Pt>(Us);
275 ei.attackedBy[Us][Pt] = 0;
277 while ((s = *pl++) != SQ_NONE)
279 // Find attacked squares, including x-ray attacks for bishops and rooks
280 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
281 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
282 : pos.attacks_from<Pt>(s);
284 if (ei.pinnedPieces[Us] & s)
285 b &= LineBB[pos.king_square(Us)][s];
287 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
289 if (b & ei.kingRing[Them])
291 ei.kingAttackersCount[Us]++;
292 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
293 Bitboard bb = b & ei.attackedBy[Them][KING];
295 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
299 b &= ~( ei.attackedBy[Them][KNIGHT]
300 | ei.attackedBy[Them][BISHOP]
301 | ei.attackedBy[Them][ROOK]);
303 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
304 : popcount<Full >(b & mobilityArea[Us]);
306 mobility[Us] += MobilityBonus[Pt][mob];
308 // Decrease score if we are attacked by an enemy pawn. The remaining part
309 // of threat evaluation must be done later when we have full attack info.
310 if (ei.attackedBy[Them][PAWN] & s)
311 score -= ThreatenedByPawn[Pt];
313 if (Pt == BISHOP || Pt == KNIGHT)
315 // Bonus for outpost square
316 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
317 score += evaluate_outpost<Pt, Us>(pos, ei, s);
319 // Bonus when behind a pawn
320 if ( relative_rank(Us, s) < RANK_5
321 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
322 score += MinorBehindPawn;
324 // Penalty for pawns on same color square of bishop
326 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
328 // An important Chess960 pattern: A cornered bishop blocked by a friendly
329 // pawn diagonally in front of it is a very serious problem, especially
330 // when that pawn is also blocked.
333 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
335 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
336 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
337 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
338 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
345 // Bonus for aligning with enemy pawns on the same rank/file
346 if (relative_rank(Us, s) >= RANK_5)
348 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
350 score += popcount<Max15>(alignedPawns) * RookOnPawn;
353 // Bonus when on an open or semi-open file
354 if (ei.pi->semiopen_file(Us, file_of(s)))
355 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
357 // Penalize when trapped by the king, even more if king cannot castle
358 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
360 Square ksq = pos.king_square(Us);
362 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
363 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
364 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
365 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
371 Tracing::write(Pt, Us, score);
373 // Recursively call evaluate_pieces() of next piece type until KING excluded
374 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
378 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
380 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
383 // evaluate_king() assigns bonuses and penalties to a king of a given color
385 template<Color Us, bool Trace>
386 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
388 const Color Them = (Us == WHITE ? BLACK : WHITE);
390 Bitboard undefended, b, b1, b2, safe;
392 const Square ksq = pos.king_square(Us);
394 // King shelter and enemy pawns storm
395 Score score = ei.pi->king_safety<Us>(pos, ksq);
397 // Main king safety evaluation
398 if (ei.kingAttackersCount[Them])
400 // Find the attacked squares around the king which have no defenders
401 // apart from the king itself
402 undefended = ei.attackedBy[Them][ALL_PIECES]
403 & ei.attackedBy[Us][KING]
404 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
405 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
406 | ei.attackedBy[Us][QUEEN]);
408 // Initialize the 'attackUnits' variable, which is used later on as an
409 // index into the KingDanger[] array. The initial value is based on the
410 // number and types of the enemy's attacking pieces, the number of
411 // attacked and undefended squares around our king and the quality of
412 // the pawn shelter (current 'score' value).
413 attackUnits = std::min(74, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
414 + 8 * ei.kingAdjacentZoneAttacksCount[Them]
415 + 25 * popcount<Max15>(undefended)
416 + 11 * (ei.pinnedPieces[Us] != 0)
417 - mg_value(score) * 31 / 256
418 - !pos.count<QUEEN>(Them) * 60;
420 // Analyse the enemy's safe queen contact checks. Firstly, find the
421 // undefended squares around the king reachable by the enemy queen...
422 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
425 // ...and then remove squares not supported by another enemy piece
426 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
427 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
430 attackUnits += QueenContactCheck * popcount<Max15>(b);
433 // Analyse the enemy's safe rook contact checks. Firstly, find the
434 // undefended squares around the king reachable by the enemy rooks...
435 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
437 // Consider only squares where the enemy's rook gives check
438 b &= PseudoAttacks[ROOK][ksq];
442 // ...and then remove squares not supported by another enemy piece
443 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
444 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
447 attackUnits += RookContactCheck * popcount<Max15>(b);
450 // Analyse the enemy's safe distance checks for sliders and knights
451 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
453 b1 = pos.attacks_from<ROOK >(ksq) & safe;
454 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
456 // Enemy queen safe checks
457 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
459 attackUnits += QueenCheck * popcount<Max15>(b);
461 // Enemy rooks safe checks
462 b = b1 & ei.attackedBy[Them][ROOK];
464 attackUnits += RookCheck * popcount<Max15>(b);
466 // Enemy bishops safe checks
467 b = b2 & ei.attackedBy[Them][BISHOP];
469 attackUnits += BishopCheck * popcount<Max15>(b);
471 // Enemy knights safe checks
472 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
474 attackUnits += KnightCheck * popcount<Max15>(b);
476 // Finally, extract the king danger score from the KingDanger[]
477 // array and subtract the score from evaluation.
478 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
482 Tracing::write(KING, Us, score);
488 // evaluate_threats() assigns bonuses according to the type of attacking piece
489 // and the type of attacked one.
491 template<Color Us, bool Trace>
492 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
494 const Color Them = (Us == WHITE ? BLACK : WHITE);
495 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
496 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
497 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
498 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
499 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
501 enum { Defended, Weak };
502 enum { Minor, Major };
504 Bitboard b, weak, defended;
505 Score score = SCORE_ZERO;
507 // Non-pawn enemies defended by a pawn
508 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
509 & ei.attackedBy[Them][PAWN];
511 // Add a bonus according to the kind of attacking pieces
514 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
516 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
518 b = defended & (ei.attackedBy[Us][ROOK]);
520 score += Threat[Defended][Major][type_of(pos.piece_on(pop_lsb(&b)))];
523 // Enemies not defended by a pawn and under our attack
524 weak = pos.pieces(Them)
525 & ~ei.attackedBy[Them][PAWN]
526 & ei.attackedBy[Us][ALL_PIECES];
528 // Add a bonus according to the kind of attacking pieces
531 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
533 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
535 b = weak & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
537 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
539 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
541 score += Hanging * popcount<Max15>(b);
543 b = weak & ei.attackedBy[Us][KING];
545 score += more_than_one(b) ? KingOnMany : KingOnOne;
548 // Add bonus for safe pawn pushes which attacks an enemy piece
549 b = pos.pieces(Us, PAWN) & ~TRank7BB;
550 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
553 & ~ei.attackedBy[Them][PAWN]
554 & (ei.attackedBy[Us][PAWN] | ~ei.attackedBy[Them][ALL_PIECES]);
556 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
558 & ~ei.attackedBy[Us][PAWN];
561 score += popcount<Max15>(b) * PawnAttackThreat;
564 Tracing::write(Tracing::THREAT, Us, score);
570 // evaluate_passed_pawns() evaluates the passed pawns of the given color
572 template<Color Us, bool Trace>
573 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
575 const Color Them = (Us == WHITE ? BLACK : WHITE);
577 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
578 Score score = SCORE_ZERO;
580 b = ei.pi->passed_pawns(Us);
584 Square s = pop_lsb(&b);
586 assert(pos.pawn_passed(Us, s));
588 int r = relative_rank(Us, s) - RANK_2;
589 int rr = r * (r - 1);
591 // Base bonus based on rank
592 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
596 Square blockSq = s + pawn_push(Us);
598 // Adjust bonus based on the king's proximity
599 ebonus += distance(pos.king_square(Them), blockSq) * 5 * rr
600 - distance(pos.king_square(Us ), blockSq) * 2 * rr;
602 // If blockSq is not the queening square then consider also a second push
603 if (relative_rank(Us, blockSq) != RANK_8)
604 ebonus -= distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
606 // If the pawn is free to advance, then increase the bonus
607 if (pos.empty(blockSq))
609 // If there is a rook or queen attacking/defending the pawn from behind,
610 // consider all the squaresToQueen. Otherwise consider only the squares
611 // in the pawn's path attacked or occupied by the enemy.
612 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
614 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
616 if (!(pos.pieces(Us) & bb))
617 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
619 if (!(pos.pieces(Them) & bb))
620 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
622 // If there aren't any enemy attacks, assign a big bonus. Otherwise
623 // assign a smaller bonus if the block square isn't attacked.
624 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
626 // If the path to queen is fully defended, assign a big bonus.
627 // Otherwise assign a smaller bonus if the block square is defended.
628 if (defendedSquares == squaresToQueen)
631 else if (defendedSquares & blockSq)
634 mbonus += k * rr, ebonus += k * rr;
636 else if (pos.pieces(Us) & blockSq)
637 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
640 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
641 ebonus += ebonus / 4;
643 score += make_score(mbonus, ebonus);
647 Tracing::write(Tracing::PASSED, Us, apply_weight(score, Weights[PassedPawns]));
649 // Add the scores to the middlegame and endgame eval
650 return apply_weight(score, Weights[PassedPawns]);
654 // evaluate_space() computes the space evaluation for a given side. The
655 // space evaluation is a simple bonus based on the number of safe squares
656 // available for minor pieces on the central four files on ranks 2--4. Safe
657 // squares one, two or three squares behind a friendly pawn are counted
658 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
659 // improve play on game opening.
661 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
663 const Color Them = (Us == WHITE ? BLACK : WHITE);
665 // Find the safe squares for our pieces inside the area defined by
666 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
667 // pawn, or if it is undefended and attacked by an enemy piece.
668 Bitboard safe = SpaceMask[Us]
669 & ~pos.pieces(Us, PAWN)
670 & ~ei.attackedBy[Them][PAWN]
671 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
673 // Find all squares which are at most three squares behind some friendly pawn
674 Bitboard behind = pos.pieces(Us, PAWN);
675 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
676 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
678 // Since SpaceMask[Us] is fully on our half of the board
679 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
681 // Count safe + (behind & safe) with a single popcount
682 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
683 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
684 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
686 return make_score(bonus * weight * weight, 0);
690 // do_evaluate() is the evaluation entry point, called directly from evaluate()
693 Value do_evaluate(const Position& pos) {
695 assert(!pos.checkers());
698 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
700 // Initialize score by reading the incrementally updated scores included
701 // in the position object (material + piece square tables).
702 // Score is computed from the point of view of white.
703 score = pos.psq_score();
705 // Probe the material hash table
706 ei.mi = Material::probe(pos);
707 score += ei.mi->imbalance();
709 // If we have a specialized evaluation function for the current material
710 // configuration, call it and return.
711 if (ei.mi->specialized_eval_exists())
712 return ei.mi->evaluate(pos);
714 // Probe the pawn hash table
715 ei.pi = Pawns::probe(pos);
716 score += apply_weight(ei.pi->pawns_score(), Weights[PawnStructure]);
718 // Initialize attack and king safety bitboards
719 init_eval_info<WHITE>(pos, ei);
720 init_eval_info<BLACK>(pos, ei);
722 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
723 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
725 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
726 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
727 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
729 // Evaluate pieces and mobility
730 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
731 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
733 // Evaluate kings after all other pieces because we need complete attack
734 // information when computing the king safety evaluation.
735 score += evaluate_king<WHITE, Trace>(pos, ei)
736 - evaluate_king<BLACK, Trace>(pos, ei);
738 // Evaluate tactical threats, we need full attack information including king
739 score += evaluate_threats<WHITE, Trace>(pos, ei)
740 - evaluate_threats<BLACK, Trace>(pos, ei);
742 // Evaluate passed pawns, we need full attack information including king
743 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
744 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
746 // If both sides have only pawns, score for potential unstoppable pawns
747 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
750 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
751 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
753 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
754 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
757 // Evaluate space for both sides, only during opening
758 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
760 Score s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
761 score += apply_weight(s, Weights[Space]);
764 // Scale winning side if position is more drawish than it appears
765 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
766 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
768 // If we don't already have an unusual scale factor, check for certain
769 // types of endgames, and use a lower scale for those.
770 if ( ei.mi->game_phase() < PHASE_MIDGAME
771 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
773 if (pos.opposite_bishops())
775 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
776 // is almost a draw, in case of KBP vs KB is even more a draw.
777 if ( pos.non_pawn_material(WHITE) == BishopValueMg
778 && pos.non_pawn_material(BLACK) == BishopValueMg)
779 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
781 // Endgame with opposite-colored bishops, but also other pieces. Still
782 // a bit drawish, but not as drawish as with only the two bishops.
784 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
786 // Endings where weaker side can place his king in front of the opponent's
787 // pawns are drawish.
788 else if ( abs(eg_value(score)) <= BishopValueEg
789 && ei.pi->pawn_span(strongSide) <= 1
790 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide)))
791 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
794 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
795 Value v = mg_value(score) * int(ei.mi->game_phase())
796 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
798 v /= int(PHASE_MIDGAME);
800 // In case of tracing add all single evaluation terms for both white and black
803 Tracing::write(Tracing::MATERIAL, pos.psq_score());
804 Tracing::write(Tracing::IMBALANCE, ei.mi->imbalance());
805 Tracing::write(PAWN, ei.pi->pawns_score());
806 Tracing::write(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
807 , apply_weight(mobility[BLACK], Weights[Mobility]));
808 Tracing::write(Tracing::SPACE, apply_weight(evaluate_space<WHITE>(pos, ei), Weights[Space])
809 , apply_weight(evaluate_space<BLACK>(pos, ei), Weights[Space]));
810 Tracing::write(Tracing::TOTAL, score);
813 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
819 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
821 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
823 void Tracing::write(int idx, Score w, Score b) {
824 scores[WHITE][idx] = w, scores[BLACK][idx] = b;
827 std::ostream& Tracing::operator<<(std::ostream& os, Term t) {
829 double wScore[] = { to_cp(mg_value(scores[WHITE][t])), to_cp(eg_value(scores[WHITE][t])) };
830 double bScore[] = { to_cp(mg_value(scores[BLACK][t])), to_cp(eg_value(scores[BLACK][t])) };
832 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
833 os << " --- --- | --- --- | ";
835 os << std::setw(5) << wScore[MG] << " " << std::setw(5) << wScore[EG] << " | "
836 << std::setw(5) << bScore[MG] << " " << std::setw(5) << bScore[EG] << " | ";
838 os << std::setw(5) << wScore[MG] - bScore[MG] << " "
839 << std::setw(5) << wScore[EG] - bScore[EG] << " \n";
844 std::string Tracing::do_trace(const Position& pos) {
846 std::memset(scores, 0, sizeof(scores));
848 Value v = do_evaluate<true>(pos);
849 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
851 std::stringstream ss;
852 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
853 << " Eval term | White | Black | Total \n"
854 << " | MG EG | MG EG | MG EG \n"
855 << "----------------+-------------+-------------+-------------\n"
856 << " Material | " << Term(MATERIAL)
857 << " Imbalance | " << Term(IMBALANCE)
858 << " Pawns | " << Term(PAWN)
859 << " Knights | " << Term(KNIGHT)
860 << " Bishop | " << Term(BISHOP)
861 << " Rooks | " << Term(ROOK)
862 << " Queens | " << Term(QUEEN)
863 << " Mobility | " << Term(MOBILITY)
864 << " King safety | " << Term(KING)
865 << " Threats | " << Term(THREAT)
866 << " Passed pawns | " << Term(PASSED)
867 << " Space | " << Term(SPACE)
868 << "----------------+-------------+-------------+-------------\n"
869 << " Total | " << Term(TOTAL);
871 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
881 /// evaluate() is the main evaluation function. It returns a static evaluation
882 /// of the position always from the point of view of the side to move.
884 Value evaluate(const Position& pos) {
885 return do_evaluate<false>(pos);
889 /// trace() is like evaluate(), but instead of returning a value, it returns
890 /// a string (suitable for outputting to stdout) that contains the detailed
891 /// descriptions and values of each evaluation term. It's mainly used for
893 std::string trace(const Position& pos) {
894 return Tracing::do_trace(pos);
898 /// init() computes evaluation weights, usually at startup
902 const double MaxSlope = 8.7;
903 const double Peak = 1280;
906 for (int i = 1; i < 400; ++i)
908 t = std::min(Peak, std::min(0.027 * i * i, t + MaxSlope));
909 KingDanger[i] = apply_weight(make_score(int(t), 0), Weights[KingSafety]);