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 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);
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[] = {
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[] = { 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);
221 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
222 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
224 // Init king safety tables only if we are going to use them
225 if (pos.non_pawn_material(Us) >= QueenValueMg)
227 ei.kingRing[Them] = b | shift_bb<Down>(b);
228 b &= ei.attackedBy[Us][PAWN];
229 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
230 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
233 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
237 // evaluate_outpost() evaluates bishop and knight outpost squares
239 template<PieceType Pt, Color Us>
240 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
242 const Color Them = (Us == WHITE ? BLACK : WHITE);
244 assert (Pt == BISHOP || Pt == KNIGHT);
246 // Initial bonus based on square
247 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
249 // Increase bonus if supported by pawn, especially if the opponent has
250 // no minor piece which can trade with the outpost piece.
251 if (bonus && (ei.attackedBy[Us][PAWN] & s))
253 if ( !pos.pieces(Them, KNIGHT)
254 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
255 bonus += bonus + bonus / 2;
260 return make_score(bonus * 2, bonus / 2);
264 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
266 template<PieceType Pt, Color Us, bool Trace>
267 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
271 Score score = SCORE_ZERO;
273 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
274 const Color Them = (Us == WHITE ? BLACK : WHITE);
275 const Square* pl = pos.list<Pt>(Us);
277 ei.attackedBy[Us][Pt] = 0;
279 while ((s = *pl++) != SQ_NONE)
281 // Find attacked squares, including x-ray attacks for bishops and rooks
282 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
283 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
284 : pos.attacks_from<Pt>(s);
286 if (ei.pinnedPieces[Us] & s)
287 b &= LineBB[pos.king_square(Us)][s];
289 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
291 if (b & ei.kingRing[Them])
293 ei.kingAttackersCount[Us]++;
294 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
295 Bitboard bb = b & ei.attackedBy[Them][KING];
297 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
301 b &= ~( ei.attackedBy[Them][KNIGHT]
302 | ei.attackedBy[Them][BISHOP]
303 | ei.attackedBy[Them][ROOK]);
305 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
306 : popcount<Full >(b & mobilityArea[Us]);
308 mobility[Us] += MobilityBonus[Pt][mob];
310 // Decrease score if we are attacked by an enemy pawn. The remaining part
311 // of threat evaluation must be done later when we have full attack info.
312 if (ei.attackedBy[Them][PAWN] & s)
313 score -= ThreatenedByPawn[Pt];
315 if (Pt == BISHOP || Pt == KNIGHT)
317 // Bonus for outpost square
318 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
319 score += evaluate_outpost<Pt, Us>(pos, ei, s);
321 // Bonus when behind a pawn
322 if ( relative_rank(Us, s) < RANK_5
323 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
324 score += MinorBehindPawn;
326 // Penalty for pawns on same color square of bishop
328 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
330 // An important Chess960 pattern: A cornered bishop blocked by a friendly
331 // pawn diagonally in front of it is a very serious problem, especially
332 // when that pawn is also blocked.
335 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
337 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
338 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
339 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
340 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
347 // Bonus for aligning with enemy pawns on the same rank/file
348 if (relative_rank(Us, s) >= RANK_5)
350 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
352 score += popcount<Max15>(alignedPawns) * RookOnPawn;
355 // Bonus when on an open or semi-open file
356 if (ei.pi->semiopen_file(Us, file_of(s)))
357 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
359 // Penalize when trapped by the king, even more if king cannot castle
360 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
362 Square ksq = pos.king_square(Us);
364 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
365 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
366 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
367 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
373 Tracing::write(Pt, Us, score);
375 // Recursively call evaluate_pieces() of next piece type until KING excluded
376 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
380 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
382 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
385 // evaluate_king() assigns bonuses and penalties to a king of a given color
387 template<Color Us, bool Trace>
388 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
390 const Color Them = (Us == WHITE ? BLACK : WHITE);
392 Bitboard undefended, b, b1, b2, safe;
394 const Square ksq = pos.king_square(Us);
396 // King shelter and enemy pawns storm
397 Score score = ei.pi->king_safety<Us>(pos, ksq);
399 // Main king safety evaluation
400 if (ei.kingAttackersCount[Them])
402 // Find the attacked squares around the king which have no defenders
403 // apart from the king itself
404 undefended = ei.attackedBy[Them][ALL_PIECES]
405 & ei.attackedBy[Us][KING]
406 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
407 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
408 | ei.attackedBy[Us][QUEEN]);
410 // Initialize the 'attackUnits' variable, which is used later on as an
411 // index into the KingDanger[] array. The initial value is based on the
412 // number and types of the enemy's attacking pieces, the number of
413 // attacked and undefended squares around our king and the quality of
414 // the pawn shelter (current 'score' value).
415 attackUnits = std::min(74, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
416 + 8 * ei.kingAdjacentZoneAttacksCount[Them]
417 + 25 * popcount<Max15>(undefended)
418 + 11 * (ei.pinnedPieces[Us] != 0)
419 - mg_value(score) * 31 / 256
420 - !pos.count<QUEEN>(Them) * 60;
422 // Analyse the enemy's safe queen contact checks. Firstly, find the
423 // undefended squares around the king reachable by the enemy queen...
424 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
427 // ...and then remove squares not supported by another enemy piece
428 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
429 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
432 attackUnits += QueenContactCheck * popcount<Max15>(b);
435 // Analyse the enemy's safe rook contact checks. Firstly, find the
436 // undefended squares around the king reachable by the enemy rooks...
437 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
439 // Consider only squares where the enemy's rook gives check
440 b &= PseudoAttacks[ROOK][ksq];
444 // ...and then remove squares not supported by another enemy piece
445 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
446 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
449 attackUnits += RookContactCheck * popcount<Max15>(b);
452 // Analyse the enemy's safe distance checks for sliders and knights
453 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
455 b1 = pos.attacks_from<ROOK >(ksq) & safe;
456 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
458 // Enemy queen safe checks
459 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
461 attackUnits += QueenCheck * popcount<Max15>(b);
463 // Enemy rooks safe checks
464 b = b1 & ei.attackedBy[Them][ROOK];
466 attackUnits += RookCheck * popcount<Max15>(b);
468 // Enemy bishops safe checks
469 b = b2 & ei.attackedBy[Them][BISHOP];
471 attackUnits += BishopCheck * popcount<Max15>(b);
473 // Enemy knights safe checks
474 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
476 attackUnits += KnightCheck * popcount<Max15>(b);
478 // Finally, extract the king danger score from the KingDanger[]
479 // array and subtract the score from evaluation.
480 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
484 Tracing::write(KING, Us, score);
490 // evaluate_threats() assigns bonuses according to the type of attacking piece
491 // and the type of attacked one.
493 template<Color Us, bool Trace>
494 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
496 const Color Them = (Us == WHITE ? BLACK : WHITE);
497 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
498 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
499 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
500 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
501 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
503 enum { Defended, Weak };
504 enum { Minor, Major };
506 Bitboard b, weak, defended;
507 Score score = SCORE_ZERO;
509 // Non-pawn enemies defended by a pawn
510 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
511 & ei.attackedBy[Them][PAWN];
513 // Add a bonus according to the kind of attacking pieces
516 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
518 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
520 b = defended & (ei.attackedBy[Us][ROOK]);
522 score += Threat[Defended][Major][type_of(pos.piece_on(pop_lsb(&b)))];
525 // Enemies not defended by a pawn and under our attack
526 weak = pos.pieces(Them)
527 & ~ei.attackedBy[Them][PAWN]
528 & ei.attackedBy[Us][ALL_PIECES];
530 // Add a bonus according to the kind of attacking pieces
533 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
535 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
537 b = weak & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
539 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
541 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
543 score += Hanging * popcount<Max15>(b);
545 b = weak & ei.attackedBy[Us][KING];
547 score += more_than_one(b) ? KingOnMany : KingOnOne;
550 // Add bonus for safe pawn pushes which attacks an enemy piece
551 b = pos.pieces(Us, PAWN) & ~TRank7BB;
552 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
555 & ~ei.attackedBy[Them][PAWN]
556 & (ei.attackedBy[Us][PAWN] | ~ei.attackedBy[Them][ALL_PIECES]);
558 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
560 & ~ei.attackedBy[Us][PAWN];
563 score += popcount<Max15>(b) * PawnAttackThreat;
566 Tracing::write(Tracing::THREAT, Us, score);
572 // evaluate_passed_pawns() evaluates the passed pawns of the given color
574 template<Color Us, bool Trace>
575 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
577 const Color Them = (Us == WHITE ? BLACK : WHITE);
579 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
580 Score score = SCORE_ZERO;
582 b = ei.pi->passed_pawns(Us);
586 Square s = pop_lsb(&b);
588 assert(pos.pawn_passed(Us, s));
590 int r = relative_rank(Us, s) - RANK_2;
591 int rr = r * (r - 1);
593 // Base bonus based on rank
594 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
598 Square blockSq = s + pawn_push(Us);
600 // Adjust bonus based on the king's proximity
601 ebonus += distance(pos.king_square(Them), blockSq) * 5 * rr
602 - distance(pos.king_square(Us ), blockSq) * 2 * rr;
604 // If blockSq is not the queening square then consider also a second push
605 if (relative_rank(Us, blockSq) != RANK_8)
606 ebonus -= distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
608 // If the pawn is free to advance, then increase the bonus
609 if (pos.empty(blockSq))
611 // If there is a rook or queen attacking/defending the pawn from behind,
612 // consider all the squaresToQueen. Otherwise consider only the squares
613 // in the pawn's path attacked or occupied by the enemy.
614 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
616 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
618 if (!(pos.pieces(Us) & bb))
619 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
621 if (!(pos.pieces(Them) & bb))
622 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
624 // If there aren't any enemy attacks, assign a big bonus. Otherwise
625 // assign a smaller bonus if the block square isn't attacked.
626 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
628 // If the path to queen is fully defended, assign a big bonus.
629 // Otherwise assign a smaller bonus if the block square is defended.
630 if (defendedSquares == squaresToQueen)
633 else if (defendedSquares & blockSq)
636 mbonus += k * rr, ebonus += k * rr;
638 else if (pos.pieces(Us) & blockSq)
639 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
642 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
643 ebonus += ebonus / 4;
645 score += make_score(mbonus, ebonus);
649 Tracing::write(Tracing::PASSED, Us, apply_weight(score, Weights[PassedPawns]));
651 // Add the scores to the middlegame and endgame eval
652 return apply_weight(score, Weights[PassedPawns]);
656 // evaluate_space() computes the space evaluation for a given side. The
657 // space evaluation is a simple bonus based on the number of safe squares
658 // available for minor pieces on the central four files on ranks 2--4. Safe
659 // squares one, two or three squares behind a friendly pawn are counted
660 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
661 // improve play on game opening.
663 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
665 const Color Them = (Us == WHITE ? BLACK : WHITE);
667 // Find the safe squares for our pieces inside the area defined by
668 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
669 // pawn, or if it is undefended and attacked by an enemy piece.
670 Bitboard safe = SpaceMask[Us]
671 & ~pos.pieces(Us, PAWN)
672 & ~ei.attackedBy[Them][PAWN]
673 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
675 // Find all squares which are at most three squares behind some friendly pawn
676 Bitboard behind = pos.pieces(Us, PAWN);
677 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
678 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
680 // Since SpaceMask[Us] is fully on our half of the board
681 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
683 // Count safe + (behind & safe) with a single popcount
684 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
685 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
686 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
688 return make_score(bonus * weight * weight, 0);
692 // do_evaluate() is the evaluation entry point, called directly from evaluate()
695 Value do_evaluate(const Position& pos) {
697 assert(!pos.checkers());
700 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
702 // Initialize score by reading the incrementally updated scores included
703 // in the position object (material + piece square tables).
704 // Score is computed from the point of view of white.
705 score = pos.psq_score();
707 // Probe the material hash table
708 ei.mi = Material::probe(pos);
709 score += ei.mi->imbalance();
711 // If we have a specialized evaluation function for the current material
712 // configuration, call it and return.
713 if (ei.mi->specialized_eval_exists())
714 return ei.mi->evaluate(pos);
716 // Probe the pawn hash table
717 ei.pi = Pawns::probe(pos);
718 score += apply_weight(ei.pi->pawns_score(), Weights[PawnStructure]);
720 // Initialize attack and king safety bitboards
721 init_eval_info<WHITE>(pos, ei);
722 init_eval_info<BLACK>(pos, ei);
724 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
725 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
727 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
728 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
729 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
731 // Evaluate pieces and mobility
732 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
733 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
735 // Evaluate kings after all other pieces because we need complete attack
736 // information when computing the king safety evaluation.
737 score += evaluate_king<WHITE, Trace>(pos, ei)
738 - evaluate_king<BLACK, Trace>(pos, ei);
740 // Evaluate tactical threats, we need full attack information including king
741 score += evaluate_threats<WHITE, Trace>(pos, ei)
742 - evaluate_threats<BLACK, Trace>(pos, ei);
744 // Evaluate passed pawns, we need full attack information including king
745 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
746 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
748 // If both sides have only pawns, score for potential unstoppable pawns
749 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
752 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
753 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
755 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
756 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
759 // Evaluate space for both sides, only during opening
760 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
762 Score s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
763 score += apply_weight(s, Weights[Space]);
766 // Scale winning side if position is more drawish than it appears
767 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
768 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
770 // If we don't already have an unusual scale factor, check for certain
771 // types of endgames, and use a lower scale for those.
772 if ( ei.mi->game_phase() < PHASE_MIDGAME
773 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
775 if (pos.opposite_bishops())
777 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
778 // is almost a draw, in case of KBP vs KB is even more a draw.
779 if ( pos.non_pawn_material(WHITE) == BishopValueMg
780 && pos.non_pawn_material(BLACK) == BishopValueMg)
781 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
783 // Endgame with opposite-colored bishops, but also other pieces. Still
784 // a bit drawish, but not as drawish as with only the two bishops.
786 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
788 // Endings where weaker side can place his king in front of the opponent's
789 // pawns are drawish.
790 else if ( abs(eg_value(score)) <= BishopValueEg
791 && ei.pi->pawn_span(strongSide) <= 1
792 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide)))
793 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
796 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
797 Value v = mg_value(score) * int(ei.mi->game_phase())
798 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
800 v /= int(PHASE_MIDGAME);
802 // In case of tracing add all single evaluation contributions for both white and black
805 Tracing::write(Tracing::MATERIAL, pos.psq_score());
806 Tracing::write(Tracing::IMBALANCE, ei.mi->imbalance());
807 Tracing::write(PAWN, ei.pi->pawns_score());
808 Tracing::write(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
809 , apply_weight(mobility[BLACK], Weights[Mobility]));
810 Tracing::write(Tracing::SPACE, apply_weight(evaluate_space<WHITE>(pos, ei), Weights[Space])
811 , apply_weight(evaluate_space<BLACK>(pos, ei), Weights[Space]));
812 Tracing::write(Tracing::TOTAL, score);
817 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
821 // Tracing function definitions
823 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
825 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
827 void Tracing::write(int idx, Score w, Score b) {
829 write(idx, WHITE, w);
830 write(idx, BLACK, b);
833 void Tracing::print(std::stringstream& ss, const char* name, int idx) {
835 Score wScore = scores[WHITE][idx];
836 Score bScore = scores[BLACK][idx];
839 case MATERIAL: case IMBALANCE: case PAWN: case TOTAL:
840 ss << std::setw(15) << name << " | --- --- | --- --- | "
841 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
842 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
845 ss << std::setw(15) << name << " | " << std::noshowpos
846 << std::setw(5) << to_cp(mg_value(wScore)) << " "
847 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
848 << std::setw(5) << to_cp(mg_value(bScore)) << " "
849 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
850 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
851 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
855 std::string Tracing::do_trace(const Position& pos) {
857 std::memset(scores, 0, sizeof(scores));
859 Value v = do_evaluate<true>(pos);
860 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
862 std::stringstream ss;
863 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
864 << " Eval term | White | Black | Total \n"
865 << " | MG EG | MG EG | MG EG \n"
866 << "----------------+-------------+-------------+-------------\n";
868 print(ss, "Material", MATERIAL);
869 print(ss, "Imbalance", IMBALANCE);
870 print(ss, "Pawns", PAWN);
871 print(ss, "Knights", KNIGHT);
872 print(ss, "Bishops", BISHOP);
873 print(ss, "Rooks", ROOK);
874 print(ss, "Queens", QUEEN);
875 print(ss, "Mobility", MOBILITY);
876 print(ss, "King safety", KING);
877 print(ss, "Threats", THREAT);
878 print(ss, "Passed pawns", PASSED);
879 print(ss, "Space", SPACE);
881 ss << "----------------+-------------+-------------+-------------\n";
882 print(ss, "Total", TOTAL);
884 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
894 /// evaluate() is the main evaluation function. It returns a static evaluation
895 /// of the position always from the point of view of the side to move.
897 Value evaluate(const Position& pos) {
898 return do_evaluate<false>(pos);
902 /// trace() is like evaluate(), but instead of returning a value, it returns
903 /// a string (suitable for outputting to stdout) that contains the detailed
904 /// descriptions and values of each evaluation term. It's mainly used for
906 std::string trace(const Position& pos) {
907 return Tracing::do_trace(pos);
911 /// init() computes evaluation weights, usually at startup
915 const double MaxSlope = 8.7;
916 const double Peak = 1280;
919 for (int i = 1; i < 400; ++i)
921 t = std::min(Peak, std::min(0.027 * i * i, t + MaxSlope));
922 KingDanger[i] = apply_weight(make_score(int(t), 0), Weights[KingSafety]);