2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 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/>.
30 #include "ucioption.h"
34 // Struct EvalInfo contains various information computed and collected
35 // by the evaluation functions.
38 // Pointers to material and pawn hash table entries
42 // attackedBy[color][piece type] is a bitboard representing all squares
43 // attacked by a given color and piece type, attackedBy[color][ALL_PIECES]
44 // contains all squares attacked by the given color.
45 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
47 // kingRing[color] is the zone around the king which is considered
48 // by the king safety evaluation. This consists of the squares directly
49 // adjacent to the king, and the three (or two, for a king on an edge file)
50 // squares two ranks in front of the king. For instance, if black's king
51 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
52 // f7, g7, h7, f6, g6 and h6.
53 Bitboard kingRing[COLOR_NB];
55 // kingAttackersCount[color] is the number of pieces of the given color
56 // which attack a square in the kingRing of the enemy king.
57 int kingAttackersCount[COLOR_NB];
59 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
60 // given color which attack a square in the kingRing of the enemy king. The
61 // weights of the individual piece types are given by the variables
62 // QueenAttackWeight, RookAttackWeight, BishopAttackWeight and
63 // KnightAttackWeight in evaluate.cpp
64 int kingAttackersWeight[COLOR_NB];
66 // kingAdjacentZoneAttacksCount[color] is the number of attacks to squares
67 // directly adjacent to the king of the given color. Pieces which attack
68 // more than one square are counted multiple times. For instance, if black's
69 // king is on g8 and there's a white knight on g5, this knight adds
70 // 2 to kingAdjacentZoneAttacksCount[BLACK].
71 int kingAdjacentZoneAttacksCount[COLOR_NB];
73 Bitboard pinnedPieces[COLOR_NB];
78 enum Terms { // First 8 entries are for PieceType
79 PST = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERMS_NB
82 Score terms[COLOR_NB][TERMS_NB];
86 double to_cp(Value v);
87 void add_term(int idx, Score term_w, Score term_b = SCORE_ZERO);
88 void format_row(std::stringstream& ss, const char* name, int idx);
89 std::string do_trace(const Position& pos);
92 // Evaluation weights, initialized from UCI options
93 enum { Mobility, PawnStructure, PassedPawns, Space, KingDangerUs, KingDangerThem };
94 struct Weight { int mg, eg; } Weights[6];
97 #define S(mg, eg) make_score(mg, eg)
99 // Internal evaluation weights. These are applied on top of the evaluation
100 // weights read from UCI parameters. The purpose is to be able to change
101 // the evaluation weights while keeping the default values of the UCI
102 // parameters at 100, which looks prettier.
104 // Values modified by Joona Kiiski
105 const Score WeightsInternal[] = {
106 S(289, 344), S(233, 201), S(221, 273), S(46, 0), S(271, 0), S(307, 0)
109 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
110 // game, indexed by piece type and number of attacked squares not occupied by
112 const Score MobilityBonus[][32] = {
114 { S(-65,-50), S(-42,-30), S(-9,-10), S( 3, 0), S(15, 10), S(27, 20), // Knights
115 S( 37, 28), S( 42, 31), S(44, 33) },
116 { S(-52,-47), S(-28,-23), S( 6, 1), S(20, 15), S(34, 29), S(48, 43), // Bishops
117 S( 60, 55), S( 68, 63), S(74, 68), S(77, 72), S(80, 75), S(82, 77),
118 S( 84, 79), S( 86, 81) },
119 { S(-47,-53), S(-31,-26), S(-5, 0), S( 1, 16), S( 7, 32), S(13, 48), // Rooks
120 S( 18, 64), S( 22, 80), S(26, 96), S(29,109), S(31,115), S(33,119),
121 S( 35,122), S( 36,123), S(37,124) },
122 { S(-42,-40), S(-28,-23), S(-5, -7), S( 0, 0), S( 6, 10), S(11, 19), // Queens
123 S( 13, 29), S( 18, 38), S(20, 40), S(21, 41), S(22, 41), S(22, 41),
124 S( 22, 41), S( 23, 41), S(24, 41), S(25, 41), S(25, 41), S(25, 41),
125 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41), S(25, 41), S(25, 41),
126 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41) }
129 // Outpost[PieceType][Square] contains bonuses for knights and bishops outposts,
130 // indexed by piece type and square (from white's point of view).
131 const Value Outpost[][SQUARE_NB] = {
133 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
134 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
135 V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0),
136 V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0),
137 V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0),
138 V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0) },
140 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
141 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
142 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
143 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
144 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
145 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0) }
148 // Threat[attacking][attacked] contains bonuses according to which piece
149 // type attacks which one.
150 const Score Threat[][PIECE_TYPE_NB] = {
151 { S(0, 0), S( 7, 39), S(24, 49), S(24, 49), S(41,100), S(41,100) }, // Minor
152 { S(0, 0), S(15, 39), S(15, 45), S(15, 45), S(15, 45), S(24, 49) } // Major
155 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
156 // type is attacked by an enemy pawn.
157 const Score ThreatenedByPawn[] = {
158 S(0, 0), S(0, 0), S(56, 70), S(56, 70), S(76, 99), S(86, 118)
163 const Score Tempo = make_score(24, 11);
164 const Score RookOn7th = make_score(11, 20);
165 const Score RookOnPawn = make_score(10, 28);
166 const Score RookOpenFile = make_score(43, 21);
167 const Score RookSemiopenFile = make_score(19, 10);
168 const Score BishopPawns = make_score( 8, 12);
169 const Score KnightPawns = make_score( 8, 4);
170 const Score MinorBehindPawn = make_score(16, 0);
171 const Score UndefendedMinor = make_score(25, 10);
172 const Score TrappedRook = make_score(90, 0);
173 const Score Unstoppable = make_score( 0, 20);
175 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
176 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
177 // happen in Chess960 games.
178 const Score TrappedBishopA1H1 = make_score(50, 50);
180 // SpaceMask[Color] contains the area of the board which is considered
181 // by the space evaluation. In the middlegame, each side is given a bonus
182 // based on how many squares inside this area are safe and available for
183 // friendly minor pieces.
184 const Bitboard SpaceMask[] = {
185 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
186 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
189 // King danger constants and variables. The king danger scores are taken
190 // from KingDanger[]. Various little "meta-bonuses" measuring the strength
191 // of the enemy attack are added up into an integer, which is used as an
192 // index to KingDanger[].
194 // KingAttackWeights[PieceType] contains king attack weights by piece type
195 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
197 // Bonuses for enemy's safe checks
198 const int QueenContactCheck = 24;
199 const int RookContactCheck = 16;
200 const int QueenCheck = 12;
201 const int RookCheck = 8;
202 const int BishopCheck = 2;
203 const int KnightCheck = 3;
205 // KingDanger[Color][attackUnits] contains the actual king danger weighted
206 // scores, indexed by color and by a calculated integer number.
207 Score KingDanger[COLOR_NB][128];
210 // apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
211 Score apply_weight(Score v, const Weight& w) {
212 return make_score(mg_value(v) * w.mg / 256, eg_value(v) * w.eg / 256);
216 // weight_option() computes the value of an evaluation weight, by combining
217 // two UCI-configurable weights (midgame and endgame) with an internal weight.
219 Weight weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight) {
221 Weight w = { Options[mgOpt] * mg_value(internalWeight) / 100,
222 Options[egOpt] * eg_value(internalWeight) / 100 };
227 // interpolate() interpolates between a middlegame and an endgame score,
228 // based on game phase. It also scales the return value by a ScaleFactor array.
230 Value interpolate(const Score& v, Phase ph, ScaleFactor sf) {
232 assert(-VALUE_INFINITE < mg_value(v) && mg_value(v) < VALUE_INFINITE);
233 assert(-VALUE_INFINITE < eg_value(v) && eg_value(v) < VALUE_INFINITE);
234 assert(PHASE_ENDGAME <= ph && ph <= PHASE_MIDGAME);
236 int eg = (eg_value(v) * int(sf)) / SCALE_FACTOR_NORMAL;
237 return Value((mg_value(v) * int(ph) + eg * int(PHASE_MIDGAME - ph)) / PHASE_MIDGAME);
241 // init_eval_info() initializes king bitboards for given color adding
242 // pawn attacks. To be done at the beginning of the evaluation.
245 void init_eval_info(const Position& pos, EvalInfo& ei) {
247 const Color Them = (Us == WHITE ? BLACK : WHITE);
248 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
250 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
252 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
253 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
255 // Init king safety tables only if we are going to use them
256 if (pos.count<QUEEN>(Us) && pos.non_pawn_material(Us) > QueenValueMg + PawnValueMg)
258 ei.kingRing[Them] = b | shift_bb<Down>(b);
259 b &= ei.attackedBy[Us][PAWN];
260 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
261 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
264 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
268 // evaluate_outposts() evaluates bishop and knight outpost squares
270 template<PieceType Pt, Color Us>
271 Score evaluate_outposts(const Position& pos, EvalInfo& ei, Square s) {
273 const Color Them = (Us == WHITE ? BLACK : WHITE);
275 assert (Pt == BISHOP || Pt == KNIGHT);
277 // Initial bonus based on square
278 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
280 // Increase bonus if supported by pawn, especially if the opponent has
281 // no minor piece which can trade with the outpost piece.
282 if (bonus && (ei.attackedBy[Us][PAWN] & s))
284 if ( !pos.pieces(Them, KNIGHT)
285 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
286 bonus += bonus + bonus / 2;
291 return make_score(bonus, bonus);
295 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
297 template<PieceType Pt, Color Us, bool Trace>
298 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
302 Score score = SCORE_ZERO;
304 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
305 const Color Them = (Us == WHITE ? BLACK : WHITE);
306 const Square* pl = pos.list<Pt>(Us);
308 ei.attackedBy[Us][Pt] = 0;
310 while ((s = *pl++) != SQ_NONE)
312 // Find attacked squares, including x-ray attacks for bishops and rooks
313 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
314 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
315 : pos.attacks_from<Pt>(s);
317 if (ei.pinnedPieces[Us] & s)
318 b &= LineBB[pos.king_square(Us)][s];
320 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
322 if (b & ei.kingRing[Them])
324 ei.kingAttackersCount[Us]++;
325 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
326 Bitboard bb = b & ei.attackedBy[Them][KING];
328 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
332 b &= ~( ei.attackedBy[Them][KNIGHT]
333 | ei.attackedBy[Them][BISHOP]
334 | ei.attackedBy[Them][ROOK]);
336 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
337 : popcount<Full >(b & mobilityArea[Us]);
339 mobility[Us] += MobilityBonus[Pt][mob];
341 // Decrease score if we are attacked by an enemy pawn. The remaining part
342 // of threat evaluation must be done later when we have full attack info.
343 if (ei.attackedBy[Them][PAWN] & s)
344 score -= ThreatenedByPawn[Pt];
346 if (Pt == BISHOP || Pt == KNIGHT)
348 // Penalty for bishop with same colored pawns
350 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
352 // Penalty for knight when there are few enemy pawns
354 score -= KnightPawns * std::max(5 - pos.count<PAWN>(Them), 0);
356 // Bishop and knight outposts squares
357 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
358 score += evaluate_outposts<Pt, Us>(pos, ei, s);
360 // Bishop or knight behind a pawn
361 if ( relative_rank(Us, s) < RANK_5
362 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
363 score += MinorBehindPawn;
368 // Rook on 7th rank and enemy king trapped on 8th
369 if ( relative_rank(Us, s) == RANK_7
370 && relative_rank(Us, pos.king_square(Them)) == RANK_8)
373 // Rook piece attacking enemy pawns on the same rank/file
374 if (relative_rank(Us, s) >= RANK_5)
376 Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
378 score += popcount<Max15>(pawns) * RookOnPawn;
381 // Give a bonus for a rook on a open or semi-open file
382 if (ei.pi->semiopen(Us, file_of(s)))
383 score += ei.pi->semiopen(Them, file_of(s)) ? RookOpenFile : RookSemiopenFile;
385 if (mob > 3 || ei.pi->semiopen(Us, file_of(s)))
388 Square ksq = pos.king_square(Us);
390 // Penalize rooks which are trapped by a king. Penalize more if the
391 // king has lost its castling capability.
392 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
393 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
394 && !ei.pi->semiopen_on_side(Us, file_of(ksq), file_of(ksq) < FILE_E))
395 score -= (TrappedRook - make_score(mob * 8, 0)) * (pos.can_castle(Us) ? 1 : 2);
398 // An important Chess960 pattern: A cornered bishop blocked by a friendly
399 // pawn diagonally in front of it is a very serious problem, especially
400 // when that pawn is also blocked.
403 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
405 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
406 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
407 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
408 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
414 Tracing::terms[Us][Pt] = score;
416 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
420 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
422 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
425 // evaluate_king() assigns bonuses and penalties to a king of a given color
427 template<Color Us, bool Trace>
428 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
430 const Color Them = (Us == WHITE ? BLACK : WHITE);
432 Bitboard undefended, b, b1, b2, safe;
434 const Square ksq = pos.king_square(Us);
436 // King shelter and enemy pawns storm
437 Score score = ei.pi->king_safety<Us>(pos, ksq);
439 // Main king safety evaluation
440 if (ei.kingAttackersCount[Them])
442 // Find the attacked squares around the king which have no defenders
443 // apart from the king itself
444 undefended = ei.attackedBy[Them][ALL_PIECES]
445 & ei.attackedBy[Us][KING]
446 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
447 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
448 | ei.attackedBy[Us][QUEEN]);
450 // Initialize the 'attackUnits' variable, which is used later on as an
451 // index to the KingDanger[] array. The initial value is based on the
452 // number and types of the enemy's attacking pieces, the number of
453 // attacked and undefended squares around our king and the quality of
454 // the pawn shelter (current 'score' value).
455 attackUnits = std::min(20, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
456 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
457 + 2 * (ei.pinnedPieces[Us] != 0)
458 - mg_value(score) / 32;
460 // Analyse the enemy's safe queen contact checks. Firstly, find the
461 // undefended squares around the king that are attacked by the enemy's
463 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
466 // ...and then remove squares not supported by another enemy piece
467 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
468 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
471 attackUnits += QueenContactCheck
473 * (Them == pos.side_to_move() ? 2 : 1);
476 // Analyse the enemy's safe rook contact checks. Firstly, find the
477 // undefended squares around the king that are attacked by the enemy's
479 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
481 // Consider only squares where the enemy's rook gives check
482 b &= PseudoAttacks[ROOK][ksq];
486 // ...and then remove squares not supported by another enemy piece
487 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
488 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
491 attackUnits += RookContactCheck
493 * (Them == pos.side_to_move() ? 2 : 1);
496 // Analyse the enemy's safe distance checks for sliders and knights
497 safe = ~(pos.pieces(Them) | ei.attackedBy[Us][ALL_PIECES]);
499 b1 = pos.attacks_from<ROOK>(ksq) & safe;
500 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
502 // Enemy queen safe checks
503 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
505 attackUnits += QueenCheck * popcount<Max15>(b);
507 // Enemy rooks safe checks
508 b = b1 & ei.attackedBy[Them][ROOK];
510 attackUnits += RookCheck * popcount<Max15>(b);
512 // Enemy bishops safe checks
513 b = b2 & ei.attackedBy[Them][BISHOP];
515 attackUnits += BishopCheck * popcount<Max15>(b);
517 // Enemy knights safe checks
518 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
520 attackUnits += KnightCheck * popcount<Max15>(b);
522 // To index KingDanger[] attackUnits must be in [0, 99] range
523 attackUnits = std::min(99, std::max(0, attackUnits));
525 // Finally, extract the king danger score from the KingDanger[]
526 // array and subtract the score from evaluation.
527 score -= KingDanger[Us == Search::RootColor][attackUnits];
531 Tracing::terms[Us][KING] = score;
537 // evaluate_threats() assigns bonuses according to the type of attacking piece
538 // and the type of attacked one.
540 template<Color Us, bool Trace>
541 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
543 const Color Them = (Us == WHITE ? BLACK : WHITE);
545 Bitboard b, undefendedMinors, weakEnemies;
546 Score score = SCORE_ZERO;
548 // Undefended minors get penalized even if they are not under attack
549 undefendedMinors = pos.pieces(Them, BISHOP, KNIGHT)
550 & ~ei.attackedBy[Them][ALL_PIECES];
552 if (undefendedMinors)
553 score += UndefendedMinor;
555 // Enemy pieces not defended by a pawn and under our attack
556 weakEnemies = pos.pieces(Them)
557 & ~ei.attackedBy[Them][PAWN]
558 & ei.attackedBy[Us][ALL_PIECES];
560 // Add a bonus according if the attacking pieces are minor or major
563 b = weakEnemies & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
565 score += Threat[0][type_of(pos.piece_on(lsb(b)))];
567 b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
569 score += Threat[1][type_of(pos.piece_on(lsb(b)))];
573 Tracing::terms[Us][Tracing::THREAT] = score;
579 // evaluate_passed_pawns() evaluates the passed pawns of the given color
581 template<Color Us, bool Trace>
582 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
584 const Color Them = (Us == WHITE ? BLACK : WHITE);
586 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares, supportingPawns;
587 Score score = SCORE_ZERO;
589 b = ei.pi->passed_pawns(Us);
593 Square s = pop_lsb(&b);
595 assert(pos.pawn_passed(Us, s));
597 int r = int(relative_rank(Us, s) - RANK_2);
598 int rr = r * (r - 1);
600 // Base bonus based on rank
601 Value mbonus = Value(17 * rr);
602 Value ebonus = Value(7 * (rr + r + 1));
606 Square blockSq = s + pawn_push(Us);
608 // Adjust bonus based on the king's proximity
609 ebonus += Value(square_distance(pos.king_square(Them), blockSq) * 5 * rr)
610 - Value(square_distance(pos.king_square(Us ), blockSq) * 2 * rr);
612 // If blockSq is not the queening square then consider also a second push
613 if (relative_rank(Us, blockSq) != RANK_8)
614 ebonus -= Value(rr * square_distance(pos.king_square(Us), blockSq + pawn_push(Us)));
616 // If the pawn is free to advance, then increase the bonus
617 if (pos.empty(blockSq))
619 squaresToQueen = forward_bb(Us, s);
621 // If there is an enemy rook or queen attacking the pawn from behind,
622 // add all X-ray attacks by the rook or queen. Otherwise consider only
623 // the squares in the pawn's path attacked or occupied by the enemy.
624 if ( unlikely(forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN))
625 && (forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
626 unsafeSquares = squaresToQueen;
628 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
630 if ( unlikely(forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN))
631 && (forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
632 defendedSquares = squaresToQueen;
634 defendedSquares = squaresToQueen & ei.attackedBy[Us][ALL_PIECES];
636 // If there aren't any enemy attacks, then assign a huge bonus.
637 // The bonus will be a bit smaller if at least the block square
638 // isn't attacked, otherwise assign the smallest possible bonus.
639 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 3;
641 // Assign a big bonus if the path to the queen is fully defended,
642 // otherwise assign a bit less of a bonus if at least the block
643 // square is defended.
644 if (defendedSquares == squaresToQueen)
647 else if (defendedSquares & blockSq)
648 k += (unsafeSquares & defendedSquares) == unsafeSquares ? 4 : 2;
650 mbonus += Value(k * rr), ebonus += Value(k * rr);
654 // Increase the bonus if the passed pawn is supported by a friendly pawn
655 // on the same rank and a bit smaller if it's on the previous rank.
656 supportingPawns = pos.pieces(Us, PAWN) & adjacent_files_bb(file_of(s));
657 if (supportingPawns & rank_bb(s))
658 ebonus += Value(r * 20);
660 else if (supportingPawns & rank_bb(s - pawn_push(Us)))
661 ebonus += Value(r * 12);
663 // Rook pawns are a special case: They are sometimes worse, and
664 // sometimes better than other passed pawns. It is difficult to find
665 // good rules for determining whether they are good or bad. For now,
666 // we try the following: Increase the value for rook pawns if the
667 // other side has no pieces apart from a knight, and decrease the
668 // value if the other side has a rook or queen.
669 if (file_of(s) == FILE_A || file_of(s) == FILE_H)
671 if (pos.non_pawn_material(Them) <= KnightValueMg)
672 ebonus += ebonus / 4;
674 else if (pos.pieces(Them, ROOK, QUEEN))
675 ebonus -= ebonus / 4;
678 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
679 ebonus += ebonus / 4;
681 score += make_score(mbonus, ebonus);
685 Tracing::terms[Us][Tracing::PASSED] = apply_weight(score, Weights[PassedPawns]);
687 // Add the scores to the middlegame and endgame eval
688 return apply_weight(score, Weights[PassedPawns]);
692 // evaluate_unstoppable_pawns() scores the most advanced among the passed and
693 // candidate pawns. In case opponent has no pieces but pawns, this is somewhat
694 // related to the possibility that pawns are unstoppable.
696 Score evaluate_unstoppable_pawns(const Position& pos, Color us, const EvalInfo& ei) {
698 Bitboard b = ei.pi->passed_pawns(us) | ei.pi->candidate_pawns(us);
700 if (!b || pos.non_pawn_material(~us))
703 return Unstoppable * int(relative_rank(us, frontmost_sq(us, b)));
707 // evaluate_space() computes the space evaluation for a given side. The
708 // space evaluation is a simple bonus based on the number of safe squares
709 // available for minor pieces on the central four files on ranks 2--4. Safe
710 // squares one, two or three squares behind a friendly pawn are counted
711 // twice. Finally, the space bonus is scaled by a weight taken from the
712 // material hash table. The aim is to improve play on game opening.
714 int evaluate_space(const Position& pos, const EvalInfo& ei) {
716 const Color Them = (Us == WHITE ? BLACK : WHITE);
718 // Find the safe squares for our pieces inside the area defined by
719 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
720 // pawn, or if it is undefended and attacked by an enemy piece.
721 Bitboard safe = SpaceMask[Us]
722 & ~pos.pieces(Us, PAWN)
723 & ~ei.attackedBy[Them][PAWN]
724 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
726 // Find all squares which are at most three squares behind some friendly pawn
727 Bitboard behind = pos.pieces(Us, PAWN);
728 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
729 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
731 // Since SpaceMask[Us] is fully on our half of the board
732 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
734 // Count safe + (behind & safe) with a single popcount
735 return popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
739 // do_evaluate() is the evaluation entry point, called directly from evaluate()
742 Value do_evaluate(const Position& pos) {
744 assert(!pos.checkers());
747 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
748 Thread* thisThread = pos.this_thread();
750 // Initialize score by reading the incrementally updated scores included
751 // in the position object (material + piece square tables) and adding a
752 // Tempo bonus. Score is computed from the point of view of white.
753 score = pos.psq_score() + (pos.side_to_move() == WHITE ? Tempo : -Tempo);
755 // Probe the material hash table
756 ei.mi = Material::probe(pos, thisThread->materialTable, thisThread->endgames);
757 score += ei.mi->material_value();
759 // If we have a specialized evaluation function for the current material
760 // configuration, call it and return.
761 if (ei.mi->specialized_eval_exists())
762 return ei.mi->evaluate(pos);
764 // Probe the pawn hash table
765 ei.pi = Pawns::probe(pos, thisThread->pawnsTable);
766 score += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
768 // Initialize attack and king safety bitboards
769 init_eval_info<WHITE>(pos, ei);
770 init_eval_info<BLACK>(pos, ei);
772 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
773 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
775 // Do not include in mobility squares protected by enemy pawns or occupied by our pieces
776 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
777 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
779 // Evaluate pieces and mobility
780 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
781 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
783 // Evaluate kings after all other pieces because we need complete attack
784 // information when computing the king safety evaluation.
785 score += evaluate_king<WHITE, Trace>(pos, ei)
786 - evaluate_king<BLACK, Trace>(pos, ei);
788 // Evaluate tactical threats, we need full attack information including king
789 score += evaluate_threats<WHITE, Trace>(pos, ei)
790 - evaluate_threats<BLACK, Trace>(pos, ei);
792 // Evaluate passed pawns, we need full attack information including king
793 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
794 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
796 // If one side has only a king, score for potential unstoppable pawns
797 if (!pos.non_pawn_material(WHITE) || !pos.non_pawn_material(BLACK))
798 score += evaluate_unstoppable_pawns(pos, WHITE, ei)
799 - evaluate_unstoppable_pawns(pos, BLACK, ei);
801 // Evaluate space for both sides, only in middlegame
802 if (ei.mi->space_weight())
804 int s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
805 score += apply_weight(s * ei.mi->space_weight(), Weights[Space]);
808 // Scale winning side if position is more drawish than it appears
809 ScaleFactor sf = eg_value(score) > VALUE_DRAW ? ei.mi->scale_factor(pos, WHITE)
810 : ei.mi->scale_factor(pos, BLACK);
812 // If we don't already have an unusual scale factor, check for opposite
813 // colored bishop endgames, and use a lower scale for those.
814 if ( ei.mi->game_phase() < PHASE_MIDGAME
815 && pos.opposite_bishops()
816 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
818 // Ignoring any pawns, do both sides only have a single bishop and no
820 if ( pos.non_pawn_material(WHITE) == BishopValueMg
821 && pos.non_pawn_material(BLACK) == BishopValueMg)
823 // Check for KBP vs KB with only a single pawn that is almost
824 // certainly a draw or at least two pawns.
825 bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
826 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
829 // Endgame with opposite-colored bishops, but also other pieces. Still
830 // a bit drawish, but not as drawish as with only the two bishops.
831 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
834 Value v = interpolate(score, ei.mi->game_phase(), sf);
836 // In case of tracing add all single evaluation contributions for both white and black
839 Tracing::add_term(Tracing::PST, pos.psq_score());
840 Tracing::add_term(Tracing::IMBALANCE, ei.mi->material_value());
841 Tracing::add_term(PAWN, ei.pi->pawns_value());
842 Tracing::add_term(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
843 , apply_weight(mobility[BLACK], Weights[Mobility]));
844 Score w = ei.mi->space_weight() * evaluate_space<WHITE>(pos, ei);
845 Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
846 Tracing::add_term(Tracing::SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
847 Tracing::add_term(Tracing::TOTAL, score);
852 return pos.side_to_move() == WHITE ? v : -v;
856 // Tracing function definitions
858 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
860 void Tracing::add_term(int idx, Score wScore, Score bScore) {
862 terms[WHITE][idx] = wScore;
863 terms[BLACK][idx] = bScore;
866 void Tracing::format_row(std::stringstream& ss, const char* name, int idx) {
868 Score wScore = terms[WHITE][idx];
869 Score bScore = terms[BLACK][idx];
872 case PST: case IMBALANCE: case PAWN: case TOTAL:
873 ss << std::setw(20) << name << " | --- --- | --- --- | "
874 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
875 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
878 ss << std::setw(20) << name << " | " << std::noshowpos
879 << std::setw(5) << to_cp(mg_value(wScore)) << " "
880 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
881 << std::setw(5) << to_cp(mg_value(bScore)) << " "
882 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
883 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
884 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
888 std::string Tracing::do_trace(const Position& pos) {
890 std::memset(terms, 0, sizeof(terms));
892 Value v = do_evaluate<true>(pos);
893 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
895 std::stringstream ss;
896 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
897 << " Eval term | White | Black | Total \n"
898 << " | MG EG | MG EG | MG EG \n"
899 << "---------------------+-------------+-------------+-------------\n";
901 format_row(ss, "Material, PST, Tempo", PST);
902 format_row(ss, "Material imbalance", IMBALANCE);
903 format_row(ss, "Pawns", PAWN);
904 format_row(ss, "Knights", KNIGHT);
905 format_row(ss, "Bishops", BISHOP);
906 format_row(ss, "Rooks", ROOK);
907 format_row(ss, "Queens", QUEEN);
908 format_row(ss, "Mobility", MOBILITY);
909 format_row(ss, "King safety", KING);
910 format_row(ss, "Threats", THREAT);
911 format_row(ss, "Passed pawns", PASSED);
912 format_row(ss, "Space", SPACE);
914 ss << "---------------------+-------------+-------------+-------------\n";
915 format_row(ss, "Total", TOTAL);
917 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
927 /// evaluate() is the main evaluation function. It returns a static evaluation
928 /// of the position always from the point of view of the side to move.
930 Value evaluate(const Position& pos) {
931 return do_evaluate<false>(pos);
935 /// trace() is like evaluate(), but instead of returning a value, it returns
936 /// a string (suitable for outputting to stdout) that contains the detailed
937 /// descriptions and values of each evaluation term. It's mainly used for
939 std::string trace(const Position& pos) {
940 return Tracing::do_trace(pos);
944 /// init() computes evaluation weights from the corresponding UCI parameters
945 /// and setup king tables.
949 Weights[Mobility] = weight_option("Mobility (Midgame)", "Mobility (Endgame)", WeightsInternal[Mobility]);
950 Weights[PawnStructure] = weight_option("Pawn Structure (Midgame)", "Pawn Structure (Endgame)", WeightsInternal[PawnStructure]);
951 Weights[PassedPawns] = weight_option("Passed Pawns (Midgame)", "Passed Pawns (Endgame)", WeightsInternal[PassedPawns]);
952 Weights[Space] = weight_option("Space", "Space", WeightsInternal[Space]);
953 Weights[KingDangerUs] = weight_option("Cowardice", "Cowardice", WeightsInternal[KingDangerUs]);
954 Weights[KingDangerThem] = weight_option("Aggressiveness", "Aggressiveness", WeightsInternal[KingDangerThem]);
956 const int MaxSlope = 30;
957 const int Peak = 1280;
959 for (int t = 0, i = 1; i < 100; ++i)
961 t = std::min(Peak, std::min(int(0.4 * i * i), t + MaxSlope));
963 KingDanger[1][i] = apply_weight(make_score(t, 0), Weights[KingDangerUs]);
964 KingDanger[0][i] = apply_weight(make_score(t, 0), Weights[KingDangerThem]);