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 MinorBehindPawn = make_score(16, 0);
170 const Score UndefendedMinor = make_score(25, 10);
171 const Score TrappedRook = make_score(90, 0);
172 const Score Unstoppable = make_score( 0, 20);
174 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
175 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
176 // happen in Chess960 games.
177 const Score TrappedBishopA1H1 = make_score(50, 50);
179 // SpaceMask[Color] contains the area of the board which is considered
180 // by the space evaluation. In the middlegame, each side is given a bonus
181 // based on how many squares inside this area are safe and available for
182 // friendly minor pieces.
183 const Bitboard SpaceMask[] = {
184 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
185 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
188 // King danger constants and variables. The king danger scores are taken
189 // from KingDanger[]. Various little "meta-bonuses" measuring the strength
190 // of the enemy attack are added up into an integer, which is used as an
191 // index to KingDanger[].
193 // KingAttackWeights[PieceType] contains king attack weights by piece type
194 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
196 // Bonuses for enemy's safe checks
197 const int QueenContactCheck = 24;
198 const int RookContactCheck = 16;
199 const int QueenCheck = 12;
200 const int RookCheck = 8;
201 const int BishopCheck = 2;
202 const int KnightCheck = 3;
204 // KingDanger[Color][attackUnits] contains the actual king danger weighted
205 // scores, indexed by color and by a calculated integer number.
206 Score KingDanger[COLOR_NB][128];
209 // apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
210 Score apply_weight(Score v, const Weight& w) {
211 return make_score(mg_value(v) * w.mg / 256, eg_value(v) * w.eg / 256);
215 // weight_option() computes the value of an evaluation weight, by combining
216 // two UCI-configurable weights (midgame and endgame) with an internal weight.
218 Weight weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight) {
220 Weight w = { Options[mgOpt] * mg_value(internalWeight) / 100,
221 Options[egOpt] * eg_value(internalWeight) / 100 };
226 // interpolate() interpolates between a middlegame and an endgame score,
227 // based on game phase. It also scales the return value by a ScaleFactor array.
229 Value interpolate(const Score& v, Phase ph, ScaleFactor sf) {
231 assert(-VALUE_INFINITE < mg_value(v) && mg_value(v) < VALUE_INFINITE);
232 assert(-VALUE_INFINITE < eg_value(v) && eg_value(v) < VALUE_INFINITE);
233 assert(PHASE_ENDGAME <= ph && ph <= PHASE_MIDGAME);
235 int eg = (eg_value(v) * int(sf)) / SCALE_FACTOR_NORMAL;
236 return Value((mg_value(v) * int(ph) + eg * int(PHASE_MIDGAME - ph)) / PHASE_MIDGAME);
240 // init_eval_info() initializes king bitboards for given color adding
241 // pawn attacks. To be done at the beginning of the evaluation.
244 void init_eval_info(const Position& pos, EvalInfo& ei) {
246 const Color Them = (Us == WHITE ? BLACK : WHITE);
247 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
249 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
251 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
252 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
254 // Init king safety tables only if we are going to use them
255 if (pos.count<QUEEN>(Us) && pos.non_pawn_material(Us) > QueenValueMg + PawnValueMg)
257 ei.kingRing[Them] = b | shift_bb<Down>(b);
258 b &= ei.attackedBy[Us][PAWN];
259 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
260 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
263 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
267 // evaluate_outposts() evaluates bishop and knight outpost squares
269 template<PieceType Pt, Color Us>
270 Score evaluate_outposts(const Position& pos, EvalInfo& ei, Square s) {
272 const Color Them = (Us == WHITE ? BLACK : WHITE);
274 assert (Pt == BISHOP || Pt == KNIGHT);
276 // Initial bonus based on square
277 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
279 // Increase bonus if supported by pawn, especially if the opponent has
280 // no minor piece which can trade with the outpost piece.
281 if (bonus && (ei.attackedBy[Us][PAWN] & s))
283 if ( !pos.pieces(Them, KNIGHT)
284 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
285 bonus += bonus + bonus / 2;
290 return make_score(bonus, bonus);
294 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
296 template<PieceType Pt, Color Us, bool Trace>
297 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
301 Score score = SCORE_ZERO;
303 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
304 const Color Them = (Us == WHITE ? BLACK : WHITE);
305 const Square* pl = pos.list<Pt>(Us);
307 ei.attackedBy[Us][Pt] = 0;
309 while ((s = *pl++) != SQ_NONE)
311 // Find attacked squares, including x-ray attacks for bishops and rooks
312 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
313 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
314 : pos.attacks_from<Pt>(s);
316 if (ei.pinnedPieces[Us] & s)
317 b &= LineBB[pos.king_square(Us)][s];
319 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
321 if (b & ei.kingRing[Them])
323 ei.kingAttackersCount[Us]++;
324 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
325 Bitboard bb = b & ei.attackedBy[Them][KING];
327 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
331 b &= ~( ei.attackedBy[Them][KNIGHT]
332 | ei.attackedBy[Them][BISHOP]
333 | ei.attackedBy[Them][ROOK]);
335 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
336 : popcount<Full >(b & mobilityArea[Us]);
338 mobility[Us] += MobilityBonus[Pt][mob];
340 // Decrease score if we are attacked by an enemy pawn. The remaining part
341 // of threat evaluation must be done later when we have full attack info.
342 if (ei.attackedBy[Them][PAWN] & s)
343 score -= ThreatenedByPawn[Pt];
345 if (Pt == BISHOP || Pt == KNIGHT)
347 // Penalty for bishop with same colored pawns
349 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
351 // Bishop and knight outposts squares
352 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
353 score += evaluate_outposts<Pt, Us>(pos, ei, s);
355 // Bishop or knight behind a pawn
356 if ( relative_rank(Us, s) < RANK_5
357 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
358 score += MinorBehindPawn;
363 // Rook on 7th rank and enemy king trapped on 8th
364 if ( relative_rank(Us, s) == RANK_7
365 && relative_rank(Us, pos.king_square(Them)) == RANK_8)
368 // Rook piece attacking enemy pawns on the same rank/file
369 if (relative_rank(Us, s) >= RANK_5)
371 Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
373 score += popcount<Max15>(pawns) * RookOnPawn;
376 // Give a bonus for a rook on a open or semi-open file
377 if (ei.pi->semiopen_file(Us, file_of(s)))
378 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOpenFile : RookSemiopenFile;
380 if (mob > 3 || ei.pi->semiopen_file(Us, file_of(s)))
383 Square ksq = pos.king_square(Us);
385 // Penalize rooks which are trapped by a king. Penalize more if the
386 // king has lost its castling capability.
387 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
388 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
389 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
390 score -= (TrappedRook - make_score(mob * 8, 0)) * (1 + !pos.can_castle(Us));
393 // An important Chess960 pattern: A cornered bishop blocked by a friendly
394 // pawn diagonally in front of it is a very serious problem, especially
395 // when that pawn is also blocked.
398 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
400 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
401 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
402 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
403 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
409 Tracing::terms[Us][Pt] = score;
411 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
415 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
417 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
420 // evaluate_king() assigns bonuses and penalties to a king of a given color
422 template<Color Us, bool Trace>
423 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
425 const Color Them = (Us == WHITE ? BLACK : WHITE);
427 Bitboard undefended, b, b1, b2, safe;
429 const Square ksq = pos.king_square(Us);
431 // King shelter and enemy pawns storm
432 Score score = ei.pi->king_safety<Us>(pos, ksq);
434 // Main king safety evaluation
435 if (ei.kingAttackersCount[Them])
437 // Find the attacked squares around the king which have no defenders
438 // apart from the king itself
439 undefended = ei.attackedBy[Them][ALL_PIECES]
440 & ei.attackedBy[Us][KING]
441 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
442 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
443 | ei.attackedBy[Us][QUEEN]);
445 // Initialize the 'attackUnits' variable, which is used later on as an
446 // index to the KingDanger[] array. The initial value is based on the
447 // number and types of the enemy's attacking pieces, the number of
448 // attacked and undefended squares around our king and the quality of
449 // the pawn shelter (current 'score' value).
450 attackUnits = std::min(20, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
451 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
452 + 2 * (ei.pinnedPieces[Us] != 0)
453 - mg_value(score) / 32;
455 // Analyse the enemy's safe queen contact checks. Firstly, find the
456 // undefended squares around the king that are attacked by the enemy's
458 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
461 // ...and then remove squares not supported by another enemy piece
462 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
463 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
466 attackUnits += QueenContactCheck
468 * (Them == pos.side_to_move() ? 2 : 1);
471 // Analyse the enemy's safe rook contact checks. Firstly, find the
472 // undefended squares around the king that are attacked by the enemy's
474 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
476 // Consider only squares where the enemy's rook gives check
477 b &= PseudoAttacks[ROOK][ksq];
481 // ...and then remove squares not supported by another enemy piece
482 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
483 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
486 attackUnits += RookContactCheck
488 * (Them == pos.side_to_move() ? 2 : 1);
491 // Analyse the enemy's safe distance checks for sliders and knights
492 safe = ~(pos.pieces(Them) | ei.attackedBy[Us][ALL_PIECES]);
494 b1 = pos.attacks_from<ROOK>(ksq) & safe;
495 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
497 // Enemy queen safe checks
498 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
500 attackUnits += QueenCheck * popcount<Max15>(b);
502 // Enemy rooks safe checks
503 b = b1 & ei.attackedBy[Them][ROOK];
505 attackUnits += RookCheck * popcount<Max15>(b);
507 // Enemy bishops safe checks
508 b = b2 & ei.attackedBy[Them][BISHOP];
510 attackUnits += BishopCheck * popcount<Max15>(b);
512 // Enemy knights safe checks
513 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
515 attackUnits += KnightCheck * popcount<Max15>(b);
517 // To index KingDanger[] attackUnits must be in [0, 99] range
518 attackUnits = std::min(99, std::max(0, attackUnits));
520 // Finally, extract the king danger score from the KingDanger[]
521 // array and subtract the score from evaluation.
522 score -= KingDanger[Us == Search::RootColor][attackUnits];
526 Tracing::terms[Us][KING] = score;
532 // evaluate_threats() assigns bonuses according to the type of attacking piece
533 // and the type of attacked one.
535 template<Color Us, bool Trace>
536 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
538 const Color Them = (Us == WHITE ? BLACK : WHITE);
540 Bitboard b, undefendedMinors, weakEnemies;
541 Score score = SCORE_ZERO;
543 // Undefended minors get penalized even if they are not under attack
544 undefendedMinors = pos.pieces(Them, BISHOP, KNIGHT)
545 & ~ei.attackedBy[Them][ALL_PIECES];
547 if (undefendedMinors)
548 score += UndefendedMinor;
550 // Enemy pieces not defended by a pawn and under our attack
551 weakEnemies = pos.pieces(Them)
552 & ~ei.attackedBy[Them][PAWN]
553 & ei.attackedBy[Us][ALL_PIECES];
555 // Add a bonus according if the attacking pieces are minor or major
558 b = weakEnemies & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
560 score += Threat[0][type_of(pos.piece_on(lsb(b)))];
562 b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
564 score += Threat[1][type_of(pos.piece_on(lsb(b)))];
568 Tracing::terms[Us][Tracing::THREAT] = score;
574 // evaluate_passed_pawns() evaluates the passed pawns of the given color
576 template<Color Us, bool Trace>
577 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
579 const Color Them = (Us == WHITE ? BLACK : WHITE);
581 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
582 Score score = SCORE_ZERO;
584 b = ei.pi->passed_pawns(Us);
588 Square s = pop_lsb(&b);
590 assert(pos.pawn_passed(Us, s));
592 int r = int(relative_rank(Us, s) - RANK_2);
593 int rr = r * (r - 1);
595 // Base bonus based on rank
596 Value mbonus = Value(17 * rr);
597 Value ebonus = Value(7 * (rr + r + 1));
601 Square blockSq = s + pawn_push(Us);
603 // Adjust bonus based on the king's proximity
604 ebonus += Value(square_distance(pos.king_square(Them), blockSq) * 5 * rr)
605 - Value(square_distance(pos.king_square(Us ), blockSq) * 2 * rr);
607 // If blockSq is not the queening square then consider also a second push
608 if (relative_rank(Us, blockSq) != RANK_8)
609 ebonus -= Value(rr * square_distance(pos.king_square(Us), blockSq + pawn_push(Us)));
611 // If the pawn is free to advance, then increase the bonus
612 if (pos.empty(blockSq))
614 squaresToQueen = forward_bb(Us, s);
616 // If there is an enemy rook or queen attacking the pawn from behind,
617 // add all X-ray attacks by the rook or queen. Otherwise consider only
618 // the squares in the pawn's path attacked or occupied by the enemy.
619 if ( unlikely(forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN))
620 && (forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
621 unsafeSquares = squaresToQueen;
623 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
625 if ( unlikely(forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN))
626 && (forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
627 defendedSquares = squaresToQueen;
629 defendedSquares = squaresToQueen & ei.attackedBy[Us][ALL_PIECES];
631 // If there aren't any enemy attacks, assign a big bonus. Otherwise
632 // assign a smaller bonus if the block square isn't attacked.
633 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
635 // If the path to queen is fully defended, assign a big bonus.
636 // Otherwise assign a smaller bonus if the block square is defended.
637 if (defendedSquares == squaresToQueen)
640 else if (defendedSquares & blockSq)
643 mbonus += Value(k * rr), ebonus += Value(k * rr);
647 // Rook pawns are a special case: They are sometimes worse, and
648 // sometimes better than other passed pawns. It is difficult to find
649 // good rules for determining whether they are good or bad. For now,
650 // we try the following: Increase the value for rook pawns if the
651 // other side has no pieces apart from a knight, and decrease the
652 // value if the other side has a rook or queen.
653 if (file_of(s) == FILE_A || file_of(s) == FILE_H)
655 if (pos.non_pawn_material(Them) <= KnightValueMg)
656 ebonus += ebonus / 4;
658 else if (pos.pieces(Them, ROOK, QUEEN))
659 ebonus -= ebonus / 4;
662 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
663 ebonus += ebonus / 4;
665 score += make_score(mbonus, ebonus);
669 Tracing::terms[Us][Tracing::PASSED] = apply_weight(score, Weights[PassedPawns]);
671 // Add the scores to the middlegame and endgame eval
672 return apply_weight(score, Weights[PassedPawns]);
676 // evaluate_unstoppable_pawns() scores the most advanced among the passed and
677 // candidate pawns. In case opponent has no pieces but pawns, this is somewhat
678 // related to the possibility that pawns are unstoppable.
680 Score evaluate_unstoppable_pawns(const Position& pos, Color us, const EvalInfo& ei) {
682 Bitboard b = ei.pi->passed_pawns(us) | ei.pi->candidate_pawns(us);
684 if (!b || pos.non_pawn_material(~us))
687 return Unstoppable * int(relative_rank(us, frontmost_sq(us, b)));
691 // evaluate_space() computes the space evaluation for a given side. The
692 // space evaluation is a simple bonus based on the number of safe squares
693 // available for minor pieces on the central four files on ranks 2--4. Safe
694 // squares one, two or three squares behind a friendly pawn are counted
695 // twice. Finally, the space bonus is scaled by a weight taken from the
696 // material hash table. The aim is to improve play on game opening.
698 int evaluate_space(const Position& pos, const EvalInfo& ei) {
700 const Color Them = (Us == WHITE ? BLACK : WHITE);
702 // Find the safe squares for our pieces inside the area defined by
703 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
704 // pawn, or if it is undefended and attacked by an enemy piece.
705 Bitboard safe = SpaceMask[Us]
706 & ~pos.pieces(Us, PAWN)
707 & ~ei.attackedBy[Them][PAWN]
708 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
710 // Find all squares which are at most three squares behind some friendly pawn
711 Bitboard behind = pos.pieces(Us, PAWN);
712 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
713 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
715 // Since SpaceMask[Us] is fully on our half of the board
716 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
718 // Count safe + (behind & safe) with a single popcount
719 return popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
723 // do_evaluate() is the evaluation entry point, called directly from evaluate()
726 Value do_evaluate(const Position& pos) {
728 assert(!pos.checkers());
731 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
732 Thread* thisThread = pos.this_thread();
734 // Initialize score by reading the incrementally updated scores included
735 // in the position object (material + piece square tables) and adding a
736 // Tempo bonus. Score is computed from the point of view of white.
737 score = pos.psq_score() + (pos.side_to_move() == WHITE ? Tempo : -Tempo);
739 // Probe the material hash table
740 ei.mi = Material::probe(pos, thisThread->materialTable, thisThread->endgames);
741 score += ei.mi->material_value();
743 // If we have a specialized evaluation function for the current material
744 // configuration, call it and return.
745 if (ei.mi->specialized_eval_exists())
746 return ei.mi->evaluate(pos);
748 // Probe the pawn hash table
749 ei.pi = Pawns::probe(pos, thisThread->pawnsTable);
750 score += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
752 // Initialize attack and king safety bitboards
753 init_eval_info<WHITE>(pos, ei);
754 init_eval_info<BLACK>(pos, ei);
756 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
757 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
759 // Do not include in mobility squares protected by enemy pawns or occupied by our pieces
760 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
761 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
763 // Evaluate pieces and mobility
764 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
765 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
767 // Evaluate kings after all other pieces because we need complete attack
768 // information when computing the king safety evaluation.
769 score += evaluate_king<WHITE, Trace>(pos, ei)
770 - evaluate_king<BLACK, Trace>(pos, ei);
772 // Evaluate tactical threats, we need full attack information including king
773 score += evaluate_threats<WHITE, Trace>(pos, ei)
774 - evaluate_threats<BLACK, Trace>(pos, ei);
776 // Evaluate passed pawns, we need full attack information including king
777 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
778 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
780 // If one side has only a king, score for potential unstoppable pawns
781 if (!pos.non_pawn_material(WHITE) || !pos.non_pawn_material(BLACK))
782 score += evaluate_unstoppable_pawns(pos, WHITE, ei)
783 - evaluate_unstoppable_pawns(pos, BLACK, ei);
785 // Evaluate space for both sides, only in middlegame
786 if (ei.mi->space_weight())
788 int s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
789 score += apply_weight(s * ei.mi->space_weight(), Weights[Space]);
792 // Scale winning side if position is more drawish than it appears
793 ScaleFactor sf = eg_value(score) > VALUE_DRAW ? ei.mi->scale_factor(pos, WHITE)
794 : ei.mi->scale_factor(pos, BLACK);
796 // If we don't already have an unusual scale factor, check for opposite
797 // colored bishop endgames, and use a lower scale for those.
798 if ( ei.mi->game_phase() < PHASE_MIDGAME
799 && pos.opposite_bishops()
800 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
802 // Ignoring any pawns, do both sides only have a single bishop and no
804 if ( pos.non_pawn_material(WHITE) == BishopValueMg
805 && pos.non_pawn_material(BLACK) == BishopValueMg)
807 // Check for KBP vs KB with only a single pawn that is almost
808 // certainly a draw or at least two pawns.
809 bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
810 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
813 // Endgame with opposite-colored bishops, but also other pieces. Still
814 // a bit drawish, but not as drawish as with only the two bishops.
815 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
818 Value v = interpolate(score, ei.mi->game_phase(), sf);
820 // In case of tracing add all single evaluation contributions for both white and black
823 Tracing::add_term(Tracing::PST, pos.psq_score());
824 Tracing::add_term(Tracing::IMBALANCE, ei.mi->material_value());
825 Tracing::add_term(PAWN, ei.pi->pawns_value());
826 Tracing::add_term(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
827 , apply_weight(mobility[BLACK], Weights[Mobility]));
828 Score w = ei.mi->space_weight() * evaluate_space<WHITE>(pos, ei);
829 Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
830 Tracing::add_term(Tracing::SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
831 Tracing::add_term(Tracing::TOTAL, score);
836 return pos.side_to_move() == WHITE ? v : -v;
840 // Tracing function definitions
842 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
844 void Tracing::add_term(int idx, Score wScore, Score bScore) {
846 terms[WHITE][idx] = wScore;
847 terms[BLACK][idx] = bScore;
850 void Tracing::format_row(std::stringstream& ss, const char* name, int idx) {
852 Score wScore = terms[WHITE][idx];
853 Score bScore = terms[BLACK][idx];
856 case PST: case IMBALANCE: case PAWN: case TOTAL:
857 ss << std::setw(20) << name << " | --- --- | --- --- | "
858 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
859 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
862 ss << std::setw(20) << name << " | " << std::noshowpos
863 << std::setw(5) << to_cp(mg_value(wScore)) << " "
864 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
865 << std::setw(5) << to_cp(mg_value(bScore)) << " "
866 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
867 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
868 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
872 std::string Tracing::do_trace(const Position& pos) {
874 std::memset(terms, 0, sizeof(terms));
876 Value v = do_evaluate<true>(pos);
877 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
879 std::stringstream ss;
880 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
881 << " Eval term | White | Black | Total \n"
882 << " | MG EG | MG EG | MG EG \n"
883 << "---------------------+-------------+-------------+-------------\n";
885 format_row(ss, "Material, PST, Tempo", PST);
886 format_row(ss, "Material imbalance", IMBALANCE);
887 format_row(ss, "Pawns", PAWN);
888 format_row(ss, "Knights", KNIGHT);
889 format_row(ss, "Bishops", BISHOP);
890 format_row(ss, "Rooks", ROOK);
891 format_row(ss, "Queens", QUEEN);
892 format_row(ss, "Mobility", MOBILITY);
893 format_row(ss, "King safety", KING);
894 format_row(ss, "Threats", THREAT);
895 format_row(ss, "Passed pawns", PASSED);
896 format_row(ss, "Space", SPACE);
898 ss << "---------------------+-------------+-------------+-------------\n";
899 format_row(ss, "Total", TOTAL);
901 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
911 /// evaluate() is the main evaluation function. It returns a static evaluation
912 /// of the position always from the point of view of the side to move.
914 Value evaluate(const Position& pos) {
915 return do_evaluate<false>(pos);
919 /// trace() is like evaluate(), but instead of returning a value, it returns
920 /// a string (suitable for outputting to stdout) that contains the detailed
921 /// descriptions and values of each evaluation term. It's mainly used for
923 std::string trace(const Position& pos) {
924 return Tracing::do_trace(pos);
928 /// init() computes evaluation weights from the corresponding UCI parameters
929 /// and setup king tables.
933 Weights[Mobility] = weight_option("Mobility (Midgame)", "Mobility (Endgame)", WeightsInternal[Mobility]);
934 Weights[PawnStructure] = weight_option("Pawn Structure (Midgame)", "Pawn Structure (Endgame)", WeightsInternal[PawnStructure]);
935 Weights[PassedPawns] = weight_option("Passed Pawns (Midgame)", "Passed Pawns (Endgame)", WeightsInternal[PassedPawns]);
936 Weights[Space] = weight_option("Space", "Space", WeightsInternal[Space]);
937 Weights[KingDangerUs] = weight_option("Cowardice", "Cowardice", WeightsInternal[KingDangerUs]);
938 Weights[KingDangerThem] = weight_option("Aggressiveness", "Aggressiveness", WeightsInternal[KingDangerThem]);
940 const int MaxSlope = 30;
941 const int Peak = 1280;
943 for (int t = 0, i = 1; i < 100; ++i)
945 t = std::min(Peak, std::min(int(0.4 * i * i), t + MaxSlope));
947 KingDanger[1][i] = apply_weight(make_score(t, 0), Weights[KingDangerUs]);
948 KingDanger[0][i] = apply_weight(make_score(t, 0), Weights[KingDangerThem]);