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)
161 // Hanging[side to move] contains a bonus for each enemy hanging piece
162 const Score Hanging[2] = { S(23, 20) , S(35, 45) };
166 const Score Tempo = make_score(24, 11);
167 const Score RookOnPawn = make_score(10, 28);
168 const Score RookOpenFile = make_score(43, 21);
169 const Score RookSemiopenFile = make_score(19, 10);
170 const Score BishopPawns = make_score( 8, 12);
171 const Score MinorBehindPawn = make_score(16, 0);
172 const Score UndefendedMinor = make_score(25, 10);
173 const Score TrappedRook = make_score(90, 0);
174 const Score Unstoppable = make_score( 0, 20);
176 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
177 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
178 // happen in Chess960 games.
179 const Score TrappedBishopA1H1 = make_score(50, 50);
181 // SpaceMask[Color] contains the area of the board which is considered
182 // by the space evaluation. In the middlegame, each side is given a bonus
183 // based on how many squares inside this area are safe and available for
184 // friendly minor pieces.
185 const Bitboard SpaceMask[] = {
186 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
187 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
190 // King danger constants and variables. The king danger scores are taken
191 // from KingDanger[]. Various little "meta-bonuses" measuring the strength
192 // of the enemy attack are added up into an integer, which is used as an
193 // index to KingDanger[].
195 // KingAttackWeights[PieceType] contains king attack weights by piece type
196 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
198 // Bonuses for enemy's safe checks
199 const int QueenContactCheck = 24;
200 const int RookContactCheck = 16;
201 const int QueenCheck = 12;
202 const int RookCheck = 8;
203 const int BishopCheck = 2;
204 const int KnightCheck = 3;
206 // KingDanger[Color][attackUnits] contains the actual king danger weighted
207 // scores, indexed by color and by a calculated integer number.
208 Score KingDanger[COLOR_NB][128];
211 // apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
212 Score apply_weight(Score v, const Weight& w) {
213 return make_score(mg_value(v) * w.mg / 256, eg_value(v) * w.eg / 256);
217 // weight_option() computes the value of an evaluation weight, by combining
218 // two UCI-configurable weights (midgame and endgame) with an internal weight.
220 Weight weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight) {
222 Weight w = { Options[mgOpt] * mg_value(internalWeight) / 100,
223 Options[egOpt] * eg_value(internalWeight) / 100 };
228 // init_eval_info() initializes king bitboards for given color adding
229 // pawn attacks. To be done at the beginning of the evaluation.
232 void init_eval_info(const Position& pos, EvalInfo& ei) {
234 const Color Them = (Us == WHITE ? BLACK : WHITE);
235 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
237 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
239 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
240 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
242 // Init king safety tables only if we are going to use them
243 if (pos.count<QUEEN>(Us) && pos.non_pawn_material(Us) > QueenValueMg + PawnValueMg)
245 ei.kingRing[Them] = b | shift_bb<Down>(b);
246 b &= ei.attackedBy[Us][PAWN];
247 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
248 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
251 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
255 // evaluate_outposts() evaluates bishop and knight outpost squares
257 template<PieceType Pt, Color Us>
258 Score evaluate_outposts(const Position& pos, EvalInfo& ei, Square s) {
260 const Color Them = (Us == WHITE ? BLACK : WHITE);
262 assert (Pt == BISHOP || Pt == KNIGHT);
264 // Initial bonus based on square
265 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
267 // Increase bonus if supported by pawn, especially if the opponent has
268 // no minor piece which can trade with the outpost piece.
269 if (bonus && (ei.attackedBy[Us][PAWN] & s))
271 if ( !pos.pieces(Them, KNIGHT)
272 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
273 bonus += bonus + bonus / 2;
278 return make_score(bonus, bonus);
282 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
284 template<PieceType Pt, Color Us, bool Trace>
285 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
289 Score score = SCORE_ZERO;
291 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
292 const Color Them = (Us == WHITE ? BLACK : WHITE);
293 const Square* pl = pos.list<Pt>(Us);
295 ei.attackedBy[Us][Pt] = 0;
297 while ((s = *pl++) != SQ_NONE)
299 // Find attacked squares, including x-ray attacks for bishops and rooks
300 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
301 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
302 : pos.attacks_from<Pt>(s);
304 if (ei.pinnedPieces[Us] & s)
305 b &= LineBB[pos.king_square(Us)][s];
307 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
309 if (b & ei.kingRing[Them])
311 ei.kingAttackersCount[Us]++;
312 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
313 Bitboard bb = b & ei.attackedBy[Them][KING];
315 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
319 b &= ~( ei.attackedBy[Them][KNIGHT]
320 | ei.attackedBy[Them][BISHOP]
321 | ei.attackedBy[Them][ROOK]);
323 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
324 : popcount<Full >(b & mobilityArea[Us]);
326 mobility[Us] += MobilityBonus[Pt][mob];
328 // Decrease score if we are attacked by an enemy pawn. The remaining part
329 // of threat evaluation must be done later when we have full attack info.
330 if (ei.attackedBy[Them][PAWN] & s)
331 score -= ThreatenedByPawn[Pt];
333 if (Pt == BISHOP || Pt == KNIGHT)
335 // Penalty for bishop with same colored pawns
337 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
339 // Bishop and knight outposts squares
340 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
341 score += evaluate_outposts<Pt, Us>(pos, ei, s);
343 // Bishop or knight behind a pawn
344 if ( relative_rank(Us, s) < RANK_5
345 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
346 score += MinorBehindPawn;
351 // Rook piece attacking enemy pawns on the same rank/file
352 if (relative_rank(Us, s) >= RANK_5)
354 Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
356 score += popcount<Max15>(pawns) * RookOnPawn;
359 // Give a bonus for a rook on a open or semi-open file
360 if (ei.pi->semiopen_file(Us, file_of(s)))
361 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOpenFile : RookSemiopenFile;
363 if (mob > 3 || ei.pi->semiopen_file(Us, file_of(s)))
366 Square ksq = pos.king_square(Us);
368 // Penalize rooks which are trapped by a king. Penalize more if the
369 // king has lost its castling capability.
370 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
371 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
372 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
373 score -= (TrappedRook - make_score(mob * 8, 0)) * (1 + !pos.can_castle(Us));
376 // An important Chess960 pattern: A cornered bishop blocked by a friendly
377 // pawn diagonally in front of it is a very serious problem, especially
378 // when that pawn is also blocked.
381 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
383 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
384 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
385 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
386 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
392 Tracing::terms[Us][Pt] = score;
394 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
398 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
400 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
403 // evaluate_king() assigns bonuses and penalties to a king of a given color
405 template<Color Us, bool Trace>
406 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
408 const Color Them = (Us == WHITE ? BLACK : WHITE);
410 Bitboard undefended, b, b1, b2, safe;
412 const Square ksq = pos.king_square(Us);
414 // King shelter and enemy pawns storm
415 Score score = ei.pi->king_safety<Us>(pos, ksq);
417 // Main king safety evaluation
418 if (ei.kingAttackersCount[Them])
420 // Find the attacked squares around the king which have no defenders
421 // apart from the king itself
422 undefended = ei.attackedBy[Them][ALL_PIECES]
423 & ei.attackedBy[Us][KING]
424 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
425 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
426 | ei.attackedBy[Us][QUEEN]);
428 // Initialize the 'attackUnits' variable, which is used later on as an
429 // index to the KingDanger[] array. The initial value is based on the
430 // number and types of the enemy's attacking pieces, the number of
431 // attacked and undefended squares around our king and the quality of
432 // the pawn shelter (current 'score' value).
433 attackUnits = std::min(20, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
434 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
435 + 2 * (ei.pinnedPieces[Us] != 0)
436 - mg_value(score) / 32;
438 // Analyse the enemy's safe queen contact checks. Firstly, find the
439 // undefended squares around the king that are attacked by the enemy's
441 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
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][ROOK]);
449 attackUnits += QueenContactCheck
451 * (Them == pos.side_to_move() ? 2 : 1);
454 // Analyse the enemy's safe rook contact checks. Firstly, find the
455 // undefended squares around the king that are attacked by the enemy's
457 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
459 // Consider only squares where the enemy's rook gives check
460 b &= PseudoAttacks[ROOK][ksq];
464 // ...and then remove squares not supported by another enemy piece
465 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
466 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
469 attackUnits += RookContactCheck
471 * (Them == pos.side_to_move() ? 2 : 1);
474 // Analyse the enemy's safe distance checks for sliders and knights
475 safe = ~(pos.pieces(Them) | ei.attackedBy[Us][ALL_PIECES]);
477 b1 = pos.attacks_from<ROOK>(ksq) & safe;
478 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
480 // Enemy queen safe checks
481 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
483 attackUnits += QueenCheck * popcount<Max15>(b);
485 // Enemy rooks safe checks
486 b = b1 & ei.attackedBy[Them][ROOK];
488 attackUnits += RookCheck * popcount<Max15>(b);
490 // Enemy bishops safe checks
491 b = b2 & ei.attackedBy[Them][BISHOP];
493 attackUnits += BishopCheck * popcount<Max15>(b);
495 // Enemy knights safe checks
496 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
498 attackUnits += KnightCheck * popcount<Max15>(b);
500 // To index KingDanger[] attackUnits must be in [0, 99] range
501 attackUnits = std::min(99, std::max(0, attackUnits));
503 // Finally, extract the king danger score from the KingDanger[]
504 // array and subtract the score from evaluation.
505 score -= KingDanger[Us == Search::RootColor][attackUnits];
509 Tracing::terms[Us][KING] = score;
515 // evaluate_threats() assigns bonuses according to the type of attacking piece
516 // and the type of attacked one.
518 template<Color Us, bool Trace>
519 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
521 const Color Them = (Us == WHITE ? BLACK : WHITE);
523 Bitboard b, undefendedMinors, weakEnemies;
524 Score score = SCORE_ZERO;
526 // Undefended minors get penalized even if they are not under attack
527 undefendedMinors = pos.pieces(Them, BISHOP, KNIGHT)
528 & ~ei.attackedBy[Them][ALL_PIECES];
530 if (undefendedMinors)
531 score += UndefendedMinor;
533 // Enemies not defended by a pawn and under our attack
534 weakEnemies = pos.pieces(Them)
535 & ~ei.attackedBy[Them][PAWN]
536 & ei.attackedBy[Us][ALL_PIECES];
538 // Add a bonus according if the attacking pieces are minor or major
541 b = weakEnemies & (ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
543 score += Threat[0][type_of(pos.piece_on(lsb(b)))];
545 b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
547 score += Threat[1][type_of(pos.piece_on(lsb(b)))];
549 b = weakEnemies & ~ei.attackedBy[Them][ALL_PIECES];
551 score += more_than_one(b) ? Hanging[Us != pos.side_to_move()] * popcount<Max15>(b)
552 : Hanging[Us == pos.side_to_move()];
556 Tracing::terms[Us][Tracing::THREAT] = score;
562 // evaluate_passed_pawns() evaluates the passed pawns of the given color
564 template<Color Us, bool Trace>
565 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
567 const Color Them = (Us == WHITE ? BLACK : WHITE);
569 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
570 Score score = SCORE_ZERO;
572 b = ei.pi->passed_pawns(Us);
576 Square s = pop_lsb(&b);
578 assert(pos.pawn_passed(Us, s));
580 int r = relative_rank(Us, s) - RANK_2;
581 int rr = r * (r - 1);
583 // Base bonus based on rank
584 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
588 Square blockSq = s + pawn_push(Us);
590 // Adjust bonus based on the king's proximity
591 ebonus += square_distance(pos.king_square(Them), blockSq) * 5 * rr
592 - square_distance(pos.king_square(Us ), blockSq) * 2 * rr;
594 // If blockSq is not the queening square then consider also a second push
595 if (relative_rank(Us, blockSq) != RANK_8)
596 ebonus -= square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
598 // If the pawn is free to advance, then increase the bonus
599 if (pos.empty(blockSq))
601 squaresToQueen = forward_bb(Us, s);
603 // If there is an enemy rook or queen attacking the pawn from behind,
604 // add all X-ray attacks by the rook or queen. Otherwise consider only
605 // the squares in the pawn's path attacked or occupied by the enemy.
606 if ( unlikely(forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN))
607 && (forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
608 unsafeSquares = squaresToQueen;
610 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
612 if ( unlikely(forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN))
613 && (forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
614 defendedSquares = squaresToQueen;
616 defendedSquares = squaresToQueen & ei.attackedBy[Us][ALL_PIECES];
618 // If there aren't any enemy attacks, assign a big bonus. Otherwise
619 // assign a smaller bonus if the block square isn't attacked.
620 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
622 // If the path to queen is fully defended, assign a big bonus.
623 // Otherwise assign a smaller bonus if the block square is defended.
624 if (defendedSquares == squaresToQueen)
627 else if (defendedSquares & blockSq)
630 mbonus += k * rr, ebonus += k * rr;
634 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
635 ebonus += ebonus / 4;
637 score += make_score(mbonus, ebonus);
641 Tracing::terms[Us][Tracing::PASSED] = apply_weight(score, Weights[PassedPawns]);
643 // Add the scores to the middlegame and endgame eval
644 return apply_weight(score, Weights[PassedPawns]);
648 // evaluate_unstoppable_pawns() scores the most advanced among the passed and
649 // candidate pawns. In case opponent has no pieces but pawns, this is somewhat
650 // related to the possibility that pawns are unstoppable.
652 Score evaluate_unstoppable_pawns(const Position& pos, Color us, const EvalInfo& ei) {
654 Bitboard b = ei.pi->passed_pawns(us) | ei.pi->candidate_pawns(us);
656 if (!b || pos.non_pawn_material(~us))
659 return Unstoppable * int(relative_rank(us, frontmost_sq(us, b)));
663 // evaluate_space() computes the space evaluation for a given side. The
664 // space evaluation is a simple bonus based on the number of safe squares
665 // available for minor pieces on the central four files on ranks 2--4. Safe
666 // squares one, two or three squares behind a friendly pawn are counted
667 // twice. Finally, the space bonus is scaled by a weight taken from the
668 // material hash table. The aim is to improve play on game opening.
670 int evaluate_space(const Position& pos, const EvalInfo& ei) {
672 const Color Them = (Us == WHITE ? BLACK : WHITE);
674 // Find the safe squares for our pieces inside the area defined by
675 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
676 // pawn, or if it is undefended and attacked by an enemy piece.
677 Bitboard safe = SpaceMask[Us]
678 & ~pos.pieces(Us, PAWN)
679 & ~ei.attackedBy[Them][PAWN]
680 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
682 // Find all squares which are at most three squares behind some friendly pawn
683 Bitboard behind = pos.pieces(Us, PAWN);
684 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
685 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
687 // Since SpaceMask[Us] is fully on our half of the board
688 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
690 // Count safe + (behind & safe) with a single popcount
691 return popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
695 // do_evaluate() is the evaluation entry point, called directly from evaluate()
698 Value do_evaluate(const Position& pos) {
700 assert(!pos.checkers());
703 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
704 Thread* thisThread = pos.this_thread();
706 // Initialize score by reading the incrementally updated scores included
707 // in the position object (material + piece square tables) and adding a
708 // Tempo bonus. Score is computed from the point of view of white.
709 score = pos.psq_score() + (pos.side_to_move() == WHITE ? Tempo : -Tempo);
711 // Probe the material hash table
712 ei.mi = Material::probe(pos, thisThread->materialTable, thisThread->endgames);
713 score += ei.mi->material_value();
715 // If we have a specialized evaluation function for the current material
716 // configuration, call it and return.
717 if (ei.mi->specialized_eval_exists())
718 return ei.mi->evaluate(pos);
720 // Probe the pawn hash table
721 ei.pi = Pawns::probe(pos, thisThread->pawnsTable);
722 score += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
724 // Initialize attack and king safety bitboards
725 init_eval_info<WHITE>(pos, ei);
726 init_eval_info<BLACK>(pos, ei);
728 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
729 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
731 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
732 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
733 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
735 // Evaluate pieces and mobility
736 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
737 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
739 // Evaluate kings after all other pieces because we need complete attack
740 // information when computing the king safety evaluation.
741 score += evaluate_king<WHITE, Trace>(pos, ei)
742 - evaluate_king<BLACK, Trace>(pos, ei);
744 // Evaluate tactical threats, we need full attack information including king
745 score += evaluate_threats<WHITE, Trace>(pos, ei)
746 - evaluate_threats<BLACK, Trace>(pos, ei);
748 // Evaluate passed pawns, we need full attack information including king
749 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
750 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
752 // If one side has only a king, score for potential unstoppable pawns
753 if (!pos.non_pawn_material(WHITE) || !pos.non_pawn_material(BLACK))
754 score += evaluate_unstoppable_pawns(pos, WHITE, ei)
755 - evaluate_unstoppable_pawns(pos, BLACK, ei);
757 // Evaluate space for both sides, only in middlegame
758 if (ei.mi->space_weight())
760 int s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
761 score += apply_weight(s * ei.mi->space_weight(), Weights[Space]);
764 // Scale winning side if position is more drawish than it appears
765 ScaleFactor sf = eg_value(score) > VALUE_DRAW ? ei.mi->scale_factor(pos, WHITE)
766 : ei.mi->scale_factor(pos, BLACK);
768 // If we don't already have an unusual scale factor, check for opposite
769 // colored bishop endgames, and use a lower scale for those.
770 if ( ei.mi->game_phase() < PHASE_MIDGAME
771 && pos.opposite_bishops()
772 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
774 // Ignoring any pawns, do both sides only have a single bishop and no
776 if ( pos.non_pawn_material(WHITE) == BishopValueMg
777 && pos.non_pawn_material(BLACK) == BishopValueMg)
779 // Check for KBP vs KB with only a single pawn that is almost
780 // certainly a draw or at least two pawns.
781 bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
782 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
785 // Endgame with opposite-colored bishops, but also other pieces. Still
786 // a bit drawish, but not as drawish as with only the two bishops.
787 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
790 // Stealmate detection
791 Color stm = pos.side_to_move();
792 if ( (ei.attackedBy[stm][ALL_PIECES] == ei.attackedBy[stm][KING])
793 && (!(ei.attackedBy[stm][KING] & ~ei.attackedBy[~stm][ALL_PIECES]))
794 && !MoveList<LEGAL>(pos).size())
795 sf = SCALE_FACTOR_DRAW;
797 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
798 Value v = mg_value(score) * int(ei.mi->game_phase())
799 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
801 v /= int(PHASE_MIDGAME);
803 // In case of tracing add all single evaluation contributions for both white and black
806 Tracing::add_term(Tracing::PST, pos.psq_score());
807 Tracing::add_term(Tracing::IMBALANCE, ei.mi->material_value());
808 Tracing::add_term(PAWN, ei.pi->pawns_value());
809 Tracing::add_term(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
810 , apply_weight(mobility[BLACK], Weights[Mobility]));
811 Score w = ei.mi->space_weight() * evaluate_space<WHITE>(pos, ei);
812 Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
813 Tracing::add_term(Tracing::SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
814 Tracing::add_term(Tracing::TOTAL, score);
819 return pos.side_to_move() == WHITE ? v : -v;
823 // Tracing function definitions
825 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
827 void Tracing::add_term(int idx, Score wScore, Score bScore) {
829 terms[WHITE][idx] = wScore;
830 terms[BLACK][idx] = bScore;
833 void Tracing::format_row(std::stringstream& ss, const char* name, int idx) {
835 Score wScore = terms[WHITE][idx];
836 Score bScore = terms[BLACK][idx];
839 case PST: case IMBALANCE: case PAWN: case TOTAL:
840 ss << std::setw(20) << 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(20) << 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(terms, 0, sizeof(terms));
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 format_row(ss, "Material, PST, Tempo", PST);
869 format_row(ss, "Material imbalance", IMBALANCE);
870 format_row(ss, "Pawns", PAWN);
871 format_row(ss, "Knights", KNIGHT);
872 format_row(ss, "Bishops", BISHOP);
873 format_row(ss, "Rooks", ROOK);
874 format_row(ss, "Queens", QUEEN);
875 format_row(ss, "Mobility", MOBILITY);
876 format_row(ss, "King safety", KING);
877 format_row(ss, "Threats", THREAT);
878 format_row(ss, "Passed pawns", PASSED);
879 format_row(ss, "Space", SPACE);
881 ss << "---------------------+-------------+-------------+-------------\n";
882 format_row(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 from the corresponding UCI parameters
912 /// and setup king tables.
916 Weights[Mobility] = weight_option("Mobility (Midgame)", "Mobility (Endgame)", WeightsInternal[Mobility]);
917 Weights[PawnStructure] = weight_option("Pawn Structure (Midgame)", "Pawn Structure (Endgame)", WeightsInternal[PawnStructure]);
918 Weights[PassedPawns] = weight_option("Passed Pawns (Midgame)", "Passed Pawns (Endgame)", WeightsInternal[PassedPawns]);
919 Weights[Space] = weight_option("Space", "Space", WeightsInternal[Space]);
920 Weights[KingDangerUs] = weight_option("Cowardice", "Cowardice", WeightsInternal[KingDangerUs]);
921 Weights[KingDangerThem] = weight_option("Aggressiveness", "Aggressiveness", WeightsInternal[KingDangerThem]);
923 const double MaxSlope = 30;
924 const double Peak = 1280;
926 for (int t = 0, i = 1; i < 100; ++i)
928 t = int(std::min(Peak, std::min(0.4 * i * i, t + MaxSlope)));
930 KingDanger[1][i] = apply_weight(make_score(t, 0), Weights[KingDangerUs]);
931 KingDanger[0][i] = apply_weight(make_score(t, 0), Weights[KingDangerThem]);