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 MATERIAL = 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, indexed by evaluation term
93 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
94 const struct Weight { int mg, eg; } Weights[] = {
95 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {318, 0}
99 #define S(mg, eg) make_score(mg, eg)
101 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
102 // game, indexed by piece type and number of attacked squares not occupied by
104 const Score MobilityBonus[][32] = {
106 { S(-65,-50), S(-42,-30), S(-9,-10), S( 3, 0), S(15, 10), S(27, 20), // Knights
107 S( 37, 28), S( 42, 31), S(44, 33) },
108 { S(-52,-47), S(-28,-23), S( 6, 1), S(20, 15), S(34, 29), S(48, 43), // Bishops
109 S( 60, 55), S( 68, 63), S(74, 68), S(77, 72), S(80, 75), S(82, 77),
110 S( 84, 79), S( 86, 81) },
111 { S(-47,-53), S(-31,-26), S(-5, 0), S( 1, 16), S( 7, 32), S(13, 48), // Rooks
112 S( 18, 64), S( 22, 80), S(26, 96), S(29,109), S(31,115), S(33,119),
113 S( 35,122), S( 36,123), S(37,124) },
114 { S(-42,-40), S(-28,-23), S(-5, -7), S( 0, 0), S( 6, 10), S(11, 19), // Queens
115 S( 13, 29), S( 18, 38), S(20, 40), S(21, 41), S(22, 41), S(22, 41),
116 S( 22, 41), S( 23, 41), S(24, 41), S(25, 41), S(25, 41), S(25, 41),
117 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41), S(25, 41), S(25, 41),
118 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41) }
121 // Outpost[PieceType][Square] contains bonuses for knights and bishops outposts,
122 // indexed by piece type and square (from white's point of view).
123 const Value Outpost[][SQUARE_NB] = {
125 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
126 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
127 V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0),
128 V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0),
129 V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0),
130 V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0) },
132 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
133 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
134 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
135 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
136 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
137 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0) }
140 // Threat[attacking][attacked] contains bonuses according to which piece
141 // type attacks which one.
142 const Score Threat[][PIECE_TYPE_NB] = {
143 { S(0, 0), S( 7, 39), S(24, 49), S(24, 49), S(41,100), S(41,100) }, // Minor
144 { S(0, 0), S(15, 39), S(15, 45), S(15, 45), S(15, 45), S(24, 49) } // Major
147 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
148 // type is attacked by an enemy pawn.
149 const Score ThreatenedByPawn[] = {
150 S(0, 0), S(0, 0), S(80, 119), S(80, 119), S(117, 199), S(127, 218)
153 // Hanging contains a bonus for each enemy hanging piece
154 const Score Hanging = S(23, 20);
158 const Score RookOnPawn = make_score(10, 28);
159 const Score RookOpenFile = make_score(43, 21);
160 const Score RookSemiopenFile = make_score(19, 10);
161 const Score BishopPawns = make_score( 8, 12);
162 const Score MinorBehindPawn = make_score(16, 0);
163 const Score TrappedRook = make_score(92, 0);
164 const Score Unstoppable = make_score( 0, 20);
166 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
167 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
168 // happen in Chess960 games.
169 const Score TrappedBishopA1H1 = make_score(50, 50);
171 // SpaceMask[Color] contains the area of the board which is considered
172 // by the space evaluation. In the middlegame, each side is given a bonus
173 // based on how many squares inside this area are safe and available for
174 // friendly minor pieces.
175 const Bitboard SpaceMask[] = {
176 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
177 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
180 // King danger constants and variables. The king danger scores are taken
181 // from KingDanger[]. Various little "meta-bonuses" measuring the strength
182 // of the enemy attack are added up into an integer, which is used as an
183 // index to KingDanger[].
185 // KingAttackWeights[PieceType] contains king attack weights by piece type
186 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
188 // Bonuses for enemy's safe checks
189 const int QueenContactCheck = 24;
190 const int RookContactCheck = 16;
191 const int QueenCheck = 12;
192 const int RookCheck = 8;
193 const int BishopCheck = 2;
194 const int KnightCheck = 3;
196 // KingDanger[attackUnits] contains the actual king danger weighted
197 // scores, indexed by a calculated integer number.
198 Score KingDanger[128];
200 const int ScalePawnSpan[2] = { 38, 56 };
202 // apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
203 Score apply_weight(Score v, const Weight& w) {
204 return make_score(mg_value(v) * w.mg / 256, eg_value(v) * w.eg / 256);
208 // init_eval_info() initializes king bitboards for given color adding
209 // pawn attacks. To be done at the beginning of the evaluation.
212 void init_eval_info(const Position& pos, EvalInfo& ei) {
214 const Color Them = (Us == WHITE ? BLACK : WHITE);
215 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
217 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
219 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
220 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
222 // Init king safety tables only if we are going to use them
223 if (pos.count<QUEEN>(Us) && pos.non_pawn_material(Us) > QueenValueMg + PawnValueMg)
225 ei.kingRing[Them] = b | shift_bb<Down>(b);
226 b &= ei.attackedBy[Us][PAWN];
227 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
228 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
231 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
235 // evaluate_outpost() evaluates bishop and knight outpost squares
237 template<PieceType Pt, Color Us>
238 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
240 const Color Them = (Us == WHITE ? BLACK : WHITE);
242 assert (Pt == BISHOP || Pt == KNIGHT);
244 // Initial bonus based on square
245 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
247 // Increase bonus if supported by pawn, especially if the opponent has
248 // no minor piece which can trade with the outpost piece.
249 if (bonus && (ei.attackedBy[Us][PAWN] & s))
251 if ( !pos.pieces(Them, KNIGHT)
252 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
253 bonus += bonus + bonus / 2;
258 return make_score(bonus, bonus);
262 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
264 template<PieceType Pt, Color Us, bool Trace>
265 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
269 Score score = SCORE_ZERO;
271 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
272 const Color Them = (Us == WHITE ? BLACK : WHITE);
273 const Square* pl = pos.list<Pt>(Us);
275 ei.attackedBy[Us][Pt] = 0;
277 while ((s = *pl++) != SQ_NONE)
279 // Find attacked squares, including x-ray attacks for bishops and rooks
280 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
281 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
282 : pos.attacks_from<Pt>(s);
284 if (ei.pinnedPieces[Us] & s)
285 b &= LineBB[pos.king_square(Us)][s];
287 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
289 if (b & ei.kingRing[Them])
291 ei.kingAttackersCount[Us]++;
292 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
293 Bitboard bb = b & ei.attackedBy[Them][KING];
295 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
299 b &= ~( ei.attackedBy[Them][KNIGHT]
300 | ei.attackedBy[Them][BISHOP]
301 | ei.attackedBy[Them][ROOK]);
303 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
304 : popcount<Full >(b & mobilityArea[Us]);
306 mobility[Us] += MobilityBonus[Pt][mob];
308 // Decrease score if we are attacked by an enemy pawn. The remaining part
309 // of threat evaluation must be done later when we have full attack info.
310 if (ei.attackedBy[Them][PAWN] & s)
311 score -= ThreatenedByPawn[Pt];
313 if (Pt == BISHOP || Pt == KNIGHT)
315 // Penalty for bishop with same colored pawns
317 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
319 // Bishop and knight outpost square
320 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
321 score += evaluate_outpost<Pt, Us>(pos, ei, s);
323 // Bishop or knight behind a pawn
324 if ( relative_rank(Us, s) < RANK_5
325 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
326 score += MinorBehindPawn;
331 // Rook piece attacking enemy pawns on the same rank/file
332 if (relative_rank(Us, s) >= RANK_5)
334 Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
336 score += popcount<Max15>(pawns) * RookOnPawn;
339 // Give a bonus for a rook on a open or semi-open file
340 if (ei.pi->semiopen_file(Us, file_of(s)))
341 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOpenFile : RookSemiopenFile;
343 if (mob > 3 || ei.pi->semiopen_file(Us, file_of(s)))
346 Square ksq = pos.king_square(Us);
348 // Penalize rooks which are trapped by a king. Penalize more if the
349 // king has lost its castling capability.
350 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
351 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
352 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
353 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
356 // An important Chess960 pattern: A cornered bishop blocked by a friendly
357 // pawn diagonally in front of it is a very serious problem, especially
358 // when that pawn is also blocked.
361 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
363 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
364 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
365 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
366 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
372 Tracing::terms[Us][Pt] = score;
374 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
378 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
380 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
383 // evaluate_king() assigns bonuses and penalties to a king of a given color
385 template<Color Us, bool Trace>
386 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
388 const Color Them = (Us == WHITE ? BLACK : WHITE);
390 Bitboard undefended, b, b1, b2, safe;
392 const Square ksq = pos.king_square(Us);
394 // King shelter and enemy pawns storm
395 Score score = ei.pi->king_safety<Us>(pos, ksq);
397 // Main king safety evaluation
398 if (ei.kingAttackersCount[Them])
400 // Find the attacked squares around the king which have no defenders
401 // apart from the king itself
402 undefended = ei.attackedBy[Them][ALL_PIECES]
403 & ei.attackedBy[Us][KING]
404 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
405 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
406 | ei.attackedBy[Us][QUEEN]);
408 // Initialize the 'attackUnits' variable, which is used later on as an
409 // index to the KingDanger[] array. The initial value is based on the
410 // number and types of the enemy's attacking pieces, the number of
411 // attacked and undefended squares around our king and the quality of
412 // the pawn shelter (current 'score' value).
413 attackUnits = std::min(20, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
414 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
415 + 2 * (ei.pinnedPieces[Us] != 0)
416 - mg_value(score) / 32;
418 // Analyse the enemy's safe queen contact checks. Firstly, find the
419 // undefended squares around the king that are attacked by the enemy's
421 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
424 // ...and then remove squares not supported by another enemy piece
425 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
426 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
429 attackUnits += QueenContactCheck * popcount<Max15>(b);
432 // Analyse the enemy's safe rook contact checks. Firstly, find the
433 // undefended squares around the king that are attacked by the enemy's
435 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
437 // Consider only squares where the enemy's rook gives check
438 b &= PseudoAttacks[ROOK][ksq];
442 // ...and then remove squares not supported by another enemy piece
443 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
444 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
447 attackUnits += RookContactCheck * popcount<Max15>(b);
450 // Analyse the enemy's safe distance checks for sliders and knights
451 safe = ~(pos.pieces(Them) | ei.attackedBy[Us][ALL_PIECES]);
453 b1 = pos.attacks_from<ROOK>(ksq) & safe;
454 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
456 // Enemy queen safe checks
457 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
459 attackUnits += QueenCheck * popcount<Max15>(b);
461 // Enemy rooks safe checks
462 b = b1 & ei.attackedBy[Them][ROOK];
464 attackUnits += RookCheck * popcount<Max15>(b);
466 // Enemy bishops safe checks
467 b = b2 & ei.attackedBy[Them][BISHOP];
469 attackUnits += BishopCheck * popcount<Max15>(b);
471 // Enemy knights safe checks
472 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
474 attackUnits += KnightCheck * popcount<Max15>(b);
476 // To index KingDanger[] attackUnits must be in [0, 99] range
477 attackUnits = std::min(99, std::max(0, attackUnits));
479 // Finally, extract the king danger score from the KingDanger[]
480 // array and subtract the score from evaluation.
481 score -= KingDanger[attackUnits];
485 Tracing::terms[Us][KING] = score;
491 // evaluate_threats() assigns bonuses according to the type of attacking piece
492 // and the type of attacked one.
494 template<Color Us, bool Trace>
495 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
497 const Color Them = (Us == WHITE ? BLACK : WHITE);
499 Bitboard b, weakEnemies, protectedEnemies;
500 Score score = SCORE_ZERO;
503 protectedEnemies = (pos.pieces(Them) ^ pos.pieces(Them,PAWN))
504 & ei.attackedBy[Them][PAWN]
505 & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
508 score += Threat[0][type_of(pos.piece_on(lsb(protectedEnemies)))];
510 // Enemies not defended by a pawn and under our attack
511 weakEnemies = pos.pieces(Them)
512 & ~ei.attackedBy[Them][PAWN]
513 & ei.attackedBy[Us][ALL_PIECES];
515 // Add a bonus according if the attacking pieces are minor or major
518 b = weakEnemies & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
520 score += Threat[0][type_of(pos.piece_on(lsb(b)))];
522 b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
524 score += Threat[1][type_of(pos.piece_on(lsb(b)))];
526 b = weakEnemies & ~ei.attackedBy[Them][ALL_PIECES];
528 score += more_than_one(b) ? Hanging * popcount<Max15>(b) : Hanging;
532 Tracing::terms[Us][Tracing::THREAT] = score;
538 // evaluate_passed_pawns() evaluates the passed pawns of the given color
540 template<Color Us, bool Trace>
541 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
543 const Color Them = (Us == WHITE ? BLACK : WHITE);
545 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
546 Score score = SCORE_ZERO;
548 b = ei.pi->passed_pawns(Us);
552 Square s = pop_lsb(&b);
554 assert(pos.pawn_passed(Us, s));
556 int r = relative_rank(Us, s) - RANK_2;
557 int rr = r * (r - 1);
559 // Base bonus based on rank
560 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
564 Square blockSq = s + pawn_push(Us);
566 // Adjust bonus based on the king's proximity
567 ebonus += square_distance(pos.king_square(Them), blockSq) * 5 * rr
568 - square_distance(pos.king_square(Us ), blockSq) * 2 * rr;
570 // If blockSq is not the queening square then consider also a second push
571 if (relative_rank(Us, blockSq) != RANK_8)
572 ebonus -= square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
574 // If the pawn is free to advance, then increase the bonus
575 if (pos.empty(blockSq))
577 squaresToQueen = forward_bb(Us, s);
579 // If there is an enemy rook or queen attacking the pawn from behind,
580 // add all X-ray attacks by the rook or queen. Otherwise consider only
581 // the squares in the pawn's path attacked or occupied by the enemy.
582 if ( unlikely(forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN))
583 && (forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
584 unsafeSquares = squaresToQueen;
586 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
588 if ( unlikely(forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN))
589 && (forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
590 defendedSquares = squaresToQueen;
592 defendedSquares = squaresToQueen & ei.attackedBy[Us][ALL_PIECES];
594 // If there aren't any enemy attacks, assign a big bonus. Otherwise
595 // assign a smaller bonus if the block square isn't attacked.
596 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
598 // If the path to queen is fully defended, assign a big bonus.
599 // Otherwise assign a smaller bonus if the block square is defended.
600 if (defendedSquares == squaresToQueen)
603 else if (defendedSquares & blockSq)
606 mbonus += k * rr, ebonus += k * rr;
608 else if(pos.pieces(Us) & blockSq)
609 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
612 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
613 ebonus += ebonus / 4;
615 score += make_score(mbonus, ebonus);
619 Tracing::terms[Us][Tracing::PASSED] = apply_weight(score, Weights[PassedPawns]);
621 // Add the scores to the middlegame and endgame eval
622 return apply_weight(score, Weights[PassedPawns]);
626 // evaluate_unstoppable_pawns() scores the most advanced among the passed and
627 // candidate pawns. In case both players have no pieces but pawns, this is
628 // somewhat related to the possibility that pawns are unstoppable.
630 Score evaluate_unstoppable_pawns(Color us, const EvalInfo& ei) {
632 Bitboard b = ei.pi->passed_pawns(us) | ei.pi->candidate_pawns(us);
634 return b ? Unstoppable * int(relative_rank(us, frontmost_sq(us, b))) : SCORE_ZERO;
638 // evaluate_space() computes the space evaluation for a given side. The
639 // space evaluation is a simple bonus based on the number of safe squares
640 // available for minor pieces on the central four files on ranks 2--4. Safe
641 // squares one, two or three squares behind a friendly pawn are counted
642 // twice. Finally, the space bonus is scaled by a weight taken from the
643 // material hash table. The aim is to improve play on game opening.
645 int evaluate_space(const Position& pos, const EvalInfo& ei) {
647 const Color Them = (Us == WHITE ? BLACK : WHITE);
649 // Find the safe squares for our pieces inside the area defined by
650 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
651 // pawn, or if it is undefended and attacked by an enemy piece.
652 Bitboard safe = SpaceMask[Us]
653 & ~pos.pieces(Us, PAWN)
654 & ~ei.attackedBy[Them][PAWN]
655 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
657 // Find all squares which are at most three squares behind some friendly pawn
658 Bitboard behind = pos.pieces(Us, PAWN);
659 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
660 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
662 // Since SpaceMask[Us] is fully on our half of the board
663 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
665 // Count safe + (behind & safe) with a single popcount
666 return popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
670 // do_evaluate() is the evaluation entry point, called directly from evaluate()
673 Value do_evaluate(const Position& pos) {
675 assert(!pos.checkers());
678 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
679 Thread* thisThread = pos.this_thread();
681 // Initialize score by reading the incrementally updated scores included
682 // in the position object (material + piece square tables).
683 // Score is computed from the point of view of white.
684 score = pos.psq_score();
686 // Probe the material hash table
687 ei.mi = Material::probe(pos, thisThread->materialTable, thisThread->endgames);
688 score += ei.mi->material_value();
690 // If we have a specialized evaluation function for the current material
691 // configuration, call it and return.
692 if (ei.mi->specialized_eval_exists())
693 return ei.mi->evaluate(pos);
695 // Probe the pawn hash table
696 ei.pi = Pawns::probe(pos, thisThread->pawnsTable);
697 score += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
699 // Initialize attack and king safety bitboards
700 init_eval_info<WHITE>(pos, ei);
701 init_eval_info<BLACK>(pos, ei);
703 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
704 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
706 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
707 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
708 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
710 // Evaluate pieces and mobility
711 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
712 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
714 // Evaluate kings after all other pieces because we need complete attack
715 // information when computing the king safety evaluation.
716 score += evaluate_king<WHITE, Trace>(pos, ei)
717 - evaluate_king<BLACK, Trace>(pos, ei);
719 // Evaluate tactical threats, we need full attack information including king
720 score += evaluate_threats<WHITE, Trace>(pos, ei)
721 - evaluate_threats<BLACK, Trace>(pos, ei);
723 // Evaluate passed pawns, we need full attack information including king
724 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
725 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
727 // If both sides have only pawns, score for potential unstoppable pawns
728 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
729 score += evaluate_unstoppable_pawns(WHITE, ei)
730 - evaluate_unstoppable_pawns(BLACK, ei);
732 // Evaluate space for both sides, only in middlegame
733 if (ei.mi->space_weight())
735 int s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
736 score += apply_weight(s * ei.mi->space_weight(), Weights[Space]);
739 // Scale winning side if position is more drawish than it appears
740 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
741 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
743 // If we don't already have an unusual scale factor, check for certain
744 // types of endgames, and use a lower scale for those.
745 if ( ei.mi->game_phase() < PHASE_MIDGAME
746 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
748 if (pos.opposite_bishops()) {
749 // Ignoring any pawns, do both sides only have a single bishop and no
751 if ( pos.non_pawn_material(WHITE) == BishopValueMg
752 && pos.non_pawn_material(BLACK) == BishopValueMg)
754 // Check for KBP vs KB with only a single pawn that is almost
755 // certainly a draw or at least two pawns.
756 bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
757 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
760 // Endgame with opposite-colored bishops, but also other pieces. Still
761 // a bit drawish, but not as drawish as with only the two bishops.
762 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
763 } else if ( abs(eg_value(score)) <= BishopValueEg
764 && ei.pi->pawn_span(strongSide) <= 1
765 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide))) {
766 // Endings where weaker side can be place his king in front of the opponent's pawns are drawish.
767 sf = ScaleFactor(ScalePawnSpan[ei.pi->pawn_span(strongSide)]);
771 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
772 Value v = mg_value(score) * int(ei.mi->game_phase())
773 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
775 v /= int(PHASE_MIDGAME);
777 // In case of tracing add all single evaluation contributions for both white and black
780 Tracing::add_term(Tracing::MATERIAL, pos.psq_score());
781 Tracing::add_term(Tracing::IMBALANCE, ei.mi->material_value());
782 Tracing::add_term(PAWN, ei.pi->pawns_value());
783 Tracing::add_term(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
784 , apply_weight(mobility[BLACK], Weights[Mobility]));
785 Score w = ei.mi->space_weight() * evaluate_space<WHITE>(pos, ei);
786 Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
787 Tracing::add_term(Tracing::SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
788 Tracing::add_term(Tracing::TOTAL, score);
793 return pos.side_to_move() == WHITE ? v : -v;
797 // Tracing function definitions
799 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
801 void Tracing::add_term(int idx, Score wScore, Score bScore) {
803 terms[WHITE][idx] = wScore;
804 terms[BLACK][idx] = bScore;
807 void Tracing::format_row(std::stringstream& ss, const char* name, int idx) {
809 Score wScore = terms[WHITE][idx];
810 Score bScore = terms[BLACK][idx];
813 case MATERIAL: case IMBALANCE: case PAWN: case TOTAL:
814 ss << std::setw(15) << name << " | --- --- | --- --- | "
815 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
816 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
819 ss << std::setw(15) << name << " | " << std::noshowpos
820 << std::setw(5) << to_cp(mg_value(wScore)) << " "
821 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
822 << std::setw(5) << to_cp(mg_value(bScore)) << " "
823 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
824 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
825 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
829 std::string Tracing::do_trace(const Position& pos) {
831 std::memset(terms, 0, sizeof(terms));
833 Value v = do_evaluate<true>(pos);
834 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
836 std::stringstream ss;
837 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
838 << " Eval term | White | Black | Total \n"
839 << " | MG EG | MG EG | MG EG \n"
840 << "----------------+-------------+-------------+-------------\n";
842 format_row(ss, "Material", MATERIAL);
843 format_row(ss, "Imbalance", IMBALANCE);
844 format_row(ss, "Pawns", PAWN);
845 format_row(ss, "Knights", KNIGHT);
846 format_row(ss, "Bishops", BISHOP);
847 format_row(ss, "Rooks", ROOK);
848 format_row(ss, "Queens", QUEEN);
849 format_row(ss, "Mobility", MOBILITY);
850 format_row(ss, "King safety", KING);
851 format_row(ss, "Threats", THREAT);
852 format_row(ss, "Passed pawns", PASSED);
853 format_row(ss, "Space", SPACE);
855 ss << "----------------+-------------+-------------+-------------\n";
856 format_row(ss, "Total", TOTAL);
858 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
868 /// evaluate() is the main evaluation function. It returns a static evaluation
869 /// of the position always from the point of view of the side to move.
871 Value evaluate(const Position& pos) {
872 return do_evaluate<false>(pos) + Tempo;
876 /// trace() is like evaluate(), but instead of returning a value, it returns
877 /// a string (suitable for outputting to stdout) that contains the detailed
878 /// descriptions and values of each evaluation term. It's mainly used for
880 std::string trace(const Position& pos) {
881 return Tracing::do_trace(pos);
885 /// init() computes evaluation weights from the corresponding UCI parameters
886 /// and setup king tables.
890 const double MaxSlope = 30;
891 const double Peak = 1280;
893 for (int t = 0, i = 1; i < 100; ++i)
895 t = int(std::min(Peak, std::min(0.4 * i * i, t + MaxSlope)));
896 KingDanger[i] = apply_weight(make_score(t, 0), Weights[KingSafety]);