2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
76 // attackedBy[color][piece type] is a bitboard representing all squares
77 // attacked by a given color and piece type (can be also ALL_PIECES).
78 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
80 // kingRing[color] is the zone around the king which is considered
81 // by the king safety evaluation. This consists of the squares directly
82 // adjacent to the king, and the three (or two, for a king on an edge file)
83 // squares two ranks in front of the king. For instance, if black's king
84 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
85 // f7, g7, h7, f6, g6 and h6.
86 Bitboard kingRing[COLOR_NB];
88 // kingAttackersCount[color] is the number of pieces of the given color
89 // which attack a square in the kingRing of the enemy king.
90 int kingAttackersCount[COLOR_NB];
92 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
93 // given color which attack a square in the kingRing of the enemy king. The
94 // weights of the individual piece types are given by the elements in the
95 // KingAttackWeights array.
96 int kingAttackersWeight[COLOR_NB];
98 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
99 // color to squares directly adjacent to the enemy king. Pieces which attack
100 // more than one square are counted multiple times. For instance, if there is
101 // a white knight on g5 and black's king is on g8, this white knight adds 2
102 // to kingAdjacentZoneAttacksCount[WHITE].
103 int kingAdjacentZoneAttacksCount[COLOR_NB];
105 Bitboard pinnedPieces[COLOR_NB];
110 #define V(v) Value(v)
111 #define S(mg, eg) make_score(mg, eg)
113 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
114 // game, indexed by piece type and number of attacked squares in the MobilityArea.
115 const Score MobilityBonus[][32] = {
117 { S(-75,-76), S(-56,-54), S(- 9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
118 S( 22, 26), S( 30, 28), S( 36, 29) },
119 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
120 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
121 S( 92, 90), S( 97, 94) },
122 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
123 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
124 S( 43,165), S( 49,168), S( 59,169) },
125 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
126 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
127 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
128 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
129 S(118,174), S(119,177), S(123,191), S(128,199) }
132 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
133 // bishops outposts, bigger if outpost piece is supported by a pawn.
134 const Score Outpost[][2] = {
135 { S(43,11), S(65,20) }, // Knights
136 { S(20, 3), S(29, 8) } // Bishops
139 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
140 // knights and bishops which can reach an outpost square in one move, bigger
141 // if outpost square is supported by a pawn.
142 const Score ReachableOutpost[][2] = {
143 { S(21, 5), S(35, 8) }, // Knights
144 { S( 8, 0), S(14, 4) } // Bishops
147 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
148 // friendly pawn on the rook file.
149 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
151 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
152 // type is attacked by a pawn which is protected or is not attacked.
153 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
154 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215) };
156 // Threat[by minor/by rook][attacked PieceType] contains
157 // bonuses according to which piece type attacks which one.
158 // Attacks on lesser pieces which are pawn-defended are not considered.
159 const Score Threat[][PIECE_TYPE_NB] = {
160 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
161 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
164 // ThreatByKing[on one/on many] contains bonuses for King attacks on
165 // pawns or pieces which are not pawn-defended.
166 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
168 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
169 // We don't use a Score because we process the two components independently.
170 const Value Passed[][RANK_NB] = {
171 { V(5), V( 5), V(31), V(73), V(166), V(252) },
172 { V(7), V(14), V(38), V(73), V(166), V(252) }
175 // PassedFile[File] contains a bonus according to the file of a passed pawn
176 const Score PassedFile[FILE_NB] = {
177 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
178 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
181 // Assorted bonuses and penalties used by evaluation
182 const Score MinorBehindPawn = S(16, 0);
183 const Score BishopPawns = S( 8, 12);
184 const Score RookOnPawn = S( 8, 24);
185 const Score TrappedRook = S(92, 0);
186 const Score SafeCheck = S(20, 20);
187 const Score OtherCheck = S(10, 10);
188 const Score ThreatByHangingPawn = S(71, 61);
189 const Score LooseEnemies = S( 0, 25);
190 const Score WeakQueen = S(35, 0);
191 const Score Hanging = S(48, 27);
192 const Score ThreatByPawnPush = S(38, 22);
193 const Score Unstoppable = S( 0, 20);
195 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
196 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
197 // happen in Chess960 games.
198 const Score TrappedBishopA1H1 = S(50, 50);
203 // King danger constants and variables. The king danger scores are looked-up
204 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
205 // of the enemy attack are added up into an integer, which is used as an
206 // index to KingDanger[].
207 Score KingDanger[512];
209 // KingAttackWeights[PieceType] contains king attack weights by piece type
210 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
212 // Penalties for enemy's safe checks
213 const int QueenContactCheck = 89;
214 const int QueenCheck = 62;
215 const int RookCheck = 57;
216 const int BishopCheck = 48;
217 const int KnightCheck = 78;
220 // eval_init() initializes king and attack bitboards for a given color
221 // adding pawn attacks. To be done at the beginning of the evaluation.
224 void eval_init(const Position& pos, EvalInfo& ei) {
226 const Color Them = (Us == WHITE ? BLACK : WHITE);
227 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
229 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
230 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
231 ei.attackedBy[Them][ALL_PIECES] |= b;
232 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
234 // Init king safety tables only if we are going to use them
235 if (pos.non_pawn_material(Us) >= QueenValueMg)
237 ei.kingRing[Them] = b | shift_bb<Down>(b);
238 b &= ei.attackedBy[Us][PAWN];
239 ei.kingAttackersCount[Us] = popcount(b);
240 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
243 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
247 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
250 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
251 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
252 const Bitboard* mobilityArea) {
255 Score score = SCORE_ZERO;
257 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
258 const Color Them = (Us == WHITE ? BLACK : WHITE);
259 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
260 : Rank5BB | Rank4BB | Rank3BB);
261 const Square* pl = pos.squares<Pt>(Us);
263 ei.attackedBy[Us][Pt] = 0;
265 while ((s = *pl++) != SQ_NONE)
267 // Find attacked squares, including x-ray attacks for bishops and rooks
268 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
269 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
270 : pos.attacks_from<Pt>(s);
272 if (ei.pinnedPieces[Us] & s)
273 b &= LineBB[pos.square<KING>(Us)][s];
275 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
277 if (b & ei.kingRing[Them])
279 ei.kingAttackersCount[Us]++;
280 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
281 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
285 b &= ~( ei.attackedBy[Them][KNIGHT]
286 | ei.attackedBy[Them][BISHOP]
287 | ei.attackedBy[Them][ROOK]);
289 int mob = popcount(b & mobilityArea[Us]);
291 mobility[Us] += MobilityBonus[Pt][mob];
293 if (Pt == BISHOP || Pt == KNIGHT)
295 // Bonus for outpost squares
296 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
298 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
301 bb &= b & ~pos.pieces(Us);
303 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
306 // Bonus when behind a pawn
307 if ( relative_rank(Us, s) < RANK_5
308 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
309 score += MinorBehindPawn;
311 // Penalty for pawns on the same color square as the bishop
313 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
315 // An important Chess960 pattern: A cornered bishop blocked by a friendly
316 // pawn diagonally in front of it is a very serious problem, especially
317 // when that pawn is also blocked.
320 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
322 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
323 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
324 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
325 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
332 // Bonus for aligning with enemy pawns on the same rank/file
333 if (relative_rank(Us, s) >= RANK_5)
334 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
336 // Bonus when on an open or semi-open file
337 if (ei.pi->semiopen_file(Us, file_of(s)))
338 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
340 // Penalize when trapped by the king, even more if the king cannot castle
343 Square ksq = pos.square<KING>(Us);
345 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
346 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
347 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
348 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
354 // Penalty if any relative pin or discovered attack against the queen
355 if (pos.slider_blockers(pos.pieces(), pos.pieces(Them, ROOK, BISHOP), s))
361 Trace::add(Pt, Us, score);
363 // Recursively call evaluate_pieces() of next piece type until KING is excluded
364 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
368 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
370 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
373 // evaluate_king() assigns bonuses and penalties to a king of a given color
375 template<Color Us, bool DoTrace>
376 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
378 const Color Them = (Us == WHITE ? BLACK : WHITE);
379 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
381 Bitboard undefended, b, b1, b2, safe, other;
383 const Square ksq = pos.square<KING>(Us);
385 // King shelter and enemy pawns storm
386 Score score = ei.pi->king_safety<Us>(pos, ksq);
388 // Main king safety evaluation
389 if (ei.kingAttackersCount[Them])
391 // Find the attacked squares which are defended only by the king...
392 undefended = ei.attackedBy[Them][ALL_PIECES]
393 & ei.attackedBy[Us][KING]
394 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
395 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
396 | ei.attackedBy[Us][QUEEN]);
398 // ... and those which are not defended at all in the larger king ring
399 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
400 & ei.kingRing[Us] & ~pos.pieces(Them);
402 // Initialize the 'attackUnits' variable, which is used later on as an
403 // index into the KingDanger[] array. The initial value is based on the
404 // number and types of the enemy's attacking pieces, the number of
405 // attacked and undefended squares around our king and the quality of
406 // the pawn shelter (current 'score' value).
407 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
408 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
409 + 21 * popcount(undefended)
410 + 12 * (popcount(b) + !!ei.pinnedPieces[Us])
411 - 64 * !pos.count<QUEEN>(Them)
412 - mg_value(score) / 8;
414 // Analyse the enemy's safe queen contact checks. Firstly, find the
415 // undefended squares around the king reachable by the enemy queen...
416 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
419 // ...and then remove squares not supported by another enemy piece
420 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
421 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
422 | ei.attackedBy[Them][KING];
424 attackUnits += QueenContactCheck * popcount(b);
427 // Analyse the safe enemy's checks which are possible on next move...
428 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
430 // ... and some other potential checks, only requiring the square to be
431 // safe from pawn-attacks, and not being occupied by a blocked pawn.
432 other = ~( ei.attackedBy[Us][PAWN]
433 | (pos.pieces(Them, PAWN) & shift_bb<Up>(pos.pieces(PAWN))));
435 b1 = pos.attacks_from<ROOK >(ksq);
436 b2 = pos.attacks_from<BISHOP>(ksq);
438 // Enemy queen safe checks
439 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
440 attackUnits += QueenCheck, score -= SafeCheck;
442 // Enemy rooks safe and other checks
443 if (b1 & ei.attackedBy[Them][ROOK] & safe)
444 attackUnits += RookCheck, score -= SafeCheck;
446 else if (b1 & ei.attackedBy[Them][ROOK] & other)
449 // Enemy bishops safe and other checks
450 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
451 attackUnits += BishopCheck, score -= SafeCheck;
453 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
456 // Enemy knights safe and other checks
457 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
459 attackUnits += KnightCheck, score -= SafeCheck;
464 // Finally, extract the king danger score from the KingDanger[]
465 // array and subtract the score from the evaluation.
466 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
470 Trace::add(KING, Us, score);
476 // evaluate_threats() assigns bonuses according to the types of the attacking
477 // and the attacked pieces.
479 template<Color Us, bool DoTrace>
480 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
482 const Color Them = (Us == WHITE ? BLACK : WHITE);
483 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
484 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
485 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
486 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
487 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
489 enum { Minor, Rook };
491 Bitboard b, weak, defended, safeThreats;
492 Score score = SCORE_ZERO;
494 // Small bonus if the opponent has loose pawns or pieces
495 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
496 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
497 score += LooseEnemies;
499 // Non-pawn enemies attacked by a pawn
500 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
504 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
505 | ei.attackedBy[Us][ALL_PIECES]);
507 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
509 if (weak ^ safeThreats)
510 score += ThreatByHangingPawn;
513 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
516 // Non-pawn enemies defended by a pawn
517 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
519 // Enemies not defended by a pawn and under our attack
520 weak = pos.pieces(Them)
521 & ~ei.attackedBy[Them][PAWN]
522 & ei.attackedBy[Us][ALL_PIECES];
524 // Add a bonus according to the kind of attacking pieces
527 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
529 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
531 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
533 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
535 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
537 b = weak & ei.attackedBy[Us][KING];
539 score += ThreatByKing[more_than_one(b)];
542 // Bonus if some pawns can safely push and attack an enemy piece
543 b = pos.pieces(Us, PAWN) & ~TRank7BB;
544 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
547 & ~ei.attackedBy[Them][PAWN]
548 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
550 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
552 & ~ei.attackedBy[Us][PAWN];
554 score += ThreatByPawnPush * popcount(b);
557 Trace::add(THREAT, Us, score);
563 // evaluate_passed_pawns() evaluates the passed pawns of the given color
565 template<Color Us, bool DoTrace>
566 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
568 const Color Them = (Us == WHITE ? BLACK : WHITE);
570 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
571 Score score = SCORE_ZERO;
573 b = ei.pi->passed_pawns(Us);
577 Square s = pop_lsb(&b);
579 assert(pos.pawn_passed(Us, s));
581 int r = relative_rank(Us, s) - RANK_2;
582 int rr = r * (r - 1);
584 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
588 Square blockSq = s + pawn_push(Us);
590 // Adjust bonus based on the king's proximity
591 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
592 - distance(pos.square<KING>(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 -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
598 // If the pawn is free to advance, then increase the bonus
599 if (pos.empty(blockSq))
601 // If there is a rook or queen attacking/defending the pawn from behind,
602 // consider all the squaresToQueen. Otherwise consider only the squares
603 // in the pawn's path attacked or occupied by the enemy.
604 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
606 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
608 if (!(pos.pieces(Us) & bb))
609 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
611 if (!(pos.pieces(Them) & bb))
612 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
614 // If there aren't any enemy attacks, assign a big bonus. Otherwise
615 // assign a smaller bonus if the block square isn't attacked.
616 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
618 // If the path to the queen is fully defended, assign a big bonus.
619 // Otherwise assign a smaller bonus if the block square is defended.
620 if (defendedSquares == squaresToQueen)
623 else if (defendedSquares & blockSq)
626 mbonus += k * rr, ebonus += k * rr;
628 else if (pos.pieces(Us) & blockSq)
629 mbonus += rr + r * 2, ebonus += rr + r * 2;
632 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
636 Trace::add(PASSED, Us, score);
638 // Add the scores to the middlegame and endgame eval
643 // evaluate_space() computes the space evaluation for a given side. The
644 // space evaluation is a simple bonus based on the number of safe squares
645 // available for minor pieces on the central four files on ranks 2--4. Safe
646 // squares one, two or three squares behind a friendly pawn are counted
647 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
648 // improve play on game opening.
650 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
652 const Color Them = (Us == WHITE ? BLACK : WHITE);
653 const Bitboard SpaceMask =
654 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
655 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
657 // Find the safe squares for our pieces inside the area defined by
658 // SpaceMask. A square is unsafe if it is attacked by an enemy
659 // pawn, or if it is undefended and attacked by an enemy piece.
660 Bitboard safe = SpaceMask
661 & ~pos.pieces(Us, PAWN)
662 & ~ei.attackedBy[Them][PAWN]
663 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
665 // Find all squares which are at most three squares behind some friendly pawn
666 Bitboard behind = pos.pieces(Us, PAWN);
667 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
668 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
670 // Since SpaceMask[Us] is fully on our half of the board...
671 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
673 // ...count safe + (behind & safe) with a single popcount
674 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
675 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
676 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
678 return make_score(bonus * weight * weight * 2 / 11, 0);
682 // evaluate_initiative() computes the initiative correction value for the
683 // position, i.e., second order bonus/malus based on the known attacking/defending
684 // status of the players.
685 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
687 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
688 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
689 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
691 // Compute the initiative bonus for the attacking side
692 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
694 // Now apply the bonus: note that we find the attacking side by extracting
695 // the sign of the endgame value, and that we carefully cap the bonus so
696 // that the endgame score will never be divided by more than two.
697 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
699 return make_score(0, value);
703 // evaluate_scale_factor() computes the scale factor for the winning side
704 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
706 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
707 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
709 // If we don't already have an unusual scale factor, check for certain
710 // types of endgames, and use a lower scale for those.
711 if ( ei.me->game_phase() < PHASE_MIDGAME
712 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
714 if (pos.opposite_bishops())
716 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
717 // is almost a draw, in case of KBP vs KB, it is even more a draw.
718 if ( pos.non_pawn_material(WHITE) == BishopValueMg
719 && pos.non_pawn_material(BLACK) == BishopValueMg)
720 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
722 // Endgame with opposite-colored bishops, but also other pieces. Still
723 // a bit drawish, but not as drawish as with only the two bishops.
725 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
727 // Endings where weaker side can place his king in front of the opponent's
728 // pawns are drawish.
729 else if ( abs(eg) <= BishopValueEg
730 && ei.pi->pawn_span(strongSide) <= 1
731 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
732 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
741 /// evaluate() is the main evaluation function. It returns a static evaluation
742 /// of the position from the point of view of the side to move.
744 template<bool DoTrace>
745 Value Eval::evaluate(const Position& pos) {
747 assert(!pos.checkers());
750 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
752 // Initialize score by reading the incrementally updated scores included in
753 // the position object (material + piece square tables). Score is computed
754 // internally from the white point of view.
755 score = pos.psq_score();
757 // Probe the material hash table
758 ei.me = Material::probe(pos);
759 score += ei.me->imbalance();
761 // If we have a specialized evaluation function for the current material
762 // configuration, call it and return.
763 if (ei.me->specialized_eval_exists())
764 return ei.me->evaluate(pos);
766 // Probe the pawn hash table
767 ei.pi = Pawns::probe(pos);
768 score += ei.pi->pawns_score();
770 // Initialize attack and king safety bitboards
771 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
772 eval_init<WHITE>(pos, ei);
773 eval_init<BLACK>(pos, ei);
775 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
776 Bitboard blockedPawns[] = {
777 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
778 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
781 // Do not include in mobility area squares protected by enemy pawns, or occupied
782 // by our blocked pawns or king.
783 Bitboard mobilityArea[] = {
784 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
785 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
788 // Evaluate all pieces but king and pawns
789 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
790 score += mobility[WHITE] - mobility[BLACK];
792 // Evaluate kings after all other pieces because we need full attack
793 // information when computing the king safety evaluation.
794 score += evaluate_king<WHITE, DoTrace>(pos, ei)
795 - evaluate_king<BLACK, DoTrace>(pos, ei);
797 // Evaluate tactical threats, we need full attack information including king
798 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
799 - evaluate_threats<BLACK, DoTrace>(pos, ei);
801 // Evaluate passed pawns, we need full attack information including king
802 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
803 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
805 // If both sides have only pawns, score for potential unstoppable pawns
806 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
809 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
810 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
812 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
813 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
816 // Evaluate space for both sides, only during opening
817 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
818 score += evaluate_space<WHITE>(pos, ei)
819 - evaluate_space<BLACK>(pos, ei);
821 // Evaluate position potential for the winning side
822 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
824 // Evaluate scale factor for the winning side
825 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
827 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
828 Value v = mg_value(score) * int(ei.me->game_phase())
829 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
831 v /= int(PHASE_MIDGAME);
833 // In case of tracing add all remaining individual evaluation terms
836 Trace::add(MATERIAL, pos.psq_score());
837 Trace::add(IMBALANCE, ei.me->imbalance());
838 Trace::add(PAWN, ei.pi->pawns_score());
839 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
840 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
841 , evaluate_space<BLACK>(pos, ei));
842 Trace::add(TOTAL, score);
845 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
848 // Explicit template instantiations
849 template Value Eval::evaluate<true >(const Position&);
850 template Value Eval::evaluate<false>(const Position&);
853 /// trace() is like evaluate(), but instead of returning a value, it returns
854 /// a string (suitable for outputting to stdout) that contains the detailed
855 /// descriptions and values of each evaluation term. Useful for debugging.
857 std::string Eval::trace(const Position& pos) {
859 std::memset(scores, 0, sizeof(scores));
861 Value v = evaluate<true>(pos);
862 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
864 std::stringstream ss;
865 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
866 << " Eval term | White | Black | Total \n"
867 << " | MG EG | MG EG | MG EG \n"
868 << "----------------+-------------+-------------+-------------\n"
869 << " Material | " << Term(MATERIAL)
870 << " Imbalance | " << Term(IMBALANCE)
871 << " Pawns | " << Term(PAWN)
872 << " Knights | " << Term(KNIGHT)
873 << " Bishop | " << Term(BISHOP)
874 << " Rooks | " << Term(ROOK)
875 << " Queens | " << Term(QUEEN)
876 << " Mobility | " << Term(MOBILITY)
877 << " King safety | " << Term(KING)
878 << " Threats | " << Term(THREAT)
879 << " Passed pawns | " << Term(PASSED)
880 << " Space | " << Term(SPACE)
881 << "----------------+-------------+-------------+-------------\n"
882 << " Total | " << Term(TOTAL);
884 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
890 /// init() computes evaluation weights, usually at startup
894 const int MaxSlope = 322;
895 const int Peak = 47410;
898 for (int i = 0; i < 400; ++i)
900 t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
901 KingDanger[i] = make_score(t * 268 / 7700, 0);