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 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
81 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
82 // pawn or squares attacked by 2 pawns are not explicitly added.
83 Bitboard attackedBy2[COLOR_NB];
85 // kingRing[color] is the zone around the king which is considered
86 // by the king safety evaluation. This consists of the squares directly
87 // adjacent to the king, and the three (or two, for a king on an edge file)
88 // squares two ranks in front of the king. For instance, if black's king
89 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
90 // f7, g7, h7, f6, g6 and h6.
91 Bitboard kingRing[COLOR_NB];
93 // kingAttackersCount[color] is the number of pieces of the given color
94 // which attack a square in the kingRing of the enemy king.
95 int kingAttackersCount[COLOR_NB];
97 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
98 // given color which attack a square in the kingRing of the enemy king. The
99 // weights of the individual piece types are given by the elements in the
100 // KingAttackWeights array.
101 int kingAttackersWeight[COLOR_NB];
103 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
104 // color to squares directly adjacent to the enemy king. Pieces which attack
105 // more than one square are counted multiple times. For instance, if there is
106 // a white knight on g5 and black's king is on g8, this white knight adds 2
107 // to kingAdjacentZoneAttacksCount[WHITE].
108 int kingAdjacentZoneAttacksCount[COLOR_NB];
110 Bitboard pinnedPieces[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
119 // game, indexed by piece type and number of attacked squares in the MobilityArea.
120 const Score MobilityBonus[][32] = {
122 { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
123 S( 22, 26), S( 30, 28), S( 36, 29) },
124 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
125 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
126 S( 92, 90), S( 97, 94) },
127 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
128 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
129 S( 43,165), S( 49,168), S( 59,169) },
130 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
131 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
132 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
133 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
134 S(118,174), S(119,177), S(123,191), S(128,199) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
138 // bishops outposts, bigger if outpost piece is supported by a pawn.
139 const Score Outpost[][2] = {
140 { S(43,11), S(65,20) }, // Knights
141 { S(20, 3), S(29, 8) } // Bishops
144 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
145 // knights and bishops which can reach an outpost square in one move, bigger
146 // if outpost square is supported by a pawn.
147 const Score ReachableOutpost[][2] = {
148 { S(21, 5), S(35, 8) }, // Knights
149 { S( 8, 0), S(14, 4) } // Bishops
152 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
153 // friendly pawn on the rook file.
154 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
156 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
157 // type is attacked by a pawn which is protected or is not attacked.
158 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
159 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
162 // Threat[by minor/by rook][attacked PieceType] contains
163 // bonuses according to which piece type attacks which one.
164 // Attacks on lesser pieces which are pawn-defended are not considered.
165 const Score Threat[][PIECE_TYPE_NB] = {
166 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
167 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
170 // ThreatByKing[on one/on many] contains bonuses for King attacks on
171 // pawns or pieces which are not pawn-defended.
172 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
174 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
175 // We don't use a Score because we process the two components independently.
176 const Value Passed[][RANK_NB] = {
177 { V(5), V( 5), V(31), V(73), V(166), V(252) },
178 { V(7), V(14), V(38), V(73), V(166), V(252) }
181 // PassedFile[File] contains a bonus according to the file of a passed pawn
182 const Score PassedFile[FILE_NB] = {
183 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
184 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
187 // Assorted bonuses and penalties used by evaluation
188 const Score MinorBehindPawn = S(16, 0);
189 const Score BishopPawns = S( 8, 12);
190 const Score RookOnPawn = S( 8, 24);
191 const Score TrappedRook = S(92, 0);
192 const Score CloseEnemies = S( 7, 0);
193 const Score SafeCheck = S(20, 20);
194 const Score OtherCheck = S(10, 10);
195 const Score ThreatByHangingPawn = S(71, 61);
196 const Score LooseEnemies = S( 0, 25);
197 const Score WeakQueen = S(35, 0);
198 const Score Hanging = S(48, 27);
199 const Score ThreatByPawnPush = S(38, 22);
200 const Score Unstoppable = S( 0, 20);
202 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
203 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
204 // happen in Chess960 games.
205 const Score TrappedBishopA1H1 = S(50, 50);
210 // KingAttackWeights[PieceType] contains king attack weights by piece type
211 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
213 // Penalties for enemy's safe checks
214 const int QueenContactCheck = 997;
215 const int QueenCheck = 695;
216 const int RookCheck = 638;
217 const int BishopCheck = 538;
218 const int KnightCheck = 874;
221 // eval_init() initializes king and attack bitboards for a given color
222 // adding pawn attacks. To be done at the beginning of the evaluation.
225 void eval_init(const Position& pos, EvalInfo& ei) {
227 const Color Them = (Us == WHITE ? BLACK : WHITE);
228 const Square Down = (Us == WHITE ? SOUTH : NORTH);
230 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
231 Bitboard b = ei.attackedBy[Them][KING];
232 ei.attackedBy[Them][ALL_PIECES] |= b;
233 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
234 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
236 // Init king safety tables only if we are going to use them
237 if (pos.non_pawn_material(Us) >= QueenValueMg)
239 ei.kingRing[Them] = b | shift<Down>(b);
240 b &= ei.attackedBy[Us][PAWN];
241 ei.kingAttackersCount[Us] = popcount(b);
242 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
245 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
249 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
252 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
253 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
254 const Bitboard* mobilityArea) {
257 Score score = SCORE_ZERO;
259 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
260 const Color Them = (Us == WHITE ? BLACK : WHITE);
261 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
262 : Rank5BB | Rank4BB | Rank3BB);
263 const Square* pl = pos.squares<Pt>(Us);
265 ei.attackedBy[Us][Pt] = 0;
267 while ((s = *pl++) != SQ_NONE)
269 // Find attacked squares, including x-ray attacks for bishops and rooks
270 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
271 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
272 : pos.attacks_from<Pt>(s);
274 if (ei.pinnedPieces[Us] & s)
275 b &= LineBB[pos.square<KING>(Us)][s];
277 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
278 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
280 if (b & ei.kingRing[Them])
282 ei.kingAttackersCount[Us]++;
283 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
284 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
288 b &= ~( ei.attackedBy[Them][KNIGHT]
289 | ei.attackedBy[Them][BISHOP]
290 | ei.attackedBy[Them][ROOK]);
292 int mob = popcount(b & mobilityArea[Us]);
294 mobility[Us] += MobilityBonus[Pt][mob];
296 if (Pt == BISHOP || Pt == KNIGHT)
298 // Bonus for outpost squares
299 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
301 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
304 bb &= b & ~pos.pieces(Us);
306 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
309 // Bonus when behind a pawn
310 if ( relative_rank(Us, s) < RANK_5
311 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
312 score += MinorBehindPawn;
314 // Penalty for pawns on the same color square as the bishop
316 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
318 // An important Chess960 pattern: A cornered bishop blocked by a friendly
319 // pawn diagonally in front of it is a very serious problem, especially
320 // when that pawn is also blocked.
323 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
325 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
326 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
327 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
328 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
335 // Bonus for aligning with enemy pawns on the same rank/file
336 if (relative_rank(Us, s) >= RANK_5)
337 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
339 // Bonus when on an open or semi-open file
340 if (ei.pi->semiopen_file(Us, file_of(s)))
341 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
343 // Penalize when trapped by the king, even more if the king cannot castle
346 Square ksq = pos.square<KING>(Us);
348 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
349 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
350 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
351 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
357 // Penalty if any relative pin or discovered attack against the queen
359 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
365 Trace::add(Pt, Us, score);
367 // Recursively call evaluate_pieces() of next piece type until KING is excluded
368 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
372 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
374 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
377 // evaluate_king() assigns bonuses and penalties to a king of a given color
379 const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
380 const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
381 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
382 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
383 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
385 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
386 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
387 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
388 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
389 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
392 template<Color Us, bool DoTrace>
393 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
395 const Color Them = (Us == WHITE ? BLACK : WHITE);
396 const Square Up = (Us == WHITE ? NORTH : SOUTH);
398 Bitboard undefended, b, b1, b2, safe, other;
400 const Square ksq = pos.square<KING>(Us);
402 // King shelter and enemy pawns storm
403 Score score = ei.pi->king_safety<Us>(pos, ksq);
405 // Main king safety evaluation
406 if (ei.kingAttackersCount[Them])
408 // Find the attacked squares which are defended only by the king...
409 undefended = ei.attackedBy[Them][ALL_PIECES]
410 & ei.attackedBy[Us][KING]
411 & ~ei.attackedBy2[Us];
413 // ... and those which are not defended at all in the larger king ring
414 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
415 & ei.kingRing[Us] & ~pos.pieces(Them);
417 // Initialize the 'kingDanger' variable, which will be transformed
418 // later into a king danger score. The initial value is based on the
419 // number and types of the enemy's attacking pieces, the number of
420 // attacked and undefended squares around our king and the quality of
421 // the pawn shelter (current 'score' value).
422 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
423 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
424 + 235 * popcount(undefended)
425 + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
426 - 717 * !pos.count<QUEEN>(Them)
427 - 7 * mg_value(score) / 5 - 5;
429 // Analyse the enemy's safe queen contact checks. Firstly, find the
430 // undefended squares around the king reachable by the enemy queen...
431 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
433 // ...and keep squares supported by another enemy piece
434 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
436 // Analyse the safe enemy's checks which are possible on next move...
437 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
439 // ... and some other potential checks, only requiring the square to be
440 // safe from pawn-attacks, and not being occupied by a blocked pawn.
441 other = ~( ei.attackedBy[Us][PAWN]
442 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
444 b1 = pos.attacks_from<ROOK >(ksq);
445 b2 = pos.attacks_from<BISHOP>(ksq);
447 // Enemy queen safe checks
448 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
449 kingDanger += QueenCheck, score -= SafeCheck;
451 // For other pieces, also consider the square safe if attacked twice,
452 // and only defended by a queen.
453 safe |= ei.attackedBy2[Them]
454 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
455 & ei.attackedBy[Us][QUEEN];
457 // Enemy rooks safe and other checks
458 if (b1 & ei.attackedBy[Them][ROOK] & safe)
459 kingDanger += RookCheck, score -= SafeCheck;
461 else if (b1 & ei.attackedBy[Them][ROOK] & other)
464 // Enemy bishops safe and other checks
465 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
466 kingDanger += BishopCheck, score -= SafeCheck;
468 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
471 // Enemy knights safe and other checks
472 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
474 kingDanger += KnightCheck, score -= SafeCheck;
479 // Compute the king danger score and subtract it from the evaluation
481 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
484 // King tropism: firstly, find squares that opponent attacks in our king flank
485 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][file_of(ksq)];
487 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
488 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
490 // Secondly, add the squares which are attacked twice in that flank and
491 // which are not defended by our pawns.
492 b = (Us == WHITE ? b << 4 : b >> 4)
493 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
495 score -= CloseEnemies * popcount(b);
498 Trace::add(KING, Us, score);
504 // evaluate_threats() assigns bonuses according to the types of the attacking
505 // and the attacked pieces.
507 template<Color Us, bool DoTrace>
508 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
510 const Color Them = (Us == WHITE ? BLACK : WHITE);
511 const Square Up = (Us == WHITE ? NORTH : SOUTH);
512 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
513 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
514 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
515 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
517 enum { Minor, Rook };
519 Bitboard b, weak, defended, safeThreats;
520 Score score = SCORE_ZERO;
522 // Small bonus if the opponent has loose pawns or pieces
523 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
524 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
525 score += LooseEnemies;
527 // Non-pawn enemies attacked by a pawn
528 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
532 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
533 | ei.attackedBy[Us][ALL_PIECES]);
535 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
537 if (weak ^ safeThreats)
538 score += ThreatByHangingPawn;
541 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
544 // Non-pawn enemies defended by a pawn
545 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
547 // Enemies not defended by a pawn and under our attack
548 weak = pos.pieces(Them)
549 & ~ei.attackedBy[Them][PAWN]
550 & ei.attackedBy[Us][ALL_PIECES];
552 // Add a bonus according to the kind of attacking pieces
555 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
557 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
559 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
561 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
563 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
565 b = weak & ei.attackedBy[Us][KING];
567 score += ThreatByKing[more_than_one(b)];
570 // Bonus if some pawns can safely push and attack an enemy piece
571 b = pos.pieces(Us, PAWN) & ~TRank7BB;
572 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
575 & ~ei.attackedBy[Them][PAWN]
576 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
578 b = (shift<Left>(b) | shift<Right>(b))
580 & ~ei.attackedBy[Us][PAWN];
582 score += ThreatByPawnPush * popcount(b);
585 Trace::add(THREAT, Us, score);
591 // evaluate_passed_pawns() evaluates the passed pawns of the given color
593 template<Color Us, bool DoTrace>
594 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
596 const Color Them = (Us == WHITE ? BLACK : WHITE);
598 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
599 Score score = SCORE_ZERO;
601 b = ei.pi->passed_pawns(Us);
605 Square s = pop_lsb(&b);
607 assert(pos.pawn_passed(Us, s));
608 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
610 int r = relative_rank(Us, s) - RANK_2;
611 int rr = r * (r - 1);
613 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
617 Square blockSq = s + pawn_push(Us);
619 // Adjust bonus based on the king's proximity
620 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
621 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
623 // If blockSq is not the queening square then consider also a second push
624 if (relative_rank(Us, blockSq) != RANK_8)
625 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
627 // If the pawn is free to advance, then increase the bonus
628 if (pos.empty(blockSq))
630 // If there is a rook or queen attacking/defending the pawn from behind,
631 // consider all the squaresToQueen. Otherwise consider only the squares
632 // in the pawn's path attacked or occupied by the enemy.
633 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
635 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
637 if (!(pos.pieces(Us) & bb))
638 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
640 if (!(pos.pieces(Them) & bb))
641 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
643 // If there aren't any enemy attacks, assign a big bonus. Otherwise
644 // assign a smaller bonus if the block square isn't attacked.
645 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
647 // If the path to the queen is fully defended, assign a big bonus.
648 // Otherwise assign a smaller bonus if the block square is defended.
649 if (defendedSquares == squaresToQueen)
652 else if (defendedSquares & blockSq)
655 mbonus += k * rr, ebonus += k * rr;
657 else if (pos.pieces(Us) & blockSq)
658 mbonus += rr + r * 2, ebonus += rr + r * 2;
661 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
665 Trace::add(PASSED, Us, score);
667 // Add the scores to the middlegame and endgame eval
672 // evaluate_space() computes the space evaluation for a given side. The
673 // space evaluation is a simple bonus based on the number of safe squares
674 // available for minor pieces on the central four files on ranks 2--4. Safe
675 // squares one, two or three squares behind a friendly pawn are counted
676 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
677 // improve play on game opening.
679 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
681 const Color Them = (Us == WHITE ? BLACK : WHITE);
682 const Bitboard SpaceMask =
683 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
684 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
686 // Find the safe squares for our pieces inside the area defined by
687 // SpaceMask. A square is unsafe if it is attacked by an enemy
688 // pawn, or if it is undefended and attacked by an enemy piece.
689 Bitboard safe = SpaceMask
690 & ~pos.pieces(Us, PAWN)
691 & ~ei.attackedBy[Them][PAWN]
692 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
694 // Find all squares which are at most three squares behind some friendly pawn
695 Bitboard behind = pos.pieces(Us, PAWN);
696 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
697 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
699 // Since SpaceMask[Us] is fully on our half of the board...
700 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
702 // ...count safe + (behind & safe) with a single popcount
703 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
704 bonus = std::min(16, bonus);
705 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
707 return make_score(bonus * weight * weight / 18, 0);
711 // evaluate_initiative() computes the initiative correction value for the
712 // position, i.e., second order bonus/malus based on the known attacking/defending
713 // status of the players.
714 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
716 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
717 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
718 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
720 // Compute the initiative bonus for the attacking side
721 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
723 // Now apply the bonus: note that we find the attacking side by extracting
724 // the sign of the endgame value, and that we carefully cap the bonus so
725 // that the endgame score will never be divided by more than two.
726 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
728 return make_score(0, value);
732 // evaluate_scale_factor() computes the scale factor for the winning side
733 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
735 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
736 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
738 // If we don't already have an unusual scale factor, check for certain
739 // types of endgames, and use a lower scale for those.
740 if ( ei.me->game_phase() < PHASE_MIDGAME
741 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
743 if (pos.opposite_bishops())
745 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
746 // is almost a draw, in case of KBP vs KB, it is even more a draw.
747 if ( pos.non_pawn_material(WHITE) == BishopValueMg
748 && pos.non_pawn_material(BLACK) == BishopValueMg)
749 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
751 // Endgame with opposite-colored bishops, but also other pieces. Still
752 // a bit drawish, but not as drawish as with only the two bishops.
754 sf = ScaleFactor(46);
756 // Endings where weaker side can place his king in front of the opponent's
757 // pawns are drawish.
758 else if ( abs(eg) <= BishopValueEg
759 && pos.count<PAWN>(strongSide) <= 2
760 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
761 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
770 /// evaluate() is the main evaluation function. It returns a static evaluation
771 /// of the position from the point of view of the side to move.
773 template<bool DoTrace>
774 Value Eval::evaluate(const Position& pos) {
776 assert(!pos.checkers());
778 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
781 // Probe the material hash table
782 ei.me = Material::probe(pos);
784 // If we have a specialized evaluation function for the current material
785 // configuration, call it and return.
786 if (ei.me->specialized_eval_exists())
787 return ei.me->evaluate(pos);
789 // Initialize score by reading the incrementally updated scores included in
790 // the position object (material + piece square tables) and the material
791 // imbalance. Score is computed internally from the white point of view.
792 Score score = pos.psq_score() + ei.me->imbalance();
794 // Probe the pawn hash table
795 ei.pi = Pawns::probe(pos);
796 score += ei.pi->pawns_score();
798 // Initialize attack and king safety bitboards
799 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
800 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
801 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
802 eval_init<WHITE>(pos, ei);
803 eval_init<BLACK>(pos, ei);
805 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
806 Bitboard blockedPawns[] = {
807 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
808 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
811 // Do not include in mobility area squares protected by enemy pawns, or occupied
812 // by our blocked pawns or king.
813 Bitboard mobilityArea[] = {
814 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
815 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
818 // Evaluate all pieces but king and pawns
819 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
820 score += mobility[WHITE] - mobility[BLACK];
822 // Evaluate kings after all other pieces because we need full attack
823 // information when computing the king safety evaluation.
824 score += evaluate_king<WHITE, DoTrace>(pos, ei)
825 - evaluate_king<BLACK, DoTrace>(pos, ei);
827 // Evaluate tactical threats, we need full attack information including king
828 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
829 - evaluate_threats<BLACK, DoTrace>(pos, ei);
831 // Evaluate passed pawns, we need full attack information including king
832 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
833 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
835 // If both sides have only pawns, score for potential unstoppable pawns
836 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
839 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
840 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
842 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
843 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
846 // Evaluate space for both sides, only during opening
847 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
848 score += evaluate_space<WHITE>(pos, ei)
849 - evaluate_space<BLACK>(pos, ei);
851 // Evaluate position potential for the winning side
852 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
854 // Evaluate scale factor for the winning side
855 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
857 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
858 Value v = mg_value(score) * int(ei.me->game_phase())
859 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
861 v /= int(PHASE_MIDGAME);
863 // In case of tracing add all remaining individual evaluation terms
866 Trace::add(MATERIAL, pos.psq_score());
867 Trace::add(IMBALANCE, ei.me->imbalance());
868 Trace::add(PAWN, ei.pi->pawns_score());
869 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
870 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
871 , evaluate_space<BLACK>(pos, ei));
872 Trace::add(TOTAL, score);
875 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
878 // Explicit template instantiations
879 template Value Eval::evaluate<true >(const Position&);
880 template Value Eval::evaluate<false>(const Position&);
883 /// trace() is like evaluate(), but instead of returning a value, it returns
884 /// a string (suitable for outputting to stdout) that contains the detailed
885 /// descriptions and values of each evaluation term. Useful for debugging.
887 std::string Eval::trace(const Position& pos) {
889 std::memset(scores, 0, sizeof(scores));
891 Value v = evaluate<true>(pos);
892 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
894 std::stringstream ss;
895 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
896 << " Eval term | White | Black | Total \n"
897 << " | MG EG | MG EG | MG EG \n"
898 << "----------------+-------------+-------------+-------------\n"
899 << " Material | " << Term(MATERIAL)
900 << " Imbalance | " << Term(IMBALANCE)
901 << " Pawns | " << Term(PAWN)
902 << " Knights | " << Term(KNIGHT)
903 << " Bishop | " << Term(BISHOP)
904 << " Rooks | " << Term(ROOK)
905 << " Queens | " << Term(QUEEN)
906 << " Mobility | " << Term(MOBILITY)
907 << " King safety | " << Term(KING)
908 << " Threats | " << Term(THREAT)
909 << " Passed pawns | " << Term(PASSED)
910 << " Space | " << Term(SPACE)
911 << "----------------+-------------+-------------+-------------\n"
912 << " Total | " << Term(TOTAL);
914 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";