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) };
161 // Threat[by minor/by rook][attacked PieceType] contains
162 // bonuses according to which piece type attacks which one.
163 // Attacks on lesser pieces which are pawn-defended are not considered.
164 const Score Threat[][PIECE_TYPE_NB] = {
165 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
166 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
169 // ThreatByKing[on one/on many] contains bonuses for King attacks on
170 // pawns or pieces which are not pawn-defended.
171 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
173 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
174 // We don't use a Score because we process the two components independently.
175 const Value Passed[][RANK_NB] = {
176 { V(5), V( 5), V(31), V(73), V(166), V(252) },
177 { V(7), V(14), V(38), V(73), V(166), V(252) }
180 // PassedFile[File] contains a bonus according to the file of a passed pawn
181 const Score PassedFile[FILE_NB] = {
182 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
183 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
186 // Assorted bonuses and penalties used by evaluation
187 const Score MinorBehindPawn = S(16, 0);
188 const Score BishopPawns = S( 8, 12);
189 const Score RookOnPawn = S( 8, 24);
190 const Score TrappedRook = S(92, 0);
191 const Score SafeCheck = S(20, 20);
192 const Score OtherCheck = S(10, 10);
193 const Score ThreatByHangingPawn = S(71, 61);
194 const Score LooseEnemies = S( 0, 25);
195 const Score WeakQueen = S(35, 0);
196 const Score Hanging = S(48, 27);
197 const Score ThreatByPawnPush = S(38, 22);
198 const Score Unstoppable = S( 0, 20);
200 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
201 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
202 // happen in Chess960 games.
203 const Score TrappedBishopA1H1 = S(50, 50);
208 // King danger constants and variables. The king danger scores are looked-up
209 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
210 // of the enemy attack are added up into an integer, which is used as an
211 // index to KingDanger[].
212 Score KingDanger[512];
214 // KingAttackWeights[PieceType] contains king attack weights by piece type
215 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
217 // Penalties for enemy's safe checks
218 const int QueenContactCheck = 89;
219 const int QueenCheck = 62;
220 const int RookCheck = 57;
221 const int BishopCheck = 48;
222 const int KnightCheck = 78;
225 // eval_init() initializes king and attack bitboards for a given color
226 // adding pawn attacks. To be done at the beginning of the evaluation.
229 void eval_init(const Position& pos, EvalInfo& ei) {
231 const Color Them = (Us == WHITE ? BLACK : WHITE);
232 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
234 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
235 Bitboard b = ei.attackedBy[Them][KING];
236 ei.attackedBy[Them][ALL_PIECES] |= b;
237 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
238 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
240 // Init king safety tables only if we are going to use them
241 if (pos.non_pawn_material(Us) >= QueenValueMg)
243 ei.kingRing[Them] = b | shift_bb<Down>(b);
244 b &= ei.attackedBy[Us][PAWN];
245 ei.kingAttackersCount[Us] = popcount(b);
246 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
249 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
253 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
256 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
257 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
258 const Bitboard* mobilityArea) {
261 Score score = SCORE_ZERO;
263 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
264 const Color Them = (Us == WHITE ? BLACK : WHITE);
265 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
266 : Rank5BB | Rank4BB | Rank3BB);
267 const Square* pl = pos.squares<Pt>(Us);
269 ei.attackedBy[Us][Pt] = 0;
271 while ((s = *pl++) != SQ_NONE)
273 // Find attacked squares, including x-ray attacks for bishops and rooks
274 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
275 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
276 : pos.attacks_from<Pt>(s);
278 if (ei.pinnedPieces[Us] & s)
279 b &= LineBB[pos.square<KING>(Us)][s];
281 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
282 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
284 if (b & ei.kingRing[Them])
286 ei.kingAttackersCount[Us]++;
287 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
288 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
292 b &= ~( ei.attackedBy[Them][KNIGHT]
293 | ei.attackedBy[Them][BISHOP]
294 | ei.attackedBy[Them][ROOK]);
296 int mob = popcount(b & mobilityArea[Us]);
298 mobility[Us] += MobilityBonus[Pt][mob];
300 if (Pt == BISHOP || Pt == KNIGHT)
302 // Bonus for outpost squares
303 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
305 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
308 bb &= b & ~pos.pieces(Us);
310 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
313 // Bonus when behind a pawn
314 if ( relative_rank(Us, s) < RANK_5
315 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
316 score += MinorBehindPawn;
318 // Penalty for pawns on the same color square as the bishop
320 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
322 // An important Chess960 pattern: A cornered bishop blocked by a friendly
323 // pawn diagonally in front of it is a very serious problem, especially
324 // when that pawn is also blocked.
327 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
329 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
330 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
331 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
332 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
339 // Bonus for aligning with enemy pawns on the same rank/file
340 if (relative_rank(Us, s) >= RANK_5)
341 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
343 // Bonus when on an open or semi-open file
344 if (ei.pi->semiopen_file(Us, file_of(s)))
345 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
347 // Penalize when trapped by the king, even more if the king cannot castle
350 Square ksq = pos.square<KING>(Us);
352 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
353 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
354 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
355 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
361 // Penalty if any relative pin or discovered attack against the queen
362 if (pos.slider_blockers(pos.pieces(), pos.pieces(Them, ROOK, BISHOP), s))
368 Trace::add(Pt, Us, score);
370 // Recursively call evaluate_pieces() of next piece type until KING is excluded
371 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
375 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
377 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
380 // evaluate_king() assigns bonuses and penalties to a king of a given color
382 template<Color Us, bool DoTrace>
383 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
385 const Color Them = (Us == WHITE ? BLACK : WHITE);
386 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
388 Bitboard undefended, b, b1, b2, safe, other;
390 const Square ksq = pos.square<KING>(Us);
392 // King shelter and enemy pawns storm
393 Score score = ei.pi->king_safety<Us>(pos, ksq);
395 // Main king safety evaluation
396 if (ei.kingAttackersCount[Them])
398 // Find the attacked squares which are defended only by the king...
399 undefended = ei.attackedBy[Them][ALL_PIECES]
400 & ei.attackedBy[Us][KING]
401 & ~ei.attackedBy2[Us];
403 // ... and those which are not defended at all in the larger king ring
404 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
405 & ei.kingRing[Us] & ~pos.pieces(Them);
407 // Initialize the 'attackUnits' variable, which is used later on as an
408 // index into the KingDanger[] array. The initial value is based on the
409 // number and types of the enemy's attacking pieces, the number of
410 // attacked and undefended squares around our king and the quality of
411 // the pawn shelter (current 'score' value).
412 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
413 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
414 + 21 * popcount(undefended)
415 + 12 * (popcount(b) + !!ei.pinnedPieces[Us])
416 - 64 * !pos.count<QUEEN>(Them)
417 - mg_value(score) / 8;
419 // Analyse the enemy's safe queen contact checks. Firstly, find the
420 // undefended squares around the king reachable by the enemy queen...
421 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
423 // ...and keep squares supported by another enemy piece
424 attackUnits += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
426 // Analyse the safe enemy's checks which are possible on next move...
427 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
429 // ... and some other potential checks, only requiring the square to be
430 // safe from pawn-attacks, and not being occupied by a blocked pawn.
431 other = ~( ei.attackedBy[Us][PAWN]
432 | (pos.pieces(Them, PAWN) & shift_bb<Up>(pos.pieces(PAWN))));
434 b1 = pos.attacks_from<ROOK >(ksq);
435 b2 = pos.attacks_from<BISHOP>(ksq);
437 // Enemy queen safe checks
438 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
439 attackUnits += QueenCheck, score -= SafeCheck;
441 // For other pieces, also consider the square safe if attacked twice,
442 // and only defended by a queen.
443 safe |= ei.attackedBy2[Them]
444 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
445 & ei.attackedBy[Us][QUEEN];
447 // Enemy rooks safe and other checks
448 if (b1 & ei.attackedBy[Them][ROOK] & safe)
449 attackUnits += RookCheck, score -= SafeCheck;
451 else if (b1 & ei.attackedBy[Them][ROOK] & other)
454 // Enemy bishops safe and other checks
455 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
456 attackUnits += BishopCheck, score -= SafeCheck;
458 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
461 // Enemy knights safe and other checks
462 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
464 attackUnits += KnightCheck, score -= SafeCheck;
469 // Finally, extract the king danger score from the KingDanger[]
470 // array and subtract the score from the evaluation.
471 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
475 Trace::add(KING, Us, score);
481 // evaluate_threats() assigns bonuses according to the types of the attacking
482 // and the attacked pieces.
484 const Bitboard WhiteCamp = Rank4BB | Rank5BB | Rank6BB | Rank7BB | Rank8BB;
485 const Bitboard BlackCamp = Rank5BB | Rank4BB | Rank3BB | Rank2BB | Rank1BB;
486 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
487 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
488 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
490 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
491 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
492 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
493 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
494 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
497 template<Color Us, bool DoTrace>
498 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
500 const Color Them = (Us == WHITE ? BLACK : WHITE);
501 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
502 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
503 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
504 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
505 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
507 enum { Minor, Rook };
509 Bitboard b, weak, defended, safeThreats;
510 Score score = SCORE_ZERO;
512 // Small bonus if the opponent has loose pawns or pieces
513 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
514 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
515 score += LooseEnemies;
517 // Non-pawn enemies attacked by a pawn
518 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
522 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
523 | ei.attackedBy[Us][ALL_PIECES]);
525 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
527 if (weak ^ safeThreats)
528 score += ThreatByHangingPawn;
531 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
534 // Non-pawn enemies defended by a pawn
535 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
537 // Enemies not defended by a pawn and under our attack
538 weak = pos.pieces(Them)
539 & ~ei.attackedBy[Them][PAWN]
540 & ei.attackedBy[Us][ALL_PIECES];
542 // Add a bonus according to the kind of attacking pieces
545 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
547 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
549 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
551 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
553 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
555 b = weak & ei.attackedBy[Us][KING];
557 score += ThreatByKing[more_than_one(b)];
560 // Bonus if some pawns can safely push and attack an enemy piece
561 b = pos.pieces(Us, PAWN) & ~TRank7BB;
562 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
565 & ~ei.attackedBy[Them][PAWN]
566 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
568 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
570 & ~ei.attackedBy[Us][PAWN];
572 score += ThreatByPawnPush * popcount(b);
574 // King tropism: firstly, find squares that we attack in the enemy king flank
575 b = ei.attackedBy[Us][ALL_PIECES] & KingFlank[Us][file_of(pos.square<KING>(Them))];
577 // Secondly, add to the bitboard the squares which we attack twice in that flank
578 // but which are not protected by a enemy pawn. Note the trick to shift away the
579 // previous attack bits to the empty part of the bitboard.
580 b = (b & ei.attackedBy2[Us] & ~ei.attackedBy[Them][PAWN])
581 | (Us == WHITE ? b >> 4 : b << 4);
583 // Count all these squares with a single popcount
584 score += make_score(7 * popcount(b), 0);
587 Trace::add(THREAT, Us, score);
593 // evaluate_passed_pawns() evaluates the passed pawns of the given color
595 template<Color Us, bool DoTrace>
596 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
598 const Color Them = (Us == WHITE ? BLACK : WHITE);
600 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
601 Score score = SCORE_ZERO;
603 b = ei.pi->passed_pawns(Us);
607 Square s = pop_lsb(&b);
609 assert(pos.pawn_passed(Us, s));
610 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
612 int r = relative_rank(Us, s) - RANK_2;
613 int rr = r * (r - 1);
615 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
619 Square blockSq = s + pawn_push(Us);
621 // Adjust bonus based on the king's proximity
622 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
623 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
625 // If blockSq is not the queening square then consider also a second push
626 if (relative_rank(Us, blockSq) != RANK_8)
627 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
629 // If the pawn is free to advance, then increase the bonus
630 if (pos.empty(blockSq))
632 // If there is a rook or queen attacking/defending the pawn from behind,
633 // consider all the squaresToQueen. Otherwise consider only the squares
634 // in the pawn's path attacked or occupied by the enemy.
635 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
637 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
639 if (!(pos.pieces(Us) & bb))
640 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
642 if (!(pos.pieces(Them) & bb))
643 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
645 // If there aren't any enemy attacks, assign a big bonus. Otherwise
646 // assign a smaller bonus if the block square isn't attacked.
647 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
649 // If the path to the queen is fully defended, assign a big bonus.
650 // Otherwise assign a smaller bonus if the block square is defended.
651 if (defendedSquares == squaresToQueen)
654 else if (defendedSquares & blockSq)
657 mbonus += k * rr, ebonus += k * rr;
659 else if (pos.pieces(Us) & blockSq)
660 mbonus += rr + r * 2, ebonus += rr + r * 2;
663 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
667 Trace::add(PASSED, Us, score);
669 // Add the scores to the middlegame and endgame eval
674 // evaluate_space() computes the space evaluation for a given side. The
675 // space evaluation is a simple bonus based on the number of safe squares
676 // available for minor pieces on the central four files on ranks 2--4. Safe
677 // squares one, two or three squares behind a friendly pawn are counted
678 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
679 // improve play on game opening.
681 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
683 const Color Them = (Us == WHITE ? BLACK : WHITE);
684 const Bitboard SpaceMask =
685 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
686 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
688 // Find the safe squares for our pieces inside the area defined by
689 // SpaceMask. A square is unsafe if it is attacked by an enemy
690 // pawn, or if it is undefended and attacked by an enemy piece.
691 Bitboard safe = SpaceMask
692 & ~pos.pieces(Us, PAWN)
693 & ~ei.attackedBy[Them][PAWN]
694 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
696 // Find all squares which are at most three squares behind some friendly pawn
697 Bitboard behind = pos.pieces(Us, PAWN);
698 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
699 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
701 // Since SpaceMask[Us] is fully on our half of the board...
702 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
704 // ...count safe + (behind & safe) with a single popcount
705 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
706 int weight = pos.count<ALL_PIECES>(Us);
708 return make_score(bonus * weight * weight / 22, 0);
712 // evaluate_initiative() computes the initiative correction value for the
713 // position, i.e., second order bonus/malus based on the known attacking/defending
714 // status of the players.
715 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
717 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
718 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
719 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
721 // Compute the initiative bonus for the attacking side
722 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
724 // Now apply the bonus: note that we find the attacking side by extracting
725 // the sign of the endgame value, and that we carefully cap the bonus so
726 // that the endgame score will never be divided by more than two.
727 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
729 return make_score(0, value);
733 // evaluate_scale_factor() computes the scale factor for the winning side
734 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
736 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
737 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
739 // If we don't already have an unusual scale factor, check for certain
740 // types of endgames, and use a lower scale for those.
741 if ( ei.me->game_phase() < PHASE_MIDGAME
742 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
744 if (pos.opposite_bishops())
746 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
747 // is almost a draw, in case of KBP vs KB, it is even more a draw.
748 if ( pos.non_pawn_material(WHITE) == BishopValueMg
749 && pos.non_pawn_material(BLACK) == BishopValueMg)
750 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
752 // Endgame with opposite-colored bishops, but also other pieces. Still
753 // a bit drawish, but not as drawish as with only the two bishops.
755 sf = ScaleFactor(46);
757 // Endings where weaker side can place his king in front of the opponent's
758 // pawns are drawish.
759 else if ( abs(eg) <= BishopValueEg
760 && ei.pi->pawn_span(strongSide) <= 1
761 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
762 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
771 /// evaluate() is the main evaluation function. It returns a static evaluation
772 /// of the position from the point of view of the side to move.
774 template<bool DoTrace>
775 Value Eval::evaluate(const Position& pos) {
777 assert(!pos.checkers());
780 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
782 // Initialize score by reading the incrementally updated scores included in
783 // the position object (material + piece square tables). Score is computed
784 // internally from the white point of view.
785 score = pos.psq_score();
787 // Probe the material hash table
788 ei.me = Material::probe(pos);
789 score += ei.me->imbalance();
791 // If we have a specialized evaluation function for the current material
792 // configuration, call it and return.
793 if (ei.me->specialized_eval_exists())
794 return ei.me->evaluate(pos);
796 // Probe the pawn hash table
797 ei.pi = Pawns::probe(pos);
798 score += ei.pi->pawns_score();
800 // Initialize attack and king safety bitboards
801 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
802 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
803 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
804 eval_init<WHITE>(pos, ei);
805 eval_init<BLACK>(pos, ei);
807 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
808 Bitboard blockedPawns[] = {
809 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
810 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
813 // Do not include in mobility area squares protected by enemy pawns, or occupied
814 // by our blocked pawns or king.
815 Bitboard mobilityArea[] = {
816 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
817 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
820 // Evaluate all pieces but king and pawns
821 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
822 score += mobility[WHITE] - mobility[BLACK];
824 // Evaluate kings after all other pieces because we need full attack
825 // information when computing the king safety evaluation.
826 score += evaluate_king<WHITE, DoTrace>(pos, ei)
827 - evaluate_king<BLACK, DoTrace>(pos, ei);
829 // Evaluate tactical threats, we need full attack information including king
830 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
831 - evaluate_threats<BLACK, DoTrace>(pos, ei);
833 // Evaluate passed pawns, we need full attack information including king
834 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
835 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
837 // If both sides have only pawns, score for potential unstoppable pawns
838 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
841 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
842 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
844 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
845 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
848 // Evaluate space for both sides, only during opening
849 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
850 score += evaluate_space<WHITE>(pos, ei)
851 - evaluate_space<BLACK>(pos, ei);
853 // Evaluate position potential for the winning side
854 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
856 // Evaluate scale factor for the winning side
857 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
859 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
860 Value v = mg_value(score) * int(ei.me->game_phase())
861 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
863 v /= int(PHASE_MIDGAME);
865 // In case of tracing add all remaining individual evaluation terms
868 Trace::add(MATERIAL, pos.psq_score());
869 Trace::add(IMBALANCE, ei.me->imbalance());
870 Trace::add(PAWN, ei.pi->pawns_score());
871 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
872 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
873 , evaluate_space<BLACK>(pos, ei));
874 Trace::add(TOTAL, score);
877 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
880 // Explicit template instantiations
881 template Value Eval::evaluate<true >(const Position&);
882 template Value Eval::evaluate<false>(const Position&);
885 /// trace() is like evaluate(), but instead of returning a value, it returns
886 /// a string (suitable for outputting to stdout) that contains the detailed
887 /// descriptions and values of each evaluation term. Useful for debugging.
889 std::string Eval::trace(const Position& pos) {
891 std::memset(scores, 0, sizeof(scores));
893 Value v = evaluate<true>(pos);
894 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
896 std::stringstream ss;
897 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
898 << " Eval term | White | Black | Total \n"
899 << " | MG EG | MG EG | MG EG \n"
900 << "----------------+-------------+-------------+-------------\n"
901 << " Material | " << Term(MATERIAL)
902 << " Imbalance | " << Term(IMBALANCE)
903 << " Pawns | " << Term(PAWN)
904 << " Knights | " << Term(KNIGHT)
905 << " Bishop | " << Term(BISHOP)
906 << " Rooks | " << Term(ROOK)
907 << " Queens | " << Term(QUEEN)
908 << " Mobility | " << Term(MOBILITY)
909 << " King safety | " << Term(KING)
910 << " Threats | " << Term(THREAT)
911 << " Passed pawns | " << Term(PASSED)
912 << " Space | " << Term(SPACE)
913 << "----------------+-------------+-------------+-------------\n"
914 << " Total | " << Term(TOTAL);
916 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
922 /// init() computes evaluation weights, usually at startup
926 const int MaxSlope = 322;
927 const int Peak = 47410;
930 for (int i = 0; i < 400; ++i)
932 t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
933 KingDanger[i] = make_score(t * 268 / 7700, 0);