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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
22 #include <cstring> // For std::memset
35 enum Term { // First 8 entries are for PieceType
36 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
39 double scores[TERM_NB][COLOR_NB][PHASE_NB];
41 double to_cp(Value v) { return double(v) / PawnValueEg; }
43 void add(int idx, Color c, Score s) {
44 scores[idx][c][MG] = to_cp(mg_value(s));
45 scores[idx][c][EG] = to_cp(eg_value(s));
48 void add(int idx, Score w, Score b = SCORE_ZERO) {
49 add(idx, WHITE, w); add(idx, BLACK, b);
52 std::ostream& operator<<(std::ostream& os, Term t) {
54 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
55 os << " --- --- | --- --- | ";
57 os << std::setw(5) << scores[t][WHITE][MG] << " "
58 << std::setw(5) << scores[t][WHITE][EG] << " | "
59 << std::setw(5) << scores[t][BLACK][MG] << " "
60 << std::setw(5) << scores[t][BLACK][EG] << " | ";
62 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
63 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
69 using namespace Trace;
71 // Struct EvalInfo contains various information computed and collected
72 // by the evaluation functions.
75 // attackedBy[color][piece type] is a bitboard representing all squares
76 // attacked by a given color and piece type (can be also ALL_PIECES).
77 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
79 // kingRing[color] is the zone around the king which is considered
80 // by the king safety evaluation. This consists of the squares directly
81 // adjacent to the king, and the three (or two, for a king on an edge file)
82 // squares two ranks in front of the king. For instance, if black's king
83 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
84 // f7, g7, h7, f6, g6 and h6.
85 Bitboard kingRing[COLOR_NB];
87 // kingAttackersCount[color] is the number of pieces of the given color
88 // which attack a square in the kingRing of the enemy king.
89 int kingAttackersCount[COLOR_NB];
91 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
92 // given color which attack a square in the kingRing of the enemy king. The
93 // weights of the individual piece types are given by the elements in the
94 // KingAttackWeights array.
95 int kingAttackersWeight[COLOR_NB];
97 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
98 // color to squares directly adjacent to the enemy king. Pieces which attack
99 // more than one square are counted multiple times. For instance, if there is
100 // a white knight on g5 and black's king is on g8, this white knight adds 2
101 // to kingAdjacentZoneAttacksCount[WHITE].
102 int kingAdjacentZoneAttacksCount[COLOR_NB];
104 Bitboard pinnedPieces[COLOR_NB];
110 // Evaluation weights, indexed by the corresponding evaluation term
111 enum { PawnStructure, PassedPawns, Space, KingSafety };
113 const struct Weight { int mg, eg; } Weights[] = {
114 {214, 203}, {193, 262}, {47, 0}, {330, 0}
117 Score operator*(Score s, const Weight& w) {
118 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
122 #define V(v) Value(v)
123 #define S(mg, eg) make_score(mg, eg)
125 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
126 // game, indexed by piece type and number of attacked squares in the MobilityArea.
127 const Score MobilityBonus[][32] = {
129 { S(-75,-76), S(-56,-54), S(- 9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
130 S( 22, 26), S( 30, 28), S( 36, 29) },
131 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
132 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
133 S( 92, 90), S( 97, 94) },
134 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
135 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
136 S( 43,165), S( 49,168), S( 59,169) },
137 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
138 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
139 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
140 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
141 S(118,174), S(119,177), S(123,191), S(128,199) }
144 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
145 // bishops outposts, bigger if outpost piece is supported by a pawn.
146 const Score Outpost[][2] = {
147 { S(42,11), S(63,17) }, // Knights
148 { S(18, 5), S(27, 8) } // Bishops
151 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
152 // knights and bishops which can reach an outpost square in one move, bigger
153 // if outpost square is supported by a pawn.
154 const Score ReachableOutpost[][2] = {
155 { S(21, 5), S(31, 8) }, // Knights
156 { S( 8, 2), S(13, 4) } // Bishops
159 // Threat[minor/rook][attacked PieceType] contains
160 // bonuses according to which piece type attacks which one.
161 // Attacks on lesser pieces which are pawn defended are not considered.
162 const Score Threat[2][PIECE_TYPE_NB] = {
163 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48,118) }, // Minor attacks
164 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // Rook attacks
167 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
168 // type is attacked by a pawn.
169 const Score ThreatenedByPawn[PIECE_TYPE_NB] = {
170 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
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(0), V( 1), V(34), V(90), V(214), V(328) },
177 { V(7), V(14), V(37), V(63), V(134), V(189) }
180 // PassedFile[File] contains a bonus according to the file of a passed pawn.
181 const Score PassedFile[] = {
182 S( 12, 10), S( 3, 10), S( 1, -8), S(-27, -12),
183 S(-27, -12), S( 1, -8), S( 3, 10), S( 12, 10)
186 const Score ThreatenedByHangingPawn = S(70, 63);
188 // Assorted bonuses and penalties used by evaluation
189 const Score KingOnOne = S( 3, 62);
190 const Score KingOnMany = S( 9,138);
191 const Score RookOnPawn = S( 7, 27);
192 const Score RookOnOpenFile = S(43, 21);
193 const Score RookOnSemiOpenFile = S(19, 10);
194 const Score BishopPawns = S( 8, 12);
195 const Score MinorBehindPawn = S(16, 0);
196 const Score TrappedRook = S(92, 0);
197 const Score Unstoppable = S( 0, 20);
198 const Score Hanging = S(48, 28);
199 const Score PawnAttackThreat = S(31, 19);
200 const Score Checked = S(20, 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 // King danger constants and variables. The king danger scores are looked-up
211 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
212 // of the enemy attack are added up into an integer, which is used as an
213 // index to KingDanger[].
214 Score KingDanger[512];
216 // KingAttackWeights[PieceType] contains king attack weights by piece type
217 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
219 // Penalties for enemy's safe checks
220 const int QueenContactCheck = 89;
221 const int QueenCheck = 50;
222 const int RookCheck = 45;
223 const int BishopCheck = 6;
224 const int KnightCheck = 14;
227 // eval_init() initializes king and attack bitboards for given color
228 // adding pawn attacks. To be done at the beginning of the evaluation.
231 void eval_init(const Position& pos, EvalInfo& ei) {
233 const Color Them = (Us == WHITE ? BLACK : WHITE);
234 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
236 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
237 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
238 ei.attackedBy[Them][ALL_PIECES] |= b;
239 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
241 // Init king safety tables only if we are going to use them
242 if (pos.non_pawn_material(Us) >= QueenValueMg)
244 ei.kingRing[Them] = b | shift_bb<Down>(b);
245 b &= ei.attackedBy[Us][PAWN];
246 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
247 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
250 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
254 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
257 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
258 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
259 const Bitboard* mobilityArea) {
262 Score score = SCORE_ZERO;
264 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
265 const Color Them = (Us == WHITE ? BLACK : WHITE);
266 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
267 : Rank5BB | Rank4BB | Rank3BB);
268 const Square* pl = pos.squares<Pt>(Us);
270 ei.attackedBy[Us][Pt] = 0;
272 while ((s = *pl++) != SQ_NONE)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
277 : pos.attacks_from<Pt>(s);
279 if (ei.pinnedPieces[Us] & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
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 bb = b & ei.attackedBy[Them][KING];
290 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
294 b &= ~( ei.attackedBy[Them][KNIGHT]
295 | ei.attackedBy[Them][BISHOP]
296 | ei.attackedBy[Them][ROOK]);
298 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
300 mobility[Us] += MobilityBonus[Pt][mob];
302 if (Pt == BISHOP || Pt == KNIGHT)
304 // Bonus for outpost squares
305 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
307 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
310 bb &= b & ~pos.pieces(Us);
312 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
315 // Bonus when behind a pawn
316 if ( relative_rank(Us, s) < RANK_5
317 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
318 score += MinorBehindPawn;
320 // Penalty for pawns on same color square of bishop
322 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
324 // An important Chess960 pattern: A cornered bishop blocked by a friendly
325 // pawn diagonally in front of it is a very serious problem, especially
326 // when that pawn is also blocked.
329 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
331 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
332 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
333 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
334 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
341 // Bonus for aligning with enemy pawns on the same rank/file
342 if (relative_rank(Us, s) >= RANK_5)
344 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
346 score += popcount<Max15>(alignedPawns) * RookOnPawn;
349 // Bonus when on an open or semi-open file
350 if (ei.pi->semiopen_file(Us, file_of(s)))
351 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
353 // Penalize when trapped by the king, even more if king cannot castle
354 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
356 Square ksq = pos.square<KING>(Us);
358 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
359 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
360 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
361 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
367 Trace::add(Pt, Us, score);
369 // Recursively call evaluate_pieces() of next piece type until KING excluded
370 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
374 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
376 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
379 // evaluate_king() assigns bonuses and penalties to a king of a given color
381 template<Color Us, bool DoTrace>
382 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
384 const Color Them = (Us == WHITE ? BLACK : WHITE);
386 Bitboard undefended, b, b1, b2, safe;
388 const Square ksq = pos.square<KING>(Us);
390 // King shelter and enemy pawns storm
391 Score score = ei.pi->king_safety<Us>(pos, ksq);
393 // Main king safety evaluation
394 if (ei.kingAttackersCount[Them])
396 // Find the attacked squares around the king which have no defenders
397 // apart from the king itself.
398 undefended = ei.attackedBy[Them][ALL_PIECES]
399 & ei.attackedBy[Us][KING]
400 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
401 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
402 | ei.attackedBy[Us][QUEEN]);
404 // Initialize the 'attackUnits' variable, which is used later on as an
405 // index into the KingDanger[] array. The initial value is based on the
406 // number and types of the enemy's attacking pieces, the number of
407 // attacked and undefended squares around our king and the quality of
408 // the pawn shelter (current 'score' value).
409 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
410 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
411 + 27 * popcount<Max15>(undefended)
412 + 11 * !!ei.pinnedPieces[Us]
413 - 64 * !pos.count<QUEEN>(Them)
414 - mg_value(score) / 8;
416 // Analyse the enemy's safe queen contact checks. Firstly, find the
417 // undefended squares around the king reachable by the enemy queen...
418 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
421 // ...and then remove squares not supported by another enemy piece
422 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
423 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
424 | ei.attackedBy[Them][KING];
427 attackUnits += QueenContactCheck * popcount<Max15>(b);
430 // Analyse the enemy's safe distance checks for sliders and knights
431 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
433 b1 = pos.attacks_from<ROOK >(ksq) & safe;
434 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
436 // Enemy queen safe checks
437 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
440 attackUnits += QueenCheck * popcount<Max15>(b);
444 // Enemy rooks safe checks
445 b = b1 & ei.attackedBy[Them][ROOK];
448 attackUnits += RookCheck * popcount<Max15>(b);
452 // Enemy bishops safe checks
453 b = b2 & ei.attackedBy[Them][BISHOP];
456 attackUnits += BishopCheck * popcount<Max15>(b);
460 // Enemy knights safe checks
461 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
464 attackUnits += KnightCheck * popcount<Max15>(b);
468 // Finally, extract the king danger score from the KingDanger[]
469 // array and subtract the score from evaluation.
470 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
474 Trace::add(KING, Us, score);
480 // evaluate_threats() assigns bonuses according to the type of attacking piece
481 // and the type of attacked one.
483 template<Color Us, bool DoTrace>
484 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
486 const Color Them = (Us == WHITE ? BLACK : WHITE);
487 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
488 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
489 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
490 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
491 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
493 enum { Minor, Rook };
495 Bitboard b, weak, defended, safeThreats;
496 Score score = SCORE_ZERO;
498 // Non-pawn enemies attacked by a pawn
499 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
503 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
504 | ei.attackedBy[Us][ALL_PIECES]);
506 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
508 if (weak ^ safeThreats)
509 score += ThreatenedByHangingPawn;
512 score += ThreatenedByPawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
515 // Non-pawn enemies defended by a pawn
516 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
518 // Enemies not defended by a pawn and under our attack
519 weak = pos.pieces(Them)
520 & ~ei.attackedBy[Them][PAWN]
521 & ei.attackedBy[Us][ALL_PIECES];
523 // Add a bonus according to the kind of attacking pieces
526 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
528 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
530 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
532 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
534 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
536 score += Hanging * popcount<Max15>(b);
538 b = weak & ei.attackedBy[Us][KING];
540 score += more_than_one(b) ? KingOnMany : KingOnOne;
543 // Bonus if some pawns can safely push and attack an enemy piece
544 b = pos.pieces(Us, PAWN) & ~TRank7BB;
545 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
548 & ~ei.attackedBy[Them][PAWN]
549 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
551 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
553 & ~ei.attackedBy[Us][PAWN];
556 score += popcount<Max15>(b) * PawnAttackThreat;
559 Trace::add(THREAT, Us, score);
565 // evaluate_passed_pawns() evaluates the passed pawns of the given color
567 template<Color Us, bool DoTrace>
568 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
570 const Color Them = (Us == WHITE ? BLACK : WHITE);
572 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
573 Score score = SCORE_ZERO;
575 b = ei.pi->passed_pawns(Us);
579 Square s = pop_lsb(&b);
581 assert(pos.pawn_passed(Us, s));
583 int r = relative_rank(Us, s) - RANK_2;
584 int rr = r * (r - 1);
586 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
590 Square blockSq = s + pawn_push(Us);
592 // Adjust bonus based on the king's proximity
593 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
594 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
596 // If blockSq is not the queening square then consider also a second push
597 if (relative_rank(Us, blockSq) != RANK_8)
598 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
600 // If the pawn is free to advance, then increase the bonus
601 if (pos.empty(blockSq))
603 // If there is a rook or queen attacking/defending the pawn from behind,
604 // consider all the squaresToQueen. Otherwise consider only the squares
605 // in the pawn's path attacked or occupied by the enemy.
606 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
608 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
610 if (!(pos.pieces(Us) & bb))
611 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
613 if (!(pos.pieces(Them) & bb))
614 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
616 // If there aren't any enemy attacks, assign a big bonus. Otherwise
617 // assign a smaller bonus if the block square isn't attacked.
618 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
620 // If the path to queen is fully defended, assign a big bonus.
621 // Otherwise assign a smaller bonus if the block square is defended.
622 if (defendedSquares == squaresToQueen)
625 else if (defendedSquares & blockSq)
628 mbonus += k * rr, ebonus += k * rr;
630 else if (pos.pieces(Us) & blockSq)
631 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
634 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
635 ebonus += ebonus / 4;
637 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
641 Trace::add(PASSED, Us, score * Weights[PassedPawns]);
643 // Add the scores to the middlegame and endgame eval
644 return score * Weights[PassedPawns];
648 // evaluate_space() computes the space evaluation for a given side. The
649 // space evaluation is a simple bonus based on the number of safe squares
650 // available for minor pieces on the central four files on ranks 2--4. Safe
651 // squares one, two or three squares behind a friendly pawn are counted
652 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
653 // improve play on game opening.
655 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
657 const Color Them = (Us == WHITE ? BLACK : WHITE);
658 const Bitboard SpaceMask =
659 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
660 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
662 // Find the safe squares for our pieces inside the area defined by
663 // SpaceMask. A square is unsafe if it is attacked by an enemy
664 // pawn, or if it is undefended and attacked by an enemy piece.
665 Bitboard safe = SpaceMask
666 & ~pos.pieces(Us, PAWN)
667 & ~ei.attackedBy[Them][PAWN]
668 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
670 // Find all squares which are at most three squares behind some friendly pawn
671 Bitboard behind = pos.pieces(Us, PAWN);
672 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
673 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
675 // Since SpaceMask[Us] is fully on our half of the board...
676 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
678 // ...count safe + (behind & safe) with a single popcount
679 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
680 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
681 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
683 return make_score(bonus * weight * weight, 0);
687 // evaluate_initiative() computes the initiative correction value for the
688 // position, i.e. second order bonus/malus based on the known attacking/defending
689 // status of the players.
690 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
692 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
693 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
695 // Compute the initiative bonus for the attacking side
696 int initiative = 8 * (pawns + asymmetry + kingDistance - 15);
698 // Now apply the bonus: note that we find the attacking side by extracting
699 // the sign of the endgame value, and that we carefully cap the bonus so
700 // that the endgame score will never be divided by more than two.
701 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
703 return make_score(0, value);
707 // evaluate_scale_factor() computes the scale factor for the winning side
708 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Score score) {
710 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
711 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
713 // If we don't already have an unusual scale factor, check for certain
714 // types of endgames, and use a lower scale for those.
715 if ( ei.me->game_phase() < PHASE_MIDGAME
716 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
718 if (pos.opposite_bishops())
720 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
721 // is almost a draw, in case of KBP vs KB is even more a draw.
722 if ( pos.non_pawn_material(WHITE) == BishopValueMg
723 && pos.non_pawn_material(BLACK) == BishopValueMg)
724 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
726 // Endgame with opposite-colored bishops, but also other pieces. Still
727 // a bit drawish, but not as drawish as with only the two bishops.
729 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
731 // Endings where weaker side can place his king in front of the opponent's
732 // pawns are drawish.
733 else if ( abs(eg_value(score)) <= BishopValueEg
734 && ei.pi->pawn_span(strongSide) <= 1
735 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
736 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
745 /// evaluate() is the main evaluation function. It returns a static evaluation
746 /// of the position from the point of view of the side to move.
748 template<bool DoTrace>
749 Value Eval::evaluate(const Position& pos) {
751 assert(!pos.checkers());
754 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
756 // Initialize score by reading the incrementally updated scores included in
757 // the position object (material + piece square tables). Score is computed
758 // internally from the white point of view.
759 score = pos.psq_score();
761 // Probe the material hash table
762 ei.me = Material::probe(pos);
763 score += ei.me->imbalance();
765 // If we have a specialized evaluation function for the current material
766 // configuration, call it and return.
767 if (ei.me->specialized_eval_exists())
768 return ei.me->evaluate(pos);
770 // Probe the pawn hash table
771 ei.pi = Pawns::probe(pos);
772 score += ei.pi->pawns_score() * Weights[PawnStructure];
774 // Initialize attack and king safety bitboards
775 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
776 eval_init<WHITE>(pos, ei);
777 eval_init<BLACK>(pos, ei);
779 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
780 Bitboard blockedPawns[] = {
781 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
782 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
785 // Do not include in mobility area squares protected by enemy pawns, or occupied
786 // by our blocked pawns or king.
787 Bitboard mobilityArea[] = {
788 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
789 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
792 // Evaluate all pieces but king and pawns
793 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
794 score += mobility[WHITE] - mobility[BLACK];
796 // Evaluate kings after all other pieces because we need full attack
797 // information when computing the king safety evaluation.
798 score += evaluate_king<WHITE, DoTrace>(pos, ei)
799 - evaluate_king<BLACK, DoTrace>(pos, ei);
801 // Evaluate tactical threats, we need full attack information including king
802 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
803 - evaluate_threats<BLACK, DoTrace>(pos, ei);
805 // Evaluate passed pawns, we need full attack information including king
806 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
807 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
809 // If both sides have only pawns, score for potential unstoppable pawns
810 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
813 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
814 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
816 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
817 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
820 // Evaluate space for both sides, only during opening
821 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
822 score += ( evaluate_space<WHITE>(pos, ei)
823 - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
825 // Evaluate position potential for the winning side
826 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
828 // Evaluate scale factor for the winning side
829 ScaleFactor sf = evaluate_scale_factor(pos, ei, score);
831 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
832 Value v = mg_value(score) * int(ei.me->game_phase())
833 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
835 v /= int(PHASE_MIDGAME);
837 // In case of tracing add all remaining individual evaluation terms
840 Trace::add(MATERIAL, pos.psq_score());
841 Trace::add(IMBALANCE, ei.me->imbalance());
842 Trace::add(PAWN, ei.pi->pawns_score());
843 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
844 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
845 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
846 Trace::add(TOTAL, score);
849 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
852 // Explicit template instantiations
853 template Value Eval::evaluate<true >(const Position&);
854 template Value Eval::evaluate<false>(const Position&);
857 /// trace() is like evaluate(), but instead of returning a value, it returns
858 /// a string (suitable for outputting to stdout) that contains the detailed
859 /// descriptions and values of each evaluation term. Useful for debugging.
861 std::string Eval::trace(const Position& pos) {
863 std::memset(scores, 0, sizeof(scores));
865 Value v = evaluate<true>(pos);
866 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
868 std::stringstream ss;
869 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
870 << " Eval term | White | Black | Total \n"
871 << " | MG EG | MG EG | MG EG \n"
872 << "----------------+-------------+-------------+-------------\n"
873 << " Material | " << Term(MATERIAL)
874 << " Imbalance | " << Term(IMBALANCE)
875 << " Pawns | " << Term(PAWN)
876 << " Knights | " << Term(KNIGHT)
877 << " Bishop | " << Term(BISHOP)
878 << " Rooks | " << Term(ROOK)
879 << " Queens | " << Term(QUEEN)
880 << " Mobility | " << Term(MOBILITY)
881 << " King safety | " << Term(KING)
882 << " Threats | " << Term(THREAT)
883 << " Passed pawns | " << Term(PASSED)
884 << " Space | " << Term(SPACE)
885 << "----------------+-------------+-------------+-------------\n"
886 << " Total | " << Term(TOTAL);
888 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
894 /// init() computes evaluation weights, usually at startup
898 const int MaxSlope = 8700;
899 const int Peak = 1280000;
902 for (int i = 0; i < 400; ++i)
904 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
905 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];