2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
22 #include <cstring> // For std::memset
37 #include "incbin/incbin.h"
40 // Macro to embed the default efficiently updatable neural network (NNUE) file
41 // data in the engine binary (using incbin.h, by Dale Weiler).
42 // This macro invocation will declare the following three variables
43 // const unsigned char gEmbeddedNNUEData[]; // a pointer to the embedded data
44 // const unsigned char *const gEmbeddedNNUEEnd; // a marker to the end
45 // const unsigned int gEmbeddedNNUESize; // the size of the embedded file
46 // Note that this does not work in Microsoft Visual Studio.
47 #if !defined(_MSC_VER) && !defined(NNUE_EMBEDDING_OFF)
48 INCBIN(EmbeddedNNUE, EvalFileDefaultName);
50 const unsigned char gEmbeddedNNUEData[1] = {0x0};
51 const unsigned char *const gEmbeddedNNUEEnd = &gEmbeddedNNUEData[1];
52 const unsigned int gEmbeddedNNUESize = 1;
57 using namespace Eval::NNUE;
62 string eval_file_loaded = "None";
64 /// NNUE::init() tries to load a NNUE network at startup time, or when the engine
65 /// receives a UCI command "setoption name EvalFile value nn-[a-z0-9]{12}.nnue"
66 /// The name of the NNUE network is always retrieved from the EvalFile option.
67 /// We search the given network in three locations: internally (the default
68 /// network may be embedded in the binary), in the active working directory and
69 /// in the engine directory. Distro packagers may define the DEFAULT_NNUE_DIRECTORY
70 /// variable to have the engine search in a special directory in their distro.
74 useNNUE = Options["Use NNUE"];
78 string eval_file = string(Options["EvalFile"]);
80 #if defined(DEFAULT_NNUE_DIRECTORY)
81 #define stringify2(x) #x
82 #define stringify(x) stringify2(x)
83 vector<string> dirs = { "<internal>" , "" , CommandLine::binaryDirectory , stringify(DEFAULT_NNUE_DIRECTORY) };
85 vector<string> dirs = { "<internal>" , "" , CommandLine::binaryDirectory };
88 for (string directory : dirs)
89 if (eval_file_loaded != eval_file)
91 if (directory != "<internal>")
93 ifstream stream(directory + eval_file, ios::binary);
94 if (load_eval(eval_file, stream))
95 eval_file_loaded = eval_file;
98 if (directory == "<internal>" && eval_file == EvalFileDefaultName)
100 // C++ way to prepare a buffer for a memory stream
101 class MemoryBuffer : public basic_streambuf<char> {
102 public: MemoryBuffer(char* p, size_t n) { setg(p, p, p + n); setp(p, p + n); }
105 MemoryBuffer buffer(const_cast<char*>(reinterpret_cast<const char*>(gEmbeddedNNUEData)),
106 size_t(gEmbeddedNNUESize));
108 istream stream(&buffer);
109 if (load_eval(eval_file, stream))
110 eval_file_loaded = eval_file;
115 /// NNUE::verify() verifies that the last net used was loaded successfully
116 void NNUE::verify() {
118 string eval_file = string(Options["EvalFile"]);
120 if (useNNUE && eval_file_loaded != eval_file)
122 UCI::OptionsMap defaults;
125 string msg1 = "If the UCI option \"Use NNUE\" is set to true, network evaluation parameters compatible with the engine must be available.";
126 string msg2 = "The option is set to true, but the network file " + eval_file + " was not loaded successfully.";
127 string msg3 = "The UCI option EvalFile might need to specify the full path, including the directory name, to the network file.";
128 string msg4 = "The default net can be downloaded from: https://tests.stockfishchess.org/api/nn/" + string(defaults["EvalFile"]);
129 string msg5 = "The engine will be terminated now.";
131 sync_cout << "info string ERROR: " << msg1 << sync_endl;
132 sync_cout << "info string ERROR: " << msg2 << sync_endl;
133 sync_cout << "info string ERROR: " << msg3 << sync_endl;
134 sync_cout << "info string ERROR: " << msg4 << sync_endl;
135 sync_cout << "info string ERROR: " << msg5 << sync_endl;
141 sync_cout << "info string NNUE evaluation using " << eval_file << " enabled" << sync_endl;
143 sync_cout << "info string classical evaluation enabled" << sync_endl;
149 enum Tracing { NO_TRACE, TRACE };
151 enum Term { // The first 8 entries are reserved for PieceType
152 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, WINNABLE, TOTAL, TERM_NB
155 Score scores[TERM_NB][COLOR_NB];
157 double to_cp(Value v) { return double(v) / PawnValueEg; }
159 void add(int idx, Color c, Score s) {
163 void add(int idx, Score w, Score b = SCORE_ZERO) {
164 scores[idx][WHITE] = w;
165 scores[idx][BLACK] = b;
168 std::ostream& operator<<(std::ostream& os, Score s) {
169 os << std::setw(5) << to_cp(mg_value(s)) << " "
170 << std::setw(5) << to_cp(eg_value(s));
174 std::ostream& operator<<(std::ostream& os, Term t) {
176 if (t == MATERIAL || t == IMBALANCE || t == WINNABLE || t == TOTAL)
177 os << " ---- ----" << " | " << " ---- ----";
179 os << scores[t][WHITE] << " | " << scores[t][BLACK];
181 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
186 using namespace Trace;
190 // Threshold for lazy and space evaluation
191 constexpr Value LazyThreshold1 = Value(1565);
192 constexpr Value LazyThreshold2 = Value(1102);
193 constexpr Value SpaceThreshold = Value(11551);
194 constexpr Value NNUEThreshold1 = Value(682);
195 constexpr Value NNUEThreshold2 = Value(176);
197 // KingAttackWeights[PieceType] contains king attack weights by piece type
198 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
200 // SafeCheck[PieceType][single/multiple] contains safe check bonus by piece type,
201 // higher if multiple safe checks are possible for that piece type.
202 constexpr int SafeCheck[][2] = {
203 {}, {}, {803, 1292}, {639, 974}, {1087, 1878}, {759, 1132}
206 #define S(mg, eg) make_score(mg, eg)
208 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
209 // indexed by piece type and number of attacked squares in the mobility area.
210 constexpr Score MobilityBonus[][32] = {
211 { S(-62,-79), S(-53,-57), S(-12,-31), S( -3,-17), S( 3, 7), S( 12, 13), // Knight
212 S( 21, 16), S( 28, 21), S( 37, 26) },
213 { S(-47,-59), S(-20,-25), S( 14, -8), S( 29, 12), S( 39, 21), S( 53, 40), // Bishop
214 S( 53, 56), S( 60, 58), S( 62, 65), S( 69, 72), S( 78, 78), S( 83, 87),
215 S( 91, 88), S( 96, 98) },
216 { S(-60,-82), S(-24,-15), S( 0, 17) ,S( 3, 43), S( 4, 72), S( 14,100), // Rook
217 S( 20,102), S( 30,122), S( 41,133), S(41 ,139), S( 41,153), S( 45,160),
218 S( 57,165), S( 58,170), S( 67,175) },
219 { S(-29,-49), S(-16,-29), S( -8, -8), S( -8, 17), S( 18, 39), S( 25, 54), // Queen
220 S( 23, 59), S( 37, 73), S( 41, 76), S( 54, 95), S( 65, 95) ,S( 68,101),
221 S( 69,124), S( 70,128), S( 70,132), S( 70,133) ,S( 71,136), S( 72,140),
222 S( 74,147), S( 76,149), S( 90,153), S(104,169), S(105,171), S(106,171),
223 S(112,178), S(114,185), S(114,187), S(119,221) }
226 // BishopPawns[distance from edge] contains a file-dependent penalty for pawns on
227 // squares of the same color as our bishop.
228 constexpr Score BishopPawns[int(FILE_NB) / 2] = {
229 S(3, 8), S(3, 9), S(2, 8), S(3, 8)
232 // KingProtector[knight/bishop] contains penalty for each distance unit to own king
233 constexpr Score KingProtector[] = { S(8, 9), S(6, 9) };
235 // Outpost[knight/bishop] contains bonuses for each knight or bishop occupying a
236 // pawn protected square on rank 4 to 6 which is also safe from a pawn attack.
237 constexpr Score Outpost[] = { S(57, 38), S(31, 24) };
239 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
240 constexpr Score PassedRank[RANK_NB] = {
241 S(0, 0), S(7, 27), S(16, 32), S(17, 40), S(64, 71), S(170, 174), S(278, 262)
244 constexpr Score RookOnClosedFile = S(10, 5);
245 constexpr Score RookOnOpenFile[] = { S(19, 6), S(47, 26) };
247 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
248 // which piece type attacks which one. Attacks on lesser pieces which are
249 // pawn-defended are not considered.
250 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
251 S(0, 0), S(5, 32), S(55, 41), S(77, 56), S(89, 119), S(79, 162)
254 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
255 S(0, 0), S(3, 44), S(37, 68), S(42, 60), S(0, 39), S(58, 43)
258 // Assorted bonuses and penalties
259 constexpr Score UncontestedOutpost = S( 1, 10);
260 constexpr Score BishopOnKingRing = S( 24, 0);
261 constexpr Score BishopXRayPawns = S( 4, 5);
262 constexpr Score CorneredBishop = S( 50, 50);
263 constexpr Score FlankAttacks = S( 8, 0);
264 constexpr Score Hanging = S( 69, 36);
265 constexpr Score KnightOnQueen = S( 16, 11);
266 constexpr Score LongDiagonalBishop = S( 45, 0);
267 constexpr Score MinorBehindPawn = S( 18, 3);
268 constexpr Score PassedFile = S( 11, 8);
269 constexpr Score PawnlessFlank = S( 17, 95);
270 constexpr Score ReachableOutpost = S( 31, 22);
271 constexpr Score RestrictedPiece = S( 7, 7);
272 constexpr Score RookOnKingRing = S( 16, 0);
273 constexpr Score SliderOnQueen = S( 60, 18);
274 constexpr Score ThreatByKing = S( 24, 89);
275 constexpr Score ThreatByPawnPush = S( 48, 39);
276 constexpr Score ThreatBySafePawn = S(173, 94);
277 constexpr Score TrappedRook = S( 55, 13);
278 constexpr Score WeakQueenProtection = S( 14, 0);
279 constexpr Score WeakQueen = S( 56, 15);
284 // Evaluation class computes and stores attacks tables and other working data
289 Evaluation() = delete;
290 explicit Evaluation(const Position& p) : pos(p) {}
291 Evaluation& operator=(const Evaluation&) = delete;
295 template<Color Us> void initialize();
296 template<Color Us, PieceType Pt> Score pieces();
297 template<Color Us> Score king() const;
298 template<Color Us> Score threats() const;
299 template<Color Us> Score passed() const;
300 template<Color Us> Score space() const;
301 Value winnable(Score score) const;
306 Bitboard mobilityArea[COLOR_NB];
307 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
309 // attackedBy[color][piece type] is a bitboard representing all squares
310 // attacked by a given color and piece type. Special "piece types" which
311 // is also calculated is ALL_PIECES.
312 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
314 // attackedBy2[color] are the squares attacked by at least 2 units of a given
315 // color, including x-rays. But diagonal x-rays through pawns are not computed.
316 Bitboard attackedBy2[COLOR_NB];
318 // kingRing[color] are the squares adjacent to the king plus some other
319 // very near squares, depending on king position.
320 Bitboard kingRing[COLOR_NB];
322 // kingAttackersCount[color] is the number of pieces of the given color
323 // which attack a square in the kingRing of the enemy king.
324 int kingAttackersCount[COLOR_NB];
326 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
327 // the given color which attack a square in the kingRing of the enemy king.
328 // The weights of the individual piece types are given by the elements in
329 // the KingAttackWeights array.
330 int kingAttackersWeight[COLOR_NB];
332 // kingAttacksCount[color] is the number of attacks by the given color to
333 // squares directly adjacent to the enemy king. Pieces which attack more
334 // than one square are counted multiple times. For instance, if there is
335 // a white knight on g5 and black's king is on g8, this white knight adds 2
336 // to kingAttacksCount[WHITE].
337 int kingAttacksCount[COLOR_NB];
341 // Evaluation::initialize() computes king and pawn attacks, and the king ring
342 // bitboard for a given color. This is done at the beginning of the evaluation.
344 template<Tracing T> template<Color Us>
345 void Evaluation<T>::initialize() {
347 constexpr Color Them = ~Us;
348 constexpr Direction Up = pawn_push(Us);
349 constexpr Direction Down = -Up;
350 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
352 const Square ksq = pos.square<KING>(Us);
354 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
356 // Find our pawns that are blocked or on the first two ranks
357 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
359 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
360 // or controlled by enemy pawns are excluded from the mobility area.
361 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
363 // Initialize attackedBy[] for king and pawns
364 attackedBy[Us][KING] = attacks_bb<KING>(ksq);
365 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
366 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
367 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
369 // Init our king safety tables
370 Square s = make_square(std::clamp(file_of(ksq), FILE_B, FILE_G),
371 std::clamp(rank_of(ksq), RANK_2, RANK_7));
372 kingRing[Us] = attacks_bb<KING>(s) | s;
374 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
375 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
377 // Remove from kingRing[] the squares defended by two pawns
378 kingRing[Us] &= ~dblAttackByPawn;
382 // Evaluation::pieces() scores pieces of a given color and type
384 template<Tracing T> template<Color Us, PieceType Pt>
385 Score Evaluation<T>::pieces() {
387 constexpr Color Them = ~Us;
388 constexpr Direction Down = -pawn_push(Us);
389 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
390 : Rank5BB | Rank4BB | Rank3BB);
391 Bitboard b1 = pos.pieces(Us, Pt);
393 Score score = SCORE_ZERO;
395 attackedBy[Us][Pt] = 0;
398 Square s = pop_lsb(&b1);
400 // Find attacked squares, including x-ray attacks for bishops and rooks
401 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
402 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
403 : attacks_bb<Pt>(s, pos.pieces());
405 if (pos.blockers_for_king(Us) & s)
406 b &= line_bb(pos.square<KING>(Us), s);
408 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
409 attackedBy[Us][Pt] |= b;
410 attackedBy[Us][ALL_PIECES] |= b;
412 if (b & kingRing[Them])
414 kingAttackersCount[Us]++;
415 kingAttackersWeight[Us] += KingAttackWeights[Pt];
416 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
419 else if (Pt == ROOK && (file_bb(s) & kingRing[Them]))
420 score += RookOnKingRing;
422 else if (Pt == BISHOP && (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & kingRing[Them]))
423 score += BishopOnKingRing;
425 int mob = popcount(b & mobilityArea[Us]);
427 mobility[Us] += MobilityBonus[Pt - 2][mob];
429 if (Pt == BISHOP || Pt == KNIGHT)
431 // Bonus if the piece is on an outpost square or can reach one
432 // Bonus for knights (UncontestedOutpost) if few relevant targets
433 bb = OutpostRanks & (attackedBy[Us][PAWN] | shift<Down>(pos.pieces(PAWN)))
434 & ~pe->pawn_attacks_span(Them);
435 Bitboard targets = pos.pieces(Them) & ~pos.pieces(PAWN);
438 && bb & s & ~CenterFiles // on a side outpost
439 && !(b & targets) // no relevant attacks
440 && (!more_than_one(targets & (s & QueenSide ? QueenSide : KingSide))))
441 score += UncontestedOutpost * popcount(pos.pieces(PAWN) & (s & QueenSide ? QueenSide : KingSide));
443 score += Outpost[Pt == BISHOP];
444 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
445 score += ReachableOutpost;
447 // Bonus for a knight or bishop shielded by pawn
448 if (shift<Down>(pos.pieces(PAWN)) & s)
449 score += MinorBehindPawn;
451 // Penalty if the piece is far from the king
452 score -= KingProtector[Pt == BISHOP] * distance(pos.square<KING>(Us), s);
454 if constexpr (Pt == BISHOP)
456 // Penalty according to the number of our pawns on the same color square as the
457 // bishop, bigger when the center files are blocked with pawns and smaller
458 // when the bishop is outside the pawn chain.
459 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
461 score -= BishopPawns[edge_distance(file_of(s))] * pos.pawns_on_same_color_squares(Us, s)
462 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
464 // Penalty for all enemy pawns x-rayed
465 score -= BishopXRayPawns * popcount(attacks_bb<BISHOP>(s) & pos.pieces(Them, PAWN));
467 // Bonus for bishop on a long diagonal which can "see" both center squares
468 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
469 score += LongDiagonalBishop;
471 // An important Chess960 pattern: a cornered bishop blocked by a friendly
472 // pawn diagonally in front of it is a very serious problem, especially
473 // when that pawn is also blocked.
474 if ( pos.is_chess960()
475 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
477 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
478 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
479 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
480 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
486 if constexpr (Pt == ROOK)
488 // Bonuses for rook on a (semi-)open or closed file
489 if (pos.is_on_semiopen_file(Us, s))
491 score += RookOnOpenFile[pos.is_on_semiopen_file(Them, s)];
495 // If our pawn on this file is blocked, increase penalty
496 if ( pos.pieces(Us, PAWN)
497 & shift<Down>(pos.pieces())
500 score -= RookOnClosedFile;
503 // Penalty when trapped by the king, even more if the king cannot castle
506 File kf = file_of(pos.square<KING>(Us));
507 if ((kf < FILE_E) == (file_of(s) < kf))
508 score -= TrappedRook * (1 + !pos.castling_rights(Us));
513 if constexpr (Pt == QUEEN)
515 // Penalty if any relative pin or discovered attack against the queen
516 Bitboard queenPinners;
517 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
522 Trace::add(Pt, Us, score);
528 // Evaluation::king() assigns bonuses and penalties to a king of a given color
530 template<Tracing T> template<Color Us>
531 Score Evaluation<T>::king() const {
533 constexpr Color Them = ~Us;
534 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
535 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
537 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
538 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
540 const Square ksq = pos.square<KING>(Us);
542 // Init the score with king shelter and enemy pawns storm
543 Score score = pe->king_safety<Us>(pos);
545 // Attacked squares defended at most once by our queen or king
546 weak = attackedBy[Them][ALL_PIECES]
548 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
550 // Analyse the safe enemy's checks which are possible on next move
551 safe = ~pos.pieces(Them);
552 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
554 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
555 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
557 // Enemy rooks checks
558 rookChecks = b1 & attackedBy[Them][ROOK] & safe;
560 kingDanger += SafeCheck[ROOK][more_than_one(rookChecks)];
562 unsafeChecks |= b1 & attackedBy[Them][ROOK];
564 // Enemy queen safe checks: count them only if the checks are from squares from
565 // which opponent cannot give a rook check, because rook checks are more valuable.
566 queenChecks = (b1 | b2) & attackedBy[Them][QUEEN] & safe
567 & ~(attackedBy[Us][QUEEN] | rookChecks);
569 kingDanger += SafeCheck[QUEEN][more_than_one(queenChecks)];
571 // Enemy bishops checks: count them only if they are from squares from which
572 // opponent cannot give a queen check, because queen checks are more valuable.
573 bishopChecks = b2 & attackedBy[Them][BISHOP] & safe
576 kingDanger += SafeCheck[BISHOP][more_than_one(bishopChecks)];
579 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
581 // Enemy knights checks
582 knightChecks = attacks_bb<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
583 if (knightChecks & safe)
584 kingDanger += SafeCheck[KNIGHT][more_than_one(knightChecks & safe)];
586 unsafeChecks |= knightChecks;
588 // Find the squares that opponent attacks in our king flank, the squares
589 // which they attack twice in that flank, and the squares that we defend.
590 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
591 b2 = b1 & attackedBy2[Them];
592 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
594 int kingFlankAttack = popcount(b1) + popcount(b2);
595 int kingFlankDefense = popcount(b3);
597 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them] // (~10 Elo)
598 + 183 * popcount(kingRing[Us] & weak) // (~15 Elo)
599 + 148 * popcount(unsafeChecks) // (~4 Elo)
600 + 98 * popcount(pos.blockers_for_king(Us)) // (~2 Elo)
601 + 69 * kingAttacksCount[Them] // (~0.5 Elo)
602 + 3 * kingFlankAttack * kingFlankAttack / 8 // (~0.5 Elo)
603 + mg_value(mobility[Them] - mobility[Us]) // (~0.5 Elo)
604 - 873 * !pos.count<QUEEN>(Them) // (~24 Elo)
605 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING]) // (~5 Elo)
606 - 6 * mg_value(score) / 8 // (~8 Elo)
607 - 4 * kingFlankDefense // (~5 Elo)
610 // Transform the kingDanger units into a Score, and subtract it from the evaluation
611 if (kingDanger > 100)
612 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
614 // Penalty when our king is on a pawnless flank
615 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
616 score -= PawnlessFlank;
618 // Penalty if king flank is under attack, potentially moving toward the king
619 score -= FlankAttacks * kingFlankAttack;
622 Trace::add(KING, Us, score);
628 // Evaluation::threats() assigns bonuses according to the types of the
629 // attacking and the attacked pieces.
631 template<Tracing T> template<Color Us>
632 Score Evaluation<T>::threats() const {
634 constexpr Color Them = ~Us;
635 constexpr Direction Up = pawn_push(Us);
636 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
638 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
639 Score score = SCORE_ZERO;
642 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
644 // Squares strongly protected by the enemy, either because they defend the
645 // square with a pawn, or because they defend the square twice and we don't.
646 stronglyProtected = attackedBy[Them][PAWN]
647 | (attackedBy2[Them] & ~attackedBy2[Us]);
649 // Non-pawn enemies, strongly protected
650 defended = nonPawnEnemies & stronglyProtected;
652 // Enemies not strongly protected and under our attack
653 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
655 // Bonus according to the kind of attacking pieces
658 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
660 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
662 b = weak & attackedBy[Us][ROOK];
664 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
666 if (weak & attackedBy[Us][KING])
667 score += ThreatByKing;
669 b = ~attackedBy[Them][ALL_PIECES]
670 | (nonPawnEnemies & attackedBy2[Us]);
671 score += Hanging * popcount(weak & b);
673 // Additional bonus if weak piece is only protected by a queen
674 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
677 // Bonus for restricting their piece moves
678 b = attackedBy[Them][ALL_PIECES]
680 & attackedBy[Us][ALL_PIECES];
681 score += RestrictedPiece * popcount(b);
683 // Protected or unattacked squares
684 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
686 // Bonus for attacking enemy pieces with our relatively safe pawns
687 b = pos.pieces(Us, PAWN) & safe;
688 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
689 score += ThreatBySafePawn * popcount(b);
691 // Find squares where our pawns can push on the next move
692 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
693 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
695 // Keep only the squares which are relatively safe
696 b &= ~attackedBy[Them][PAWN] & safe;
698 // Bonus for safe pawn threats on the next move
699 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
700 score += ThreatByPawnPush * popcount(b);
702 // Bonus for threats on the next moves against enemy queen
703 if (pos.count<QUEEN>(Them) == 1)
705 bool queenImbalance = pos.count<QUEEN>() == 1;
707 Square s = pos.square<QUEEN>(Them);
708 safe = mobilityArea[Us]
709 & ~pos.pieces(Us, PAWN)
710 & ~stronglyProtected;
712 b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
714 score += KnightOnQueen * popcount(b & safe) * (1 + queenImbalance);
716 b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
717 | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
719 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]) * (1 + queenImbalance);
723 Trace::add(THREAT, Us, score);
728 // Evaluation::passed() evaluates the passed pawns and candidate passed
729 // pawns of the given color.
731 template<Tracing T> template<Color Us>
732 Score Evaluation<T>::passed() const {
734 constexpr Color Them = ~Us;
735 constexpr Direction Up = pawn_push(Us);
736 constexpr Direction Down = -Up;
738 auto king_proximity = [&](Color c, Square s) {
739 return std::min(distance(pos.square<KING>(c), s), 5);
742 Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
743 Score score = SCORE_ZERO;
745 b = pe->passed_pawns(Us);
747 blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
750 helpers = shift<Up>(pos.pieces(Us, PAWN))
752 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
754 // Remove blocked candidate passers that don't have help to pass
756 | shift<WEST>(helpers)
757 | shift<EAST>(helpers);
762 Square s = pop_lsb(&b);
764 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
766 int r = relative_rank(Us, s);
768 Score bonus = PassedRank[r];
773 Square blockSq = s + Up;
775 // Adjust bonus based on the king's proximity
776 bonus += make_score(0, ( king_proximity(Them, blockSq) * 19 / 4
777 - king_proximity(Us, blockSq) * 2) * w);
779 // If blockSq is not the queening square then consider also a second push
781 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
783 // If the pawn is free to advance, then increase the bonus
784 if (pos.empty(blockSq))
786 squaresToQueen = forward_file_bb(Us, s);
787 unsafeSquares = passed_pawn_span(Us, s);
789 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
791 if (!(pos.pieces(Them) & bb))
792 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
794 // If there are no enemy pieces or attacks on passed pawn span, assign a big bonus.
795 // Or if there is some, but they are all attacked by our pawns, assign a bit smaller bonus.
796 // Otherwise assign a smaller bonus if the path to queen is not attacked
797 // and even smaller bonus if it is attacked but block square is not.
798 int k = !unsafeSquares ? 36 :
799 !(unsafeSquares & ~attackedBy[Us][PAWN]) ? 30 :
800 !(unsafeSquares & squaresToQueen) ? 17 :
801 !(unsafeSquares & blockSq) ? 7 :
804 // Assign a larger bonus if the block square is defended
805 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
808 bonus += make_score(k * w, k * w);
812 score += bonus - PassedFile * edge_distance(file_of(s));
816 Trace::add(PASSED, Us, score);
822 // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
823 // play in the opening. It is based on the number of safe squares on the four central files
824 // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
825 // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
827 template<Tracing T> template<Color Us>
828 Score Evaluation<T>::space() const {
830 // Early exit if, for example, both queens or 6 minor pieces have been exchanged
831 if (pos.non_pawn_material() < SpaceThreshold)
834 constexpr Color Them = ~Us;
835 constexpr Direction Down = -pawn_push(Us);
836 constexpr Bitboard SpaceMask =
837 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
838 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
840 // Find the available squares for our pieces inside the area defined by SpaceMask
841 Bitboard safe = SpaceMask
842 & ~pos.pieces(Us, PAWN)
843 & ~attackedBy[Them][PAWN];
845 // Find all squares which are at most three squares behind some friendly pawn
846 Bitboard behind = pos.pieces(Us, PAWN);
847 behind |= shift<Down>(behind);
848 behind |= shift<Down+Down>(behind);
850 // Compute space score based on the number of safe squares and number of our pieces
851 // increased with number of total blocked pawns in position.
852 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
853 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
854 Score score = make_score(bonus * weight * weight / 16, 0);
857 Trace::add(SPACE, Us, score);
863 // Evaluation::winnable() adjusts the midgame and endgame score components, based on
864 // the known attacking/defending status of the players. The final value is derived
865 // by interpolation from the midgame and endgame values.
868 Value Evaluation<T>::winnable(Score score) const {
870 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
871 + int(rank_of(pos.square<KING>(WHITE)) - rank_of(pos.square<KING>(BLACK)));
873 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
874 && (pos.pieces(PAWN) & KingSide);
876 bool almostUnwinnable = outflanking < 0
877 && !pawnsOnBothFlanks;
879 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
880 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
882 // Compute the initiative bonus for the attacking side
883 int complexity = 9 * pe->passed_count()
884 + 12 * pos.count<PAWN>()
886 + 21 * pawnsOnBothFlanks
888 + 51 * !pos.non_pawn_material()
889 - 43 * almostUnwinnable
892 Value mg = mg_value(score);
893 Value eg = eg_value(score);
895 // Now apply the bonus: note that we find the attacking side by extracting the
896 // sign of the midgame or endgame values, and that we carefully cap the bonus
897 // so that the midgame and endgame scores do not change sign after the bonus.
898 int u = ((mg > 0) - (mg < 0)) * std::clamp(complexity + 50, -abs(mg), 0);
899 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
904 // Compute the scale factor for the winning side
905 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
906 int sf = me->scale_factor(pos, strongSide);
908 // If scale factor is not already specific, scale down via general heuristics
909 if (sf == SCALE_FACTOR_NORMAL)
911 if (pos.opposite_bishops())
913 // For pure opposite colored bishops endgames use scale factor
914 // based on the number of passed pawns of the strong side.
915 if ( pos.non_pawn_material(WHITE) == BishopValueMg
916 && pos.non_pawn_material(BLACK) == BishopValueMg)
917 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
918 // For every other opposite colored bishops endgames use scale factor
919 // based on the number of all pieces of the strong side.
921 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
923 // For rook endgames with strong side not having overwhelming pawn number advantage
924 // and its pawns being on one flank and weak side protecting its pieces with a king
925 // use lower scale factor.
926 else if ( pos.non_pawn_material(WHITE) == RookValueMg
927 && pos.non_pawn_material(BLACK) == RookValueMg
928 && pos.count<PAWN>(strongSide) - pos.count<PAWN>(~strongSide) <= 1
929 && bool(KingSide & pos.pieces(strongSide, PAWN)) != bool(QueenSide & pos.pieces(strongSide, PAWN))
930 && (attacks_bb<KING>(pos.square<KING>(~strongSide)) & pos.pieces(~strongSide, PAWN)))
932 // For queen vs no queen endgames use scale factor
933 // based on number of minors of side that doesn't have queen.
934 else if (pos.count<QUEEN>() == 1)
935 sf = 37 + 3 * (pos.count<QUEEN>(WHITE) == 1 ? pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK)
936 : pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE));
937 // In every other case use scale factor based on
938 // the number of pawns of the strong side reduced if pawns are on a single flank.
940 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide)) - 4 * !pawnsOnBothFlanks;
942 // Reduce scale factor in case of pawns being on a single flank
943 sf -= 4 * !pawnsOnBothFlanks;
946 // Interpolate between the middlegame and (scaled by 'sf') endgame score
947 v = mg * int(me->game_phase())
948 + eg * int(PHASE_MIDGAME - me->game_phase()) * ScaleFactor(sf) / SCALE_FACTOR_NORMAL;
953 Trace::add(WINNABLE, make_score(u, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL - eg_value(score)));
954 Trace::add(TOTAL, make_score(mg, eg * ScaleFactor(sf) / SCALE_FACTOR_NORMAL));
961 // Evaluation::value() is the main function of the class. It computes the various
962 // parts of the evaluation and returns the value of the position from the point
963 // of view of the side to move.
966 Value Evaluation<T>::value() {
968 assert(!pos.checkers());
970 // Probe the material hash table
971 me = Material::probe(pos);
973 // If we have a specialized evaluation function for the current material
974 // configuration, call it and return.
975 if (me->specialized_eval_exists())
976 return me->evaluate(pos);
978 // Initialize score by reading the incrementally updated scores included in
979 // the position object (material + piece square tables) and the material
980 // imbalance. Score is computed internally from the white point of view.
981 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
983 // Probe the pawn hash table
984 pe = Pawns::probe(pos);
985 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
987 // Early exit if score is high
988 auto lazy_skip = [&](Value lazyThreshold) {
989 return abs(mg_value(score) + eg_value(score)) / 2 > lazyThreshold + pos.non_pawn_material() / 64;
992 if (lazy_skip(LazyThreshold1))
995 // Main evaluation begins here
999 // Pieces evaluated first (also populates attackedBy, attackedBy2).
1000 // Note that the order of evaluation of the terms is left unspecified.
1001 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
1002 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
1003 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
1004 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
1006 score += mobility[WHITE] - mobility[BLACK];
1008 // More complex interactions that require fully populated attack bitboards
1009 score += king< WHITE>() - king< BLACK>()
1010 + passed< WHITE>() - passed< BLACK>();
1012 if (lazy_skip(LazyThreshold2))
1015 score += threats<WHITE>() - threats<BLACK>()
1016 + space< WHITE>() - space< BLACK>();
1019 // Derive single value from mg and eg parts of score
1020 Value v = winnable(score);
1022 // In case of tracing add all remaining individual evaluation terms
1025 Trace::add(MATERIAL, pos.psq_score());
1026 Trace::add(IMBALANCE, me->imbalance());
1027 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
1028 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
1034 // Side to move point of view
1035 v = (pos.side_to_move() == WHITE ? v : -v) + Tempo;
1043 /// evaluate() is the evaluator for the outer world. It returns a static
1044 /// evaluation of the position from the point of view of the side to move.
1046 Value Eval::evaluate(const Position& pos) {
1051 v = Evaluation<NO_TRACE>(pos).value();
1054 // Scale and shift NNUE for compatibility with search and classical evaluation
1055 auto adjusted_NNUE = [&](){
1056 int mat = pos.non_pawn_material() + 2 * PawnValueMg * pos.count<PAWN>();
1057 return NNUE::evaluate(pos) * (641 + mat / 32 - 4 * pos.rule50_count()) / 1024 + Tempo;
1060 // If there is PSQ imbalance use classical eval, with small probability if it is small
1061 Value psq = Value(abs(eg_value(pos.psq_score())));
1062 int r50 = 16 + pos.rule50_count();
1063 bool largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
1064 bool classical = largePsq || (psq > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB));
1066 // Use classical evaluation for really low piece endgames.
1067 // The most critical case is a bishop + A/H file pawn vs naked king draw.
1068 bool strongClassical = pos.non_pawn_material() < 2 * RookValueMg && pos.count<PAWN>() < 2;
1070 v = classical || strongClassical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();
1072 // If the classical eval is small and imbalance large, use NNUE nevertheless.
1073 // For the case of opposite colored bishops, switch to NNUE eval with
1074 // small probability if the classical eval is less than the threshold.
1075 if ( largePsq && !strongClassical
1076 && ( abs(v) * 16 < NNUEThreshold2 * r50
1077 || ( pos.opposite_bishops()
1078 && abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50
1079 && !(pos.this_thread()->nodes & 0xB))))
1080 v = adjusted_NNUE();
1083 // Damp down the evaluation linearly when shuffling
1084 v = v * (100 - pos.rule50_count()) / 100;
1086 // Guarantee evaluation does not hit the tablebase range
1087 v = std::clamp(v, VALUE_TB_LOSS_IN_MAX_PLY + 1, VALUE_TB_WIN_IN_MAX_PLY - 1);
1092 /// trace() is like evaluate(), but instead of returning a value, it returns
1093 /// a string (suitable for outputting to stdout) that contains the detailed
1094 /// descriptions and values of each evaluation term. Useful for debugging.
1095 /// Trace scores are from white's point of view
1097 std::string Eval::trace(const Position& pos) {
1100 return "Final evaluation: none (in check)";
1102 std::stringstream ss;
1103 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2);
1107 std::memset(scores, 0, sizeof(scores));
1109 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
1111 v = Evaluation<TRACE>(pos).value();
1113 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
1114 << " Term | White | Black | Total \n"
1115 << " | MG EG | MG EG | MG EG \n"
1116 << " ------------+-------------+-------------+------------\n"
1117 << " Material | " << Term(MATERIAL)
1118 << " Imbalance | " << Term(IMBALANCE)
1119 << " Pawns | " << Term(PAWN)
1120 << " Knights | " << Term(KNIGHT)
1121 << " Bishops | " << Term(BISHOP)
1122 << " Rooks | " << Term(ROOK)
1123 << " Queens | " << Term(QUEEN)
1124 << " Mobility | " << Term(MOBILITY)
1125 << " King safety | " << Term(KING)
1126 << " Threats | " << Term(THREAT)
1127 << " Passed | " << Term(PASSED)
1128 << " Space | " << Term(SPACE)
1129 << " Winnable | " << Term(WINNABLE)
1130 << " ------------+-------------+-------------+------------\n"
1131 << " Total | " << Term(TOTAL);
1133 v = pos.side_to_move() == WHITE ? v : -v;
1135 ss << "\nClassical evaluation: " << to_cp(v) << " (white side)\n";
1139 v = NNUE::evaluate(pos);
1140 v = pos.side_to_move() == WHITE ? v : -v;
1141 ss << "\nNNUE evaluation: " << to_cp(v) << " (white side)\n";
1145 v = pos.side_to_move() == WHITE ? v : -v;
1146 ss << "\nFinal evaluation: " << to_cp(v) << " (white side)\n";