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) 2015-2019 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 <cstddef> // For offsetof()
24 #include <cstring> // For std::memset, std::memcmp
35 #include "syzygy/tbprobe.h"
41 Key psq[PIECE_NB][SQUARE_NB];
42 Key enpassant[FILE_NB];
43 Key castling[CASTLING_RIGHT_NB];
49 const string PieceToChar(" PNBRQK pnbrqk");
51 constexpr Piece Pieces[] = { W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
52 B_PAWN, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING };
54 // min_attacker() is a helper function used by see_ge() to locate the least
55 // valuable attacker for the side to move, remove the attacker we just found
56 // from the bitboards and scan for new X-ray attacks behind it.
59 PieceType min_attacker(const Bitboard* byTypeBB, Square to, Bitboard stmAttackers,
60 Bitboard& occupied, Bitboard& attackers) {
62 Bitboard b = stmAttackers & byTypeBB[Pt];
64 return min_attacker<Pt + 1>(byTypeBB, to, stmAttackers, occupied, attackers);
66 occupied ^= lsb(b); // Remove the attacker from occupied
68 // Add any X-ray attack behind the just removed piece. For instance with
69 // rooks in a8 and a7 attacking a1, after removing a7 we add rook in a8.
70 // Note that new added attackers can be of any color.
71 if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
72 attackers |= attacks_bb<BISHOP>(to, occupied) & (byTypeBB[BISHOP] | byTypeBB[QUEEN]);
74 if (Pt == ROOK || Pt == QUEEN)
75 attackers |= attacks_bb<ROOK>(to, occupied) & (byTypeBB[ROOK] | byTypeBB[QUEEN]);
77 // X-ray may add already processed pieces because byTypeBB[] is constant: in
78 // the rook example, now attackers contains _again_ rook in a7, so remove it.
79 attackers &= occupied;
84 PieceType min_attacker<KING>(const Bitboard*, Square, Bitboard, Bitboard&, Bitboard&) {
85 return KING; // No need to update bitboards: it is the last cycle
91 /// operator<<(Position) returns an ASCII representation of the position
93 std::ostream& operator<<(std::ostream& os, const Position& pos) {
95 os << "\n +---+---+---+---+---+---+---+---+\n";
97 for (Rank r = RANK_8; r >= RANK_1; --r)
99 for (File f = FILE_A; f <= FILE_H; ++f)
100 os << " | " << PieceToChar[pos.piece_on(make_square(f, r))];
102 os << " |\n +---+---+---+---+---+---+---+---+\n";
105 os << "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase
106 << std::setfill('0') << std::setw(16) << pos.key()
107 << std::setfill(' ') << std::dec << "\nCheckers: ";
109 for (Bitboard b = pos.checkers(); b; )
110 os << UCI::square(pop_lsb(&b)) << " ";
112 if ( int(Tablebases::MaxCardinality) >= popcount(pos.pieces())
113 && !pos.can_castle(ANY_CASTLING))
117 p.set(pos.fen(), pos.is_chess960(), &st, pos.this_thread());
118 Tablebases::ProbeState s1, s2;
119 Tablebases::WDLScore wdl = Tablebases::probe_wdl(p, &s1);
120 int dtz = Tablebases::probe_dtz(p, &s2);
121 os << "\nTablebases WDL: " << std::setw(4) << wdl << " (" << s1 << ")"
122 << "\nTablebases DTZ: " << std::setw(4) << dtz << " (" << s2 << ")";
129 // Marcel van Kervinck's cuckoo algorithm for fast detection of "upcoming repetition"
130 // situations. Description of the algorithm in the following paper:
131 // https://marcelk.net/2013-04-06/paper/upcoming-rep-v2.pdf
133 // First and second hash functions for indexing the cuckoo tables
134 inline int H1(Key h) { return h & 0x1fff; }
135 inline int H2(Key h) { return (h >> 16) & 0x1fff; }
137 // Cuckoo tables with Zobrist hashes of valid reversible moves, and the moves themselves
139 Move cuckooMove[8192];
142 /// Position::init() initializes at startup the various arrays used to compute
145 void Position::init() {
149 for (Piece pc : Pieces)
150 for (Square s = SQ_A1; s <= SQ_H8; ++s)
151 Zobrist::psq[pc][s] = rng.rand<Key>();
153 for (File f = FILE_A; f <= FILE_H; ++f)
154 Zobrist::enpassant[f] = rng.rand<Key>();
156 for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
158 Zobrist::castling[cr] = 0;
162 Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
163 Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
167 Zobrist::side = rng.rand<Key>();
168 Zobrist::noPawns = rng.rand<Key>();
170 // Prepare the cuckoo tables
171 std::memset(cuckoo, 0, sizeof(cuckoo));
172 std::memset(cuckooMove, 0, sizeof(cuckooMove));
174 for (Piece pc : Pieces)
175 for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
176 for (Square s2 = Square(s1 + 1); s2 <= SQ_H8; ++s2)
177 if (PseudoAttacks[type_of(pc)][s1] & s2)
179 Move move = make_move(s1, s2);
180 Key key = Zobrist::psq[pc][s1] ^ Zobrist::psq[pc][s2] ^ Zobrist::side;
184 std::swap(cuckoo[i], key);
185 std::swap(cuckooMove[i], move);
186 if (move == MOVE_NONE) // Arrived at empty slot?
188 i = (i == H1(key)) ? H2(key) : H1(key); // Push victim to alternative slot
192 assert(count == 3668);
196 /// Position::set() initializes the position object with the given FEN string.
197 /// This function is not very robust - make sure that input FENs are correct,
198 /// this is assumed to be the responsibility of the GUI.
200 Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Thread* th) {
202 A FEN string defines a particular position using only the ASCII character set.
204 A FEN string contains six fields separated by a space. The fields are:
206 1) Piece placement (from white's perspective). Each rank is described, starting
207 with rank 8 and ending with rank 1. Within each rank, the contents of each
208 square are described from file A through file H. Following the Standard
209 Algebraic Notation (SAN), each piece is identified by a single letter taken
210 from the standard English names. White pieces are designated using upper-case
211 letters ("PNBRQK") whilst Black uses lowercase ("pnbrqk"). Blank squares are
212 noted using digits 1 through 8 (the number of blank squares), and "/"
215 2) Active color. "w" means white moves next, "b" means black.
217 3) Castling availability. If neither side can castle, this is "-". Otherwise,
218 this has one or more letters: "K" (White can castle kingside), "Q" (White
219 can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
220 can castle queenside).
222 4) En passant target square (in algebraic notation). If there's no en passant
223 target square, this is "-". If a pawn has just made a 2-square move, this
224 is the position "behind" the pawn. This is recorded only if there is a pawn
225 in position to make an en passant capture, and if there really is a pawn
226 that might have advanced two squares.
228 5) Halfmove clock. This is the number of halfmoves since the last pawn advance
229 or capture. This is used to determine if a draw can be claimed under the
232 6) Fullmove number. The number of the full move. It starts at 1, and is
233 incremented after Black's move.
236 unsigned char col, row, token;
239 std::istringstream ss(fenStr);
241 std::memset(this, 0, sizeof(Position));
242 std::memset(si, 0, sizeof(StateInfo));
243 std::fill_n(&pieceList[0][0], sizeof(pieceList) / sizeof(Square), SQ_NONE);
248 // 1. Piece placement
249 while ((ss >> token) && !isspace(token))
252 sq += (token - '0') * EAST; // Advance the given number of files
254 else if (token == '/')
257 else if ((idx = PieceToChar.find(token)) != string::npos)
259 put_piece(Piece(idx), sq);
266 sideToMove = (token == 'w' ? WHITE : BLACK);
269 // 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
270 // Shredder-FEN that uses the letters of the columns on which the rooks began
271 // the game instead of KQkq and also X-FEN standard that, in case of Chess960,
272 // if an inner rook is associated with the castling right, the castling tag is
273 // replaced by the file letter of the involved rook, as for the Shredder-FEN.
274 while ((ss >> token) && !isspace(token))
277 Color c = islower(token) ? BLACK : WHITE;
278 Piece rook = make_piece(c, ROOK);
280 token = char(toupper(token));
283 for (rsq = relative_square(c, SQ_H1); piece_on(rsq) != rook; --rsq) {}
285 else if (token == 'Q')
286 for (rsq = relative_square(c, SQ_A1); piece_on(rsq) != rook; ++rsq) {}
288 else if (token >= 'A' && token <= 'H')
289 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
294 set_castling_right(c, rsq);
297 // 4. En passant square. Ignore if no pawn capture is possible
298 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
299 && ((ss >> row) && (row == '3' || row == '6')))
301 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
303 if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))
304 || !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove))))
305 st->epSquare = SQ_NONE;
308 st->epSquare = SQ_NONE;
310 // 5-6. Halfmove clock and fullmove number
311 ss >> std::skipws >> st->rule50 >> gamePly;
313 // Convert from fullmove starting from 1 to gamePly starting from 0,
314 // handle also common incorrect FEN with fullmove = 0.
315 gamePly = std::max(2 * (gamePly - 1), 0) + (sideToMove == BLACK);
317 chess960 = isChess960;
327 /// Position::set_castling_right() is a helper function used to set castling
328 /// rights given the corresponding color and the rook starting square.
330 void Position::set_castling_right(Color c, Square rfrom) {
332 Square kfrom = square<KING>(c);
333 CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
334 CastlingRight cr = (c | cs);
336 st->castlingRights |= cr;
337 castlingRightsMask[kfrom] |= cr;
338 castlingRightsMask[rfrom] |= cr;
339 castlingRookSquare[cr] = rfrom;
341 Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
342 Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
344 for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
345 if (s != kfrom && s != rfrom)
346 castlingPath[cr] |= s;
348 for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
349 if (s != kfrom && s != rfrom)
350 castlingPath[cr] |= s;
354 /// Position::set_check_info() sets king attacks to detect if a move gives check
356 void Position::set_check_info(StateInfo* si) const {
358 si->blockersForKing[WHITE] = slider_blockers(pieces(BLACK), square<KING>(WHITE), si->pinners[BLACK]);
359 si->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK), si->pinners[WHITE]);
361 Square ksq = square<KING>(~sideToMove);
363 si->checkSquares[PAWN] = attacks_from<PAWN>(ksq, ~sideToMove);
364 si->checkSquares[KNIGHT] = attacks_from<KNIGHT>(ksq);
365 si->checkSquares[BISHOP] = attacks_from<BISHOP>(ksq);
366 si->checkSquares[ROOK] = attacks_from<ROOK>(ksq);
367 si->checkSquares[QUEEN] = si->checkSquares[BISHOP] | si->checkSquares[ROOK];
368 si->checkSquares[KING] = 0;
372 /// Position::set_state() computes the hash keys of the position, and other
373 /// data that once computed is updated incrementally as moves are made.
374 /// The function is only used when a new position is set up, and to verify
375 /// the correctness of the StateInfo data when running in debug mode.
377 void Position::set_state(StateInfo* si) const {
379 si->key = si->materialKey = 0;
380 si->pawnKey = Zobrist::noPawns;
381 si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
382 si->checkersBB = attackers_to(square<KING>(sideToMove)) & pieces(~sideToMove);
386 for (Bitboard b = pieces(); b; )
388 Square s = pop_lsb(&b);
389 Piece pc = piece_on(s);
390 si->key ^= Zobrist::psq[pc][s];
393 if (si->epSquare != SQ_NONE)
394 si->key ^= Zobrist::enpassant[file_of(si->epSquare)];
396 if (sideToMove == BLACK)
397 si->key ^= Zobrist::side;
399 si->key ^= Zobrist::castling[si->castlingRights];
401 for (Bitboard b = pieces(PAWN); b; )
403 Square s = pop_lsb(&b);
404 si->pawnKey ^= Zobrist::psq[piece_on(s)][s];
407 for (Piece pc : Pieces)
409 if (type_of(pc) != PAWN && type_of(pc) != KING)
410 si->nonPawnMaterial[color_of(pc)] += pieceCount[pc] * PieceValue[MG][pc];
412 for (int cnt = 0; cnt < pieceCount[pc]; ++cnt)
413 si->materialKey ^= Zobrist::psq[pc][cnt];
418 /// Position::set() is an overload to initialize the position object with
419 /// the given endgame code string like "KBPKN". It is mainly a helper to
420 /// get the material key out of an endgame code.
422 Position& Position::set(const string& code, Color c, StateInfo* si) {
424 assert(code.length() > 0 && code.length() < 8);
425 assert(code[0] == 'K');
427 string sides[] = { code.substr(code.find('K', 1)), // Weak
428 code.substr(0, code.find('K', 1)) }; // Strong
430 std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
432 string fenStr = "8/" + sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/"
433 + sides[1] + char(8 - sides[1].length() + '0') + "/8 w - - 0 10";
435 return set(fenStr, false, si, nullptr);
439 /// Position::fen() returns a FEN representation of the position. In case of
440 /// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function.
442 const string Position::fen() const {
445 std::ostringstream ss;
447 for (Rank r = RANK_8; r >= RANK_1; --r)
449 for (File f = FILE_A; f <= FILE_H; ++f)
451 for (emptyCnt = 0; f <= FILE_H && empty(make_square(f, r)); ++f)
458 ss << PieceToChar[piece_on(make_square(f, r))];
465 ss << (sideToMove == WHITE ? " w " : " b ");
467 if (can_castle(WHITE_OO))
468 ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE_OO ))) : 'K');
470 if (can_castle(WHITE_OOO))
471 ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE_OOO))) : 'Q');
473 if (can_castle(BLACK_OO))
474 ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK_OO ))) : 'k');
476 if (can_castle(BLACK_OOO))
477 ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK_OOO))) : 'q');
479 if (!can_castle(ANY_CASTLING))
482 ss << (ep_square() == SQ_NONE ? " - " : " " + UCI::square(ep_square()) + " ")
483 << st->rule50 << " " << 1 + (gamePly - (sideToMove == BLACK)) / 2;
489 /// Position::slider_blockers() returns a bitboard of all the pieces (both colors)
490 /// that are blocking attacks on the square 's' from 'sliders'. A piece blocks a
491 /// slider if removing that piece from the board would result in a position where
492 /// square 's' is attacked. For example, a king-attack blocking piece can be either
493 /// a pinned or a discovered check piece, according if its color is the opposite
494 /// or the same of the color of the slider.
496 Bitboard Position::slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const {
498 Bitboard blockers = 0;
501 // Snipers are sliders that attack 's' when a piece and other snipers are removed
502 Bitboard snipers = ( (PseudoAttacks[ ROOK][s] & pieces(QUEEN, ROOK))
503 | (PseudoAttacks[BISHOP][s] & pieces(QUEEN, BISHOP))) & sliders;
504 Bitboard occupancy = pieces() & ~snipers;
508 Square sniperSq = pop_lsb(&snipers);
509 Bitboard b = between_bb(s, sniperSq) & occupancy;
511 if (b && !more_than_one(b))
514 if (b & pieces(color_of(piece_on(s))))
522 /// Position::attackers_to() computes a bitboard of all pieces which attack a
523 /// given square. Slider attacks use the occupied bitboard to indicate occupancy.
525 Bitboard Position::attackers_to(Square s, Bitboard occupied) const {
527 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
528 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
529 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
530 | (attacks_bb< ROOK>(s, occupied) & pieces( ROOK, QUEEN))
531 | (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
532 | (attacks_from<KING>(s) & pieces(KING));
536 /// Position::legal() tests whether a pseudo-legal move is legal
538 bool Position::legal(Move m) const {
542 Color us = sideToMove;
543 Square from = from_sq(m);
544 Square to = to_sq(m);
546 assert(color_of(moved_piece(m)) == us);
547 assert(piece_on(square<KING>(us)) == make_piece(us, KING));
549 // En passant captures are a tricky special case. Because they are rather
550 // uncommon, we do it simply by testing whether the king is attacked after
552 if (type_of(m) == ENPASSANT)
554 Square ksq = square<KING>(us);
555 Square capsq = to - pawn_push(us);
556 Bitboard occupied = (pieces() ^ from ^ capsq) | to;
558 assert(to == ep_square());
559 assert(moved_piece(m) == make_piece(us, PAWN));
560 assert(piece_on(capsq) == make_piece(~us, PAWN));
561 assert(piece_on(to) == NO_PIECE);
563 return !(attacks_bb< ROOK>(ksq, occupied) & pieces(~us, QUEEN, ROOK))
564 && !(attacks_bb<BISHOP>(ksq, occupied) & pieces(~us, QUEEN, BISHOP));
567 // Castling moves generation does not check if the castling path is clear of
568 // enemy attacks, it is delayed at a later time: now!
569 if (type_of(m) == CASTLING)
571 // After castling, the rook and king final positions are the same in
572 // Chess960 as they would be in standard chess.
573 to = relative_square(us, to > from ? SQ_G1 : SQ_C1);
574 Direction step = to > from ? WEST : EAST;
576 for (Square s = to; s != from; s += step)
577 if (attackers_to(s) & pieces(~us))
580 // In case of Chess960, verify that when moving the castling rook we do
581 // not discover some hidden checker.
582 // For instance an enemy queen in SQ_A1 when castling rook is in SQ_B1.
584 || !(attacks_bb<ROOK>(to, pieces() ^ to_sq(m)) & pieces(~us, ROOK, QUEEN));
587 // If the moving piece is a king, check whether the destination square is
588 // attacked by the opponent.
589 if (type_of(piece_on(from)) == KING)
590 return !(attackers_to(to) & pieces(~us));
592 // A non-king move is legal if and only if it is not pinned or it
593 // is moving along the ray towards or away from the king.
594 return !(blockers_for_king(us) & from)
595 || aligned(from, to, square<KING>(us));
599 /// Position::pseudo_legal() takes a random move and tests whether the move is
600 /// pseudo legal. It is used to validate moves from TT that can be corrupted
601 /// due to SMP concurrent access or hash position key aliasing.
603 bool Position::pseudo_legal(const Move m) const {
605 Color us = sideToMove;
606 Square from = from_sq(m);
607 Square to = to_sq(m);
608 Piece pc = moved_piece(m);
610 // Use a slower but simpler function for uncommon cases
611 if (type_of(m) != NORMAL)
612 return MoveList<LEGAL>(*this).contains(m);
614 // Is not a promotion, so promotion piece must be empty
615 if (promotion_type(m) - KNIGHT != NO_PIECE_TYPE)
618 // If the 'from' square is not occupied by a piece belonging to the side to
619 // move, the move is obviously not legal.
620 if (pc == NO_PIECE || color_of(pc) != us)
623 // The destination square cannot be occupied by a friendly piece
627 // Handle the special case of a pawn move
628 if (type_of(pc) == PAWN)
630 // We have already handled promotion moves, so destination
631 // cannot be on the 8th/1st rank.
632 if (rank_of(to) == relative_rank(us, RANK_8))
635 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
636 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
637 && !( (from + 2 * pawn_push(us) == to) // Not a double push
638 && (rank_of(from) == relative_rank(us, RANK_2))
640 && empty(to - pawn_push(us))))
643 else if (!(attacks_from(type_of(pc), from) & to))
646 // Evasions generator already takes care to avoid some kind of illegal moves
647 // and legal() relies on this. We therefore have to take care that the same
648 // kind of moves are filtered out here.
651 if (type_of(pc) != KING)
653 // Double check? In this case a king move is required
654 if (more_than_one(checkers()))
657 // Our move must be a blocking evasion or a capture of the checking piece
658 if (!((between_bb(lsb(checkers()), square<KING>(us)) | checkers()) & to))
661 // In case of king moves under check we have to remove king so as to catch
662 // invalid moves like b1a1 when opposite queen is on c1.
663 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
671 /// Position::gives_check() tests whether a pseudo-legal move gives a check
673 bool Position::gives_check(Move m) const {
676 assert(color_of(moved_piece(m)) == sideToMove);
678 Square from = from_sq(m);
679 Square to = to_sq(m);
681 // Is there a direct check?
682 if (st->checkSquares[type_of(piece_on(from))] & to)
685 // Is there a discovered check?
686 if ( (st->blockersForKing[~sideToMove] & from)
687 && !aligned(from, to, square<KING>(~sideToMove)))
696 return attacks_bb(promotion_type(m), to, pieces() ^ from) & square<KING>(~sideToMove);
698 // En passant capture with check? We have already handled the case
699 // of direct checks and ordinary discovered check, so the only case we
700 // need to handle is the unusual case of a discovered check through
701 // the captured pawn.
704 Square capsq = make_square(file_of(to), rank_of(from));
705 Bitboard b = (pieces() ^ from ^ capsq) | to;
707 return (attacks_bb< ROOK>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, ROOK))
708 | (attacks_bb<BISHOP>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, BISHOP));
713 Square rfrom = to; // Castling is encoded as 'King captures the rook'
714 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
715 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
717 return (PseudoAttacks[ROOK][rto] & square<KING>(~sideToMove))
718 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & square<KING>(~sideToMove));
727 /// Position::do_move() makes a move, and saves all information necessary
728 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
729 /// moves should be filtered out before this function is called.
731 void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
734 assert(&newSt != st);
736 thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
737 Key k = st->key ^ Zobrist::side;
739 // Copy some fields of the old state to our new StateInfo object except the
740 // ones which are going to be recalculated from scratch anyway and then switch
741 // our state pointer to point to the new (ready to be updated) state.
742 std::memcpy(&newSt, st, offsetof(StateInfo, key));
746 // Increment ply counters. In particular, rule50 will be reset to zero later on
747 // in case of a capture or a pawn move.
752 Color us = sideToMove;
754 Square from = from_sq(m);
755 Square to = to_sq(m);
756 Piece pc = piece_on(from);
757 Piece captured = type_of(m) == ENPASSANT ? make_piece(them, PAWN) : piece_on(to);
759 assert(color_of(pc) == us);
760 assert(captured == NO_PIECE || color_of(captured) == (type_of(m) != CASTLING ? them : us));
761 assert(type_of(captured) != KING);
763 if (type_of(m) == CASTLING)
765 assert(pc == make_piece(us, KING));
766 assert(captured == make_piece(us, ROOK));
769 do_castling<true>(us, from, to, rfrom, rto);
771 k ^= Zobrist::psq[captured][rfrom] ^ Zobrist::psq[captured][rto];
779 // If the captured piece is a pawn, update pawn hash key, otherwise
780 // update non-pawn material.
781 if (type_of(captured) == PAWN)
783 if (type_of(m) == ENPASSANT)
785 capsq -= pawn_push(us);
787 assert(pc == make_piece(us, PAWN));
788 assert(to == st->epSquare);
789 assert(relative_rank(us, to) == RANK_6);
790 assert(piece_on(to) == NO_PIECE);
791 assert(piece_on(capsq) == make_piece(them, PAWN));
793 board[capsq] = NO_PIECE; // Not done by remove_piece()
796 st->pawnKey ^= Zobrist::psq[captured][capsq];
799 st->nonPawnMaterial[them] -= PieceValue[MG][captured];
801 // Update board and piece lists
802 remove_piece(captured, capsq);
804 // Update material hash key and prefetch access to materialTable
805 k ^= Zobrist::psq[captured][capsq];
806 st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
807 prefetch(thisThread->materialTable[st->materialKey]);
809 // Reset rule 50 counter
814 k ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
816 // Reset en passant square
817 if (st->epSquare != SQ_NONE)
819 k ^= Zobrist::enpassant[file_of(st->epSquare)];
820 st->epSquare = SQ_NONE;
823 // Update castling rights if needed
824 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
826 int cr = castlingRightsMask[from] | castlingRightsMask[to];
827 k ^= Zobrist::castling[st->castlingRights & cr];
828 st->castlingRights &= ~cr;
831 // Move the piece. The tricky Chess960 castling is handled earlier
832 if (type_of(m) != CASTLING)
833 move_piece(pc, from, to);
835 // If the moving piece is a pawn do some special extra work
836 if (type_of(pc) == PAWN)
838 // Set en-passant square if the moved pawn can be captured
839 if ( (int(to) ^ int(from)) == 16
840 && (attacks_from<PAWN>(to - pawn_push(us), us) & pieces(them, PAWN)))
842 st->epSquare = to - pawn_push(us);
843 k ^= Zobrist::enpassant[file_of(st->epSquare)];
846 else if (type_of(m) == PROMOTION)
848 Piece promotion = make_piece(us, promotion_type(m));
850 assert(relative_rank(us, to) == RANK_8);
851 assert(type_of(promotion) >= KNIGHT && type_of(promotion) <= QUEEN);
853 remove_piece(pc, to);
854 put_piece(promotion, to);
857 k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
858 st->pawnKey ^= Zobrist::psq[pc][to];
859 st->materialKey ^= Zobrist::psq[promotion][pieceCount[promotion]-1]
860 ^ Zobrist::psq[pc][pieceCount[pc]];
863 st->nonPawnMaterial[us] += PieceValue[MG][promotion];
866 // Update pawn hash key and prefetch access to pawnsTable
867 st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
868 prefetch2(thisThread->pawnsTable[st->pawnKey]);
870 // Reset rule 50 draw counter
875 st->capturedPiece = captured;
877 // Update the key with the final value
880 // Calculate checkers bitboard (if move gives check)
881 st->checkersBB = givesCheck ? attackers_to(square<KING>(them)) & pieces(us) : 0;
883 sideToMove = ~sideToMove;
885 // Update king attacks used for fast check detection
892 /// Position::undo_move() unmakes a move. When it returns, the position should
893 /// be restored to exactly the same state as before the move was made.
895 void Position::undo_move(Move m) {
899 sideToMove = ~sideToMove;
901 Color us = sideToMove;
902 Square from = from_sq(m);
903 Square to = to_sq(m);
904 Piece pc = piece_on(to);
906 assert(empty(from) || type_of(m) == CASTLING);
907 assert(type_of(st->capturedPiece) != KING);
909 if (type_of(m) == PROMOTION)
911 assert(relative_rank(us, to) == RANK_8);
912 assert(type_of(pc) == promotion_type(m));
913 assert(type_of(pc) >= KNIGHT && type_of(pc) <= QUEEN);
915 remove_piece(pc, to);
916 pc = make_piece(us, PAWN);
920 if (type_of(m) == CASTLING)
923 do_castling<false>(us, from, to, rfrom, rto);
927 move_piece(pc, to, from); // Put the piece back at the source square
929 if (st->capturedPiece)
933 if (type_of(m) == ENPASSANT)
935 capsq -= pawn_push(us);
937 assert(type_of(pc) == PAWN);
938 assert(to == st->previous->epSquare);
939 assert(relative_rank(us, to) == RANK_6);
940 assert(piece_on(capsq) == NO_PIECE);
941 assert(st->capturedPiece == make_piece(~us, PAWN));
944 put_piece(st->capturedPiece, capsq); // Restore the captured piece
948 // Finally point our state pointer back to the previous state
956 /// Position::do_castling() is a helper used to do/undo a castling move. This
957 /// is a bit tricky in Chess960 where from/to squares can overlap.
959 void Position::do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto) {
961 bool kingSide = to > from;
962 rfrom = to; // Castling is encoded as "king captures friendly rook"
963 rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
964 to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
966 // Remove both pieces first since squares could overlap in Chess960
967 remove_piece(make_piece(us, KING), Do ? from : to);
968 remove_piece(make_piece(us, ROOK), Do ? rfrom : rto);
969 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
970 put_piece(make_piece(us, KING), Do ? to : from);
971 put_piece(make_piece(us, ROOK), Do ? rto : rfrom);
975 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
976 /// the side to move without executing any move on the board.
978 void Position::do_null_move(StateInfo& newSt) {
981 assert(&newSt != st);
983 std::memcpy(&newSt, st, sizeof(StateInfo));
987 if (st->epSquare != SQ_NONE)
989 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
990 st->epSquare = SQ_NONE;
993 st->key ^= Zobrist::side;
994 prefetch(TT.first_entry(st->key));
997 st->pliesFromNull = 0;
999 sideToMove = ~sideToMove;
1003 assert(pos_is_ok());
1006 void Position::undo_null_move() {
1008 assert(!checkers());
1011 sideToMove = ~sideToMove;
1015 /// Position::key_after() computes the new hash key after the given move. Needed
1016 /// for speculative prefetch. It doesn't recognize special moves like castling,
1017 /// en-passant and promotions.
1019 Key Position::key_after(Move m) const {
1021 Square from = from_sq(m);
1022 Square to = to_sq(m);
1023 Piece pc = piece_on(from);
1024 Piece captured = piece_on(to);
1025 Key k = st->key ^ Zobrist::side;
1028 k ^= Zobrist::psq[captured][to];
1030 return k ^ Zobrist::psq[pc][to] ^ Zobrist::psq[pc][from];
1034 /// Position::see_ge (Static Exchange Evaluation Greater or Equal) tests if the
1035 /// SEE value of move is greater or equal to the given threshold. We'll use an
1036 /// algorithm similar to alpha-beta pruning with a null window.
1038 bool Position::see_ge(Move m, Value threshold) const {
1042 // Only deal with normal moves, assume others pass a simple see
1043 if (type_of(m) != NORMAL)
1044 return VALUE_ZERO >= threshold;
1046 Bitboard stmAttackers;
1047 Square from = from_sq(m), to = to_sq(m);
1048 PieceType nextVictim = type_of(piece_on(from));
1049 Color us = color_of(piece_on(from));
1050 Color stm = ~us; // First consider opponent's move
1051 Value balance; // Values of the pieces taken by us minus opponent's ones
1053 // The opponent may be able to recapture so this is the best result
1055 balance = PieceValue[MG][piece_on(to)] - threshold;
1057 if (balance < VALUE_ZERO)
1060 // Now assume the worst possible result: that the opponent can
1061 // capture our piece for free.
1062 balance -= PieceValue[MG][nextVictim];
1064 // If it is enough (like in PxQ) then return immediately. Note that
1065 // in case nextVictim == KING we always return here, this is ok
1066 // if the given move is legal.
1067 if (balance >= VALUE_ZERO)
1070 // Find all attackers to the destination square, with the moving piece
1071 // removed, but possibly an X-ray attacker added behind it.
1072 Bitboard occupied = pieces() ^ from ^ to;
1073 Bitboard attackers = attackers_to(to, occupied) & occupied;
1077 stmAttackers = attackers & pieces(stm);
1079 // Don't allow pinned pieces to attack (except the king) as long as
1080 // any pinners are on their original square.
1081 if (st->pinners[~stm] & occupied)
1082 stmAttackers &= ~st->blockersForKing[stm];
1084 // If stm has no more attackers then give up: stm loses
1088 // Locate and remove the next least valuable attacker, and add to
1089 // the bitboard 'attackers' the possibly X-ray attackers behind it.
1090 nextVictim = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1092 stm = ~stm; // Switch side to move
1094 // Negamax the balance with alpha = balance, beta = balance+1 and
1095 // add nextVictim's value.
1097 // (balance, balance+1) -> (-balance-1, -balance)
1099 assert(balance < VALUE_ZERO);
1101 balance = -balance - 1 - PieceValue[MG][nextVictim];
1103 // If balance is still non-negative after giving away nextVictim then we
1104 // win. The only thing to be careful about it is that we should revert
1105 // stm if we captured with the king when the opponent still has attackers.
1106 if (balance >= VALUE_ZERO)
1108 if (nextVictim == KING && (attackers & pieces(stm)))
1112 assert(nextVictim != KING);
1114 return us != stm; // We break the above loop when stm loses
1118 /// Position::is_draw() tests whether the position is drawn by 50-move rule
1119 /// or by repetition. It does not detect stalemates.
1121 bool Position::is_draw(int ply) const {
1123 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1126 int end = std::min(st->rule50, st->pliesFromNull);
1131 StateInfo* stp = st->previous->previous;
1134 for (int i = 4; i <= end; i += 2)
1136 stp = stp->previous->previous;
1138 // Return a draw score if a position repeats once earlier but strictly
1139 // after the root, or repeats twice before or at the root.
1140 if ( stp->key == st->key
1141 && ++cnt + (ply > i) == 2)
1149 // Position::has_repeated() tests whether there has been at least one repetition
1150 // of positions since the last capture or pawn move.
1152 bool Position::has_repeated() const {
1154 StateInfo* stc = st;
1157 int i = 4, end = std::min(stc->rule50, stc->pliesFromNull);
1162 StateInfo* stp = stc->previous->previous;
1165 stp = stp->previous->previous;
1167 if (stp->key == stc->key)
1173 stc = stc->previous;
1178 /// Position::has_game_cycle() tests if the position has a move which draws by repetition,
1179 /// or an earlier position has a move that directly reaches the current position.
1181 bool Position::has_game_cycle(int ply) const {
1185 int end = std::min(st->rule50, st->pliesFromNull);
1190 Key originalKey = st->key;
1191 StateInfo* stp = st->previous;
1193 for (int i = 3; i <= end; i += 2)
1195 stp = stp->previous->previous;
1197 Key moveKey = originalKey ^ stp->key;
1198 if ( (j = H1(moveKey), cuckoo[j] == moveKey)
1199 || (j = H2(moveKey), cuckoo[j] == moveKey))
1201 Move move = cuckooMove[j];
1202 Square s1 = from_sq(move);
1203 Square s2 = to_sq(move);
1205 if (!(between_bb(s1, s2) & pieces()))
1207 // In the cuckoo table, both moves Rc1c5 and Rc5c1 are stored in the same
1208 // location. We select the legal one by reversing the move variable if necessary.
1210 move = make_move(s2, s1);
1215 // For repetitions before or at the root, require one more
1216 StateInfo* next_stp = stp;
1217 for (int k = i + 2; k <= end; k += 2)
1219 next_stp = next_stp->previous->previous;
1220 if (next_stp->key == stp->key)
1230 /// Position::flip() flips position with the white and black sides reversed. This
1231 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1233 void Position::flip() {
1236 std::stringstream ss(fen());
1238 for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
1240 std::getline(ss, token, r > RANK_1 ? '/' : ' ');
1241 f.insert(0, token + (f.empty() ? " " : "/"));
1244 ss >> token; // Active color
1245 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1247 ss >> token; // Castling availability
1250 std::transform(f.begin(), f.end(), f.begin(),
1251 [](char c) { return char(islower(c) ? toupper(c) : tolower(c)); });
1253 ss >> token; // En passant square
1254 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1256 std::getline(ss, token); // Half and full moves
1259 set(f, is_chess960(), st, this_thread());
1261 assert(pos_is_ok());
1265 /// Position::pos_is_ok() performs some consistency checks for the
1266 /// position object and raises an asserts if something wrong is detected.
1267 /// This is meant to be helpful when debugging.
1269 bool Position::pos_is_ok() const {
1271 constexpr bool Fast = true; // Quick (default) or full check?
1273 if ( (sideToMove != WHITE && sideToMove != BLACK)
1274 || piece_on(square<KING>(WHITE)) != W_KING
1275 || piece_on(square<KING>(BLACK)) != B_KING
1276 || ( ep_square() != SQ_NONE
1277 && relative_rank(sideToMove, ep_square()) != RANK_6))
1278 assert(0 && "pos_is_ok: Default");
1283 if ( pieceCount[W_KING] != 1
1284 || pieceCount[B_KING] != 1
1285 || attackers_to(square<KING>(~sideToMove)) & pieces(sideToMove))
1286 assert(0 && "pos_is_ok: Kings");
1288 if ( (pieces(PAWN) & (Rank1BB | Rank8BB))
1289 || pieceCount[W_PAWN] > 8
1290 || pieceCount[B_PAWN] > 8)
1291 assert(0 && "pos_is_ok: Pawns");
1293 if ( (pieces(WHITE) & pieces(BLACK))
1294 || (pieces(WHITE) | pieces(BLACK)) != pieces()
1295 || popcount(pieces(WHITE)) > 16
1296 || popcount(pieces(BLACK)) > 16)
1297 assert(0 && "pos_is_ok: Bitboards");
1299 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1300 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1301 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1302 assert(0 && "pos_is_ok: Bitboards");
1306 if (std::memcmp(&si, st, sizeof(StateInfo)))
1307 assert(0 && "pos_is_ok: State");
1309 for (Piece pc : Pieces)
1311 if ( pieceCount[pc] != popcount(pieces(color_of(pc), type_of(pc)))
1312 || pieceCount[pc] != std::count(board, board + SQUARE_NB, pc))
1313 assert(0 && "pos_is_ok: Pieces");
1315 for (int i = 0; i < pieceCount[pc]; ++i)
1316 if (board[pieceList[pc][i]] != pc || index[pieceList[pc][i]] != i)
1317 assert(0 && "pos_is_ok: Index");
1320 for (Color c = WHITE; c <= BLACK; ++c)
1321 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1323 if (!can_castle(c | s))
1326 if ( piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1327 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s)
1328 || (castlingRightsMask[square<KING>(c)] & (c | s)) != (c | s))
1329 assert(0 && "pos_is_ok: Castling");