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) 2015-2018 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"
40 extern Score psq[PIECE_NB][SQUARE_NB];
45 Key psq[PIECE_NB][SQUARE_NB];
46 Key enpassant[FILE_NB];
47 Key castling[CASTLING_RIGHT_NB];
53 const string PieceToChar(" PNBRQK pnbrqk");
55 constexpr Piece Pieces[] = { W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
56 B_PAWN, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING };
58 // min_attacker() is a helper function used by see_ge() to locate the least
59 // valuable attacker for the side to move, remove the attacker we just found
60 // from the bitboards and scan for new X-ray attacks behind it.
63 PieceType min_attacker(const Bitboard* byTypeBB, Square to, Bitboard stmAttackers,
64 Bitboard& occupied, Bitboard& attackers) {
66 Bitboard b = stmAttackers & byTypeBB[Pt];
68 return min_attacker<Pt + 1>(byTypeBB, to, stmAttackers, occupied, attackers);
70 occupied ^= lsb(b); // Remove the attacker from occupied
72 // Add any X-ray attack behind the just removed piece. For instance with
73 // rooks in a8 and a7 attacking a1, after removing a7 we add rook in a8.
74 // Note that new added attackers can be of any color.
75 if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
76 attackers |= attacks_bb<BISHOP>(to, occupied) & (byTypeBB[BISHOP] | byTypeBB[QUEEN]);
78 if (Pt == ROOK || Pt == QUEEN)
79 attackers |= attacks_bb<ROOK>(to, occupied) & (byTypeBB[ROOK] | byTypeBB[QUEEN]);
81 // X-ray may add already processed pieces because byTypeBB[] is constant: in
82 // the rook example, now attackers contains _again_ rook in a7, so remove it.
83 attackers &= occupied;
88 PieceType min_attacker<KING>(const Bitboard*, Square, Bitboard, Bitboard&, Bitboard&) {
89 return KING; // No need to update bitboards: it is the last cycle
95 /// operator<<(Position) returns an ASCII representation of the position
97 std::ostream& operator<<(std::ostream& os, const Position& pos) {
99 os << "\n +---+---+---+---+---+---+---+---+\n";
101 for (Rank r = RANK_8; r >= RANK_1; --r)
103 for (File f = FILE_A; f <= FILE_H; ++f)
104 os << " | " << PieceToChar[pos.piece_on(make_square(f, r))];
106 os << " |\n +---+---+---+---+---+---+---+---+\n";
109 os << "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase
110 << std::setfill('0') << std::setw(16) << pos.key()
111 << std::setfill(' ') << std::dec << "\nCheckers: ";
113 for (Bitboard b = pos.checkers(); b; )
114 os << UCI::square(pop_lsb(&b)) << " ";
116 if ( int(Tablebases::MaxCardinality) >= popcount(pos.pieces())
117 && !pos.can_castle(ANY_CASTLING))
121 p.set(pos.fen(), pos.is_chess960(), &st, pos.this_thread());
122 Tablebases::ProbeState s1, s2;
123 Tablebases::WDLScore wdl = Tablebases::probe_wdl(p, &s1);
124 int dtz = Tablebases::probe_dtz(p, &s2);
125 os << "\nTablebases WDL: " << std::setw(4) << wdl << " (" << s1 << ")"
126 << "\nTablebases DTZ: " << std::setw(4) << dtz << " (" << s2 << ")";
133 /// Position::init() initializes at startup the various arrays used to compute
136 void Position::init() {
140 for (Piece pc : Pieces)
141 for (Square s = SQ_A1; s <= SQ_H8; ++s)
142 Zobrist::psq[pc][s] = rng.rand<Key>();
144 for (File f = FILE_A; f <= FILE_H; ++f)
145 Zobrist::enpassant[f] = rng.rand<Key>();
147 for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
149 Zobrist::castling[cr] = 0;
153 Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
154 Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
158 Zobrist::side = rng.rand<Key>();
159 Zobrist::noPawns = rng.rand<Key>();
163 /// Position::set() initializes the position object with the given FEN string.
164 /// This function is not very robust - make sure that input FENs are correct,
165 /// this is assumed to be the responsibility of the GUI.
167 Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Thread* th) {
169 A FEN string defines a particular position using only the ASCII character set.
171 A FEN string contains six fields separated by a space. The fields are:
173 1) Piece placement (from white's perspective). Each rank is described, starting
174 with rank 8 and ending with rank 1. Within each rank, the contents of each
175 square are described from file A through file H. Following the Standard
176 Algebraic Notation (SAN), each piece is identified by a single letter taken
177 from the standard English names. White pieces are designated using upper-case
178 letters ("PNBRQK") whilst Black uses lowercase ("pnbrqk"). Blank squares are
179 noted using digits 1 through 8 (the number of blank squares), and "/"
182 2) Active color. "w" means white moves next, "b" means black.
184 3) Castling availability. If neither side can castle, this is "-". Otherwise,
185 this has one or more letters: "K" (White can castle kingside), "Q" (White
186 can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
187 can castle queenside).
189 4) En passant target square (in algebraic notation). If there's no en passant
190 target square, this is "-". If a pawn has just made a 2-square move, this
191 is the position "behind" the pawn. This is recorded only if there is a pawn
192 in position to make an en passant capture, and if there really is a pawn
193 that might have advanced two squares.
195 5) Halfmove clock. This is the number of halfmoves since the last pawn advance
196 or capture. This is used to determine if a draw can be claimed under the
199 6) Fullmove number. The number of the full move. It starts at 1, and is
200 incremented after Black's move.
203 unsigned char col, row, token;
206 std::istringstream ss(fenStr);
208 std::memset(this, 0, sizeof(Position));
209 std::memset(si, 0, sizeof(StateInfo));
210 std::fill_n(&pieceList[0][0], sizeof(pieceList) / sizeof(Square), SQ_NONE);
215 // 1. Piece placement
216 while ((ss >> token) && !isspace(token))
219 sq += (token - '0') * EAST; // Advance the given number of files
221 else if (token == '/')
224 else if ((idx = PieceToChar.find(token)) != string::npos)
226 put_piece(Piece(idx), sq);
233 sideToMove = (token == 'w' ? WHITE : BLACK);
236 // 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
237 // Shredder-FEN that uses the letters of the columns on which the rooks began
238 // the game instead of KQkq and also X-FEN standard that, in case of Chess960,
239 // if an inner rook is associated with the castling right, the castling tag is
240 // replaced by the file letter of the involved rook, as for the Shredder-FEN.
241 while ((ss >> token) && !isspace(token))
244 Color c = islower(token) ? BLACK : WHITE;
245 Piece rook = make_piece(c, ROOK);
247 token = char(toupper(token));
250 for (rsq = relative_square(c, SQ_H1); piece_on(rsq) != rook; --rsq) {}
252 else if (token == 'Q')
253 for (rsq = relative_square(c, SQ_A1); piece_on(rsq) != rook; ++rsq) {}
255 else if (token >= 'A' && token <= 'H')
256 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
261 set_castling_right(c, rsq);
264 // 4. En passant square. Ignore if no pawn capture is possible
265 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
266 && ((ss >> row) && (row == '3' || row == '6')))
268 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
270 if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))
271 || !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove))))
272 st->epSquare = SQ_NONE;
275 st->epSquare = SQ_NONE;
277 // 5-6. Halfmove clock and fullmove number
278 ss >> std::skipws >> st->rule50 >> gamePly;
280 // Convert from fullmove starting from 1 to gamePly starting from 0,
281 // handle also common incorrect FEN with fullmove = 0.
282 gamePly = std::max(2 * (gamePly - 1), 0) + (sideToMove == BLACK);
284 chess960 = isChess960;
294 /// Position::set_castling_right() is a helper function used to set castling
295 /// rights given the corresponding color and the rook starting square.
297 void Position::set_castling_right(Color c, Square rfrom) {
299 Square kfrom = square<KING>(c);
300 CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
301 CastlingRight cr = (c | cs);
303 st->castlingRights |= cr;
304 castlingRightsMask[kfrom] |= cr;
305 castlingRightsMask[rfrom] |= cr;
306 castlingRookSquare[cr] = rfrom;
308 Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
309 Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
311 for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
312 if (s != kfrom && s != rfrom)
313 castlingPath[cr] |= s;
315 for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
316 if (s != kfrom && s != rfrom)
317 castlingPath[cr] |= s;
321 /// Position::set_check_info() sets king attacks to detect if a move gives check
323 void Position::set_check_info(StateInfo* si) const {
325 si->blockersForKing[WHITE] = slider_blockers(pieces(BLACK), square<KING>(WHITE), si->pinners[BLACK]);
326 si->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK), si->pinners[WHITE]);
328 Square ksq = square<KING>(~sideToMove);
330 si->checkSquares[PAWN] = attacks_from<PAWN>(ksq, ~sideToMove);
331 si->checkSquares[KNIGHT] = attacks_from<KNIGHT>(ksq);
332 si->checkSquares[BISHOP] = attacks_from<BISHOP>(ksq);
333 si->checkSquares[ROOK] = attacks_from<ROOK>(ksq);
334 si->checkSquares[QUEEN] = si->checkSquares[BISHOP] | si->checkSquares[ROOK];
335 si->checkSquares[KING] = 0;
339 /// Position::set_state() computes the hash keys of the position, and other
340 /// data that once computed is updated incrementally as moves are made.
341 /// The function is only used when a new position is set up, and to verify
342 /// the correctness of the StateInfo data when running in debug mode.
344 void Position::set_state(StateInfo* si) const {
346 si->key = si->materialKey = 0;
347 si->pawnKey = Zobrist::noPawns;
348 si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
349 si->psq = SCORE_ZERO;
350 si->checkersBB = attackers_to(square<KING>(sideToMove)) & pieces(~sideToMove);
354 for (Bitboard b = pieces(); b; )
356 Square s = pop_lsb(&b);
357 Piece pc = piece_on(s);
358 si->key ^= Zobrist::psq[pc][s];
359 si->psq += PSQT::psq[pc][s];
362 if (si->epSquare != SQ_NONE)
363 si->key ^= Zobrist::enpassant[file_of(si->epSquare)];
365 if (sideToMove == BLACK)
366 si->key ^= Zobrist::side;
368 si->key ^= Zobrist::castling[si->castlingRights];
370 for (Bitboard b = pieces(PAWN); b; )
372 Square s = pop_lsb(&b);
373 si->pawnKey ^= Zobrist::psq[piece_on(s)][s];
376 for (Piece pc : Pieces)
378 if (type_of(pc) != PAWN && type_of(pc) != KING)
379 si->nonPawnMaterial[color_of(pc)] += pieceCount[pc] * PieceValue[MG][pc];
381 for (int cnt = 0; cnt < pieceCount[pc]; ++cnt)
382 si->materialKey ^= Zobrist::psq[pc][cnt];
387 /// Position::set() is an overload to initialize the position object with
388 /// the given endgame code string like "KBPKN". It is mainly a helper to
389 /// get the material key out of an endgame code.
391 Position& Position::set(const string& code, Color c, StateInfo* si) {
393 assert(code.length() > 0 && code.length() < 8);
394 assert(code[0] == 'K');
396 string sides[] = { code.substr(code.find('K', 1)), // Weak
397 code.substr(0, code.find('K', 1)) }; // Strong
399 std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
401 string fenStr = "8/" + sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/"
402 + sides[1] + char(8 - sides[1].length() + '0') + "/8 w - - 0 10";
404 return set(fenStr, false, si, nullptr);
408 /// Position::fen() returns a FEN representation of the position. In case of
409 /// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function.
411 const string Position::fen() const {
414 std::ostringstream ss;
416 for (Rank r = RANK_8; r >= RANK_1; --r)
418 for (File f = FILE_A; f <= FILE_H; ++f)
420 for (emptyCnt = 0; f <= FILE_H && empty(make_square(f, r)); ++f)
427 ss << PieceToChar[piece_on(make_square(f, r))];
434 ss << (sideToMove == WHITE ? " w " : " b ");
436 if (can_castle(WHITE_OO))
437 ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | KING_SIDE))) : 'K');
439 if (can_castle(WHITE_OOO))
440 ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | QUEEN_SIDE))) : 'Q');
442 if (can_castle(BLACK_OO))
443 ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | KING_SIDE))) : 'k');
445 if (can_castle(BLACK_OOO))
446 ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | QUEEN_SIDE))) : 'q');
448 if (!can_castle(WHITE) && !can_castle(BLACK))
451 ss << (ep_square() == SQ_NONE ? " - " : " " + UCI::square(ep_square()) + " ")
452 << st->rule50 << " " << 1 + (gamePly - (sideToMove == BLACK)) / 2;
458 /// Position::slider_blockers() returns a bitboard of all the pieces (both colors)
459 /// that are blocking attacks on the square 's' from 'sliders'. A piece blocks a
460 /// slider if removing that piece from the board would result in a position where
461 /// square 's' is attacked. For example, a king-attack blocking piece can be either
462 /// a pinned or a discovered check piece, according if its color is the opposite
463 /// or the same of the color of the slider.
465 Bitboard Position::slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const {
467 Bitboard blockers = 0;
470 // Snipers are sliders that attack 's' when a piece is removed
471 Bitboard snipers = ( (PseudoAttacks[ ROOK][s] & pieces(QUEEN, ROOK))
472 | (PseudoAttacks[BISHOP][s] & pieces(QUEEN, BISHOP))) & sliders;
476 Square sniperSq = pop_lsb(&snipers);
477 Bitboard b = between_bb(s, sniperSq) & pieces();
479 if (b && !more_than_one(b))
482 if (b & pieces(color_of(piece_on(s))))
490 /// Position::attackers_to() computes a bitboard of all pieces which attack a
491 /// given square. Slider attacks use the occupied bitboard to indicate occupancy.
493 Bitboard Position::attackers_to(Square s, Bitboard occupied) const {
495 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
496 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
497 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
498 | (attacks_bb< ROOK>(s, occupied) & pieces( ROOK, QUEEN))
499 | (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
500 | (attacks_from<KING>(s) & pieces(KING));
504 /// Position::legal() tests whether a pseudo-legal move is legal
506 bool Position::legal(Move m) const {
510 Color us = sideToMove;
511 Square from = from_sq(m);
513 assert(color_of(moved_piece(m)) == us);
514 assert(piece_on(square<KING>(us)) == make_piece(us, KING));
516 // En passant captures are a tricky special case. Because they are rather
517 // uncommon, we do it simply by testing whether the king is attacked after
519 if (type_of(m) == ENPASSANT)
521 Square ksq = square<KING>(us);
522 Square to = to_sq(m);
523 Square capsq = to - pawn_push(us);
524 Bitboard occupied = (pieces() ^ from ^ capsq) | to;
526 assert(to == ep_square());
527 assert(moved_piece(m) == make_piece(us, PAWN));
528 assert(piece_on(capsq) == make_piece(~us, PAWN));
529 assert(piece_on(to) == NO_PIECE);
531 return !(attacks_bb< ROOK>(ksq, occupied) & pieces(~us, QUEEN, ROOK))
532 && !(attacks_bb<BISHOP>(ksq, occupied) & pieces(~us, QUEEN, BISHOP));
535 // If the moving piece is a king, check whether the destination
536 // square is attacked by the opponent. Castling moves are checked
537 // for legality during move generation.
538 if (type_of(piece_on(from)) == KING)
539 return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
541 // A non-king move is legal if and only if it is not pinned or it
542 // is moving along the ray towards or away from the king.
543 return !(blockers_for_king(us) & from)
544 || aligned(from, to_sq(m), square<KING>(us));
548 /// Position::pseudo_legal() takes a random move and tests whether the move is
549 /// pseudo legal. It is used to validate moves from TT that can be corrupted
550 /// due to SMP concurrent access or hash position key aliasing.
552 bool Position::pseudo_legal(const Move m) const {
554 Color us = sideToMove;
555 Square from = from_sq(m);
556 Square to = to_sq(m);
557 Piece pc = moved_piece(m);
559 // Use a slower but simpler function for uncommon cases
560 if (type_of(m) != NORMAL)
561 return MoveList<LEGAL>(*this).contains(m);
563 // Is not a promotion, so promotion piece must be empty
564 if (promotion_type(m) - KNIGHT != NO_PIECE_TYPE)
567 // If the 'from' square is not occupied by a piece belonging to the side to
568 // move, the move is obviously not legal.
569 if (pc == NO_PIECE || color_of(pc) != us)
572 // The destination square cannot be occupied by a friendly piece
576 // Handle the special case of a pawn move
577 if (type_of(pc) == PAWN)
579 // We have already handled promotion moves, so destination
580 // cannot be on the 8th/1st rank.
581 if (rank_of(to) == relative_rank(us, RANK_8))
584 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
585 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
586 && !( (from + 2 * pawn_push(us) == to) // Not a double push
587 && (rank_of(from) == relative_rank(us, RANK_2))
589 && empty(to - pawn_push(us))))
592 else if (!(attacks_from(type_of(pc), from) & to))
595 // Evasions generator already takes care to avoid some kind of illegal moves
596 // and legal() relies on this. We therefore have to take care that the same
597 // kind of moves are filtered out here.
600 if (type_of(pc) != KING)
602 // Double check? In this case a king move is required
603 if (more_than_one(checkers()))
606 // Our move must be a blocking evasion or a capture of the checking piece
607 if (!((between_bb(lsb(checkers()), square<KING>(us)) | checkers()) & to))
610 // In case of king moves under check we have to remove king so as to catch
611 // invalid moves like b1a1 when opposite queen is on c1.
612 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
620 /// Position::gives_check() tests whether a pseudo-legal move gives a check
622 bool Position::gives_check(Move m) const {
625 assert(color_of(moved_piece(m)) == sideToMove);
627 Square from = from_sq(m);
628 Square to = to_sq(m);
630 // Is there a direct check?
631 if (st->checkSquares[type_of(piece_on(from))] & to)
634 // Is there a discovered check?
635 if ( (st->blockersForKing[~sideToMove] & from)
636 && !aligned(from, to, square<KING>(~sideToMove)))
645 return attacks_bb(promotion_type(m), to, pieces() ^ from) & square<KING>(~sideToMove);
647 // En passant capture with check? We have already handled the case
648 // of direct checks and ordinary discovered check, so the only case we
649 // need to handle is the unusual case of a discovered check through
650 // the captured pawn.
653 Square capsq = make_square(file_of(to), rank_of(from));
654 Bitboard b = (pieces() ^ from ^ capsq) | to;
656 return (attacks_bb< ROOK>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, ROOK))
657 | (attacks_bb<BISHOP>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, BISHOP));
662 Square rfrom = to; // Castling is encoded as 'King captures the rook'
663 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
664 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
666 return (PseudoAttacks[ROOK][rto] & square<KING>(~sideToMove))
667 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & square<KING>(~sideToMove));
676 /// Position::do_move() makes a move, and saves all information necessary
677 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
678 /// moves should be filtered out before this function is called.
680 void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
683 assert(&newSt != st);
685 thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
686 Key k = st->key ^ Zobrist::side;
688 // Copy some fields of the old state to our new StateInfo object except the
689 // ones which are going to be recalculated from scratch anyway and then switch
690 // our state pointer to point to the new (ready to be updated) state.
691 std::memcpy(&newSt, st, offsetof(StateInfo, key));
695 // Increment ply counters. In particular, rule50 will be reset to zero later on
696 // in case of a capture or a pawn move.
701 Color us = sideToMove;
703 Square from = from_sq(m);
704 Square to = to_sq(m);
705 Piece pc = piece_on(from);
706 Piece captured = type_of(m) == ENPASSANT ? make_piece(them, PAWN) : piece_on(to);
708 assert(color_of(pc) == us);
709 assert(captured == NO_PIECE || color_of(captured) == (type_of(m) != CASTLING ? them : us));
710 assert(type_of(captured) != KING);
712 if (type_of(m) == CASTLING)
714 assert(pc == make_piece(us, KING));
715 assert(captured == make_piece(us, ROOK));
718 do_castling<true>(us, from, to, rfrom, rto);
720 st->psq += PSQT::psq[captured][rto] - PSQT::psq[captured][rfrom];
721 k ^= Zobrist::psq[captured][rfrom] ^ Zobrist::psq[captured][rto];
729 // If the captured piece is a pawn, update pawn hash key, otherwise
730 // update non-pawn material.
731 if (type_of(captured) == PAWN)
733 if (type_of(m) == ENPASSANT)
735 capsq -= pawn_push(us);
737 assert(pc == make_piece(us, PAWN));
738 assert(to == st->epSquare);
739 assert(relative_rank(us, to) == RANK_6);
740 assert(piece_on(to) == NO_PIECE);
741 assert(piece_on(capsq) == make_piece(them, PAWN));
743 board[capsq] = NO_PIECE; // Not done by remove_piece()
746 st->pawnKey ^= Zobrist::psq[captured][capsq];
749 st->nonPawnMaterial[them] -= PieceValue[MG][captured];
751 // Update board and piece lists
752 remove_piece(captured, capsq);
754 // Update material hash key and prefetch access to materialTable
755 k ^= Zobrist::psq[captured][capsq];
756 st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
757 prefetch(thisThread->materialTable[st->materialKey]);
759 // Update incremental scores
760 st->psq -= PSQT::psq[captured][capsq];
762 // Reset rule 50 counter
767 k ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
769 // Reset en passant square
770 if (st->epSquare != SQ_NONE)
772 k ^= Zobrist::enpassant[file_of(st->epSquare)];
773 st->epSquare = SQ_NONE;
776 // Update castling rights if needed
777 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
779 int cr = castlingRightsMask[from] | castlingRightsMask[to];
780 k ^= Zobrist::castling[st->castlingRights & cr];
781 st->castlingRights &= ~cr;
784 // Move the piece. The tricky Chess960 castling is handled earlier
785 if (type_of(m) != CASTLING)
786 move_piece(pc, from, to);
788 // If the moving piece is a pawn do some special extra work
789 if (type_of(pc) == PAWN)
791 // Set en-passant square if the moved pawn can be captured
792 if ( (int(to) ^ int(from)) == 16
793 && (attacks_from<PAWN>(to - pawn_push(us), us) & pieces(them, PAWN)))
795 st->epSquare = to - pawn_push(us);
796 k ^= Zobrist::enpassant[file_of(st->epSquare)];
799 else if (type_of(m) == PROMOTION)
801 Piece promotion = make_piece(us, promotion_type(m));
803 assert(relative_rank(us, to) == RANK_8);
804 assert(type_of(promotion) >= KNIGHT && type_of(promotion) <= QUEEN);
806 remove_piece(pc, to);
807 put_piece(promotion, to);
810 k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
811 st->pawnKey ^= Zobrist::psq[pc][to];
812 st->materialKey ^= Zobrist::psq[promotion][pieceCount[promotion]-1]
813 ^ Zobrist::psq[pc][pieceCount[pc]];
815 // Update incremental score
816 st->psq += PSQT::psq[promotion][to] - PSQT::psq[pc][to];
819 st->nonPawnMaterial[us] += PieceValue[MG][promotion];
822 // Update pawn hash key and prefetch access to pawnsTable
823 st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
824 prefetch2(thisThread->pawnsTable[st->pawnKey]);
826 // Reset rule 50 draw counter
830 // Update incremental scores
831 st->psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
834 st->capturedPiece = captured;
836 // Update the key with the final value
839 // Calculate checkers bitboard (if move gives check)
840 st->checkersBB = givesCheck ? attackers_to(square<KING>(them)) & pieces(us) : 0;
842 sideToMove = ~sideToMove;
844 // Update king attacks used for fast check detection
851 /// Position::undo_move() unmakes a move. When it returns, the position should
852 /// be restored to exactly the same state as before the move was made.
854 void Position::undo_move(Move m) {
858 sideToMove = ~sideToMove;
860 Color us = sideToMove;
861 Square from = from_sq(m);
862 Square to = to_sq(m);
863 Piece pc = piece_on(to);
865 assert(empty(from) || type_of(m) == CASTLING);
866 assert(type_of(st->capturedPiece) != KING);
868 if (type_of(m) == PROMOTION)
870 assert(relative_rank(us, to) == RANK_8);
871 assert(type_of(pc) == promotion_type(m));
872 assert(type_of(pc) >= KNIGHT && type_of(pc) <= QUEEN);
874 remove_piece(pc, to);
875 pc = make_piece(us, PAWN);
879 if (type_of(m) == CASTLING)
882 do_castling<false>(us, from, to, rfrom, rto);
886 move_piece(pc, to, from); // Put the piece back at the source square
888 if (st->capturedPiece)
892 if (type_of(m) == ENPASSANT)
894 capsq -= pawn_push(us);
896 assert(type_of(pc) == PAWN);
897 assert(to == st->previous->epSquare);
898 assert(relative_rank(us, to) == RANK_6);
899 assert(piece_on(capsq) == NO_PIECE);
900 assert(st->capturedPiece == make_piece(~us, PAWN));
903 put_piece(st->capturedPiece, capsq); // Restore the captured piece
907 // Finally point our state pointer back to the previous state
915 /// Position::do_castling() is a helper used to do/undo a castling move. This
916 /// is a bit tricky in Chess960 where from/to squares can overlap.
918 void Position::do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto) {
920 bool kingSide = to > from;
921 rfrom = to; // Castling is encoded as "king captures friendly rook"
922 rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
923 to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
925 // Remove both pieces first since squares could overlap in Chess960
926 remove_piece(make_piece(us, KING), Do ? from : to);
927 remove_piece(make_piece(us, ROOK), Do ? rfrom : rto);
928 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
929 put_piece(make_piece(us, KING), Do ? to : from);
930 put_piece(make_piece(us, ROOK), Do ? rto : rfrom);
934 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
935 /// the side to move without executing any move on the board.
937 void Position::do_null_move(StateInfo& newSt) {
940 assert(&newSt != st);
942 std::memcpy(&newSt, st, sizeof(StateInfo));
946 if (st->epSquare != SQ_NONE)
948 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
949 st->epSquare = SQ_NONE;
952 st->key ^= Zobrist::side;
953 prefetch(TT.first_entry(st->key));
956 st->pliesFromNull = 0;
958 sideToMove = ~sideToMove;
965 void Position::undo_null_move() {
970 sideToMove = ~sideToMove;
974 /// Position::key_after() computes the new hash key after the given move. Needed
975 /// for speculative prefetch. It doesn't recognize special moves like castling,
976 /// en-passant and promotions.
978 Key Position::key_after(Move m) const {
980 Square from = from_sq(m);
981 Square to = to_sq(m);
982 Piece pc = piece_on(from);
983 Piece captured = piece_on(to);
984 Key k = st->key ^ Zobrist::side;
987 k ^= Zobrist::psq[captured][to];
989 return k ^ Zobrist::psq[pc][to] ^ Zobrist::psq[pc][from];
993 /// Position::see_ge (Static Exchange Evaluation Greater or Equal) tests if the
994 /// SEE value of move is greater or equal to the given threshold. We'll use an
995 /// algorithm similar to alpha-beta pruning with a null window.
997 bool Position::see_ge(Move m, Value threshold) const {
1001 // Only deal with normal moves, assume others pass a simple see
1002 if (type_of(m) != NORMAL)
1003 return VALUE_ZERO >= threshold;
1005 Bitboard stmAttackers;
1006 Square from = from_sq(m), to = to_sq(m);
1007 PieceType nextVictim = type_of(piece_on(from));
1008 Color us = color_of(piece_on(from));
1009 Color stm = ~us; // First consider opponent's move
1010 Value balance; // Values of the pieces taken by us minus opponent's ones
1012 // The opponent may be able to recapture so this is the best result
1014 balance = PieceValue[MG][piece_on(to)] - threshold;
1016 if (balance < VALUE_ZERO)
1019 // Now assume the worst possible result: that the opponent can
1020 // capture our piece for free.
1021 balance -= PieceValue[MG][nextVictim];
1023 // If it is enough (like in PxQ) then return immediately. Note that
1024 // in case nextVictim == KING we always return here, this is ok
1025 // if the given move is legal.
1026 if (balance >= VALUE_ZERO)
1029 // Find all attackers to the destination square, with the moving piece
1030 // removed, but possibly an X-ray attacker added behind it.
1031 Bitboard occupied = pieces() ^ from ^ to;
1032 Bitboard attackers = attackers_to(to, occupied) & occupied;
1036 stmAttackers = attackers & pieces(stm);
1038 // Don't allow pinned pieces to attack (except the king) as long as
1039 // all pinners are on their original square.
1040 if (!(st->pinners[~stm] & ~occupied))
1041 stmAttackers &= ~st->blockersForKing[stm];
1043 // If stm has no more attackers then give up: stm loses
1047 // Locate and remove the next least valuable attacker, and add to
1048 // the bitboard 'attackers' the possibly X-ray attackers behind it.
1049 nextVictim = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1051 stm = ~stm; // Switch side to move
1053 // Negamax the balance with alpha = balance, beta = balance+1 and
1054 // add nextVictim's value.
1056 // (balance, balance+1) -> (-balance-1, -balance)
1058 assert(balance < VALUE_ZERO);
1060 balance = -balance - 1 - PieceValue[MG][nextVictim];
1062 // If balance is still non-negative after giving away nextVictim then we
1063 // win. The only thing to be careful about it is that we should revert
1064 // stm if we captured with the king when the opponent still has attackers.
1065 if (balance >= VALUE_ZERO)
1067 if (nextVictim == KING && (attackers & pieces(stm)))
1071 assert(nextVictim != KING);
1073 return us != stm; // We break the above loop when stm loses
1077 /// Position::is_draw() tests whether the position is drawn by 50-move rule
1078 /// or by repetition. It does not detect stalemates.
1080 bool Position::is_draw(int ply) const {
1082 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1085 int end = std::min(st->rule50, st->pliesFromNull);
1090 StateInfo* stp = st->previous->previous;
1093 for (int i = 4; i <= end; i += 2)
1095 stp = stp->previous->previous;
1097 // Return a draw score if a position repeats once earlier but strictly
1098 // after the root, or repeats twice before or at the root.
1099 if ( stp->key == st->key
1100 && ++cnt + (ply > i) == 2)
1108 // Position::has_repeated() tests whether there has been at least one repetition
1109 // of positions since the last capture or pawn move.
1111 bool Position::has_repeated() const {
1113 StateInfo* stc = st;
1116 int i = 4, e = std::min(stc->rule50, stc->pliesFromNull);
1121 StateInfo* stp = st->previous->previous;
1124 stp = stp->previous->previous;
1126 if (stp->key == stc->key)
1132 stc = stc->previous;
1137 /// Position::flip() flips position with the white and black sides reversed. This
1138 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1140 void Position::flip() {
1143 std::stringstream ss(fen());
1145 for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
1147 std::getline(ss, token, r > RANK_1 ? '/' : ' ');
1148 f.insert(0, token + (f.empty() ? " " : "/"));
1151 ss >> token; // Active color
1152 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1154 ss >> token; // Castling availability
1157 std::transform(f.begin(), f.end(), f.begin(),
1158 [](char c) { return char(islower(c) ? toupper(c) : tolower(c)); });
1160 ss >> token; // En passant square
1161 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1163 std::getline(ss, token); // Half and full moves
1166 set(f, is_chess960(), st, this_thread());
1168 assert(pos_is_ok());
1172 /// Position::pos_is_ok() performs some consistency checks for the
1173 /// position object and raises an asserts if something wrong is detected.
1174 /// This is meant to be helpful when debugging.
1176 bool Position::pos_is_ok() const {
1178 constexpr bool Fast = true; // Quick (default) or full check?
1180 if ( (sideToMove != WHITE && sideToMove != BLACK)
1181 || piece_on(square<KING>(WHITE)) != W_KING
1182 || piece_on(square<KING>(BLACK)) != B_KING
1183 || ( ep_square() != SQ_NONE
1184 && relative_rank(sideToMove, ep_square()) != RANK_6))
1185 assert(0 && "pos_is_ok: Default");
1190 if ( pieceCount[W_KING] != 1
1191 || pieceCount[B_KING] != 1
1192 || attackers_to(square<KING>(~sideToMove)) & pieces(sideToMove))
1193 assert(0 && "pos_is_ok: Kings");
1195 if ( (pieces(PAWN) & (Rank1BB | Rank8BB))
1196 || pieceCount[W_PAWN] > 8
1197 || pieceCount[B_PAWN] > 8)
1198 assert(0 && "pos_is_ok: Pawns");
1200 if ( (pieces(WHITE) & pieces(BLACK))
1201 || (pieces(WHITE) | pieces(BLACK)) != pieces()
1202 || popcount(pieces(WHITE)) > 16
1203 || popcount(pieces(BLACK)) > 16)
1204 assert(0 && "pos_is_ok: Bitboards");
1206 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1207 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1208 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1209 assert(0 && "pos_is_ok: Bitboards");
1213 if (std::memcmp(&si, st, sizeof(StateInfo)))
1214 assert(0 && "pos_is_ok: State");
1216 for (Piece pc : Pieces)
1218 if ( pieceCount[pc] != popcount(pieces(color_of(pc), type_of(pc)))
1219 || pieceCount[pc] != std::count(board, board + SQUARE_NB, pc))
1220 assert(0 && "pos_is_ok: Pieces");
1222 for (int i = 0; i < pieceCount[pc]; ++i)
1223 if (board[pieceList[pc][i]] != pc || index[pieceList[pc][i]] != i)
1224 assert(0 && "pos_is_ok: Index");
1227 for (Color c = WHITE; c <= BLACK; ++c)
1228 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1230 if (!can_castle(c | s))
1233 if ( piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1234 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s)
1235 || (castlingRightsMask[square<KING>(c)] & (c | s)) != (c | s))
1236 assert(0 && "pos_is_ok: Castling");