2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
41 #include "ucioption.h"
47 static inline bool isZero(char c) { return c == '0'; }
49 struct PieceLetters : public std::map<char, Piece> {
53 operator[]('K') = WK; operator[]('k') = BK;
54 operator[]('Q') = WQ; operator[]('q') = BQ;
55 operator[]('R') = WR; operator[]('r') = BR;
56 operator[]('B') = WB; operator[]('b') = BB;
57 operator[]('N') = WN; operator[]('n') = BN;
58 operator[]('P') = WP; operator[]('p') = BP;
59 operator[](' ') = PIECE_NONE; operator[]('.') = PIECE_NONE_DARK_SQ;
62 char from_piece(Piece p) const {
64 std::map<char, Piece>::const_iterator it;
65 for (it = begin(); it != end(); ++it)
76 //// Constants and variables
79 /// Bonus for having the side to move (modified by Joona Kiiski)
81 static const Score TempoValue = make_score(48, 22);
84 Key Position::zobrist[2][8][64];
85 Key Position::zobEp[64];
86 Key Position::zobCastle[16];
87 Key Position::zobSideToMove;
88 Key Position::zobExclusion;
90 Score Position::PieceSquareTable[16][64];
92 static PieceLetters pieceLetters;
94 // Material values used by SEE, indexed by PieceType
95 const Value Position::seeValues[] = {
96 VALUE_ZERO, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
97 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
103 CheckInfo::CheckInfo(const Position& pos) {
105 Color us = pos.side_to_move();
106 Color them = opposite_color(us);
108 ksq = pos.king_square(them);
109 dcCandidates = pos.discovered_check_candidates(us);
111 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
112 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
113 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
114 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
115 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
116 checkSq[KING] = EmptyBoardBB;
120 /// Position c'tors. Here we always create a copy of the original position
121 /// or the FEN string, we want the new born Position object do not depend
122 /// on any external data so we detach state pointer from the source one.
124 Position::Position(const Position& pos, int th) {
126 memcpy(this, &pos, sizeof(Position));
127 detach(); // Always detach() in copy c'tor to avoid surprises
132 Position::Position(const string& fen, int th) {
139 /// Position::detach() copies the content of the current state and castling
140 /// masks inside the position itself. This is needed when the st pointee could
141 /// become stale, as example because the caller is about to going out of scope.
143 void Position::detach() {
147 st->previous = NULL; // as a safe guard
151 /// Position::from_fen() initializes the position object with the given FEN
152 /// string. This function is not very robust - make sure that input FENs are
153 /// correct (this is assumed to be the responsibility of the GUI).
155 void Position::from_fen(const string& fen) {
157 A FEN string defines a particular position using only the ASCII character set.
159 A FEN string contains six fields. The separator between fields is a space. The fields are:
161 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
162 with rank 1; within each rank, the contents of each square are described from file a through file h.
163 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
164 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
165 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
166 of blank squares), and "/" separate ranks.
168 2) Active color. "w" means white moves next, "b" means black.
170 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
171 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
172 kingside), and/or "q" (Black can castle queenside).
174 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
175 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
176 regardless of whether there is a pawn in position to make an en passant capture.
178 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
179 to determine if a draw can be claimed under the fifty-move rule.
181 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
185 std::istringstream ss(fen);
191 // 1. Piece placement field
192 while (ss.get(token) && token != ' ')
196 file += File(token - '0'); // Skip the given number of files
199 else if (token == '/')
206 if (pieceLetters.find(token) == pieceLetters.end())
209 put_piece(pieceLetters[token], make_square(file, rank));
214 if (!ss.get(token) || (token != 'w' && token != 'b'))
217 sideToMove = (token == 'w' ? WHITE : BLACK);
219 if (!ss.get(token) || token != ' ')
222 // 3. Castling availability
223 while (ss.get(token) && token != ' ')
228 if (!set_castling_rights(token))
232 // 4. En passant square -- ignore if no capture is possible
234 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
235 && (ss.get(row) && (row == '3' || row == '6')))
237 Square fenEpSquare = make_square(file_from_char(col), rank_from_char(row));
238 Color them = opposite_color(sideToMove);
240 if (attacks_from<PAWN>(fenEpSquare, them) & pieces(PAWN, sideToMove))
241 st->epSquare = fenEpSquare;
244 // 5-6. Halfmove clock and fullmove number are not parsed
246 // Various initialisations
247 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
248 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
249 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
250 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
251 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
252 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
254 isChess960 = initialKFile != FILE_E
255 || initialQRFile != FILE_A
256 || initialKRFile != FILE_H;
260 st->key = compute_key();
261 st->pawnKey = compute_pawn_key();
262 st->materialKey = compute_material_key();
263 st->value = compute_value();
264 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
265 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
269 cout << "Error in FEN string: " << fen << endl;
273 /// Position::set_castling_rights() sets castling parameters castling avaiability.
274 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
275 /// that uses the letters of the columns on which the rooks began the game instead
276 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
277 /// associated with the castling right, the traditional castling tag will be replaced
278 /// by the file letter of the involved rook as for the Shredder-FEN.
280 bool Position::set_castling_rights(char token) {
282 Color c = token >= 'a' ? BLACK : WHITE;
283 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
284 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
285 Piece rook = (c == WHITE ? WR : BR);
287 initialKFile = square_file(king_square(c));
288 token = char(toupper(token));
292 for (Square sq = sqH; sq >= sqA; sq--)
293 if (piece_on(sq) == rook)
296 initialKRFile = square_file(sq);
300 else if (token == 'Q')
302 for (Square sq = sqA; sq <= sqH; sq++)
303 if (piece_on(sq) == rook)
306 initialQRFile = square_file(sq);
310 else if (token >= 'A' && token <= 'H')
312 File rookFile = File(token - 'A') + FILE_A;
313 if (rookFile < initialKFile)
316 initialQRFile = rookFile;
321 initialKRFile = rookFile;
330 /// Position::to_fen() returns a FEN representation of the position. In case
331 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
333 const string Position::to_fen() const {
339 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
341 for (File file = FILE_A; file <= FILE_H; file++)
343 sq = make_square(file, rank);
345 if (square_is_occupied(sq))
348 fen += pieceLetters.from_piece(piece_on(sq));
358 fen.erase(std::remove_if(fen.begin(), fen.end(), isZero), fen.end());
359 fen.erase(--fen.end());
360 fen += (sideToMove == WHITE ? " w " : " b ");
362 if (st->castleRights != CASTLES_NONE)
364 if (can_castle_kingside(WHITE))
365 fen += isChess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
367 if (can_castle_queenside(WHITE))
368 fen += isChess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
370 if (can_castle_kingside(BLACK))
371 fen += isChess960 ? file_to_char(initialKRFile) : 'k';
373 if (can_castle_queenside(BLACK))
374 fen += isChess960 ? file_to_char(initialQRFile) : 'q';
378 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
383 /// Position::print() prints an ASCII representation of the position to
384 /// the standard output. If a move is given then also the san is printed.
386 void Position::print(Move move) const {
388 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
389 static bool requestPending = false;
391 // Check for reentrancy, as example when called from inside
392 // MovePicker that is used also here in move_to_san()
396 requestPending = true;
400 Position p(*this, thread());
401 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
402 cout << "\nMove is: " << dd << move_to_san(p, move);
405 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
407 cout << dottedLine << '|';
408 for (File file = FILE_A; file <= FILE_H; file++)
410 Square sq = make_square(file, rank);
411 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
412 Piece piece = piece_on(sq);
414 if (piece == PIECE_NONE && square_color(sq) == DARK)
415 piece = PIECE_NONE_DARK_SQ;
417 cout << c << pieceLetters.from_piece(piece) << c << '|';
420 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
421 requestPending = false;
425 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
426 /// king) pieces for the given color and for the given pinner type. Or, when
427 /// template parameter FindPinned is false, the pieces of the given color
428 /// candidate for a discovery check against the enemy king.
429 /// Bitboard checkersBB must be already updated when looking for pinners.
431 template<bool FindPinned>
432 Bitboard Position::hidden_checkers(Color c) const {
434 Bitboard result = EmptyBoardBB;
435 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
437 // Pinned pieces protect our king, dicovery checks attack
439 Square ksq = king_square(FindPinned ? c : opposite_color(c));
441 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
442 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
444 if (FindPinned && pinners)
445 pinners &= ~st->checkersBB;
449 Square s = pop_1st_bit(&pinners);
450 Bitboard b = squares_between(s, ksq) & occupied_squares();
454 if ( !(b & (b - 1)) // Only one bit set?
455 && (b & pieces_of_color(c))) // Is an our piece?
462 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
463 /// king) pieces for the given color. Note that checkersBB bitboard must
464 /// be already updated.
466 Bitboard Position::pinned_pieces(Color c) const {
468 return hidden_checkers<true>(c);
472 /// Position:discovered_check_candidates() returns a bitboard containing all
473 /// pieces for the given side which are candidates for giving a discovered
474 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
475 /// to be already updated.
477 Bitboard Position::discovered_check_candidates(Color c) const {
479 return hidden_checkers<false>(c);
482 /// Position::attackers_to() computes a bitboard containing all pieces which
483 /// attacks a given square.
485 Bitboard Position::attackers_to(Square s) const {
487 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
488 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
489 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
490 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
491 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
492 | (attacks_from<KING>(s) & pieces(KING));
495 /// Position::attacks_from() computes a bitboard of all attacks
496 /// of a given piece put in a given square.
498 Bitboard Position::attacks_from(Piece p, Square s) const {
500 assert(square_is_ok(s));
504 case WP: return attacks_from<PAWN>(s, WHITE);
505 case BP: return attacks_from<PAWN>(s, BLACK);
506 case WN: case BN: return attacks_from<KNIGHT>(s);
507 case WB: case BB: return attacks_from<BISHOP>(s);
508 case WR: case BR: return attacks_from<ROOK>(s);
509 case WQ: case BQ: return attacks_from<QUEEN>(s);
510 case WK: case BK: return attacks_from<KING>(s);
517 /// Position::move_attacks_square() tests whether a move from the current
518 /// position attacks a given square.
520 bool Position::move_attacks_square(Move m, Square s) const {
522 assert(move_is_ok(m));
523 assert(square_is_ok(s));
526 Square f = move_from(m), t = move_to(m);
528 assert(square_is_occupied(f));
530 if (bit_is_set(attacks_from(piece_on(f), t), s))
533 // Move the piece and scan for X-ray attacks behind it
534 occ = occupied_squares();
535 do_move_bb(&occ, make_move_bb(f, t));
536 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
537 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
538 & pieces_of_color(color_of_piece_on(f));
540 // If we have attacks we need to verify that are caused by our move
541 // and are not already existent ones.
542 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
546 /// Position::find_checkers() computes the checkersBB bitboard, which
547 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
548 /// currently works by calling Position::attackers_to, which is probably
549 /// inefficient. Consider rewriting this function to use the last move
550 /// played, like in non-bitboard versions of Glaurung.
552 void Position::find_checkers() {
554 Color us = side_to_move();
555 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
559 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
561 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
564 assert(move_is_ok(m));
565 assert(pinned == pinned_pieces(side_to_move()));
567 // Castling moves are checked for legality during move generation.
568 if (move_is_castle(m))
571 Color us = side_to_move();
572 Square from = move_from(m);
574 assert(color_of_piece_on(from) == us);
575 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
577 // En passant captures are a tricky special case. Because they are
578 // rather uncommon, we do it simply by testing whether the king is attacked
579 // after the move is made
582 Color them = opposite_color(us);
583 Square to = move_to(m);
584 Square capsq = make_square(square_file(to), square_rank(from));
585 Bitboard b = occupied_squares();
586 Square ksq = king_square(us);
588 assert(to == ep_square());
589 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
590 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
591 assert(piece_on(to) == PIECE_NONE);
594 clear_bit(&b, capsq);
597 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
598 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
601 // If the moving piece is a king, check whether the destination
602 // square is attacked by the opponent.
603 if (type_of_piece_on(from) == KING)
604 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
606 // A non-king move is legal if and only if it is not pinned or it
607 // is moving along the ray towards or away from the king.
609 || !bit_is_set(pinned, from)
610 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
614 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
616 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
620 Color us = side_to_move();
621 Square from = move_from(m);
622 Square to = move_to(m);
624 // King moves and en-passant captures are verified in pl_move_is_legal()
625 if (type_of_piece_on(from) == KING || move_is_ep(m))
626 return pl_move_is_legal(m, pinned);
628 Bitboard target = checkers();
629 Square checksq = pop_1st_bit(&target);
631 if (target) // double check ?
634 // Our move must be a blocking evasion or a capture of the checking piece
635 target = squares_between(checksq, king_square(us)) | checkers();
636 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
640 /// Position::move_is_check() tests whether a pseudo-legal move is a check
642 bool Position::move_is_check(Move m) const {
644 return move_is_check(m, CheckInfo(*this));
647 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
650 assert(move_is_ok(m));
651 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
652 assert(color_of_piece_on(move_from(m)) == side_to_move());
653 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
655 Square from = move_from(m);
656 Square to = move_to(m);
657 PieceType pt = type_of_piece_on(from);
660 if (bit_is_set(ci.checkSq[pt], to))
664 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
666 // For pawn and king moves we need to verify also direction
667 if ( (pt != PAWN && pt != KING)
668 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
672 // Can we skip the ugly special cases ?
673 if (!move_is_special(m))
676 Color us = side_to_move();
677 Bitboard b = occupied_squares();
679 // Promotion with check ?
680 if (move_is_promotion(m))
684 switch (move_promotion_piece(m))
687 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
689 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
691 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
693 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
699 // En passant capture with check ? We have already handled the case
700 // of direct checks and ordinary discovered check, the only case we
701 // need to handle is the unusual case of a discovered check through
702 // the captured pawn.
705 Square capsq = make_square(square_file(to), square_rank(from));
707 clear_bit(&b, capsq);
709 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
710 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
713 // Castling with check ?
714 if (move_is_castle(m))
716 Square kfrom, kto, rfrom, rto;
722 kto = relative_square(us, SQ_G1);
723 rto = relative_square(us, SQ_F1);
725 kto = relative_square(us, SQ_C1);
726 rto = relative_square(us, SQ_D1);
728 clear_bit(&b, kfrom);
729 clear_bit(&b, rfrom);
732 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
739 /// Position::do_move() makes a move, and saves all information necessary
740 /// to a StateInfo object. The move is assumed to be legal.
741 /// Pseudo-legal moves should be filtered out before this function is called.
743 void Position::do_move(Move m, StateInfo& newSt) {
746 do_move(m, newSt, ci, move_is_check(m, ci));
749 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
752 assert(move_is_ok(m));
757 // Copy some fields of old state to our new StateInfo object except the
758 // ones which are recalculated from scratch anyway, then switch our state
759 // pointer to point to the new, ready to be updated, state.
760 struct ReducedStateInfo {
761 Key pawnKey, materialKey;
762 int castleRights, rule50, gamePly, pliesFromNull;
769 memcpy(&newSt, st, sizeof(ReducedStateInfo));
774 // Save the current key to the history[] array, in order to be able to
775 // detect repetition draws.
776 history[st->gamePly++] = key;
778 // Update side to move
779 key ^= zobSideToMove;
781 // Increment the 50 moves rule draw counter. Resetting it to zero in the
782 // case of non-reversible moves is taken care of later.
786 if (move_is_castle(m))
793 Color us = side_to_move();
794 Color them = opposite_color(us);
795 Square from = move_from(m);
796 Square to = move_to(m);
797 bool ep = move_is_ep(m);
798 bool pm = move_is_promotion(m);
800 Piece piece = piece_on(from);
801 PieceType pt = type_of_piece(piece);
802 PieceType capture = ep ? PAWN : type_of_piece_on(to);
804 assert(color_of_piece_on(from) == us);
805 assert(color_of_piece_on(to) == them || square_is_empty(to));
806 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
807 assert(!pm || relative_rank(us, to) == RANK_8);
810 do_capture_move(key, capture, them, to, ep);
813 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
815 // Reset en passant square
816 if (st->epSquare != SQ_NONE)
818 key ^= zobEp[st->epSquare];
819 st->epSquare = SQ_NONE;
822 // Update castle rights, try to shortcut a common case
823 int cm = castleRightsMask[from] & castleRightsMask[to];
824 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
826 key ^= zobCastle[st->castleRights];
827 st->castleRights &= castleRightsMask[from];
828 st->castleRights &= castleRightsMask[to];
829 key ^= zobCastle[st->castleRights];
832 // Prefetch TT access as soon as we know key is updated
833 prefetch((char*)TT.first_entry(key));
836 Bitboard move_bb = make_move_bb(from, to);
837 do_move_bb(&(byColorBB[us]), move_bb);
838 do_move_bb(&(byTypeBB[pt]), move_bb);
839 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
841 board[to] = board[from];
842 board[from] = PIECE_NONE;
844 // Update piece lists, note that index[from] is not updated and
845 // becomes stale. This works as long as index[] is accessed just
846 // by known occupied squares.
847 index[to] = index[from];
848 pieceList[us][pt][index[to]] = to;
850 // If the moving piece was a pawn do some special extra work
853 // Reset rule 50 draw counter
856 // Update pawn hash key and prefetch in L1/L2 cache
857 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
858 prefetchPawn(st->pawnKey, threadID);
860 // Set en passant square, only if moved pawn can be captured
861 if ((to ^ from) == 16)
863 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
865 st->epSquare = Square((int(from) + int(to)) / 2);
866 key ^= zobEp[st->epSquare];
870 if (pm) // promotion ?
872 PieceType promotion = move_promotion_piece(m);
874 assert(promotion >= KNIGHT && promotion <= QUEEN);
876 // Insert promoted piece instead of pawn
877 clear_bit(&(byTypeBB[PAWN]), to);
878 set_bit(&(byTypeBB[promotion]), to);
879 board[to] = piece_of_color_and_type(us, promotion);
881 // Update piece counts
882 pieceCount[us][promotion]++;
883 pieceCount[us][PAWN]--;
885 // Update material key
886 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
887 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
889 // Update piece lists, move the last pawn at index[to] position
890 // and shrink the list. Add a new promotion piece to the list.
891 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
892 index[lastPawnSquare] = index[to];
893 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
894 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
895 index[to] = pieceCount[us][promotion] - 1;
896 pieceList[us][promotion][index[to]] = to;
898 // Partially revert hash keys update
899 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
900 st->pawnKey ^= zobrist[us][PAWN][to];
902 // Partially revert and update incremental scores
903 st->value -= pst(us, PAWN, to);
904 st->value += pst(us, promotion, to);
907 st->npMaterial[us] += PieceValueMidgame[promotion];
911 // Update incremental scores
912 st->value += pst_delta(piece, from, to);
915 st->capturedType = capture;
917 // Update the key with the final value
920 // Update checkers bitboard, piece must be already moved
921 st->checkersBB = EmptyBoardBB;
926 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
930 if (bit_is_set(ci.checkSq[pt], to))
931 st->checkersBB = SetMaskBB[to];
934 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
937 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
940 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
946 sideToMove = opposite_color(sideToMove);
947 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
953 /// Position::do_capture_move() is a private method used to update captured
954 /// piece info. It is called from the main Position::do_move function.
956 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
958 assert(capture != KING);
962 // If the captured piece was a pawn, update pawn hash key,
963 // otherwise update non-pawn material.
966 if (ep) // en passant ?
968 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
970 assert(to == st->epSquare);
971 assert(relative_rank(opposite_color(them), to) == RANK_6);
972 assert(piece_on(to) == PIECE_NONE);
973 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
975 board[capsq] = PIECE_NONE;
977 st->pawnKey ^= zobrist[them][PAWN][capsq];
980 st->npMaterial[them] -= PieceValueMidgame[capture];
982 // Remove captured piece
983 clear_bit(&(byColorBB[them]), capsq);
984 clear_bit(&(byTypeBB[capture]), capsq);
985 clear_bit(&(byTypeBB[0]), capsq);
988 key ^= zobrist[them][capture][capsq];
990 // Update incremental scores
991 st->value -= pst(them, capture, capsq);
993 // Update piece count
994 pieceCount[them][capture]--;
996 // Update material hash key
997 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
999 // Update piece list, move the last piece at index[capsq] position
1001 // WARNING: This is a not perfectly revresible operation. When we
1002 // will reinsert the captured piece in undo_move() we will put it
1003 // at the end of the list and not in its original place, it means
1004 // index[] and pieceList[] are not guaranteed to be invariant to a
1005 // do_move() + undo_move() sequence.
1006 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1007 index[lastPieceSquare] = index[capsq];
1008 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1009 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1011 // Reset rule 50 counter
1016 /// Position::do_castle_move() is a private method used to make a castling
1017 /// move. It is called from the main Position::do_move function. Note that
1018 /// castling moves are encoded as "king captures friendly rook" moves, for
1019 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1021 void Position::do_castle_move(Move m) {
1023 assert(move_is_ok(m));
1024 assert(move_is_castle(m));
1026 Color us = side_to_move();
1027 Color them = opposite_color(us);
1029 // Reset capture field
1030 st->capturedType = PIECE_TYPE_NONE;
1032 // Find source squares for king and rook
1033 Square kfrom = move_from(m);
1034 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1037 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1038 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1040 // Find destination squares for king and rook
1041 if (rfrom > kfrom) // O-O
1043 kto = relative_square(us, SQ_G1);
1044 rto = relative_square(us, SQ_F1);
1046 kto = relative_square(us, SQ_C1);
1047 rto = relative_square(us, SQ_D1);
1050 // Remove pieces from source squares:
1051 clear_bit(&(byColorBB[us]), kfrom);
1052 clear_bit(&(byTypeBB[KING]), kfrom);
1053 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1054 clear_bit(&(byColorBB[us]), rfrom);
1055 clear_bit(&(byTypeBB[ROOK]), rfrom);
1056 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1058 // Put pieces on destination squares:
1059 set_bit(&(byColorBB[us]), kto);
1060 set_bit(&(byTypeBB[KING]), kto);
1061 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1062 set_bit(&(byColorBB[us]), rto);
1063 set_bit(&(byTypeBB[ROOK]), rto);
1064 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1066 // Update board array
1067 Piece king = piece_of_color_and_type(us, KING);
1068 Piece rook = piece_of_color_and_type(us, ROOK);
1069 board[kfrom] = board[rfrom] = PIECE_NONE;
1073 // Update piece lists
1074 pieceList[us][KING][index[kfrom]] = kto;
1075 pieceList[us][ROOK][index[rfrom]] = rto;
1076 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1077 index[kto] = index[kfrom];
1080 // Update incremental scores
1081 st->value += pst_delta(king, kfrom, kto);
1082 st->value += pst_delta(rook, rfrom, rto);
1085 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1086 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1088 // Clear en passant square
1089 if (st->epSquare != SQ_NONE)
1091 st->key ^= zobEp[st->epSquare];
1092 st->epSquare = SQ_NONE;
1095 // Update castling rights
1096 st->key ^= zobCastle[st->castleRights];
1097 st->castleRights &= castleRightsMask[kfrom];
1098 st->key ^= zobCastle[st->castleRights];
1100 // Reset rule 50 counter
1103 // Update checkers BB
1104 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1107 sideToMove = opposite_color(sideToMove);
1108 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1114 /// Position::undo_move() unmakes a move. When it returns, the position should
1115 /// be restored to exactly the same state as before the move was made.
1117 void Position::undo_move(Move m) {
1120 assert(move_is_ok(m));
1122 sideToMove = opposite_color(sideToMove);
1124 if (move_is_castle(m))
1126 undo_castle_move(m);
1130 Color us = side_to_move();
1131 Color them = opposite_color(us);
1132 Square from = move_from(m);
1133 Square to = move_to(m);
1134 bool ep = move_is_ep(m);
1135 bool pm = move_is_promotion(m);
1137 PieceType pt = type_of_piece_on(to);
1139 assert(square_is_empty(from));
1140 assert(color_of_piece_on(to) == us);
1141 assert(!pm || relative_rank(us, to) == RANK_8);
1142 assert(!ep || to == st->previous->epSquare);
1143 assert(!ep || relative_rank(us, to) == RANK_6);
1144 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1146 if (pm) // promotion ?
1148 PieceType promotion = move_promotion_piece(m);
1151 assert(promotion >= KNIGHT && promotion <= QUEEN);
1152 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1154 // Replace promoted piece with a pawn
1155 clear_bit(&(byTypeBB[promotion]), to);
1156 set_bit(&(byTypeBB[PAWN]), to);
1158 // Update piece counts
1159 pieceCount[us][promotion]--;
1160 pieceCount[us][PAWN]++;
1162 // Update piece list replacing promotion piece with a pawn
1163 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1164 index[lastPromotionSquare] = index[to];
1165 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1166 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1167 index[to] = pieceCount[us][PAWN] - 1;
1168 pieceList[us][PAWN][index[to]] = to;
1171 // Put the piece back at the source square
1172 Bitboard move_bb = make_move_bb(to, from);
1173 do_move_bb(&(byColorBB[us]), move_bb);
1174 do_move_bb(&(byTypeBB[pt]), move_bb);
1175 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1177 board[from] = piece_of_color_and_type(us, pt);
1178 board[to] = PIECE_NONE;
1180 // Update piece list
1181 index[from] = index[to];
1182 pieceList[us][pt][index[from]] = from;
1184 if (st->capturedType)
1189 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1191 assert(st->capturedType != KING);
1192 assert(!ep || square_is_empty(capsq));
1194 // Restore the captured piece
1195 set_bit(&(byColorBB[them]), capsq);
1196 set_bit(&(byTypeBB[st->capturedType]), capsq);
1197 set_bit(&(byTypeBB[0]), capsq);
1199 board[capsq] = piece_of_color_and_type(them, st->capturedType);
1201 // Update piece count
1202 pieceCount[them][st->capturedType]++;
1204 // Update piece list, add a new captured piece in capsq square
1205 index[capsq] = pieceCount[them][st->capturedType] - 1;
1206 pieceList[them][st->capturedType][index[capsq]] = capsq;
1209 // Finally point our state pointer back to the previous state
1216 /// Position::undo_castle_move() is a private method used to unmake a castling
1217 /// move. It is called from the main Position::undo_move function. Note that
1218 /// castling moves are encoded as "king captures friendly rook" moves, for
1219 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1221 void Position::undo_castle_move(Move m) {
1223 assert(move_is_ok(m));
1224 assert(move_is_castle(m));
1226 // When we have arrived here, some work has already been done by
1227 // Position::undo_move. In particular, the side to move has been switched,
1228 // so the code below is correct.
1229 Color us = side_to_move();
1231 // Find source squares for king and rook
1232 Square kfrom = move_from(m);
1233 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1236 // Find destination squares for king and rook
1237 if (rfrom > kfrom) // O-O
1239 kto = relative_square(us, SQ_G1);
1240 rto = relative_square(us, SQ_F1);
1242 kto = relative_square(us, SQ_C1);
1243 rto = relative_square(us, SQ_D1);
1246 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1247 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1249 // Remove pieces from destination squares:
1250 clear_bit(&(byColorBB[us]), kto);
1251 clear_bit(&(byTypeBB[KING]), kto);
1252 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1253 clear_bit(&(byColorBB[us]), rto);
1254 clear_bit(&(byTypeBB[ROOK]), rto);
1255 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1257 // Put pieces on source squares:
1258 set_bit(&(byColorBB[us]), kfrom);
1259 set_bit(&(byTypeBB[KING]), kfrom);
1260 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1261 set_bit(&(byColorBB[us]), rfrom);
1262 set_bit(&(byTypeBB[ROOK]), rfrom);
1263 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1266 board[rto] = board[kto] = PIECE_NONE;
1267 board[rfrom] = piece_of_color_and_type(us, ROOK);
1268 board[kfrom] = piece_of_color_and_type(us, KING);
1270 // Update piece lists
1271 pieceList[us][KING][index[kto]] = kfrom;
1272 pieceList[us][ROOK][index[rto]] = rfrom;
1273 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1274 index[kfrom] = index[kto];
1277 // Finally point our state pointer back to the previous state
1284 /// Position::do_null_move makes() a "null move": It switches the side to move
1285 /// and updates the hash key without executing any move on the board.
1287 void Position::do_null_move(StateInfo& backupSt) {
1290 assert(!is_check());
1292 // Back up the information necessary to undo the null move to the supplied
1293 // StateInfo object.
1294 // Note that differently from normal case here backupSt is actually used as
1295 // a backup storage not as a new state to be used.
1296 backupSt.key = st->key;
1297 backupSt.epSquare = st->epSquare;
1298 backupSt.value = st->value;
1299 backupSt.previous = st->previous;
1300 backupSt.pliesFromNull = st->pliesFromNull;
1301 st->previous = &backupSt;
1303 // Save the current key to the history[] array, in order to be able to
1304 // detect repetition draws.
1305 history[st->gamePly++] = st->key;
1307 // Update the necessary information
1308 if (st->epSquare != SQ_NONE)
1309 st->key ^= zobEp[st->epSquare];
1311 st->key ^= zobSideToMove;
1312 prefetch((char*)TT.first_entry(st->key));
1314 sideToMove = opposite_color(sideToMove);
1315 st->epSquare = SQ_NONE;
1317 st->pliesFromNull = 0;
1318 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1322 /// Position::undo_null_move() unmakes a "null move".
1324 void Position::undo_null_move() {
1327 assert(!is_check());
1329 // Restore information from the our backup StateInfo object
1330 StateInfo* backupSt = st->previous;
1331 st->key = backupSt->key;
1332 st->epSquare = backupSt->epSquare;
1333 st->value = backupSt->value;
1334 st->previous = backupSt->previous;
1335 st->pliesFromNull = backupSt->pliesFromNull;
1337 // Update the necessary information
1338 sideToMove = opposite_color(sideToMove);
1344 /// Position::see() is a static exchange evaluator: It tries to estimate the
1345 /// material gain or loss resulting from a move. There are three versions of
1346 /// this function: One which takes a destination square as input, one takes a
1347 /// move, and one which takes a 'from' and a 'to' square. The function does
1348 /// not yet understand promotions captures.
1350 int Position::see(Move m) const {
1352 assert(move_is_ok(m));
1353 return see(move_from(m), move_to(m));
1356 int Position::see_sign(Move m) const {
1358 assert(move_is_ok(m));
1360 Square from = move_from(m);
1361 Square to = move_to(m);
1363 // Early return if SEE cannot be negative because captured piece value
1364 // is not less then capturing one. Note that king moves always return
1365 // here because king midgame value is set to 0.
1366 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1369 return see(from, to);
1372 int Position::see(Square from, Square to) const {
1374 Bitboard occ, attackers, stmAttackers, b;
1375 int swapList[32], slIndex = 1;
1376 PieceType capturedType, pt;
1379 assert(square_is_ok(from));
1380 assert(square_is_ok(to));
1382 capturedType = type_of_piece_on(to);
1384 // King cannot be recaptured
1385 if (capturedType == KING)
1386 return seeValues[capturedType];
1388 occ = occupied_squares();
1390 // Handle en passant moves
1391 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1393 Square capQq = (side_to_move() == WHITE) ? (to - DELTA_N) : (to - DELTA_S);
1395 assert(capturedType == PIECE_TYPE_NONE);
1396 assert(type_of_piece_on(capQq) == PAWN);
1398 // Remove the captured pawn
1399 clear_bit(&occ, capQq);
1400 capturedType = PAWN;
1403 // Find all attackers to the destination square, with the moving piece
1404 // removed, but possibly an X-ray attacker added behind it.
1405 clear_bit(&occ, from);
1406 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1407 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1408 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1409 | (attacks_from<KING>(to) & pieces(KING))
1410 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1411 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1413 // If the opponent has no attackers we are finished
1414 stm = opposite_color(color_of_piece_on(from));
1415 stmAttackers = attackers & pieces_of_color(stm);
1417 return seeValues[capturedType];
1419 // The destination square is defended, which makes things rather more
1420 // difficult to compute. We proceed by building up a "swap list" containing
1421 // the material gain or loss at each stop in a sequence of captures to the
1422 // destination square, where the sides alternately capture, and always
1423 // capture with the least valuable piece. After each capture, we look for
1424 // new X-ray attacks from behind the capturing piece.
1425 swapList[0] = seeValues[capturedType];
1426 capturedType = type_of_piece_on(from);
1429 // Locate the least valuable attacker for the side to move. The loop
1430 // below looks like it is potentially infinite, but it isn't. We know
1431 // that the side to move still has at least one attacker left.
1432 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1435 // Remove the attacker we just found from the 'attackers' bitboard,
1436 // and scan for new X-ray attacks behind the attacker.
1437 b = stmAttackers & pieces(pt);
1438 occ ^= (b & (~b + 1));
1439 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1440 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1442 attackers &= occ; // Cut out pieces we've already done
1444 // Add the new entry to the swap list
1445 assert(slIndex < 32);
1446 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1449 // Remember the value of the capturing piece, and change the side to move
1450 // before beginning the next iteration
1452 stm = opposite_color(stm);
1453 stmAttackers = attackers & pieces_of_color(stm);
1455 // Stop after a king capture
1456 if (pt == KING && stmAttackers)
1458 assert(slIndex < 32);
1459 swapList[slIndex++] = QueenValueMidgame*10;
1462 } while (stmAttackers);
1464 // Having built the swap list, we negamax through it to find the best
1465 // achievable score from the point of view of the side to move
1467 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1473 /// Position::clear() erases the position object to a pristine state, with an
1474 /// empty board, white to move, and no castling rights.
1476 void Position::clear() {
1479 memset(st, 0, sizeof(StateInfo));
1480 st->epSquare = SQ_NONE;
1481 startPosPlyCounter = 0;
1484 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1485 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1486 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1487 memset(index, 0, sizeof(int) * 64);
1489 for (int i = 0; i < 64; i++)
1490 board[i] = PIECE_NONE;
1492 for (int i = 0; i < 8; i++)
1493 for (int j = 0; j < 16; j++)
1494 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1496 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1497 castleRightsMask[sq] = ALL_CASTLES;
1500 initialKFile = FILE_E;
1501 initialKRFile = FILE_H;
1502 initialQRFile = FILE_A;
1506 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1507 /// UCI interface code, whenever a non-reversible move is made in a
1508 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1509 /// for the program to handle games of arbitrary length, as long as the GUI
1510 /// handles draws by the 50 move rule correctly.
1512 void Position::reset_game_ply() {
1517 void Position::inc_startpos_ply_counter() {
1519 startPosPlyCounter++;
1522 /// Position::put_piece() puts a piece on the given square of the board,
1523 /// updating the board array, bitboards, and piece counts.
1525 void Position::put_piece(Piece p, Square s) {
1527 Color c = color_of_piece(p);
1528 PieceType pt = type_of_piece(p);
1531 index[s] = pieceCount[c][pt];
1532 pieceList[c][pt][index[s]] = s;
1534 set_bit(&(byTypeBB[pt]), s);
1535 set_bit(&(byColorBB[c]), s);
1536 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1538 pieceCount[c][pt]++;
1542 /// Position::allow_oo() gives the given side the right to castle kingside.
1543 /// Used when setting castling rights during parsing of FEN strings.
1545 void Position::allow_oo(Color c) {
1547 st->castleRights |= (1 + int(c));
1551 /// Position::allow_ooo() gives the given side the right to castle queenside.
1552 /// Used when setting castling rights during parsing of FEN strings.
1554 void Position::allow_ooo(Color c) {
1556 st->castleRights |= (4 + 4*int(c));
1560 /// Position::compute_key() computes the hash key of the position. The hash
1561 /// key is usually updated incrementally as moves are made and unmade, the
1562 /// compute_key() function is only used when a new position is set up, and
1563 /// to verify the correctness of the hash key when running in debug mode.
1565 Key Position::compute_key() const {
1569 for (Square s = SQ_A1; s <= SQ_H8; s++)
1570 if (square_is_occupied(s))
1571 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1573 if (ep_square() != SQ_NONE)
1574 result ^= zobEp[ep_square()];
1576 result ^= zobCastle[st->castleRights];
1577 if (side_to_move() == BLACK)
1578 result ^= zobSideToMove;
1584 /// Position::compute_pawn_key() computes the hash key of the position. The
1585 /// hash key is usually updated incrementally as moves are made and unmade,
1586 /// the compute_pawn_key() function is only used when a new position is set
1587 /// up, and to verify the correctness of the pawn hash key when running in
1590 Key Position::compute_pawn_key() const {
1596 for (Color c = WHITE; c <= BLACK; c++)
1598 b = pieces(PAWN, c);
1601 s = pop_1st_bit(&b);
1602 result ^= zobrist[c][PAWN][s];
1609 /// Position::compute_material_key() computes the hash key of the position.
1610 /// The hash key is usually updated incrementally as moves are made and unmade,
1611 /// the compute_material_key() function is only used when a new position is set
1612 /// up, and to verify the correctness of the material hash key when running in
1615 Key Position::compute_material_key() const {
1618 for (Color c = WHITE; c <= BLACK; c++)
1619 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1621 int count = piece_count(c, pt);
1622 for (int i = 0; i < count; i++)
1623 result ^= zobrist[c][pt][i];
1629 /// Position::compute_value() compute the incremental scores for the middle
1630 /// game and the endgame. These functions are used to initialize the incremental
1631 /// scores when a new position is set up, and to verify that the scores are correctly
1632 /// updated by do_move and undo_move when the program is running in debug mode.
1633 Score Position::compute_value() const {
1635 Score result = SCORE_ZERO;
1639 for (Color c = WHITE; c <= BLACK; c++)
1640 for (PieceType pt = PAWN; pt <= KING; pt++)
1645 s = pop_1st_bit(&b);
1646 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1647 result += pst(c, pt, s);
1651 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1656 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1657 /// game material score for the given side. Material scores are updated
1658 /// incrementally during the search, this function is only used while
1659 /// initializing a new Position object.
1661 Value Position::compute_non_pawn_material(Color c) const {
1663 Value result = VALUE_ZERO;
1665 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1667 Bitboard b = pieces(pt, c);
1670 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1673 result += PieceValueMidgame[pt];
1680 /// Position::is_draw() tests whether the position is drawn by material,
1681 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1682 /// must be done by the search.
1684 bool Position::is_draw() const {
1686 // Draw by material?
1688 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1691 // Draw by the 50 moves rule?
1692 if (st->rule50 > 99 && (st->rule50 > 100 || !is_mate()))
1695 // Draw by repetition?
1696 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1697 if (history[st->gamePly - i] == st->key)
1704 /// Position::is_mate() returns true or false depending on whether the
1705 /// side to move is checkmated.
1707 bool Position::is_mate() const {
1709 MoveStack moves[MOVES_MAX];
1710 return is_check() && (generate_moves(*this, moves) == moves);
1714 /// Position::has_mate_threat() tests whether the side to move is under
1715 /// a threat of being mated in one from the current position.
1717 bool Position::has_mate_threat() {
1719 MoveStack mlist[MOVES_MAX], *last, *cur;
1721 bool mateFound = false;
1723 // If we are under check it's up to evasions to do the job
1727 // First pass the move to our opponent doing a null move
1730 // Then generate pseudo-legal moves that give check
1731 last = generate_non_capture_checks(*this, mlist);
1732 last = generate_captures(*this, last);
1734 // Loop through the moves, and see if one of them gives mate
1735 Bitboard pinned = pinned_pieces(sideToMove);
1736 CheckInfo ci(*this);
1737 for (cur = mlist; cur != last && !mateFound; cur++)
1739 Move move = cur->move;
1740 if ( !pl_move_is_legal(move, pinned)
1741 || !move_is_check(move, ci))
1744 do_move(move, st2, ci, true);
1757 /// Position::init_zobrist() is a static member function which initializes at
1758 /// startup the various arrays used to compute hash keys.
1760 void Position::init_zobrist() {
1764 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1765 zobrist[i][j][k] = Key(genrand_int64());
1767 for (i = 0; i < 64; i++)
1768 zobEp[i] = Key(genrand_int64());
1770 for (i = 0; i < 16; i++)
1771 zobCastle[i] = Key(genrand_int64());
1773 zobSideToMove = Key(genrand_int64());
1774 zobExclusion = Key(genrand_int64());
1778 /// Position::init_piece_square_tables() initializes the piece square tables.
1779 /// This is a two-step operation: First, the white halves of the tables are
1780 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1781 /// of the tables are initialized by mirroring and changing the sign of the
1782 /// corresponding white scores.
1784 void Position::init_piece_square_tables() {
1786 for (Square s = SQ_A1; s <= SQ_H8; s++)
1787 for (Piece p = WP; p <= WK; p++)
1788 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1790 for (Square s = SQ_A1; s <= SQ_H8; s++)
1791 for (Piece p = BP; p <= BK; p++)
1792 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1796 /// Position::flipped_copy() makes a copy of the input position, but with
1797 /// the white and black sides reversed. This is only useful for debugging,
1798 /// especially for finding evaluation symmetry bugs.
1800 void Position::flipped_copy(const Position& pos) {
1802 assert(pos.is_ok());
1805 threadID = pos.thread();
1808 for (Square s = SQ_A1; s <= SQ_H8; s++)
1809 if (!pos.square_is_empty(s))
1810 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1813 sideToMove = opposite_color(pos.side_to_move());
1816 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1817 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1818 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1819 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1821 initialKFile = pos.initialKFile;
1822 initialKRFile = pos.initialKRFile;
1823 initialQRFile = pos.initialQRFile;
1825 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1826 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1827 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1828 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1829 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1830 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1832 // En passant square
1833 if (pos.st->epSquare != SQ_NONE)
1834 st->epSquare = flip_square(pos.st->epSquare);
1840 st->key = compute_key();
1841 st->pawnKey = compute_pawn_key();
1842 st->materialKey = compute_material_key();
1844 // Incremental scores
1845 st->value = compute_value();
1848 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1849 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1855 /// Position::is_ok() performs some consitency checks for the position object.
1856 /// This is meant to be helpful when debugging.
1858 bool Position::is_ok(int* failedStep) const {
1860 // What features of the position should be verified?
1861 static const bool debugBitboards = false;
1862 static const bool debugKingCount = false;
1863 static const bool debugKingCapture = false;
1864 static const bool debugCheckerCount = false;
1865 static const bool debugKey = false;
1866 static const bool debugMaterialKey = false;
1867 static const bool debugPawnKey = false;
1868 static const bool debugIncrementalEval = false;
1869 static const bool debugNonPawnMaterial = false;
1870 static const bool debugPieceCounts = false;
1871 static const bool debugPieceList = false;
1872 static const bool debugCastleSquares = false;
1874 if (failedStep) *failedStep = 1;
1877 if (!color_is_ok(side_to_move()))
1880 // Are the king squares in the position correct?
1881 if (failedStep) (*failedStep)++;
1882 if (piece_on(king_square(WHITE)) != WK)
1885 if (failedStep) (*failedStep)++;
1886 if (piece_on(king_square(BLACK)) != BK)
1890 if (failedStep) (*failedStep)++;
1891 if (!file_is_ok(initialKRFile))
1894 if (!file_is_ok(initialQRFile))
1897 // Do both sides have exactly one king?
1898 if (failedStep) (*failedStep)++;
1901 int kingCount[2] = {0, 0};
1902 for (Square s = SQ_A1; s <= SQ_H8; s++)
1903 if (type_of_piece_on(s) == KING)
1904 kingCount[color_of_piece_on(s)]++;
1906 if (kingCount[0] != 1 || kingCount[1] != 1)
1910 // Can the side to move capture the opponent's king?
1911 if (failedStep) (*failedStep)++;
1912 if (debugKingCapture)
1914 Color us = side_to_move();
1915 Color them = opposite_color(us);
1916 Square ksq = king_square(them);
1917 if (attackers_to(ksq) & pieces_of_color(us))
1921 // Is there more than 2 checkers?
1922 if (failedStep) (*failedStep)++;
1923 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1927 if (failedStep) (*failedStep)++;
1930 // The intersection of the white and black pieces must be empty
1931 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1934 // The union of the white and black pieces must be equal to all
1936 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1939 // Separate piece type bitboards must have empty intersections
1940 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1941 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1942 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1946 // En passant square OK?
1947 if (failedStep) (*failedStep)++;
1948 if (ep_square() != SQ_NONE)
1950 // The en passant square must be on rank 6, from the point of view of the
1952 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1957 if (failedStep) (*failedStep)++;
1958 if (debugKey && st->key != compute_key())
1961 // Pawn hash key OK?
1962 if (failedStep) (*failedStep)++;
1963 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1966 // Material hash key OK?
1967 if (failedStep) (*failedStep)++;
1968 if (debugMaterialKey && st->materialKey != compute_material_key())
1971 // Incremental eval OK?
1972 if (failedStep) (*failedStep)++;
1973 if (debugIncrementalEval && st->value != compute_value())
1976 // Non-pawn material OK?
1977 if (failedStep) (*failedStep)++;
1978 if (debugNonPawnMaterial)
1980 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1983 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1988 if (failedStep) (*failedStep)++;
1989 if (debugPieceCounts)
1990 for (Color c = WHITE; c <= BLACK; c++)
1991 for (PieceType pt = PAWN; pt <= KING; pt++)
1992 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1995 if (failedStep) (*failedStep)++;
1998 for (Color c = WHITE; c <= BLACK; c++)
1999 for (PieceType pt = PAWN; pt <= KING; pt++)
2000 for (int i = 0; i < pieceCount[c][pt]; i++)
2002 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2005 if (index[piece_list(c, pt, i)] != i)
2010 if (failedStep) (*failedStep)++;
2011 if (debugCastleSquares) {
2012 for (Color c = WHITE; c <= BLACK; c++) {
2013 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2015 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2018 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2020 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2022 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2024 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2028 if (failedStep) *failedStep = 0;