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 : 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)
78 Key Position::zobrist[2][8][64];
79 Key Position::zobEp[64];
80 Key Position::zobCastle[16];
81 Key Position::zobSideToMove;
82 Key Position::zobExclusion;
84 Score Position::PieceSquareTable[16][64];
86 static PieceLetters pieceLetters;
91 CheckInfo::CheckInfo(const Position& pos) {
93 Color us = pos.side_to_move();
94 Color them = opposite_color(us);
96 ksq = pos.king_square(them);
97 dcCandidates = pos.discovered_check_candidates(us);
99 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
100 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
101 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
102 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
103 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
104 checkSq[KING] = EmptyBoardBB;
108 /// Position c'tors. Here we always create a copy of the original position
109 /// or the FEN string, we want the new born Position object do not depend
110 /// on any external data so we detach state pointer from the source one.
112 Position::Position(int th) : threadID(th) {}
114 Position::Position(const Position& pos, int th) {
116 memcpy(this, &pos, sizeof(Position));
117 detach(); // Always detach() in copy c'tor to avoid surprises
121 Position::Position(const string& fen, int th) {
128 /// Position::detach() copies the content of the current state and castling
129 /// masks inside the position itself. This is needed when the st pointee could
130 /// become stale, as example because the caller is about to going out of scope.
132 void Position::detach() {
136 st->previous = NULL; // as a safe guard
140 /// Position::from_fen() initializes the position object with the given FEN
141 /// string. This function is not very robust - make sure that input FENs are
142 /// correct (this is assumed to be the responsibility of the GUI).
144 void Position::from_fen(const string& fen) {
146 A FEN string defines a particular position using only the ASCII character set.
148 A FEN string contains six fields. The separator between fields is a space. The fields are:
150 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
151 with rank 1; within each rank, the contents of each square are described from file a through file h.
152 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
153 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
154 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
155 of blank squares), and "/" separate ranks.
157 2) Active color. "w" means white moves next, "b" means black.
159 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
160 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
161 kingside), and/or "q" (Black can castle queenside).
163 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
164 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
165 regardless of whether there is a pawn in position to make an en passant capture.
167 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
168 to determine if a draw can be claimed under the fifty-move rule.
170 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
174 std::istringstream ss(fen);
180 // 1. Piece placement field
181 while (ss.get(token) && token != ' ')
185 file += token - '0'; // Skip the given number of files
188 else if (token == '/')
195 if (pieceLetters.find(token) == pieceLetters.end())
198 put_piece(pieceLetters[token], make_square(file, rank));
203 if (!ss.get(token) || (token != 'w' && token != 'b'))
206 sideToMove = (token == 'w' ? WHITE : BLACK);
208 if (!ss.get(token) || token != ' ')
211 // 3. Castling availability
212 while (ss.get(token) && token != ' ')
217 if (!set_castling_rights(token))
221 // 4. En passant square -- ignore if no capture is possible
223 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
224 && (ss.get(row) && (row == '3' || row == '6')))
226 Square fenEpSquare = make_square(file_from_char(col), rank_from_char(row));
227 Color them = opposite_color(sideToMove);
229 if (attacks_from<PAWN>(fenEpSquare, them) & pieces(PAWN, sideToMove))
230 st->epSquare = fenEpSquare;
233 // 5-6. Halfmove clock and fullmove number are not parsed
235 // Various initialisations
236 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
237 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
238 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
239 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
240 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
241 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
245 st->key = compute_key();
246 st->pawnKey = compute_pawn_key();
247 st->materialKey = compute_material_key();
248 st->value = compute_value();
249 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
250 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
254 cout << "Error in FEN string: " << fen << endl;
258 /// Position::set_castling_rights() sets castling parameters castling avaiability.
259 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
260 /// that uses the letters of the columns on which the rooks began the game instead
261 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
262 /// associated with the castling right, the traditional castling tag will be replaced
263 /// by the file letter of the involved rook as for the Shredder-FEN.
265 bool Position::set_castling_rights(char token) {
267 Color c = token >= 'a' ? BLACK : WHITE;
268 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
269 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
270 Piece rook = (c == WHITE ? WR : BR);
272 initialKFile = square_file(king_square(c));
273 token = char(toupper(token));
277 for (Square sq = sqH; sq >= sqA; sq--)
278 if (piece_on(sq) == rook)
281 initialKRFile = square_file(sq);
285 else if (token == 'Q')
287 for (Square sq = sqA; sq <= sqH; sq++)
288 if (piece_on(sq) == rook)
291 initialQRFile = square_file(sq);
295 else if (token >= 'A' && token <= 'H')
297 File rookFile = File(token - 'A') + FILE_A;
298 if (rookFile < initialKFile)
301 initialQRFile = rookFile;
306 initialKRFile = rookFile;
315 /// Position::to_fen() returns a FEN representation of the position. In case
316 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
318 const string Position::to_fen() const {
324 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
326 for (File file = FILE_A; file <= FILE_H; file++)
328 sq = make_square(file, rank);
330 if (square_is_occupied(sq))
333 fen += pieceLetters.from_piece(piece_on(sq));
343 fen.erase(std::remove_if(fen.begin(), fen.end(), isZero), fen.end());
344 fen.erase(--fen.end());
345 fen += (sideToMove == WHITE ? " w " : " b ");
347 if (st->castleRights != CASTLES_NONE)
349 const bool Chess960 = initialKFile != FILE_E
350 || initialQRFile != FILE_A
351 || initialKRFile != FILE_H;
353 if (can_castle_kingside(WHITE))
354 fen += Chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
356 if (can_castle_queenside(WHITE))
357 fen += Chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
359 if (can_castle_kingside(BLACK))
360 fen += Chess960 ? file_to_char(initialKRFile) : 'k';
362 if (can_castle_queenside(BLACK))
363 fen += Chess960 ? file_to_char(initialQRFile) : 'q';
367 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
372 /// Position::print() prints an ASCII representation of the position to
373 /// the standard output. If a move is given then also the san is print.
375 void Position::print(Move move) const {
377 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
378 static bool requestPending = false;
380 // Check for reentrancy, as example when called from inside
381 // MovePicker that is used also here in move_to_san()
385 requestPending = true;
389 Position p(*this, thread());
390 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
391 cout << "\nMove is: " << dd << move_to_san(p, move);
394 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
396 cout << dottedLine << '|';
397 for (File file = FILE_A; file <= FILE_H; file++)
399 Square sq = make_square(file, rank);
400 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
401 Piece piece = piece_on(sq);
403 if (piece == PIECE_NONE && square_color(sq) == DARK)
404 piece = PIECE_NONE_DARK_SQ;
406 cout << c << pieceLetters.from_piece(piece) << c << '|';
409 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
410 requestPending = false;
414 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
415 /// king) pieces for the given color and for the given pinner type. Or, when
416 /// template parameter FindPinned is false, the pieces of the given color
417 /// candidate for a discovery check against the enemy king.
418 /// Bitboard checkersBB must be already updated when looking for pinners.
420 template<bool FindPinned>
421 Bitboard Position::hidden_checkers(Color c) const {
423 Bitboard result = EmptyBoardBB;
424 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
426 // Pinned pieces protect our king, dicovery checks attack
428 Square ksq = king_square(FindPinned ? c : opposite_color(c));
430 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
431 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
433 if (FindPinned && pinners)
434 pinners &= ~st->checkersBB;
438 Square s = pop_1st_bit(&pinners);
439 Bitboard b = squares_between(s, ksq) & occupied_squares();
443 if ( !(b & (b - 1)) // Only one bit set?
444 && (b & pieces_of_color(c))) // Is an our piece?
451 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
452 /// king) pieces for the given color. Note that checkersBB bitboard must
453 /// be already updated.
455 Bitboard Position::pinned_pieces(Color c) const {
457 return hidden_checkers<true>(c);
461 /// Position:discovered_check_candidates() returns a bitboard containing all
462 /// pieces for the given side which are candidates for giving a discovered
463 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
464 /// to be already updated.
466 Bitboard Position::discovered_check_candidates(Color c) const {
468 return hidden_checkers<false>(c);
471 /// Position::attackers_to() computes a bitboard containing all pieces which
472 /// attacks a given square.
474 Bitboard Position::attackers_to(Square s) const {
476 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
477 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
478 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
479 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
480 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
481 | (attacks_from<KING>(s) & pieces(KING));
484 /// Position::attacks_from() computes a bitboard of all attacks
485 /// of a given piece put in a given square.
487 Bitboard Position::attacks_from(Piece p, Square s) const {
489 assert(square_is_ok(s));
493 case WP: return attacks_from<PAWN>(s, WHITE);
494 case BP: return attacks_from<PAWN>(s, BLACK);
495 case WN: case BN: return attacks_from<KNIGHT>(s);
496 case WB: case BB: return attacks_from<BISHOP>(s);
497 case WR: case BR: return attacks_from<ROOK>(s);
498 case WQ: case BQ: return attacks_from<QUEEN>(s);
499 case WK: case BK: return attacks_from<KING>(s);
506 /// Position::move_attacks_square() tests whether a move from the current
507 /// position attacks a given square.
509 bool Position::move_attacks_square(Move m, Square s) const {
511 assert(move_is_ok(m));
512 assert(square_is_ok(s));
514 Square f = move_from(m), t = move_to(m);
516 assert(square_is_occupied(f));
518 if (bit_is_set(attacks_from(piece_on(f), t), s))
521 // Move the piece and scan for X-ray attacks behind it
522 Bitboard occ = occupied_squares();
523 Color us = color_of_piece_on(f);
526 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
527 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
529 // If we have attacks we need to verify that are caused by our move
530 // and are not already existent ones.
531 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
535 /// Position::find_checkers() computes the checkersBB bitboard, which
536 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
537 /// currently works by calling Position::attackers_to, which is probably
538 /// inefficient. Consider rewriting this function to use the last move
539 /// played, like in non-bitboard versions of Glaurung.
541 void Position::find_checkers() {
543 Color us = side_to_move();
544 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
548 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
550 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
553 assert(move_is_ok(m));
554 assert(pinned == pinned_pieces(side_to_move()));
556 // Castling moves are checked for legality during move generation.
557 if (move_is_castle(m))
560 Color us = side_to_move();
561 Square from = move_from(m);
563 assert(color_of_piece_on(from) == us);
564 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
566 // En passant captures are a tricky special case. Because they are
567 // rather uncommon, we do it simply by testing whether the king is attacked
568 // after the move is made
571 Color them = opposite_color(us);
572 Square to = move_to(m);
573 Square capsq = make_square(square_file(to), square_rank(from));
574 Bitboard b = occupied_squares();
575 Square ksq = king_square(us);
577 assert(to == ep_square());
578 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
579 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
580 assert(piece_on(to) == PIECE_NONE);
583 clear_bit(&b, capsq);
586 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
587 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
590 // If the moving piece is a king, check whether the destination
591 // square is attacked by the opponent.
592 if (type_of_piece_on(from) == KING)
593 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
595 // A non-king move is legal if and only if it is not pinned or it
596 // is moving along the ray towards or away from the king.
598 || !bit_is_set(pinned, from)
599 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
603 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
605 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
609 Color us = side_to_move();
610 Square from = move_from(m);
611 Square to = move_to(m);
613 // King moves and en-passant captures are verified in pl_move_is_legal()
614 if (type_of_piece_on(from) == KING || move_is_ep(m))
615 return pl_move_is_legal(m, pinned);
617 Bitboard target = checkers();
618 Square checksq = pop_1st_bit(&target);
620 if (target) // double check ?
623 // Our move must be a blocking evasion or a capture of the checking piece
624 target = squares_between(checksq, king_square(us)) | checkers();
625 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
629 /// Position::move_is_check() tests whether a pseudo-legal move is a check
631 bool Position::move_is_check(Move m) const {
633 return move_is_check(m, CheckInfo(*this));
636 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
639 assert(move_is_ok(m));
640 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
641 assert(color_of_piece_on(move_from(m)) == side_to_move());
642 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
644 Square from = move_from(m);
645 Square to = move_to(m);
646 PieceType pt = type_of_piece_on(from);
649 if (bit_is_set(ci.checkSq[pt], to))
653 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
655 // For pawn and king moves we need to verify also direction
656 if ( (pt != PAWN && pt != KING)
657 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
661 // Can we skip the ugly special cases ?
662 if (!move_is_special(m))
665 Color us = side_to_move();
666 Bitboard b = occupied_squares();
668 // Promotion with check ?
669 if (move_is_promotion(m))
673 switch (move_promotion_piece(m))
676 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
678 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
680 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
682 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
688 // En passant capture with check ? We have already handled the case
689 // of direct checks and ordinary discovered check, the only case we
690 // need to handle is the unusual case of a discovered check through
691 // the captured pawn.
694 Square capsq = make_square(square_file(to), square_rank(from));
696 clear_bit(&b, capsq);
698 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
699 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
702 // Castling with check ?
703 if (move_is_castle(m))
705 Square kfrom, kto, rfrom, rto;
711 kto = relative_square(us, SQ_G1);
712 rto = relative_square(us, SQ_F1);
714 kto = relative_square(us, SQ_C1);
715 rto = relative_square(us, SQ_D1);
717 clear_bit(&b, kfrom);
718 clear_bit(&b, rfrom);
721 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
728 /// Position::do_move() makes a move, and saves all information necessary
729 /// to a StateInfo object. The move is assumed to be legal.
730 /// Pseudo-legal moves should be filtered out before this function is called.
732 void Position::do_move(Move m, StateInfo& newSt) {
735 do_move(m, newSt, ci, move_is_check(m, ci));
738 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
741 assert(move_is_ok(m));
745 // Copy some fields of old state to our new StateInfo object except the
746 // ones which are recalculated from scratch anyway, then switch our state
747 // pointer to point to the new, ready to be updated, state.
748 struct ReducedStateInfo {
749 Key pawnKey, materialKey;
750 int castleRights, rule50, gamePly, pliesFromNull;
756 memcpy(&newSt, st, sizeof(ReducedStateInfo));
760 // Save the current key to the history[] array, in order to be able to
761 // detect repetition draws.
762 history[st->gamePly++] = key;
764 // Update side to move
765 key ^= zobSideToMove;
767 // Increment the 50 moves rule draw counter. Resetting it to zero in the
768 // case of non-reversible moves is taken care of later.
772 if (move_is_castle(m))
779 Color us = side_to_move();
780 Color them = opposite_color(us);
781 Square from = move_from(m);
782 Square to = move_to(m);
783 bool ep = move_is_ep(m);
784 bool pm = move_is_promotion(m);
786 Piece piece = piece_on(from);
787 PieceType pt = type_of_piece(piece);
788 PieceType capture = ep ? PAWN : type_of_piece_on(to);
790 assert(color_of_piece_on(from) == us);
791 assert(color_of_piece_on(to) == them || square_is_empty(to));
792 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
793 assert(!pm || relative_rank(us, to) == RANK_8);
796 do_capture_move(key, capture, them, to, ep);
799 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
801 // Reset en passant square
802 if (st->epSquare != SQ_NONE)
804 key ^= zobEp[st->epSquare];
805 st->epSquare = SQ_NONE;
808 // Update castle rights, try to shortcut a common case
809 int cm = castleRightsMask[from] & castleRightsMask[to];
810 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
812 key ^= zobCastle[st->castleRights];
813 st->castleRights &= castleRightsMask[from];
814 st->castleRights &= castleRightsMask[to];
815 key ^= zobCastle[st->castleRights];
818 // Prefetch TT access as soon as we know key is updated
819 prefetch((char*)TT.first_entry(key));
822 Bitboard move_bb = make_move_bb(from, to);
823 do_move_bb(&(byColorBB[us]), move_bb);
824 do_move_bb(&(byTypeBB[pt]), move_bb);
825 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
827 board[to] = board[from];
828 board[from] = PIECE_NONE;
830 // Update piece lists, note that index[from] is not updated and
831 // becomes stale. This works as long as index[] is accessed just
832 // by known occupied squares.
833 index[to] = index[from];
834 pieceList[us][pt][index[to]] = to;
836 // If the moving piece was a pawn do some special extra work
839 // Reset rule 50 draw counter
842 // Update pawn hash key
843 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
845 // Set en passant square, only if moved pawn can be captured
846 if ((to ^ from) == 16)
848 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
850 st->epSquare = Square((int(from) + int(to)) / 2);
851 key ^= zobEp[st->epSquare];
855 if (pm) // promotion ?
857 PieceType promotion = move_promotion_piece(m);
859 assert(promotion >= KNIGHT && promotion <= QUEEN);
861 // Insert promoted piece instead of pawn
862 clear_bit(&(byTypeBB[PAWN]), to);
863 set_bit(&(byTypeBB[promotion]), to);
864 board[to] = piece_of_color_and_type(us, promotion);
866 // Update piece counts
867 pieceCount[us][promotion]++;
868 pieceCount[us][PAWN]--;
870 // Update material key
871 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
872 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
874 // Update piece lists, move the last pawn at index[to] position
875 // and shrink the list. Add a new promotion piece to the list.
876 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
877 index[lastPawnSquare] = index[to];
878 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
879 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
880 index[to] = pieceCount[us][promotion] - 1;
881 pieceList[us][promotion][index[to]] = to;
883 // Partially revert hash keys update
884 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
885 st->pawnKey ^= zobrist[us][PAWN][to];
887 // Partially revert and update incremental scores
888 st->value -= pst(us, PAWN, to);
889 st->value += pst(us, promotion, to);
892 st->npMaterial[us] += piece_value_midgame(promotion);
896 // Update incremental scores
897 st->value += pst_delta(piece, from, to);
900 st->capturedType = capture;
902 // Update the key with the final value
905 // Update checkers bitboard, piece must be already moved
906 st->checkersBB = EmptyBoardBB;
911 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
915 if (bit_is_set(ci.checkSq[pt], to))
916 st->checkersBB = SetMaskBB[to];
919 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
922 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
925 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
931 sideToMove = opposite_color(sideToMove);
932 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
938 /// Position::do_capture_move() is a private method used to update captured
939 /// piece info. It is called from the main Position::do_move function.
941 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
943 assert(capture != KING);
947 // If the captured piece was a pawn, update pawn hash key,
948 // otherwise update non-pawn material.
951 if (ep) // en passant ?
953 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
955 assert(to == st->epSquare);
956 assert(relative_rank(opposite_color(them), to) == RANK_6);
957 assert(piece_on(to) == PIECE_NONE);
958 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
960 board[capsq] = PIECE_NONE;
962 st->pawnKey ^= zobrist[them][PAWN][capsq];
965 st->npMaterial[them] -= piece_value_midgame(capture);
967 // Remove captured piece
968 clear_bit(&(byColorBB[them]), capsq);
969 clear_bit(&(byTypeBB[capture]), capsq);
970 clear_bit(&(byTypeBB[0]), capsq);
973 key ^= zobrist[them][capture][capsq];
975 // Update incremental scores
976 st->value -= pst(them, capture, capsq);
978 // Update piece count
979 pieceCount[them][capture]--;
981 // Update material hash key
982 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
984 // Update piece list, move the last piece at index[capsq] position
986 // WARNING: This is a not perfectly revresible operation. When we
987 // will reinsert the captured piece in undo_move() we will put it
988 // at the end of the list and not in its original place, it means
989 // index[] and pieceList[] are not guaranteed to be invariant to a
990 // do_move() + undo_move() sequence.
991 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
992 index[lastPieceSquare] = index[capsq];
993 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
994 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
996 // Reset rule 50 counter
1001 /// Position::do_castle_move() is a private method used to make a castling
1002 /// move. It is called from the main Position::do_move function. Note that
1003 /// castling moves are encoded as "king captures friendly rook" moves, for
1004 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1006 void Position::do_castle_move(Move m) {
1008 assert(move_is_ok(m));
1009 assert(move_is_castle(m));
1011 Color us = side_to_move();
1012 Color them = opposite_color(us);
1014 // Reset capture field
1015 st->capturedType = PIECE_TYPE_NONE;
1017 // Find source squares for king and rook
1018 Square kfrom = move_from(m);
1019 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1022 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1023 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1025 // Find destination squares for king and rook
1026 if (rfrom > kfrom) // O-O
1028 kto = relative_square(us, SQ_G1);
1029 rto = relative_square(us, SQ_F1);
1031 kto = relative_square(us, SQ_C1);
1032 rto = relative_square(us, SQ_D1);
1035 // Remove pieces from source squares:
1036 clear_bit(&(byColorBB[us]), kfrom);
1037 clear_bit(&(byTypeBB[KING]), kfrom);
1038 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1039 clear_bit(&(byColorBB[us]), rfrom);
1040 clear_bit(&(byTypeBB[ROOK]), rfrom);
1041 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1043 // Put pieces on destination squares:
1044 set_bit(&(byColorBB[us]), kto);
1045 set_bit(&(byTypeBB[KING]), kto);
1046 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1047 set_bit(&(byColorBB[us]), rto);
1048 set_bit(&(byTypeBB[ROOK]), rto);
1049 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1051 // Update board array
1052 Piece king = piece_of_color_and_type(us, KING);
1053 Piece rook = piece_of_color_and_type(us, ROOK);
1054 board[kfrom] = board[rfrom] = PIECE_NONE;
1058 // Update piece lists
1059 pieceList[us][KING][index[kfrom]] = kto;
1060 pieceList[us][ROOK][index[rfrom]] = rto;
1061 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1062 index[kto] = index[kfrom];
1065 // Update incremental scores
1066 st->value += pst_delta(king, kfrom, kto);
1067 st->value += pst_delta(rook, rfrom, rto);
1070 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1071 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1073 // Clear en passant square
1074 if (st->epSquare != SQ_NONE)
1076 st->key ^= zobEp[st->epSquare];
1077 st->epSquare = SQ_NONE;
1080 // Update castling rights
1081 st->key ^= zobCastle[st->castleRights];
1082 st->castleRights &= castleRightsMask[kfrom];
1083 st->key ^= zobCastle[st->castleRights];
1085 // Reset rule 50 counter
1088 // Update checkers BB
1089 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1092 sideToMove = opposite_color(sideToMove);
1093 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1099 /// Position::undo_move() unmakes a move. When it returns, the position should
1100 /// be restored to exactly the same state as before the move was made.
1102 void Position::undo_move(Move m) {
1105 assert(move_is_ok(m));
1107 sideToMove = opposite_color(sideToMove);
1109 if (move_is_castle(m))
1111 undo_castle_move(m);
1115 Color us = side_to_move();
1116 Color them = opposite_color(us);
1117 Square from = move_from(m);
1118 Square to = move_to(m);
1119 bool ep = move_is_ep(m);
1120 bool pm = move_is_promotion(m);
1122 PieceType pt = type_of_piece_on(to);
1124 assert(square_is_empty(from));
1125 assert(color_of_piece_on(to) == us);
1126 assert(!pm || relative_rank(us, to) == RANK_8);
1127 assert(!ep || to == st->previous->epSquare);
1128 assert(!ep || relative_rank(us, to) == RANK_6);
1129 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1131 if (pm) // promotion ?
1133 PieceType promotion = move_promotion_piece(m);
1136 assert(promotion >= KNIGHT && promotion <= QUEEN);
1137 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1139 // Replace promoted piece with a pawn
1140 clear_bit(&(byTypeBB[promotion]), to);
1141 set_bit(&(byTypeBB[PAWN]), to);
1143 // Update piece counts
1144 pieceCount[us][promotion]--;
1145 pieceCount[us][PAWN]++;
1147 // Update piece list replacing promotion piece with a pawn
1148 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1149 index[lastPromotionSquare] = index[to];
1150 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1151 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1152 index[to] = pieceCount[us][PAWN] - 1;
1153 pieceList[us][PAWN][index[to]] = to;
1156 // Put the piece back at the source square
1157 Bitboard move_bb = make_move_bb(to, from);
1158 do_move_bb(&(byColorBB[us]), move_bb);
1159 do_move_bb(&(byTypeBB[pt]), move_bb);
1160 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1162 board[from] = piece_of_color_and_type(us, pt);
1163 board[to] = PIECE_NONE;
1165 // Update piece list
1166 index[from] = index[to];
1167 pieceList[us][pt][index[from]] = from;
1169 if (st->capturedType)
1174 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1176 assert(st->capturedType != KING);
1177 assert(!ep || square_is_empty(capsq));
1179 // Restore the captured piece
1180 set_bit(&(byColorBB[them]), capsq);
1181 set_bit(&(byTypeBB[st->capturedType]), capsq);
1182 set_bit(&(byTypeBB[0]), capsq);
1184 board[capsq] = piece_of_color_and_type(them, st->capturedType);
1186 // Update piece count
1187 pieceCount[them][st->capturedType]++;
1189 // Update piece list, add a new captured piece in capsq square
1190 index[capsq] = pieceCount[them][st->capturedType] - 1;
1191 pieceList[them][st->capturedType][index[capsq]] = capsq;
1194 // Finally point our state pointer back to the previous state
1201 /// Position::undo_castle_move() is a private method used to unmake a castling
1202 /// move. It is called from the main Position::undo_move function. Note that
1203 /// castling moves are encoded as "king captures friendly rook" moves, for
1204 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1206 void Position::undo_castle_move(Move m) {
1208 assert(move_is_ok(m));
1209 assert(move_is_castle(m));
1211 // When we have arrived here, some work has already been done by
1212 // Position::undo_move. In particular, the side to move has been switched,
1213 // so the code below is correct.
1214 Color us = side_to_move();
1216 // Find source squares for king and rook
1217 Square kfrom = move_from(m);
1218 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1221 // Find destination squares for king and rook
1222 if (rfrom > kfrom) // O-O
1224 kto = relative_square(us, SQ_G1);
1225 rto = relative_square(us, SQ_F1);
1227 kto = relative_square(us, SQ_C1);
1228 rto = relative_square(us, SQ_D1);
1231 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1232 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1234 // Remove pieces from destination squares:
1235 clear_bit(&(byColorBB[us]), kto);
1236 clear_bit(&(byTypeBB[KING]), kto);
1237 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1238 clear_bit(&(byColorBB[us]), rto);
1239 clear_bit(&(byTypeBB[ROOK]), rto);
1240 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1242 // Put pieces on source squares:
1243 set_bit(&(byColorBB[us]), kfrom);
1244 set_bit(&(byTypeBB[KING]), kfrom);
1245 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1246 set_bit(&(byColorBB[us]), rfrom);
1247 set_bit(&(byTypeBB[ROOK]), rfrom);
1248 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1251 board[rto] = board[kto] = PIECE_NONE;
1252 board[rfrom] = piece_of_color_and_type(us, ROOK);
1253 board[kfrom] = piece_of_color_and_type(us, KING);
1255 // Update piece lists
1256 pieceList[us][KING][index[kto]] = kfrom;
1257 pieceList[us][ROOK][index[rto]] = rfrom;
1258 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1259 index[kfrom] = index[kto];
1262 // Finally point our state pointer back to the previous state
1269 /// Position::do_null_move makes() a "null move": It switches the side to move
1270 /// and updates the hash key without executing any move on the board.
1272 void Position::do_null_move(StateInfo& backupSt) {
1275 assert(!is_check());
1277 // Back up the information necessary to undo the null move to the supplied
1278 // StateInfo object.
1279 // Note that differently from normal case here backupSt is actually used as
1280 // a backup storage not as a new state to be used.
1281 backupSt.key = st->key;
1282 backupSt.epSquare = st->epSquare;
1283 backupSt.value = st->value;
1284 backupSt.previous = st->previous;
1285 backupSt.pliesFromNull = st->pliesFromNull;
1286 st->previous = &backupSt;
1288 // Save the current key to the history[] array, in order to be able to
1289 // detect repetition draws.
1290 history[st->gamePly++] = st->key;
1292 // Update the necessary information
1293 if (st->epSquare != SQ_NONE)
1294 st->key ^= zobEp[st->epSquare];
1296 st->key ^= zobSideToMove;
1297 prefetch((char*)TT.first_entry(st->key));
1299 sideToMove = opposite_color(sideToMove);
1300 st->epSquare = SQ_NONE;
1302 st->pliesFromNull = 0;
1303 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1307 /// Position::undo_null_move() unmakes a "null move".
1309 void Position::undo_null_move() {
1312 assert(!is_check());
1314 // Restore information from the our backup StateInfo object
1315 StateInfo* backupSt = st->previous;
1316 st->key = backupSt->key;
1317 st->epSquare = backupSt->epSquare;
1318 st->value = backupSt->value;
1319 st->previous = backupSt->previous;
1320 st->pliesFromNull = backupSt->pliesFromNull;
1322 // Update the necessary information
1323 sideToMove = opposite_color(sideToMove);
1329 /// Position::see() is a static exchange evaluator: It tries to estimate the
1330 /// material gain or loss resulting from a move. There are three versions of
1331 /// this function: One which takes a destination square as input, one takes a
1332 /// move, and one which takes a 'from' and a 'to' square. The function does
1333 /// not yet understand promotions captures.
1335 int Position::see(Square to) const {
1337 assert(square_is_ok(to));
1338 return see(SQ_NONE, to);
1341 int Position::see(Move m) const {
1343 assert(move_is_ok(m));
1344 return see(move_from(m), move_to(m));
1347 int Position::see_sign(Move m) const {
1349 assert(move_is_ok(m));
1351 Square from = move_from(m);
1352 Square to = move_to(m);
1354 // Early return if SEE cannot be negative because captured piece value
1355 // is not less then capturing one. Note that king moves always return
1356 // here because king midgame value is set to 0.
1357 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1360 return see(from, to);
1363 int Position::see(Square from, Square to) const {
1366 static const int seeValues[18] = {
1367 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1368 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1369 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1370 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1374 Bitboard attackers, stmAttackers, b;
1376 assert(square_is_ok(from) || from == SQ_NONE);
1377 assert(square_is_ok(to));
1379 // Initialize colors
1380 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1381 Color them = opposite_color(us);
1383 // Initialize pieces
1384 Piece piece = piece_on(from);
1385 Piece capture = piece_on(to);
1386 Bitboard occ = occupied_squares();
1388 // King cannot be recaptured
1389 if (type_of_piece(piece) == KING)
1390 return seeValues[capture];
1392 // Handle en passant moves
1393 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1395 assert(capture == PIECE_NONE);
1397 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1398 capture = piece_on(capQq);
1399 assert(type_of_piece_on(capQq) == PAWN);
1401 // Remove the captured pawn
1402 clear_bit(&occ, capQq);
1407 // Find all attackers to the destination square, with the moving piece
1408 // removed, but possibly an X-ray attacker added behind it.
1409 clear_bit(&occ, from);
1410 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1411 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1412 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1413 | (attacks_from<KING>(to) & pieces(KING))
1414 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1415 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1417 if (from != SQ_NONE)
1420 // If we don't have any attacker we are finished
1421 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1424 // Locate the least valuable attacker to the destination square
1425 // and use it to initialize from square.
1426 stmAttackers = attackers & pieces_of_color(us);
1428 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1431 from = first_1(stmAttackers & pieces(pt));
1432 piece = piece_on(from);
1435 // If the opponent has no attackers we are finished
1436 stmAttackers = attackers & pieces_of_color(them);
1438 return seeValues[capture];
1440 attackers &= occ; // Remove the moving piece
1442 // The destination square is defended, which makes things rather more
1443 // difficult to compute. We proceed by building up a "swap list" containing
1444 // the material gain or loss at each stop in a sequence of captures to the
1445 // destination square, where the sides alternately capture, and always
1446 // capture with the least valuable piece. After each capture, we look for
1447 // new X-ray attacks from behind the capturing piece.
1448 int lastCapturingPieceValue = seeValues[piece];
1449 int swapList[32], n = 1;
1453 swapList[0] = seeValues[capture];
1456 // Locate the least valuable attacker for the side to move. The loop
1457 // below looks like it is potentially infinite, but it isn't. We know
1458 // that the side to move still has at least one attacker left.
1459 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1462 // Remove the attacker we just found from the 'attackers' bitboard,
1463 // and scan for new X-ray attacks behind the attacker.
1464 b = stmAttackers & pieces(pt);
1465 occ ^= (b & (~b + 1));
1466 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1467 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1471 // Add the new entry to the swap list
1473 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1476 // Remember the value of the capturing piece, and change the side to move
1477 // before beginning the next iteration
1478 lastCapturingPieceValue = seeValues[pt];
1479 c = opposite_color(c);
1480 stmAttackers = attackers & pieces_of_color(c);
1482 // Stop after a king capture
1483 if (pt == KING && stmAttackers)
1486 swapList[n++] = QueenValueMidgame*10;
1489 } while (stmAttackers);
1491 // Having built the swap list, we negamax through it to find the best
1492 // achievable score from the point of view of the side to move
1494 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1500 /// Position::clear() erases the position object to a pristine state, with an
1501 /// empty board, white to move, and no castling rights.
1503 void Position::clear() {
1506 memset(st, 0, sizeof(StateInfo));
1507 st->epSquare = SQ_NONE;
1508 startPosPlyCounter = 0;
1510 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1511 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1512 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1513 memset(index, 0, sizeof(int) * 64);
1515 for (int i = 0; i < 64; i++)
1516 board[i] = PIECE_NONE;
1518 for (int i = 0; i < 8; i++)
1519 for (int j = 0; j < 16; j++)
1520 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1522 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1523 castleRightsMask[sq] = ALL_CASTLES;
1526 initialKFile = FILE_E;
1527 initialKRFile = FILE_H;
1528 initialQRFile = FILE_A;
1532 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1533 /// UCI interface code, whenever a non-reversible move is made in a
1534 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1535 /// for the program to handle games of arbitrary length, as long as the GUI
1536 /// handles draws by the 50 move rule correctly.
1538 void Position::reset_game_ply() {
1543 void Position::inc_startpos_ply_counter() {
1545 startPosPlyCounter++;
1548 /// Position::put_piece() puts a piece on the given square of the board,
1549 /// updating the board array, bitboards, and piece counts.
1551 void Position::put_piece(Piece p, Square s) {
1553 Color c = color_of_piece(p);
1554 PieceType pt = type_of_piece(p);
1557 index[s] = pieceCount[c][pt];
1558 pieceList[c][pt][index[s]] = s;
1560 set_bit(&(byTypeBB[pt]), s);
1561 set_bit(&(byColorBB[c]), s);
1562 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1564 pieceCount[c][pt]++;
1568 /// Position::allow_oo() gives the given side the right to castle kingside.
1569 /// Used when setting castling rights during parsing of FEN strings.
1571 void Position::allow_oo(Color c) {
1573 st->castleRights |= (1 + int(c));
1577 /// Position::allow_ooo() gives the given side the right to castle queenside.
1578 /// Used when setting castling rights during parsing of FEN strings.
1580 void Position::allow_ooo(Color c) {
1582 st->castleRights |= (4 + 4*int(c));
1586 /// Position::compute_key() computes the hash key of the position. The hash
1587 /// key is usually updated incrementally as moves are made and unmade, the
1588 /// compute_key() function is only used when a new position is set up, and
1589 /// to verify the correctness of the hash key when running in debug mode.
1591 Key Position::compute_key() const {
1593 Key result = Key(0ULL);
1595 for (Square s = SQ_A1; s <= SQ_H8; s++)
1596 if (square_is_occupied(s))
1597 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1599 if (ep_square() != SQ_NONE)
1600 result ^= zobEp[ep_square()];
1602 result ^= zobCastle[st->castleRights];
1603 if (side_to_move() == BLACK)
1604 result ^= zobSideToMove;
1610 /// Position::compute_pawn_key() computes the hash key of the position. The
1611 /// hash key is usually updated incrementally as moves are made and unmade,
1612 /// the compute_pawn_key() function is only used when a new position is set
1613 /// up, and to verify the correctness of the pawn hash key when running in
1616 Key Position::compute_pawn_key() const {
1618 Key result = Key(0ULL);
1622 for (Color c = WHITE; c <= BLACK; c++)
1624 b = pieces(PAWN, c);
1627 s = pop_1st_bit(&b);
1628 result ^= zobrist[c][PAWN][s];
1635 /// Position::compute_material_key() computes the hash key of the position.
1636 /// The hash key is usually updated incrementally as moves are made and unmade,
1637 /// the compute_material_key() function is only used when a new position is set
1638 /// up, and to verify the correctness of the material hash key when running in
1641 Key Position::compute_material_key() const {
1643 Key result = Key(0ULL);
1644 for (Color c = WHITE; c <= BLACK; c++)
1645 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1647 int count = piece_count(c, pt);
1648 for (int i = 0; i < count; i++)
1649 result ^= zobrist[c][pt][i];
1655 /// Position::compute_value() compute the incremental scores for the middle
1656 /// game and the endgame. These functions are used to initialize the incremental
1657 /// scores when a new position is set up, and to verify that the scores are correctly
1658 /// updated by do_move and undo_move when the program is running in debug mode.
1659 Score Position::compute_value() const {
1661 Score result = make_score(0, 0);
1665 for (Color c = WHITE; c <= BLACK; c++)
1666 for (PieceType pt = PAWN; pt <= KING; pt++)
1671 s = pop_1st_bit(&b);
1672 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1673 result += pst(c, pt, s);
1677 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1682 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1683 /// game material score for the given side. Material scores are updated
1684 /// incrementally during the search, this function is only used while
1685 /// initializing a new Position object.
1687 Value Position::compute_non_pawn_material(Color c) const {
1689 Value result = Value(0);
1691 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1693 Bitboard b = pieces(pt, c);
1696 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1698 result += piece_value_midgame(pt);
1705 /// Position::is_draw() tests whether the position is drawn by material,
1706 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1707 /// must be done by the search.
1708 // FIXME: Currently we are not handling 50 move rule correctly when in check
1710 bool Position::is_draw() const {
1712 // Draw by material?
1714 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1717 // Draw by the 50 moves rule?
1718 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1721 // Draw by repetition?
1722 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1723 if (history[st->gamePly - i] == st->key)
1730 /// Position::is_mate() returns true or false depending on whether the
1731 /// side to move is checkmated.
1733 bool Position::is_mate() const {
1735 MoveStack moves[256];
1736 return is_check() && (generate_moves(*this, moves) == moves);
1740 /// Position::has_mate_threat() tests whether the side to move is under
1741 /// a threat of being mated in one from the current position.
1743 bool Position::has_mate_threat() {
1745 MoveStack mlist[256], *last, *cur;
1747 bool mateFound = false;
1749 // If we are under check it's up to evasions to do the job
1753 // First pass the move to our opponent doing a null move
1756 // Then generate pseudo-legal moves that give check
1757 last = generate_non_capture_checks(*this, mlist);
1758 last = generate_captures(*this, last);
1760 // Loop through the moves, and see if one of them gives mate
1761 Bitboard pinned = pinned_pieces(sideToMove);
1762 CheckInfo ci(*this);
1763 for (cur = mlist; cur != last && !mateFound; cur++)
1765 Move move = cur->move;
1766 if ( !pl_move_is_legal(move, pinned)
1767 || !move_is_check(move, ci))
1770 do_move(move, st2, ci, true);
1783 /// Position::init_zobrist() is a static member function which initializes at
1784 /// startup the various arrays used to compute hash keys.
1786 void Position::init_zobrist() {
1790 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1791 zobrist[i][j][k] = Key(genrand_int64());
1793 for (i = 0; i < 64; i++)
1794 zobEp[i] = Key(genrand_int64());
1796 for (i = 0; i < 16; i++)
1797 zobCastle[i] = Key(genrand_int64());
1799 zobSideToMove = Key(genrand_int64());
1800 zobExclusion = Key(genrand_int64());
1804 /// Position::init_piece_square_tables() initializes the piece square tables.
1805 /// This is a two-step operation: First, the white halves of the tables are
1806 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1807 /// of the tables are initialized by mirroring and changing the sign of the
1808 /// corresponding white scores.
1810 void Position::init_piece_square_tables() {
1812 for (Square s = SQ_A1; s <= SQ_H8; s++)
1813 for (Piece p = WP; p <= WK; p++)
1814 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1816 for (Square s = SQ_A1; s <= SQ_H8; s++)
1817 for (Piece p = BP; p <= BK; p++)
1818 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1822 /// Position::flipped_copy() makes a copy of the input position, but with
1823 /// the white and black sides reversed. This is only useful for debugging,
1824 /// especially for finding evaluation symmetry bugs.
1826 void Position::flipped_copy(const Position& pos) {
1828 assert(pos.is_ok());
1831 threadID = pos.thread();
1834 for (Square s = SQ_A1; s <= SQ_H8; s++)
1835 if (!pos.square_is_empty(s))
1836 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1839 sideToMove = opposite_color(pos.side_to_move());
1842 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1843 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1844 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1845 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1847 initialKFile = pos.initialKFile;
1848 initialKRFile = pos.initialKRFile;
1849 initialQRFile = pos.initialQRFile;
1851 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1852 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1853 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1854 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1855 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1856 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1858 // En passant square
1859 if (pos.st->epSquare != SQ_NONE)
1860 st->epSquare = flip_square(pos.st->epSquare);
1866 st->key = compute_key();
1867 st->pawnKey = compute_pawn_key();
1868 st->materialKey = compute_material_key();
1870 // Incremental scores
1871 st->value = compute_value();
1874 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1875 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1881 /// Position::is_ok() performs some consitency checks for the position object.
1882 /// This is meant to be helpful when debugging.
1884 bool Position::is_ok(int* failedStep) const {
1886 // What features of the position should be verified?
1887 static const bool debugBitboards = false;
1888 static const bool debugKingCount = false;
1889 static const bool debugKingCapture = false;
1890 static const bool debugCheckerCount = false;
1891 static const bool debugKey = false;
1892 static const bool debugMaterialKey = false;
1893 static const bool debugPawnKey = false;
1894 static const bool debugIncrementalEval = false;
1895 static const bool debugNonPawnMaterial = false;
1896 static const bool debugPieceCounts = false;
1897 static const bool debugPieceList = false;
1898 static const bool debugCastleSquares = false;
1900 if (failedStep) *failedStep = 1;
1903 if (!color_is_ok(side_to_move()))
1906 // Are the king squares in the position correct?
1907 if (failedStep) (*failedStep)++;
1908 if (piece_on(king_square(WHITE)) != WK)
1911 if (failedStep) (*failedStep)++;
1912 if (piece_on(king_square(BLACK)) != BK)
1916 if (failedStep) (*failedStep)++;
1917 if (!file_is_ok(initialKRFile))
1920 if (!file_is_ok(initialQRFile))
1923 // Do both sides have exactly one king?
1924 if (failedStep) (*failedStep)++;
1927 int kingCount[2] = {0, 0};
1928 for (Square s = SQ_A1; s <= SQ_H8; s++)
1929 if (type_of_piece_on(s) == KING)
1930 kingCount[color_of_piece_on(s)]++;
1932 if (kingCount[0] != 1 || kingCount[1] != 1)
1936 // Can the side to move capture the opponent's king?
1937 if (failedStep) (*failedStep)++;
1938 if (debugKingCapture)
1940 Color us = side_to_move();
1941 Color them = opposite_color(us);
1942 Square ksq = king_square(them);
1943 if (attackers_to(ksq) & pieces_of_color(us))
1947 // Is there more than 2 checkers?
1948 if (failedStep) (*failedStep)++;
1949 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1953 if (failedStep) (*failedStep)++;
1956 // The intersection of the white and black pieces must be empty
1957 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1960 // The union of the white and black pieces must be equal to all
1962 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1965 // Separate piece type bitboards must have empty intersections
1966 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1967 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1968 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1972 // En passant square OK?
1973 if (failedStep) (*failedStep)++;
1974 if (ep_square() != SQ_NONE)
1976 // The en passant square must be on rank 6, from the point of view of the
1978 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1983 if (failedStep) (*failedStep)++;
1984 if (debugKey && st->key != compute_key())
1987 // Pawn hash key OK?
1988 if (failedStep) (*failedStep)++;
1989 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1992 // Material hash key OK?
1993 if (failedStep) (*failedStep)++;
1994 if (debugMaterialKey && st->materialKey != compute_material_key())
1997 // Incremental eval OK?
1998 if (failedStep) (*failedStep)++;
1999 if (debugIncrementalEval && st->value != compute_value())
2002 // Non-pawn material OK?
2003 if (failedStep) (*failedStep)++;
2004 if (debugNonPawnMaterial)
2006 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2009 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2014 if (failedStep) (*failedStep)++;
2015 if (debugPieceCounts)
2016 for (Color c = WHITE; c <= BLACK; c++)
2017 for (PieceType pt = PAWN; pt <= KING; pt++)
2018 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
2021 if (failedStep) (*failedStep)++;
2024 for (Color c = WHITE; c <= BLACK; c++)
2025 for (PieceType pt = PAWN; pt <= KING; pt++)
2026 for (int i = 0; i < pieceCount[c][pt]; i++)
2028 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2031 if (index[piece_list(c, pt, i)] != i)
2036 if (failedStep) (*failedStep)++;
2037 if (debugCastleSquares) {
2038 for (Color c = WHITE; c <= BLACK; c++) {
2039 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2041 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2044 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2046 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2048 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2050 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2054 if (failedStep) *failedStep = 0;