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"
49 //// Position's static data definitions
52 Key Position::zobrist[2][8][64];
53 Key Position::zobEp[64];
54 Key Position::zobCastle[16];
55 Key Position::zobSideToMove;
56 Key Position::zobExclusion;
58 Score Position::PieceSquareTable[16][64];
60 // Material values used by SEE, indexed by PieceType
61 const Value Position::seeValues[] = {
63 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
64 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
70 // Bonus for having the side to move (modified by Joona Kiiski)
71 const Score TempoValue = make_score(48, 22);
73 bool isZero(char c) { return c == '0'; }
75 struct PieceLetters : public std::map<char, Piece> {
79 operator[]('K') = WK; operator[]('k') = BK;
80 operator[]('Q') = WQ; operator[]('q') = BQ;
81 operator[]('R') = WR; operator[]('r') = BR;
82 operator[]('B') = WB; operator[]('b') = BB;
83 operator[]('N') = WN; operator[]('n') = BN;
84 operator[]('P') = WP; operator[]('p') = BP;
85 operator[](' ') = PIECE_NONE; operator[]('.') = PIECE_NONE_DARK_SQ;
88 char from_piece(Piece p) const {
90 std::map<char, Piece>::const_iterator it;
91 for (it = begin(); it != end(); ++it)
104 CheckInfo::CheckInfo(const Position& pos) {
106 Color us = pos.side_to_move();
107 Color them = opposite_color(us);
109 ksq = pos.king_square(them);
110 dcCandidates = pos.discovered_check_candidates(us);
112 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
113 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
114 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
115 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
116 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
117 checkSq[KING] = EmptyBoardBB;
121 /// Position c'tors. Here we always create a copy of the original position
122 /// or the FEN string, we want the new born Position object do not depend
123 /// on any external data so we detach state pointer from the source one.
125 Position::Position(const Position& pos, int th) {
127 memcpy(this, &pos, sizeof(Position));
128 detach(); // Always detach() in copy c'tor to avoid surprises
133 Position::Position(const string& fen, int th) {
140 /// Position::detach() copies the content of the current state and castling
141 /// masks inside the position itself. This is needed when the st pointee could
142 /// become stale, as example because the caller is about to going out of scope.
144 void Position::detach() {
148 st->previous = NULL; // as a safe guard
152 /// Position::from_fen() initializes the position object with the given FEN
153 /// string. This function is not very robust - make sure that input FENs are
154 /// correct (this is assumed to be the responsibility of the GUI).
156 void Position::from_fen(const string& fen) {
158 A FEN string defines a particular position using only the ASCII character set.
160 A FEN string contains six fields. The separator between fields is a space. The fields are:
162 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
163 with rank 1; within each rank, the contents of each square are described from file a through file h.
164 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
165 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
166 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
167 of blank squares), and "/" separate ranks.
169 2) Active color. "w" means white moves next, "b" means black.
171 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
172 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
173 kingside), and/or "q" (Black can castle queenside).
175 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
176 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
177 regardless of whether there is a pawn in position to make an en passant capture.
179 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
180 to determine if a draw can be claimed under the fifty-move rule.
182 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
186 std::istringstream ss(fen);
192 // 1. Piece placement field
193 while (ss.get(token) && token != ' ')
197 file += File(token - '0'); // Skip the given number of files
200 else if (token == '/')
207 if (pieceLetters.find(token) == pieceLetters.end())
210 put_piece(pieceLetters[token], make_square(file, rank));
215 if (!ss.get(token) || (token != 'w' && token != 'b'))
218 sideToMove = (token == 'w' ? WHITE : BLACK);
220 if (!ss.get(token) || token != ' ')
223 // 3. Castling availability
224 while (ss.get(token) && token != ' ')
229 if (!set_castling_rights(token))
233 // 4. En passant square -- ignore if no capture is possible
235 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
236 && (ss.get(row) && (row == '3' || row == '6')))
238 Square fenEpSquare = make_square(file_from_char(col), rank_from_char(row));
239 Color them = opposite_color(sideToMove);
241 if (attacks_from<PAWN>(fenEpSquare, them) & pieces(PAWN, sideToMove))
242 st->epSquare = fenEpSquare;
245 // 5-6. Halfmove clock and fullmove number are not parsed
247 // Various initialisations
248 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
249 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
250 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
251 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
252 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
253 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
255 isChess960 = initialKFile != FILE_E
256 || initialQRFile != FILE_A
257 || initialKRFile != FILE_H;
261 st->key = compute_key();
262 st->pawnKey = compute_pawn_key();
263 st->materialKey = compute_material_key();
264 st->value = compute_value();
265 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
266 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
270 cout << "Error in FEN string: " << fen << endl;
274 /// Position::set_castling_rights() sets castling parameters castling avaiability.
275 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
276 /// that uses the letters of the columns on which the rooks began the game instead
277 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
278 /// associated with the castling right, the traditional castling tag will be replaced
279 /// by the file letter of the involved rook as for the Shredder-FEN.
281 bool Position::set_castling_rights(char token) {
283 Color c = token >= 'a' ? BLACK : WHITE;
284 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
285 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
286 Piece rook = (c == WHITE ? WR : BR);
288 initialKFile = square_file(king_square(c));
289 token = char(toupper(token));
293 for (Square sq = sqH; sq >= sqA; sq--)
294 if (piece_on(sq) == rook)
297 initialKRFile = square_file(sq);
301 else if (token == 'Q')
303 for (Square sq = sqA; sq <= sqH; sq++)
304 if (piece_on(sq) == rook)
307 initialQRFile = square_file(sq);
311 else if (token >= 'A' && token <= 'H')
313 File rookFile = File(token - 'A') + FILE_A;
314 if (rookFile < initialKFile)
317 initialQRFile = rookFile;
322 initialKRFile = rookFile;
331 /// Position::to_fen() returns a FEN representation of the position. In case
332 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
334 const string Position::to_fen() const {
340 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
342 for (File file = FILE_A; file <= FILE_H; file++)
344 sq = make_square(file, rank);
346 if (square_is_occupied(sq))
349 fen += pieceLetters.from_piece(piece_on(sq));
359 fen.erase(std::remove_if(fen.begin(), fen.end(), isZero), fen.end());
360 fen.erase(--fen.end());
361 fen += (sideToMove == WHITE ? " w " : " b ");
363 if (st->castleRights != CASTLES_NONE)
365 if (can_castle_kingside(WHITE))
366 fen += isChess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
368 if (can_castle_queenside(WHITE))
369 fen += isChess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
371 if (can_castle_kingside(BLACK))
372 fen += isChess960 ? file_to_char(initialKRFile) : 'k';
374 if (can_castle_queenside(BLACK))
375 fen += isChess960 ? file_to_char(initialQRFile) : 'q';
379 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
384 /// Position::print() prints an ASCII representation of the position to
385 /// the standard output. If a move is given then also the san is printed.
387 void Position::print(Move move) const {
389 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
390 static bool requestPending = false;
392 // Check for reentrancy, as example when called from inside
393 // MovePicker that is used also here in move_to_san()
397 requestPending = true;
401 Position p(*this, thread());
402 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
403 cout << "\nMove is: " << dd << move_to_san(p, move);
406 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
408 cout << dottedLine << '|';
409 for (File file = FILE_A; file <= FILE_H; file++)
411 Square sq = make_square(file, rank);
412 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
413 Piece piece = piece_on(sq);
415 if (piece == PIECE_NONE && square_color(sq) == DARK)
416 piece = PIECE_NONE_DARK_SQ;
418 cout << c << pieceLetters.from_piece(piece) << c << '|';
421 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
422 requestPending = false;
426 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
427 /// king) pieces for the given color and for the given pinner type. Or, when
428 /// template parameter FindPinned is false, the pieces of the given color
429 /// candidate for a discovery check against the enemy king.
430 /// Bitboard checkersBB must be already updated when looking for pinners.
432 template<bool FindPinned>
433 Bitboard Position::hidden_checkers(Color c) const {
435 Bitboard result = EmptyBoardBB;
436 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
438 // Pinned pieces protect our king, dicovery checks attack
440 Square ksq = king_square(FindPinned ? c : opposite_color(c));
442 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
443 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
445 if (FindPinned && pinners)
446 pinners &= ~st->checkersBB;
450 Square s = pop_1st_bit(&pinners);
451 Bitboard b = squares_between(s, ksq) & occupied_squares();
455 if ( !(b & (b - 1)) // Only one bit set?
456 && (b & pieces_of_color(c))) // Is an our piece?
463 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
464 /// king) pieces for the given color. Note that checkersBB bitboard must
465 /// be already updated.
467 Bitboard Position::pinned_pieces(Color c) const {
469 return hidden_checkers<true>(c);
473 /// Position:discovered_check_candidates() returns a bitboard containing all
474 /// pieces for the given side which are candidates for giving a discovered
475 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
476 /// to be already updated.
478 Bitboard Position::discovered_check_candidates(Color c) const {
480 return hidden_checkers<false>(c);
483 /// Position::attackers_to() computes a bitboard containing all pieces which
484 /// attacks a given square.
486 Bitboard Position::attackers_to(Square s) const {
488 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
489 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
490 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
491 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
492 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
493 | (attacks_from<KING>(s) & pieces(KING));
496 /// Position::attacks_from() computes a bitboard of all attacks
497 /// of a given piece put in a given square.
499 Bitboard Position::attacks_from(Piece p, Square s) const {
501 assert(square_is_ok(s));
505 case WP: return attacks_from<PAWN>(s, WHITE);
506 case BP: return attacks_from<PAWN>(s, BLACK);
507 case WN: case BN: return attacks_from<KNIGHT>(s);
508 case WB: case BB: return attacks_from<BISHOP>(s);
509 case WR: case BR: return attacks_from<ROOK>(s);
510 case WQ: case BQ: return attacks_from<QUEEN>(s);
511 case WK: case BK: return attacks_from<KING>(s);
518 /// Position::move_attacks_square() tests whether a move from the current
519 /// position attacks a given square.
521 bool Position::move_attacks_square(Move m, Square s) const {
523 assert(move_is_ok(m));
524 assert(square_is_ok(s));
527 Square f = move_from(m), t = move_to(m);
529 assert(square_is_occupied(f));
531 if (bit_is_set(attacks_from(piece_on(f), t), s))
534 // Move the piece and scan for X-ray attacks behind it
535 occ = occupied_squares();
536 do_move_bb(&occ, make_move_bb(f, t));
537 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
538 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
539 & pieces_of_color(color_of_piece_on(f));
541 // If we have attacks we need to verify that are caused by our move
542 // and are not already existent ones.
543 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
547 /// Position::find_checkers() computes the checkersBB bitboard, which
548 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
549 /// currently works by calling Position::attackers_to, which is probably
550 /// inefficient. Consider rewriting this function to use the last move
551 /// played, like in non-bitboard versions of Glaurung.
553 void Position::find_checkers() {
555 Color us = side_to_move();
556 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
560 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
562 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
565 assert(move_is_ok(m));
566 assert(pinned == pinned_pieces(side_to_move()));
568 // Castling moves are checked for legality during move generation.
569 if (move_is_castle(m))
572 Color us = side_to_move();
573 Square from = move_from(m);
575 assert(color_of_piece_on(from) == us);
576 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
578 // En passant captures are a tricky special case. Because they are
579 // rather uncommon, we do it simply by testing whether the king is attacked
580 // after the move is made
583 Color them = opposite_color(us);
584 Square to = move_to(m);
585 Square capsq = make_square(square_file(to), square_rank(from));
586 Bitboard b = occupied_squares();
587 Square ksq = king_square(us);
589 assert(to == ep_square());
590 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
591 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
592 assert(piece_on(to) == PIECE_NONE);
595 clear_bit(&b, capsq);
598 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
599 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
602 // If the moving piece is a king, check whether the destination
603 // square is attacked by the opponent.
604 if (type_of_piece_on(from) == KING)
605 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
607 // A non-king move is legal if and only if it is not pinned or it
608 // is moving along the ray towards or away from the king.
610 || !bit_is_set(pinned, from)
611 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
615 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
617 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
621 Color us = side_to_move();
622 Square from = move_from(m);
623 Square to = move_to(m);
625 // King moves and en-passant captures are verified in pl_move_is_legal()
626 if (type_of_piece_on(from) == KING || move_is_ep(m))
627 return pl_move_is_legal(m, pinned);
629 Bitboard target = checkers();
630 Square checksq = pop_1st_bit(&target);
632 if (target) // double check ?
635 // Our move must be a blocking evasion or a capture of the checking piece
636 target = squares_between(checksq, king_square(us)) | checkers();
637 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
641 /// Position::move_is_check() tests whether a pseudo-legal move is a check
643 bool Position::move_is_check(Move m) const {
645 return move_is_check(m, CheckInfo(*this));
648 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
651 assert(move_is_ok(m));
652 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
653 assert(color_of_piece_on(move_from(m)) == side_to_move());
654 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
656 Square from = move_from(m);
657 Square to = move_to(m);
658 PieceType pt = type_of_piece_on(from);
661 if (bit_is_set(ci.checkSq[pt], to))
665 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
667 // For pawn and king moves we need to verify also direction
668 if ( (pt != PAWN && pt != KING)
669 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
673 // Can we skip the ugly special cases ?
674 if (!move_is_special(m))
677 Color us = side_to_move();
678 Bitboard b = occupied_squares();
680 // Promotion with check ?
681 if (move_is_promotion(m))
685 switch (move_promotion_piece(m))
688 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
690 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
692 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
694 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
700 // En passant capture with check ? We have already handled the case
701 // of direct checks and ordinary discovered check, the only case we
702 // need to handle is the unusual case of a discovered check through
703 // the captured pawn.
706 Square capsq = make_square(square_file(to), square_rank(from));
708 clear_bit(&b, capsq);
710 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
711 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
714 // Castling with check ?
715 if (move_is_castle(m))
717 Square kfrom, kto, rfrom, rto;
723 kto = relative_square(us, SQ_G1);
724 rto = relative_square(us, SQ_F1);
726 kto = relative_square(us, SQ_C1);
727 rto = relative_square(us, SQ_D1);
729 clear_bit(&b, kfrom);
730 clear_bit(&b, rfrom);
733 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
740 /// Position::do_move() makes a move, and saves all information necessary
741 /// to a StateInfo object. The move is assumed to be legal.
742 /// Pseudo-legal moves should be filtered out before this function is called.
744 void Position::do_move(Move m, StateInfo& newSt) {
747 do_move(m, newSt, ci, move_is_check(m, ci));
750 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
753 assert(move_is_ok(m));
758 // Copy some fields of old state to our new StateInfo object except the
759 // ones which are recalculated from scratch anyway, then switch our state
760 // pointer to point to the new, ready to be updated, state.
761 struct ReducedStateInfo {
762 Key pawnKey, materialKey;
763 int castleRights, rule50, gamePly, pliesFromNull;
770 memcpy(&newSt, st, sizeof(ReducedStateInfo));
775 // Save the current key to the history[] array, in order to be able to
776 // detect repetition draws.
777 history[st->gamePly++] = key;
779 // Update side to move
780 key ^= zobSideToMove;
782 // Increment the 50 moves rule draw counter. Resetting it to zero in the
783 // case of non-reversible moves is taken care of later.
787 if (move_is_castle(m))
794 Color us = side_to_move();
795 Color them = opposite_color(us);
796 Square from = move_from(m);
797 Square to = move_to(m);
798 bool ep = move_is_ep(m);
799 bool pm = move_is_promotion(m);
801 Piece piece = piece_on(from);
802 PieceType pt = type_of_piece(piece);
803 PieceType capture = ep ? PAWN : type_of_piece_on(to);
805 assert(color_of_piece_on(from) == us);
806 assert(color_of_piece_on(to) == them || square_is_empty(to));
807 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
808 assert(!pm || relative_rank(us, to) == RANK_8);
811 do_capture_move(key, capture, them, to, ep);
814 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
816 // Reset en passant square
817 if (st->epSquare != SQ_NONE)
819 key ^= zobEp[st->epSquare];
820 st->epSquare = SQ_NONE;
823 // Update castle rights, try to shortcut a common case
824 int cm = castleRightsMask[from] & castleRightsMask[to];
825 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
827 key ^= zobCastle[st->castleRights];
828 st->castleRights &= castleRightsMask[from];
829 st->castleRights &= castleRightsMask[to];
830 key ^= zobCastle[st->castleRights];
833 // Prefetch TT access as soon as we know key is updated
834 prefetch((char*)TT.first_entry(key));
837 Bitboard move_bb = make_move_bb(from, to);
838 do_move_bb(&(byColorBB[us]), move_bb);
839 do_move_bb(&(byTypeBB[pt]), move_bb);
840 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
842 board[to] = board[from];
843 board[from] = PIECE_NONE;
845 // Update piece lists, note that index[from] is not updated and
846 // becomes stale. This works as long as index[] is accessed just
847 // by known occupied squares.
848 index[to] = index[from];
849 pieceList[us][pt][index[to]] = to;
851 // If the moving piece was a pawn do some special extra work
854 // Reset rule 50 draw counter
857 // Update pawn hash key and prefetch in L1/L2 cache
858 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
859 prefetchPawn(st->pawnKey, threadID);
861 // Set en passant square, only if moved pawn can be captured
862 if ((to ^ from) == 16)
864 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
866 st->epSquare = Square((int(from) + int(to)) / 2);
867 key ^= zobEp[st->epSquare];
871 if (pm) // promotion ?
873 PieceType promotion = move_promotion_piece(m);
875 assert(promotion >= KNIGHT && promotion <= QUEEN);
877 // Insert promoted piece instead of pawn
878 clear_bit(&(byTypeBB[PAWN]), to);
879 set_bit(&(byTypeBB[promotion]), to);
880 board[to] = piece_of_color_and_type(us, promotion);
882 // Update piece counts
883 pieceCount[us][promotion]++;
884 pieceCount[us][PAWN]--;
886 // Update material key
887 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
888 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
890 // Update piece lists, move the last pawn at index[to] position
891 // and shrink the list. Add a new promotion piece to the list.
892 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
893 index[lastPawnSquare] = index[to];
894 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
895 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
896 index[to] = pieceCount[us][promotion] - 1;
897 pieceList[us][promotion][index[to]] = to;
899 // Partially revert hash keys update
900 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
901 st->pawnKey ^= zobrist[us][PAWN][to];
903 // Partially revert and update incremental scores
904 st->value -= pst(us, PAWN, to);
905 st->value += pst(us, promotion, to);
908 st->npMaterial[us] += PieceValueMidgame[promotion];
912 // Update incremental scores
913 st->value += pst_delta(piece, from, to);
916 st->capturedType = capture;
918 // Update the key with the final value
921 // Update checkers bitboard, piece must be already moved
922 st->checkersBB = EmptyBoardBB;
927 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
931 if (bit_is_set(ci.checkSq[pt], to))
932 st->checkersBB = SetMaskBB[to];
935 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
938 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
941 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
947 sideToMove = opposite_color(sideToMove);
948 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
954 /// Position::do_capture_move() is a private method used to update captured
955 /// piece info. It is called from the main Position::do_move function.
957 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
959 assert(capture != KING);
963 // If the captured piece was a pawn, update pawn hash key,
964 // otherwise update non-pawn material.
967 if (ep) // en passant ?
969 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
971 assert(to == st->epSquare);
972 assert(relative_rank(opposite_color(them), to) == RANK_6);
973 assert(piece_on(to) == PIECE_NONE);
974 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
976 board[capsq] = PIECE_NONE;
978 st->pawnKey ^= zobrist[them][PAWN][capsq];
981 st->npMaterial[them] -= PieceValueMidgame[capture];
983 // Remove captured piece
984 clear_bit(&(byColorBB[them]), capsq);
985 clear_bit(&(byTypeBB[capture]), capsq);
986 clear_bit(&(byTypeBB[0]), capsq);
989 key ^= zobrist[them][capture][capsq];
991 // Update incremental scores
992 st->value -= pst(them, capture, capsq);
994 // Update piece count
995 pieceCount[them][capture]--;
997 // Update material hash key
998 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1000 // Update piece list, move the last piece at index[capsq] position
1002 // WARNING: This is a not perfectly revresible operation. When we
1003 // will reinsert the captured piece in undo_move() we will put it
1004 // at the end of the list and not in its original place, it means
1005 // index[] and pieceList[] are not guaranteed to be invariant to a
1006 // do_move() + undo_move() sequence.
1007 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1008 index[lastPieceSquare] = index[capsq];
1009 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1010 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1012 // Reset rule 50 counter
1017 /// Position::do_castle_move() is a private method used to make a castling
1018 /// move. It is called from the main Position::do_move function. Note that
1019 /// castling moves are encoded as "king captures friendly rook" moves, for
1020 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1022 void Position::do_castle_move(Move m) {
1024 assert(move_is_ok(m));
1025 assert(move_is_castle(m));
1027 Color us = side_to_move();
1028 Color them = opposite_color(us);
1030 // Reset capture field
1031 st->capturedType = PIECE_TYPE_NONE;
1033 // Find source squares for king and rook
1034 Square kfrom = move_from(m);
1035 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1038 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1039 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1041 // Find destination squares for king and rook
1042 if (rfrom > kfrom) // O-O
1044 kto = relative_square(us, SQ_G1);
1045 rto = relative_square(us, SQ_F1);
1047 kto = relative_square(us, SQ_C1);
1048 rto = relative_square(us, SQ_D1);
1051 // Remove pieces from source squares:
1052 clear_bit(&(byColorBB[us]), kfrom);
1053 clear_bit(&(byTypeBB[KING]), kfrom);
1054 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1055 clear_bit(&(byColorBB[us]), rfrom);
1056 clear_bit(&(byTypeBB[ROOK]), rfrom);
1057 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1059 // Put pieces on destination squares:
1060 set_bit(&(byColorBB[us]), kto);
1061 set_bit(&(byTypeBB[KING]), kto);
1062 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1063 set_bit(&(byColorBB[us]), rto);
1064 set_bit(&(byTypeBB[ROOK]), rto);
1065 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1067 // Update board array
1068 Piece king = piece_of_color_and_type(us, KING);
1069 Piece rook = piece_of_color_and_type(us, ROOK);
1070 board[kfrom] = board[rfrom] = PIECE_NONE;
1074 // Update piece lists
1075 pieceList[us][KING][index[kfrom]] = kto;
1076 pieceList[us][ROOK][index[rfrom]] = rto;
1077 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1078 index[kto] = index[kfrom];
1081 // Update incremental scores
1082 st->value += pst_delta(king, kfrom, kto);
1083 st->value += pst_delta(rook, rfrom, rto);
1086 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1087 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1089 // Clear en passant square
1090 if (st->epSquare != SQ_NONE)
1092 st->key ^= zobEp[st->epSquare];
1093 st->epSquare = SQ_NONE;
1096 // Update castling rights
1097 st->key ^= zobCastle[st->castleRights];
1098 st->castleRights &= castleRightsMask[kfrom];
1099 st->key ^= zobCastle[st->castleRights];
1101 // Reset rule 50 counter
1104 // Update checkers BB
1105 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1108 sideToMove = opposite_color(sideToMove);
1109 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1115 /// Position::undo_move() unmakes a move. When it returns, the position should
1116 /// be restored to exactly the same state as before the move was made.
1118 void Position::undo_move(Move m) {
1121 assert(move_is_ok(m));
1123 sideToMove = opposite_color(sideToMove);
1125 if (move_is_castle(m))
1127 undo_castle_move(m);
1131 Color us = side_to_move();
1132 Color them = opposite_color(us);
1133 Square from = move_from(m);
1134 Square to = move_to(m);
1135 bool ep = move_is_ep(m);
1136 bool pm = move_is_promotion(m);
1138 PieceType pt = type_of_piece_on(to);
1140 assert(square_is_empty(from));
1141 assert(color_of_piece_on(to) == us);
1142 assert(!pm || relative_rank(us, to) == RANK_8);
1143 assert(!ep || to == st->previous->epSquare);
1144 assert(!ep || relative_rank(us, to) == RANK_6);
1145 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1147 if (pm) // promotion ?
1149 PieceType promotion = move_promotion_piece(m);
1152 assert(promotion >= KNIGHT && promotion <= QUEEN);
1153 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1155 // Replace promoted piece with a pawn
1156 clear_bit(&(byTypeBB[promotion]), to);
1157 set_bit(&(byTypeBB[PAWN]), to);
1159 // Update piece counts
1160 pieceCount[us][promotion]--;
1161 pieceCount[us][PAWN]++;
1163 // Update piece list replacing promotion piece with a pawn
1164 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1165 index[lastPromotionSquare] = index[to];
1166 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1167 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1168 index[to] = pieceCount[us][PAWN] - 1;
1169 pieceList[us][PAWN][index[to]] = to;
1172 // Put the piece back at the source square
1173 Bitboard move_bb = make_move_bb(to, from);
1174 do_move_bb(&(byColorBB[us]), move_bb);
1175 do_move_bb(&(byTypeBB[pt]), move_bb);
1176 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1178 board[from] = piece_of_color_and_type(us, pt);
1179 board[to] = PIECE_NONE;
1181 // Update piece list
1182 index[from] = index[to];
1183 pieceList[us][pt][index[from]] = from;
1185 if (st->capturedType)
1190 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1192 assert(st->capturedType != KING);
1193 assert(!ep || square_is_empty(capsq));
1195 // Restore the captured piece
1196 set_bit(&(byColorBB[them]), capsq);
1197 set_bit(&(byTypeBB[st->capturedType]), capsq);
1198 set_bit(&(byTypeBB[0]), capsq);
1200 board[capsq] = piece_of_color_and_type(them, st->capturedType);
1202 // Update piece count
1203 pieceCount[them][st->capturedType]++;
1205 // Update piece list, add a new captured piece in capsq square
1206 index[capsq] = pieceCount[them][st->capturedType] - 1;
1207 pieceList[them][st->capturedType][index[capsq]] = capsq;
1210 // Finally point our state pointer back to the previous state
1217 /// Position::undo_castle_move() is a private method used to unmake a castling
1218 /// move. It is called from the main Position::undo_move function. Note that
1219 /// castling moves are encoded as "king captures friendly rook" moves, for
1220 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1222 void Position::undo_castle_move(Move m) {
1224 assert(move_is_ok(m));
1225 assert(move_is_castle(m));
1227 // When we have arrived here, some work has already been done by
1228 // Position::undo_move. In particular, the side to move has been switched,
1229 // so the code below is correct.
1230 Color us = side_to_move();
1232 // Find source squares for king and rook
1233 Square kfrom = move_from(m);
1234 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1237 // Find destination squares for king and rook
1238 if (rfrom > kfrom) // O-O
1240 kto = relative_square(us, SQ_G1);
1241 rto = relative_square(us, SQ_F1);
1243 kto = relative_square(us, SQ_C1);
1244 rto = relative_square(us, SQ_D1);
1247 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1248 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1250 // Remove pieces from destination squares:
1251 clear_bit(&(byColorBB[us]), kto);
1252 clear_bit(&(byTypeBB[KING]), kto);
1253 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1254 clear_bit(&(byColorBB[us]), rto);
1255 clear_bit(&(byTypeBB[ROOK]), rto);
1256 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1258 // Put pieces on source squares:
1259 set_bit(&(byColorBB[us]), kfrom);
1260 set_bit(&(byTypeBB[KING]), kfrom);
1261 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1262 set_bit(&(byColorBB[us]), rfrom);
1263 set_bit(&(byTypeBB[ROOK]), rfrom);
1264 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1267 board[rto] = board[kto] = PIECE_NONE;
1268 board[rfrom] = piece_of_color_and_type(us, ROOK);
1269 board[kfrom] = piece_of_color_and_type(us, KING);
1271 // Update piece lists
1272 pieceList[us][KING][index[kto]] = kfrom;
1273 pieceList[us][ROOK][index[rto]] = rfrom;
1274 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1275 index[kfrom] = index[kto];
1278 // Finally point our state pointer back to the previous state
1285 /// Position::do_null_move makes() a "null move": It switches the side to move
1286 /// and updates the hash key without executing any move on the board.
1288 void Position::do_null_move(StateInfo& backupSt) {
1291 assert(!is_check());
1293 // Back up the information necessary to undo the null move to the supplied
1294 // StateInfo object.
1295 // Note that differently from normal case here backupSt is actually used as
1296 // a backup storage not as a new state to be used.
1297 backupSt.key = st->key;
1298 backupSt.epSquare = st->epSquare;
1299 backupSt.value = st->value;
1300 backupSt.previous = st->previous;
1301 backupSt.pliesFromNull = st->pliesFromNull;
1302 st->previous = &backupSt;
1304 // Save the current key to the history[] array, in order to be able to
1305 // detect repetition draws.
1306 history[st->gamePly++] = st->key;
1308 // Update the necessary information
1309 if (st->epSquare != SQ_NONE)
1310 st->key ^= zobEp[st->epSquare];
1312 st->key ^= zobSideToMove;
1313 prefetch((char*)TT.first_entry(st->key));
1315 sideToMove = opposite_color(sideToMove);
1316 st->epSquare = SQ_NONE;
1318 st->pliesFromNull = 0;
1319 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1323 /// Position::undo_null_move() unmakes a "null move".
1325 void Position::undo_null_move() {
1328 assert(!is_check());
1330 // Restore information from the our backup StateInfo object
1331 StateInfo* backupSt = st->previous;
1332 st->key = backupSt->key;
1333 st->epSquare = backupSt->epSquare;
1334 st->value = backupSt->value;
1335 st->previous = backupSt->previous;
1336 st->pliesFromNull = backupSt->pliesFromNull;
1338 // Update the necessary information
1339 sideToMove = opposite_color(sideToMove);
1345 /// Position::see() is a static exchange evaluator: It tries to estimate the
1346 /// material gain or loss resulting from a move. There are three versions of
1347 /// this function: One which takes a destination square as input, one takes a
1348 /// move, and one which takes a 'from' and a 'to' square. The function does
1349 /// not yet understand promotions captures.
1351 int Position::see(Move m) const {
1353 assert(move_is_ok(m));
1354 return see(move_from(m), move_to(m));
1357 int Position::see_sign(Move m) const {
1359 assert(move_is_ok(m));
1361 Square from = move_from(m);
1362 Square to = move_to(m);
1364 // Early return if SEE cannot be negative because captured piece value
1365 // is not less then capturing one. Note that king moves always return
1366 // here because king midgame value is set to 0.
1367 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1370 return see(from, to);
1373 int Position::see(Square from, Square to) const {
1375 Bitboard occ, attackers, stmAttackers, b;
1376 int swapList[32], slIndex = 1;
1377 PieceType capturedType, pt;
1380 assert(square_is_ok(from));
1381 assert(square_is_ok(to));
1383 capturedType = type_of_piece_on(to);
1385 // King cannot be recaptured
1386 if (capturedType == KING)
1387 return seeValues[capturedType];
1389 occ = occupied_squares();
1391 // Handle en passant moves
1392 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1394 Square capQq = (side_to_move() == WHITE) ? (to - DELTA_N) : (to - DELTA_S);
1396 assert(capturedType == PIECE_TYPE_NONE);
1397 assert(type_of_piece_on(capQq) == PAWN);
1399 // Remove the captured pawn
1400 clear_bit(&occ, capQq);
1401 capturedType = PAWN;
1404 // Find all attackers to the destination square, with the moving piece
1405 // removed, but possibly an X-ray attacker added behind it.
1406 clear_bit(&occ, from);
1407 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1408 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1409 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1410 | (attacks_from<KING>(to) & pieces(KING))
1411 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1412 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1414 // If the opponent has no attackers we are finished
1415 stm = opposite_color(color_of_piece_on(from));
1416 stmAttackers = attackers & pieces_of_color(stm);
1418 return seeValues[capturedType];
1420 // The destination square is defended, which makes things rather more
1421 // difficult to compute. We proceed by building up a "swap list" containing
1422 // the material gain or loss at each stop in a sequence of captures to the
1423 // destination square, where the sides alternately capture, and always
1424 // capture with the least valuable piece. After each capture, we look for
1425 // new X-ray attacks from behind the capturing piece.
1426 swapList[0] = seeValues[capturedType];
1427 capturedType = type_of_piece_on(from);
1430 // Locate the least valuable attacker for the side to move. The loop
1431 // below looks like it is potentially infinite, but it isn't. We know
1432 // that the side to move still has at least one attacker left.
1433 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1436 // Remove the attacker we just found from the 'attackers' bitboard,
1437 // and scan for new X-ray attacks behind the attacker.
1438 b = stmAttackers & pieces(pt);
1439 occ ^= (b & (~b + 1));
1440 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1441 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1443 attackers &= occ; // Cut out pieces we've already done
1445 // Add the new entry to the swap list
1446 assert(slIndex < 32);
1447 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1450 // Remember the value of the capturing piece, and change the side to move
1451 // before beginning the next iteration
1453 stm = opposite_color(stm);
1454 stmAttackers = attackers & pieces_of_color(stm);
1456 // Stop after a king capture
1457 if (pt == KING && stmAttackers)
1459 assert(slIndex < 32);
1460 swapList[slIndex++] = QueenValueMidgame*10;
1463 } while (stmAttackers);
1465 // Having built the swap list, we negamax through it to find the best
1466 // achievable score from the point of view of the side to move
1468 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1474 /// Position::clear() erases the position object to a pristine state, with an
1475 /// empty board, white to move, and no castling rights.
1477 void Position::clear() {
1480 memset(st, 0, sizeof(StateInfo));
1481 st->epSquare = SQ_NONE;
1482 startPosPlyCounter = 0;
1485 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1486 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1487 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1488 memset(index, 0, sizeof(int) * 64);
1490 for (int i = 0; i < 64; i++)
1491 board[i] = PIECE_NONE;
1493 for (int i = 0; i < 8; i++)
1494 for (int j = 0; j < 16; j++)
1495 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1497 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1498 castleRightsMask[sq] = ALL_CASTLES;
1501 initialKFile = FILE_E;
1502 initialKRFile = FILE_H;
1503 initialQRFile = FILE_A;
1507 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1508 /// UCI interface code, whenever a non-reversible move is made in a
1509 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1510 /// for the program to handle games of arbitrary length, as long as the GUI
1511 /// handles draws by the 50 move rule correctly.
1513 void Position::reset_game_ply() {
1518 void Position::inc_startpos_ply_counter() {
1520 startPosPlyCounter++;
1523 /// Position::put_piece() puts a piece on the given square of the board,
1524 /// updating the board array, bitboards, and piece counts.
1526 void Position::put_piece(Piece p, Square s) {
1528 Color c = color_of_piece(p);
1529 PieceType pt = type_of_piece(p);
1532 index[s] = pieceCount[c][pt];
1533 pieceList[c][pt][index[s]] = s;
1535 set_bit(&(byTypeBB[pt]), s);
1536 set_bit(&(byColorBB[c]), s);
1537 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1539 pieceCount[c][pt]++;
1543 /// Position::allow_oo() gives the given side the right to castle kingside.
1544 /// Used when setting castling rights during parsing of FEN strings.
1546 void Position::allow_oo(Color c) {
1548 st->castleRights |= (1 + int(c));
1552 /// Position::allow_ooo() gives the given side the right to castle queenside.
1553 /// Used when setting castling rights during parsing of FEN strings.
1555 void Position::allow_ooo(Color c) {
1557 st->castleRights |= (4 + 4*int(c));
1561 /// Position::compute_key() computes the hash key of the position. The hash
1562 /// key is usually updated incrementally as moves are made and unmade, the
1563 /// compute_key() function is only used when a new position is set up, and
1564 /// to verify the correctness of the hash key when running in debug mode.
1566 Key Position::compute_key() const {
1570 for (Square s = SQ_A1; s <= SQ_H8; s++)
1571 if (square_is_occupied(s))
1572 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1574 if (ep_square() != SQ_NONE)
1575 result ^= zobEp[ep_square()];
1577 result ^= zobCastle[st->castleRights];
1578 if (side_to_move() == BLACK)
1579 result ^= zobSideToMove;
1585 /// Position::compute_pawn_key() computes the hash key of the position. The
1586 /// hash key is usually updated incrementally as moves are made and unmade,
1587 /// the compute_pawn_key() function is only used when a new position is set
1588 /// up, and to verify the correctness of the pawn hash key when running in
1591 Key Position::compute_pawn_key() const {
1597 for (Color c = WHITE; c <= BLACK; c++)
1599 b = pieces(PAWN, c);
1602 s = pop_1st_bit(&b);
1603 result ^= zobrist[c][PAWN][s];
1610 /// Position::compute_material_key() computes the hash key of the position.
1611 /// The hash key is usually updated incrementally as moves are made and unmade,
1612 /// the compute_material_key() function is only used when a new position is set
1613 /// up, and to verify the correctness of the material hash key when running in
1616 Key Position::compute_material_key() const {
1619 for (Color c = WHITE; c <= BLACK; c++)
1620 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1622 int count = piece_count(c, pt);
1623 for (int i = 0; i < count; i++)
1624 result ^= zobrist[c][pt][i];
1630 /// Position::compute_value() compute the incremental scores for the middle
1631 /// game and the endgame. These functions are used to initialize the incremental
1632 /// scores when a new position is set up, and to verify that the scores are correctly
1633 /// updated by do_move and undo_move when the program is running in debug mode.
1634 Score Position::compute_value() const {
1636 Score result = SCORE_ZERO;
1640 for (Color c = WHITE; c <= BLACK; c++)
1641 for (PieceType pt = PAWN; pt <= KING; pt++)
1646 s = pop_1st_bit(&b);
1647 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1648 result += pst(c, pt, s);
1652 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1657 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1658 /// game material score for the given side. Material scores are updated
1659 /// incrementally during the search, this function is only used while
1660 /// initializing a new Position object.
1662 Value Position::compute_non_pawn_material(Color c) const {
1664 Value result = VALUE_ZERO;
1666 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1668 Bitboard b = pieces(pt, c);
1671 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1674 result += PieceValueMidgame[pt];
1681 /// Position::is_draw() tests whether the position is drawn by material,
1682 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1683 /// must be done by the search.
1685 bool Position::is_draw() const {
1687 // Draw by material?
1689 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1692 // Draw by the 50 moves rule?
1693 if (st->rule50 > 99 && (st->rule50 > 100 || !is_mate()))
1696 // Draw by repetition?
1697 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1698 if (history[st->gamePly - i] == st->key)
1705 /// Position::is_mate() returns true or false depending on whether the
1706 /// side to move is checkmated.
1708 bool Position::is_mate() const {
1710 MoveStack moves[MOVES_MAX];
1711 return is_check() && (generate_moves(*this, moves) == moves);
1715 /// Position::has_mate_threat() tests whether the side to move is under
1716 /// a threat of being mated in one from the current position.
1718 bool Position::has_mate_threat() {
1720 MoveStack mlist[MOVES_MAX], *last, *cur;
1722 bool mateFound = false;
1724 // If we are under check it's up to evasions to do the job
1728 // First pass the move to our opponent doing a null move
1731 // Then generate pseudo-legal moves that give check
1732 last = generate_non_capture_checks(*this, mlist);
1733 last = generate_captures(*this, last);
1735 // Loop through the moves, and see if one of them gives mate
1736 Bitboard pinned = pinned_pieces(sideToMove);
1737 CheckInfo ci(*this);
1738 for (cur = mlist; cur != last && !mateFound; cur++)
1740 Move move = cur->move;
1741 if ( !pl_move_is_legal(move, pinned)
1742 || !move_is_check(move, ci))
1745 do_move(move, st2, ci, true);
1758 /// Position::init_zobrist() is a static member function which initializes at
1759 /// startup the various arrays used to compute hash keys.
1761 void Position::init_zobrist() {
1766 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1767 zobrist[i][j][k] = RKiss.rand<Key>();
1769 for (i = 0; i < 64; i++)
1770 zobEp[i] = RKiss.rand<Key>();
1772 for (i = 0; i < 16; i++)
1773 zobCastle[i] = RKiss.rand<Key>();
1775 zobSideToMove = RKiss.rand<Key>();
1776 zobExclusion = RKiss.rand<Key>();
1780 /// Position::init_piece_square_tables() initializes the piece square tables.
1781 /// This is a two-step operation: First, the white halves of the tables are
1782 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1783 /// of the tables are initialized by mirroring and changing the sign of the
1784 /// corresponding white scores.
1786 void Position::init_piece_square_tables() {
1788 for (Square s = SQ_A1; s <= SQ_H8; s++)
1789 for (Piece p = WP; p <= WK; p++)
1790 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1792 for (Square s = SQ_A1; s <= SQ_H8; s++)
1793 for (Piece p = BP; p <= BK; p++)
1794 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1798 /// Position::flipped_copy() makes a copy of the input position, but with
1799 /// the white and black sides reversed. This is only useful for debugging,
1800 /// especially for finding evaluation symmetry bugs.
1802 void Position::flipped_copy(const Position& pos) {
1804 assert(pos.is_ok());
1807 threadID = pos.thread();
1810 for (Square s = SQ_A1; s <= SQ_H8; s++)
1811 if (!pos.square_is_empty(s))
1812 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1815 sideToMove = opposite_color(pos.side_to_move());
1818 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1819 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1820 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1821 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1823 initialKFile = pos.initialKFile;
1824 initialKRFile = pos.initialKRFile;
1825 initialQRFile = pos.initialQRFile;
1827 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1828 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1829 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1830 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1831 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1832 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1834 // En passant square
1835 if (pos.st->epSquare != SQ_NONE)
1836 st->epSquare = flip_square(pos.st->epSquare);
1842 st->key = compute_key();
1843 st->pawnKey = compute_pawn_key();
1844 st->materialKey = compute_material_key();
1846 // Incremental scores
1847 st->value = compute_value();
1850 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1851 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1857 /// Position::is_ok() performs some consitency checks for the position object.
1858 /// This is meant to be helpful when debugging.
1860 bool Position::is_ok(int* failedStep) const {
1862 // What features of the position should be verified?
1863 static const bool debugBitboards = false;
1864 static const bool debugKingCount = false;
1865 static const bool debugKingCapture = false;
1866 static const bool debugCheckerCount = false;
1867 static const bool debugKey = false;
1868 static const bool debugMaterialKey = false;
1869 static const bool debugPawnKey = false;
1870 static const bool debugIncrementalEval = false;
1871 static const bool debugNonPawnMaterial = false;
1872 static const bool debugPieceCounts = false;
1873 static const bool debugPieceList = false;
1874 static const bool debugCastleSquares = false;
1876 if (failedStep) *failedStep = 1;
1879 if (!color_is_ok(side_to_move()))
1882 // Are the king squares in the position correct?
1883 if (failedStep) (*failedStep)++;
1884 if (piece_on(king_square(WHITE)) != WK)
1887 if (failedStep) (*failedStep)++;
1888 if (piece_on(king_square(BLACK)) != BK)
1892 if (failedStep) (*failedStep)++;
1893 if (!file_is_ok(initialKRFile))
1896 if (!file_is_ok(initialQRFile))
1899 // Do both sides have exactly one king?
1900 if (failedStep) (*failedStep)++;
1903 int kingCount[2] = {0, 0};
1904 for (Square s = SQ_A1; s <= SQ_H8; s++)
1905 if (type_of_piece_on(s) == KING)
1906 kingCount[color_of_piece_on(s)]++;
1908 if (kingCount[0] != 1 || kingCount[1] != 1)
1912 // Can the side to move capture the opponent's king?
1913 if (failedStep) (*failedStep)++;
1914 if (debugKingCapture)
1916 Color us = side_to_move();
1917 Color them = opposite_color(us);
1918 Square ksq = king_square(them);
1919 if (attackers_to(ksq) & pieces_of_color(us))
1923 // Is there more than 2 checkers?
1924 if (failedStep) (*failedStep)++;
1925 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1929 if (failedStep) (*failedStep)++;
1932 // The intersection of the white and black pieces must be empty
1933 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1936 // The union of the white and black pieces must be equal to all
1938 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1941 // Separate piece type bitboards must have empty intersections
1942 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1943 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1944 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1948 // En passant square OK?
1949 if (failedStep) (*failedStep)++;
1950 if (ep_square() != SQ_NONE)
1952 // The en passant square must be on rank 6, from the point of view of the
1954 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1959 if (failedStep) (*failedStep)++;
1960 if (debugKey && st->key != compute_key())
1963 // Pawn hash key OK?
1964 if (failedStep) (*failedStep)++;
1965 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1968 // Material hash key OK?
1969 if (failedStep) (*failedStep)++;
1970 if (debugMaterialKey && st->materialKey != compute_material_key())
1973 // Incremental eval OK?
1974 if (failedStep) (*failedStep)++;
1975 if (debugIncrementalEval && st->value != compute_value())
1978 // Non-pawn material OK?
1979 if (failedStep) (*failedStep)++;
1980 if (debugNonPawnMaterial)
1982 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1985 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1990 if (failedStep) (*failedStep)++;
1991 if (debugPieceCounts)
1992 for (Color c = WHITE; c <= BLACK; c++)
1993 for (PieceType pt = PAWN; pt <= KING; pt++)
1994 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1997 if (failedStep) (*failedStep)++;
2000 for (Color c = WHITE; c <= BLACK; c++)
2001 for (PieceType pt = PAWN; pt <= KING; pt++)
2002 for (int i = 0; i < pieceCount[c][pt]; i++)
2004 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2007 if (index[piece_list(c, pt, i)] != i)
2012 if (failedStep) (*failedStep)++;
2013 if (debugCastleSquares) {
2014 for (Color c = WHITE; c <= BLACK; c++) {
2015 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2017 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2020 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2022 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2024 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2026 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2030 if (failedStep) *failedStep = 0;