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  1. /*
  2.   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  3.   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  4.   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
  5.   Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
  6.  
  7.   Stockfish is free software: you can redistribute it and/or modify
  8.   it under the terms of the GNU General Public License as published by
  9.   the Free Software Foundation, either version 3 of the License, or
  10.   (at your option) any later version.
  11.  
  12.   Stockfish is distributed in the hope that it will be useful,
  13.   but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15.   GNU General Public License for more details.
  16.  
  17.   You should have received a copy of the GNU General Public License
  18.   along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19. */
  20.  
  21. #ifndef POSITION_H_INCLUDED
  22. #define POSITION_H_INCLUDED
  23.  
  24. #include <cassert>
  25. #include <deque>
  26. #include <memory> // For std::unique_ptr
  27. #include <string>
  28.  
  29. #include "bitboard.h"
  30. #include "types.h"
  31.  
  32.  
  33. /// StateInfo struct stores information needed to restore a Position object to
  34. /// its previous state when we retract a move. Whenever a move is made on the
  35. /// board (by calling Position::do_move), a StateInfo object must be passed.
  36.  
  37. struct StateInfo {
  38.  
  39.   // Copied when making a move
  40.   Key    pawnKey;
  41.   Key    materialKey;
  42.   Value  nonPawnMaterial[COLOR_NB];
  43.   int    castlingRights;
  44.   int    rule50;
  45.   int    pliesFromNull;
  46.   Score  psq;
  47.   Square epSquare;
  48.  
  49.   // Not copied when making a move (will be recomputed anyhow)
  50.   Key        key;
  51.   Bitboard   checkersBB;
  52.   Piece      capturedPiece;
  53.   StateInfo* previous;
  54.   Bitboard   blockersForKing[COLOR_NB];
  55.   Bitboard   pinnersForKing[COLOR_NB];
  56.   Bitboard   checkSquares[PIECE_TYPE_NB];
  57. };
  58.  
  59. /// A list to keep track of the position states along the setup moves (from the
  60. /// start position to the position just before the search starts). Needed by
  61. /// 'draw by repetition' detection. Use a std::deque because pointers to
  62. /// elements are not invalidated upon list resizing.
  63. typedef std::unique_ptr<std::deque<StateInfo>> StateListPtr;
  64.  
  65.  
  66. /// Position class stores information regarding the board representation as
  67. /// pieces, side to move, hash keys, castling info, etc. Important methods are
  68. /// do_move() and undo_move(), used by the search to update node info when
  69. /// traversing the search tree.
  70. class Thread;
  71.  
  72. class Position {
  73. public:
  74.   static void init();
  75.  
  76.   Position() = default;
  77.   Position(const Position&) = delete;
  78.   Position& operator=(const Position&) = delete;
  79.  
  80.   // FEN string input/output
  81.   Position& set(const std::string& fenStr, bool isChess960, StateInfo* si, Thread* th);
  82.   Position& set(const std::string& code, Color c, StateInfo* si);
  83.   const std::string fen() const;
  84.  
  85.   // Position representation
  86.   Bitboard pieces() const;
  87.   Bitboard pieces(PieceType pt) const;
  88.   Bitboard pieces(PieceType pt1, PieceType pt2) const;
  89.   Bitboard pieces(Color c) const;
  90.   Bitboard pieces(Color c, PieceType pt) const;
  91.   Bitboard pieces(Color c, PieceType pt1, PieceType pt2) const;
  92.   Piece piece_on(Square s) const;
  93.   Square ep_square() const;
  94.   bool empty(Square s) const;
  95.   template<PieceType Pt> int count(Color c) const;
  96.   template<PieceType Pt> int count() const;
  97.   template<PieceType Pt> const Square* squares(Color c) const;
  98.   template<PieceType Pt> Square square(Color c) const;
  99.  
  100.   // Castling
  101.   int can_castle(Color c) const;
  102.   int can_castle(CastlingRight cr) const;
  103.   bool castling_impeded(CastlingRight cr) const;
  104.   Square castling_rook_square(CastlingRight cr) const;
  105.  
  106.   // Checking
  107.   Bitboard checkers() const;
  108.   Bitboard discovered_check_candidates() const;
  109.   Bitboard pinned_pieces(Color c) const;
  110.   Bitboard check_squares(PieceType pt) const;
  111.  
  112.   // Attacks to/from a given square
  113.   Bitboard attackers_to(Square s) const;
  114.   Bitboard attackers_to(Square s, Bitboard occupied) const;
  115.   Bitboard attacks_from(PieceType pt, Square s) const;
  116.   template<PieceType> Bitboard attacks_from(Square s) const;
  117.   template<PieceType> Bitboard attacks_from(Square s, Color c) const;
  118.   Bitboard slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const;
  119.  
  120.   // Properties of moves
  121.   bool legal(Move m) const;
  122.   bool pseudo_legal(const Move m) const;
  123.   bool capture(Move m) const;
  124.   bool capture_or_promotion(Move m) const;
  125.   bool gives_check(Move m) const;
  126.   bool advanced_pawn_push(Move m) const;
  127.   Piece moved_piece(Move m) const;
  128.   Piece captured_piece() const;
  129.  
  130.   // Piece specific
  131.   bool pawn_passed(Color c, Square s) const;
  132.   bool opposite_bishops() const;
  133.  
  134.   // Doing and undoing moves
  135.   void do_move(Move m, StateInfo& newSt);
  136.   void do_move(Move m, StateInfo& newSt, bool givesCheck);
  137.   void undo_move(Move m);
  138.   void do_null_move(StateInfo& newSt);
  139.   void undo_null_move();
  140.  
  141.   // Static Exchange Evaluation
  142.   bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
  143.  
  144.   // Accessing hash keys
  145.   Key key() const;
  146.   Key key_after(Move m) const;
  147.   Key material_key() const;
  148.   Key pawn_key() const;
  149.  
  150.   // Other properties of the position
  151.   Color side_to_move() const;
  152.   int game_ply() const;
  153.   bool is_chess960() const;
  154.   Thread* this_thread() const;
  155.   bool is_draw(int ply) const;
  156.   int rule50_count() const;
  157.   Score psq_score() const;
  158.   Value non_pawn_material(Color c) const;
  159.   Value non_pawn_material() const;
  160.  
  161.   // Position consistency check, for debugging
  162.   bool pos_is_ok() const;
  163.   void flip();
  164.  
  165. private:
  166.   // Initialization helpers (used while setting up a position)
  167.   void set_castling_right(Color c, Square rfrom);
  168.   void set_state(StateInfo* si) const;
  169.   void set_check_info(StateInfo* si) const;
  170.  
  171.   // Other helpers
  172.   void put_piece(Piece pc, Square s);
  173.   void remove_piece(Piece pc, Square s);
  174.   void move_piece(Piece pc, Square from, Square to);
  175.   template<bool Do>
  176.   void do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto);
  177.  
  178.   // Data members
  179.   Piece board[SQUARE_NB];
  180.   Bitboard byTypeBB[PIECE_TYPE_NB];
  181.   Bitboard byColorBB[COLOR_NB];
  182.   int pieceCount[PIECE_NB];
  183.   Square pieceList[PIECE_NB][16];
  184.   int index[SQUARE_NB];
  185.   int castlingRightsMask[SQUARE_NB];
  186.   Square castlingRookSquare[CASTLING_RIGHT_NB];
  187.   Bitboard castlingPath[CASTLING_RIGHT_NB];
  188.   int gamePly;
  189.   Color sideToMove;
  190.   Thread* thisThread;
  191.   StateInfo* st;
  192.   bool chess960;
  193. };
  194.  
  195. extern std::ostream& operator<<(std::ostream& os, const Position& pos);
  196.  
  197. inline Color Position::side_to_move() const {
  198.   return sideToMove;
  199. }
  200.  
  201. inline bool Position::empty(Square s) const {
  202.   return board[s] == NO_PIECE;
  203. }
  204.  
  205. inline Piece Position::piece_on(Square s) const {
  206.   return board[s];
  207. }
  208.  
  209. inline Piece Position::moved_piece(Move m) const {
  210.   return board[from_sq(m)];
  211. }
  212.  
  213. inline Bitboard Position::pieces() const {
  214.   return byTypeBB[ALL_PIECES];
  215. }
  216.  
  217. inline Bitboard Position::pieces(PieceType pt) const {
  218.   return byTypeBB[pt];
  219. }
  220.  
  221. inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
  222.   return byTypeBB[pt1] | byTypeBB[pt2];
  223. }
  224.  
  225. inline Bitboard Position::pieces(Color c) const {
  226.   return byColorBB[c];
  227. }
  228.  
  229. inline Bitboard Position::pieces(Color c, PieceType pt) const {
  230.   return byColorBB[c] & byTypeBB[pt];
  231. }
  232.  
  233. inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
  234.   return byColorBB[c] & (byTypeBB[pt1] | byTypeBB[pt2]);
  235. }
  236.  
  237. template<PieceType Pt> inline int Position::count(Color c) const {
  238.   return pieceCount[make_piece(c, Pt)];
  239. }
  240.  
  241. template<PieceType Pt> inline int Position::count() const {
  242.   return pieceCount[make_piece(WHITE, Pt)] + pieceCount[make_piece(BLACK, Pt)];
  243. }
  244.  
  245. template<PieceType Pt> inline const Square* Position::squares(Color c) const {
  246.   return pieceList[make_piece(c, Pt)];
  247. }
  248.  
  249. template<PieceType Pt> inline Square Position::square(Color c) const {
  250.   assert(pieceCount[make_piece(c, Pt)] == 1);
  251.   return pieceList[make_piece(c, Pt)][0];
  252. }
  253.  
  254. inline Square Position::ep_square() const {
  255.   return st->epSquare;
  256. }
  257.  
  258. inline int Position::can_castle(CastlingRight cr) const {
  259.   return st->castlingRights & cr;
  260. }
  261.  
  262. inline int Position::can_castle(Color c) const {
  263.   return st->castlingRights & ((WHITE_OO | WHITE_OOO) << (2 * c));
  264. }
  265.  
  266. inline bool Position::castling_impeded(CastlingRight cr) const {
  267.   return byTypeBB[ALL_PIECES] & castlingPath[cr];
  268. }
  269.  
  270. inline Square Position::castling_rook_square(CastlingRight cr) const {
  271.   return castlingRookSquare[cr];
  272. }
  273.  
  274. template<PieceType Pt>
  275. inline Bitboard Position::attacks_from(Square s) const {
  276.   assert(Pt != PAWN);
  277.   return  Pt == BISHOP || Pt == ROOK ? attacks_bb<Pt>(s, byTypeBB[ALL_PIECES])
  278.         : Pt == QUEEN  ? attacks_from<ROOK>(s) | attacks_from<BISHOP>(s)
  279.         : PseudoAttacks[Pt][s];
  280. }
  281.  
  282. template<>
  283. inline Bitboard Position::attacks_from<PAWN>(Square s, Color c) const {
  284.   return PawnAttacks[c][s];
  285. }
  286.  
  287. inline Bitboard Position::attacks_from(PieceType pt, Square s) const {
  288.   return attacks_bb(pt, s, byTypeBB[ALL_PIECES]);
  289. }
  290.  
  291. inline Bitboard Position::attackers_to(Square s) const {
  292.   return attackers_to(s, byTypeBB[ALL_PIECES]);
  293. }
  294.  
  295. inline Bitboard Position::checkers() const {
  296.   return st->checkersBB;
  297. }
  298.  
  299. inline Bitboard Position::discovered_check_candidates() const {
  300.   return st->blockersForKing[~sideToMove] & pieces(sideToMove);
  301. }
  302.  
  303. inline Bitboard Position::pinned_pieces(Color c) const {
  304.   return st->blockersForKing[c] & pieces(c);
  305. }
  306.  
  307. inline Bitboard Position::check_squares(PieceType pt) const {
  308.   return st->checkSquares[pt];
  309. }
  310.  
  311. inline bool Position::pawn_passed(Color c, Square s) const {
  312.   return !(pieces(~c, PAWN) & passed_pawn_mask(c, s));
  313. }
  314.  
  315. inline bool Position::advanced_pawn_push(Move m) const {
  316.   return   type_of(moved_piece(m)) == PAWN
  317.         && relative_rank(sideToMove, from_sq(m)) > RANK_4;
  318. }
  319.  
  320. inline Key Position::key() const {
  321.   return st->key;
  322. }
  323.  
  324. inline Key Position::pawn_key() const {
  325.   return st->pawnKey;
  326. }
  327.  
  328. inline Key Position::material_key() const {
  329.   return st->materialKey;
  330. }
  331.  
  332. inline Score Position::psq_score() const {
  333.   return st->psq;
  334. }
  335.  
  336. inline Value Position::non_pawn_material(Color c) const {
  337.   return st->nonPawnMaterial[c];
  338. }
  339.  
  340. inline Value Position::non_pawn_material() const {
  341.   return st->nonPawnMaterial[WHITE] + st->nonPawnMaterial[BLACK];
  342. }
  343.  
  344. inline int Position::game_ply() const {
  345.   return gamePly;
  346. }
  347.  
  348. inline int Position::rule50_count() const {
  349.   return st->rule50;
  350. }
  351.  
  352. inline bool Position::opposite_bishops() const {
  353.   return   pieceCount[W_BISHOP] == 1
  354.         && pieceCount[B_BISHOP] == 1
  355.         && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
  356. }
  357.  
  358. inline bool Position::is_chess960() const {
  359.   return chess960;
  360. }
  361.  
  362. inline bool Position::capture_or_promotion(Move m) const {
  363.   assert(is_ok(m));
  364.   return type_of(m) != NORMAL ? type_of(m) != CASTLING : !empty(to_sq(m));
  365. }
  366.  
  367. inline bool Position::capture(Move m) const {
  368.   assert(is_ok(m));
  369.   // Castling is encoded as "king captures rook"
  370.   return (!empty(to_sq(m)) && type_of(m) != CASTLING) || type_of(m) == ENPASSANT;
  371. }
  372.  
  373. inline Piece Position::captured_piece() const {
  374.   return st->capturedPiece;
  375. }
  376.  
  377. inline Thread* Position::this_thread() const {
  378.   return thisThread;
  379. }
  380.  
  381. inline void Position::put_piece(Piece pc, Square s) {
  382.  
  383.   board[s] = pc;
  384.   byTypeBB[ALL_PIECES] |= s;
  385.   byTypeBB[type_of(pc)] |= s;
  386.   byColorBB[color_of(pc)] |= s;
  387.   index[s] = pieceCount[pc]++;
  388.   pieceList[pc][index[s]] = s;
  389.   pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
  390. }
  391.  
  392. inline void Position::remove_piece(Piece pc, Square s) {
  393.  
  394.   // WARNING: This is not a reversible operation. If we remove a piece in
  395.   // do_move() and then replace it in undo_move() we will put it at the end of
  396.   // the list and not in its original place, it means index[] and pieceList[]
  397.   // are not invariant to a do_move() + undo_move() sequence.
  398.   byTypeBB[ALL_PIECES] ^= s;
  399.   byTypeBB[type_of(pc)] ^= s;
  400.   byColorBB[color_of(pc)] ^= s;
  401.   /* board[s] = NO_PIECE;  Not needed, overwritten by the capturing one */
  402.   Square lastSquare = pieceList[pc][--pieceCount[pc]];
  403.   index[lastSquare] = index[s];
  404.   pieceList[pc][index[lastSquare]] = lastSquare;
  405.   pieceList[pc][pieceCount[pc]] = SQ_NONE;
  406.   pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
  407. }
  408.  
  409. inline void Position::move_piece(Piece pc, Square from, Square to) {
  410.  
  411.   // index[from] is not updated and becomes stale. This works as long as index[]
  412.   // is accessed just by known occupied squares.
  413.   Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
  414.   byTypeBB[ALL_PIECES] ^= from_to_bb;
  415.   byTypeBB[type_of(pc)] ^= from_to_bb;
  416.   byColorBB[color_of(pc)] ^= from_to_bb;
  417.   board[from] = NO_PIECE;
  418.   board[to] = pc;
  419.   index[to] = index[from];
  420.   pieceList[pc][index[to]] = to;
  421. }
  422.  
  423. inline void Position::do_move(Move m, StateInfo& newSt) {
  424.   do_move(m, newSt, gives_check(m));
  425. }
  426.  
  427. #endif // #ifndef POSITION_H_INCLUDED
  428.