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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) 2015-2019 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.   Square epSquare;
  47.  
  48.   // Not copied when making a move (will be recomputed anyhow)
  49.   Key        key;
  50.   Bitboard   checkersBB;
  51.   Piece      capturedPiece;
  52.   StateInfo* previous;
  53.   Bitboard   blockersForKing[COLOR_NB];
  54.   Bitboard   pinners[COLOR_NB];
  55.   Bitboard   checkSquares[PIECE_TYPE_NB];
  56. };
  57.  
  58. /// A list to keep track of the position states along the setup moves (from the
  59. /// start position to the position just before the search starts). Needed by
  60. /// 'draw by repetition' detection. Use a std::deque because pointers to
  61. /// elements are not invalidated upon list resizing.
  62. typedef std::unique_ptr<std::deque<StateInfo>> StateListPtr;
  63.  
  64.  
  65. /// Position class stores information regarding the board representation as
  66. /// pieces, side to move, hash keys, castling info, etc. Important methods are
  67. /// do_move() and undo_move(), used by the search to update node info when
  68. /// traversing the search tree.
  69. class Thread;
  70.  
  71. class Position {
  72. public:
  73.   static void init();
  74.  
  75.   Position() = default;
  76.   Position(const Position&) = delete;
  77.   Position& operator=(const Position&) = delete;
  78.  
  79.   // FEN string input/output
  80.   Position& set(const std::string& fenStr, bool isChess960, StateInfo* si, Thread* th);
  81.   Position& set(const std::string& code, Color c, StateInfo* si);
  82.   const std::string fen() const;
  83.  
  84.   // Position representation
  85.   Bitboard pieces() const;
  86.   Bitboard pieces(PieceType pt) const;
  87.   Bitboard pieces(PieceType pt1, PieceType pt2) const;
  88.   Bitboard pieces(Color c) const;
  89.   Bitboard pieces(Color c, PieceType pt) const;
  90.   Bitboard pieces(Color c, PieceType pt1, PieceType pt2) const;
  91.   Piece piece_on(Square s) const;
  92.   Square ep_square() const;
  93.   bool empty(Square s) const;
  94.   template<PieceType Pt> int count(Color c) const;
  95.   template<PieceType Pt> int count() const;
  96.   template<PieceType Pt> const Square* squares(Color c) const;
  97.   template<PieceType Pt> Square square(Color c) const;
  98.  
  99.   // Castling
  100.   int can_castle(Color c) const;
  101.   int can_castle(CastlingRight cr) const;
  102.   bool castling_impeded(CastlingRight cr) const;
  103.   Square castling_rook_square(CastlingRight cr) const;
  104.  
  105.   // Checking
  106.   Bitboard checkers() const;
  107.   Bitboard blockers_for_king(Color c) const;
  108.   Bitboard check_squares(PieceType pt) const;
  109.  
  110.   // Attacks to/from a given square
  111.   Bitboard attackers_to(Square s) const;
  112.   Bitboard attackers_to(Square s, Bitboard occupied) const;
  113.   Bitboard attacks_from(PieceType pt, Square s) const;
  114.   template<PieceType> Bitboard attacks_from(Square s) const;
  115.   template<PieceType> Bitboard attacks_from(Square s, Color c) const;
  116.   Bitboard slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const;
  117.  
  118.   // Properties of moves
  119.   bool legal(Move m) const;
  120.   bool pseudo_legal(const Move m) const;
  121.   bool capture(Move m) const;
  122.   bool capture_or_promotion(Move m) const;
  123.   bool gives_check(Move m) const;
  124.   bool advanced_pawn_push(Move m) const;
  125.   Piece moved_piece(Move m) const;
  126.   Piece captured_piece() const;
  127.  
  128.   // Piece specific
  129.   bool pawn_passed(Color c, Square s) const;
  130.   bool opposite_bishops() const;
  131.  
  132.   // Doing and undoing moves
  133.   void do_move(Move m, StateInfo& newSt);
  134.   void do_move(Move m, StateInfo& newSt, bool givesCheck);
  135.   void undo_move(Move m);
  136.   void do_null_move(StateInfo& newSt);
  137.   void undo_null_move();
  138.  
  139.   // Static Exchange Evaluation
  140.   bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
  141.  
  142.   // Accessing hash keys
  143.   Key key() const;
  144.   Key key_after(Move m) const;
  145.   Key material_key() const;
  146.   Key pawn_key() const;
  147.  
  148.   // Other properties of the position
  149.   Color side_to_move() const;
  150.   int game_ply() const;
  151.   bool is_chess960() const;
  152.   Thread* this_thread() const;
  153.   bool is_draw(int ply) const;
  154.   bool has_game_cycle(int ply) const;
  155.   bool has_repeated() 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.   Score psq;
  191.   Thread* thisThread;
  192.   StateInfo* st;
  193.   bool chess960;
  194. };
  195.  
  196. namespace PSQT {
  197.   extern Score psq[PIECE_NB][SQUARE_NB];
  198. }
  199.  
  200. extern std::ostream& operator<<(std::ostream& os, const Position& pos);
  201.  
  202. inline Color Position::side_to_move() const {
  203.   return sideToMove;
  204. }
  205.  
  206. inline bool Position::empty(Square s) const {
  207.   return board[s] == NO_PIECE;
  208. }
  209.  
  210. inline Piece Position::piece_on(Square s) const {
  211.   return board[s];
  212. }
  213.  
  214. inline Piece Position::moved_piece(Move m) const {
  215.   return board[from_sq(m)];
  216. }
  217.  
  218. inline Bitboard Position::pieces() const {
  219.   return byTypeBB[ALL_PIECES];
  220. }
  221.  
  222. inline Bitboard Position::pieces(PieceType pt) const {
  223.   return byTypeBB[pt];
  224. }
  225.  
  226. inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
  227.   return byTypeBB[pt1] | byTypeBB[pt2];
  228. }
  229.  
  230. inline Bitboard Position::pieces(Color c) const {
  231.   return byColorBB[c];
  232. }
  233.  
  234. inline Bitboard Position::pieces(Color c, PieceType pt) const {
  235.   return byColorBB[c] & byTypeBB[pt];
  236. }
  237.  
  238. inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
  239.   return byColorBB[c] & (byTypeBB[pt1] | byTypeBB[pt2]);
  240. }
  241.  
  242. template<PieceType Pt> inline int Position::count(Color c) const {
  243.   return pieceCount[make_piece(c, Pt)];
  244. }
  245.  
  246. template<PieceType Pt> inline int Position::count() const {
  247.   return pieceCount[make_piece(WHITE, Pt)] + pieceCount[make_piece(BLACK, Pt)];
  248. }
  249.  
  250. template<PieceType Pt> inline const Square* Position::squares(Color c) const {
  251.   return pieceList[make_piece(c, Pt)];
  252. }
  253.  
  254. template<PieceType Pt> inline Square Position::square(Color c) const {
  255.   assert(pieceCount[make_piece(c, Pt)] == 1);
  256.   return pieceList[make_piece(c, Pt)][0];
  257. }
  258.  
  259. inline Square Position::ep_square() const {
  260.   return st->epSquare;
  261. }
  262.  
  263. inline int Position::can_castle(CastlingRight cr) const {
  264.   return st->castlingRights & cr;
  265. }
  266.  
  267. inline int Position::can_castle(Color c) const {
  268.   return st->castlingRights & ((WHITE_OO | WHITE_OOO) << (2 * c));
  269. }
  270.  
  271. inline bool Position::castling_impeded(CastlingRight cr) const {
  272.   return byTypeBB[ALL_PIECES] & castlingPath[cr];
  273. }
  274.  
  275. inline Square Position::castling_rook_square(CastlingRight cr) const {
  276.   return castlingRookSquare[cr];
  277. }
  278.  
  279. template<PieceType Pt>
  280. inline Bitboard Position::attacks_from(Square s) const {
  281.   assert(Pt != PAWN);
  282.   return  Pt == BISHOP || Pt == ROOK ? attacks_bb<Pt>(s, byTypeBB[ALL_PIECES])
  283.         : Pt == QUEEN  ? attacks_from<ROOK>(s) | attacks_from<BISHOP>(s)
  284.         : PseudoAttacks[Pt][s];
  285. }
  286.  
  287. template<>
  288. inline Bitboard Position::attacks_from<PAWN>(Square s, Color c) const {
  289.   return PawnAttacks[c][s];
  290. }
  291.  
  292. inline Bitboard Position::attacks_from(PieceType pt, Square s) const {
  293.   return attacks_bb(pt, s, byTypeBB[ALL_PIECES]);
  294. }
  295.  
  296. inline Bitboard Position::attackers_to(Square s) const {
  297.   return attackers_to(s, byTypeBB[ALL_PIECES]);
  298. }
  299.  
  300. inline Bitboard Position::checkers() const {
  301.   return st->checkersBB;
  302. }
  303.  
  304. inline Bitboard Position::blockers_for_king(Color c) const {
  305.   return st->blockersForKing[c];
  306. }
  307.  
  308. inline Bitboard Position::check_squares(PieceType pt) const {
  309.   return st->checkSquares[pt];
  310. }
  311.  
  312. inline bool Position::pawn_passed(Color c, Square s) const {
  313.   return !(pieces(~c, PAWN) & passed_pawn_mask(c, s));
  314. }
  315.  
  316. inline bool Position::advanced_pawn_push(Move m) const {
  317.   return   type_of(moved_piece(m)) == PAWN
  318.         && relative_rank(sideToMove, from_sq(m)) > RANK_4;
  319. }
  320.  
  321. inline Key Position::key() const {
  322.   return st->key;
  323. }
  324.  
  325. inline Key Position::pawn_key() const {
  326.   return st->pawnKey;
  327. }
  328.  
  329. inline Key Position::material_key() const {
  330.   return st->materialKey;
  331. }
  332.  
  333. inline Score Position::psq_score() const {
  334.   return psq;
  335. }
  336.  
  337. inline Value Position::non_pawn_material(Color c) const {
  338.   return st->nonPawnMaterial[c];
  339. }
  340.  
  341. inline Value Position::non_pawn_material() const {
  342.   return st->nonPawnMaterial[WHITE] + st->nonPawnMaterial[BLACK];
  343. }
  344.  
  345. inline int Position::game_ply() const {
  346.   return gamePly;
  347. }
  348.  
  349. inline int Position::rule50_count() const {
  350.   return st->rule50;
  351. }
  352.  
  353. inline bool Position::opposite_bishops() const {
  354.   return   pieceCount[W_BISHOP] == 1
  355.         && pieceCount[B_BISHOP] == 1
  356.         && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
  357. }
  358.  
  359. inline bool Position::is_chess960() const {
  360.   return chess960;
  361. }
  362.  
  363. inline bool Position::capture_or_promotion(Move m) const {
  364.   assert(is_ok(m));
  365.   return type_of(m) != NORMAL ? type_of(m) != CASTLING : !empty(to_sq(m));
  366. }
  367.  
  368. inline bool Position::capture(Move m) const {
  369.   assert(is_ok(m));
  370.   // Castling is encoded as "king captures rook"
  371.   return (!empty(to_sq(m)) && type_of(m) != CASTLING) || type_of(m) == ENPASSANT;
  372. }
  373.  
  374. inline Piece Position::captured_piece() const {
  375.   return st->capturedPiece;
  376. }
  377.  
  378. inline Thread* Position::this_thread() const {
  379.   return thisThread;
  380. }
  381.  
  382. inline void Position::put_piece(Piece pc, Square s) {
  383.  
  384.   board[s] = pc;
  385.   byTypeBB[ALL_PIECES] |= s;
  386.   byTypeBB[type_of(pc)] |= s;
  387.   byColorBB[color_of(pc)] |= s;
  388.   index[s] = pieceCount[pc]++;
  389.   pieceList[pc][index[s]] = s;
  390.   pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
  391.   psq += PSQT::psq[pc][s];
  392. }
  393.  
  394. inline void Position::remove_piece(Piece pc, Square s) {
  395.  
  396.   // WARNING: This is not a reversible operation. If we remove a piece in
  397.   // do_move() and then replace it in undo_move() we will put it at the end of
  398.   // the list and not in its original place, it means index[] and pieceList[]
  399.   // are not invariant to a do_move() + undo_move() sequence.
  400.   byTypeBB[ALL_PIECES] ^= s;
  401.   byTypeBB[type_of(pc)] ^= s;
  402.   byColorBB[color_of(pc)] ^= s;
  403.   /* board[s] = NO_PIECE;  Not needed, overwritten by the capturing one */
  404.   Square lastSquare = pieceList[pc][--pieceCount[pc]];
  405.   index[lastSquare] = index[s];
  406.   pieceList[pc][index[lastSquare]] = lastSquare;
  407.   pieceList[pc][pieceCount[pc]] = SQ_NONE;
  408.   pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
  409.   psq -= PSQT::psq[pc][s];
  410. }
  411.  
  412. inline void Position::move_piece(Piece pc, Square from, Square to) {
  413.  
  414.   // index[from] is not updated and becomes stale. This works as long as index[]
  415.   // is accessed just by known occupied squares.
  416.   Bitboard fromTo = SquareBB[from] ^ SquareBB[to];
  417.   byTypeBB[ALL_PIECES] ^= fromTo;
  418.   byTypeBB[type_of(pc)] ^= fromTo;
  419.   byColorBB[color_of(pc)] ^= fromTo;
  420.   board[from] = NO_PIECE;
  421.   board[to] = pc;
  422.   index[to] = index[from];
  423.   pieceList[pc][index[to]] = to;
  424.   psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
  425. }
  426.  
  427. inline void Position::do_move(Move m, StateInfo& newSt) {
  428.   do_move(m, newSt, gives_check(m));
  429. }
  430.  
  431. #endif // #ifndef POSITION_H_INCLUDED
  432.