position.h

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad

  Stockfish is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef POSITION_H_INCLUDED
#define POSITION_H_INCLUDED

#include <cassert>
#include <cstddef>

#include "bitboard.h"
#include "types.h"


/// The checkInfo struct is initialized at c'tor time and keeps info used
/// to detect if a move gives check.
class Position;
struct Thread;

struct CheckInfo {

  explicit CheckInfo(const Position&);

  Bitboard dcCandidates;
  Bitboard pinned;
  Bitboard checkSq[PIECE_TYPE_NB];
  Square ksq;
};


/// The StateInfo struct stores information needed to restore a Position
/// object to its previous state when we retract a move. Whenever a move
/// is made on the board (by calling Position::do_move), a StateInfo
/// object must be passed as a parameter.

struct StateInfo {
  Key pawnKey, materialKey;
  Value npMaterial[COLOR_NB];
  int castlingFlags, rule50, pliesFromNull;
  Score psq;
  Square epSquare;

  Key key;
  Bitboard checkersBB;
  PieceType capturedType;
  StateInfo* previous;
};


/// When making a move the current StateInfo up to 'key' excluded is copied to
/// the new one. Here we calculate the quad words (64bits) needed to be copied.
const size_t StateCopySize64 = offsetof(StateInfo, key) / sizeof(uint64_t) + 1;


/// The Position class stores the information regarding the board representation
/// like pieces, side to move, hash keys, castling info, etc. The most important
/// methods are do_move() and undo_move(), used by the search to update node info
/// when traversing the search tree.

class Position {
public:
  Position() {}
  Position(const Position& p, Thread* t) { *this = p; thisThread = t; }
  Position(const std::string& f, bool c960, Thread* t) { set(f, c960, t); }
  Position& operator=(const Position&);
  static void init();

  // Text input/output
  void set(const std::string& fenStr, bool isChess960, Thread* th);
  const std::string fen() const;
  const std::string pretty(Move m = MOVE_NONE) const;

  // Position representation
  Bitboard pieces() const;
  Bitboard pieces(PieceType pt) const;
  Bitboard pieces(PieceType pt1, PieceType pt2) const;
  Bitboard pieces(Color c) const;
  Bitboard pieces(Color c, PieceType pt) const;
  Bitboard pieces(Color c, PieceType pt1, PieceType pt2) const;
  Piece piece_on(Square s) const;
  Square king_square(Color c) const;
  Square ep_square() const;
  bool empty(Square s) const;
  template<PieceType Pt> int count(Color c) const;
  template<PieceType Pt> const Square* list(Color c) const;

  // Castling
  int can_castle(CastlingFlag f) const;
  int can_castle(Color c) const;
  bool castling_impeded(Color c, CastlingSide s) const;
  Square castling_rook_square(Color c, CastlingSide s) const;

  // Checking
  Bitboard checkers() const;
  Bitboard discovered_check_candidates() const;
  Bitboard pinned_pieces(Color c) const;

  // Attacks to/from a given square
  Bitboard attackers_to(Square s) const;
  Bitboard attackers_to(Square s, Bitboard occ) const;
  Bitboard attacks_from(Piece p, Square s) const;
  template<PieceType> Bitboard attacks_from(Square s) const;
  template<PieceType> Bitboard attacks_from(Square s, Color c) const;

  // Properties of moves
  bool legal(Move m, Bitboard pinned) const;
  bool pseudo_legal(const Move m) const;
  bool capture(Move m) const;
  bool capture_or_promotion(Move m) const;
  bool gives_check(Move m, const CheckInfo& ci) const;
  bool advanced_pawn_push(Move m) const;
  Piece moved_piece(Move m) const;
  PieceType captured_piece_type() const;

  // Piece specific
  bool pawn_passed(Color c, Square s) const;
  bool pawn_on_7th(Color c) const;
  bool bishop_pair(Color c) const;
  bool opposite_bishops() const;

  // Doing and undoing moves
  void do_move(Move m, StateInfo& st);
  void do_move(Move m, StateInfo& st, const CheckInfo& ci, bool moveIsCheck);
  void undo_move(Move m);
  void do_null_move(StateInfo& st);
  void undo_null_move();

  // Static exchange evaluation
  Value see(Move m) const;
  Value see_sign(Move m) const;

  // Accessing hash keys
  Key key() const;
  Key exclusion_key() const;
  Key pawn_key() const;
  Key material_key() const;

  // Incremental piece-square evaluation
  Score psq_score() const;
  Value non_pawn_material(Color c) const;

  // Other properties of the position
  Color side_to_move() const;
  int game_ply() const;
  bool is_chess960() const;
  Thread* this_thread() const;
  uint64_t nodes_searched() const;
  void set_nodes_searched(uint64_t n);
  bool is_draw() const;

  // Position consistency check, for debugging
  bool pos_is_ok(int* failedStep = NULL) const;
  void flip();

private:
  // Initialization helpers (used while setting up a position)
  void clear();
  void set_castling_flag(Color c, Square rfrom);

  // Helper functions
  void do_castling(Square kfrom, Square kto, Square rfrom, Square rto);
  Bitboard check_blockers(Color c, Color kingColor) const;
  void put_piece(Square s, Color c, PieceType pt);
  void remove_piece(Square s, Color c, PieceType pt);
  void move_piece(Square from, Square to, Color c, PieceType pt);

  // Computing hash keys from scratch (for initialization and debugging)
  Key compute_key() const;
  Key compute_pawn_key() const;
  Key compute_material_key() const;

  // Computing incremental evaluation scores and material counts
  Score compute_psq_score() const;
  Value compute_non_pawn_material(Color c) const;

  // Board and pieces
  Piece board[SQUARE_NB];
  Bitboard byTypeBB[PIECE_TYPE_NB];
  Bitboard byColorBB[COLOR_NB];
  int pieceCount[COLOR_NB][PIECE_TYPE_NB];
  Square pieceList[COLOR_NB][PIECE_TYPE_NB][16];
  int index[SQUARE_NB];

  // Other info
  int castlingFlagsMask[SQUARE_NB];
  Square castlingRookSquare[COLOR_NB][CASTLING_SIDE_NB];
  Bitboard castlingPath[COLOR_NB][CASTLING_SIDE_NB];
  StateInfo startState;
  uint64_t nodes;
  int gamePly;
  Color sideToMove;
  Thread* thisThread;
  StateInfo* st;
  int chess960;
};

inline uint64_t Position::nodes_searched() const {
  return nodes;
}

inline void Position::set_nodes_searched(uint64_t n) {
  nodes = n;
}

inline Piece Position::piece_on(Square s) const {
  return board[s];
}

inline Piece Position::moved_piece(Move m) const {
  return board[from_sq(m)];
}

inline bool Position::empty(Square s) const {
  return board[s] == NO_PIECE;
}

inline Color Position::side_to_move() const {
  return sideToMove;
}

inline Bitboard Position::pieces() const {
  return byTypeBB[ALL_PIECES];
}

inline Bitboard Position::pieces(PieceType pt) const {
  return byTypeBB[pt];
}

inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
  return byTypeBB[pt1] | byTypeBB[pt2];
}

inline Bitboard Position::pieces(Color c) const {
  return byColorBB[c];
}

inline Bitboard Position::pieces(Color c, PieceType pt) const {
  return byColorBB[c] & byTypeBB[pt];
}

inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
  return byColorBB[c] & (byTypeBB[pt1] | byTypeBB[pt2]);
}

template<PieceType Pt> inline int Position::count(Color c) const {
  return pieceCount[c][Pt];
}

template<PieceType Pt> inline const Square* Position::list(Color c) const {
  return pieceList[c][Pt];
}

inline Square Position::ep_square() const {
  return st->epSquare;
}

inline Square Position::king_square(Color c) const {
  return pieceList[c][KING][0];
}

inline int Position::can_castle(CastlingFlag f) const {
  return st->castlingFlags & f;
}

inline int Position::can_castle(Color c) const {
  return st->castlingFlags & ((WHITE_OO | WHITE_OOO) << (2 * c));
}

inline bool Position::castling_impeded(Color c, CastlingSide s) const {
  return byTypeBB[ALL_PIECES] & castlingPath[c][s];
}

inline Square Position::castling_rook_square(Color c, CastlingSide s) const {
  return castlingRookSquare[c][s];
}

template<PieceType Pt>
inline Bitboard Position::attacks_from(Square s) const {

  return  Pt == BISHOP || Pt == ROOK ? attacks_bb<Pt>(s, pieces())
        : Pt == QUEEN  ? attacks_from<ROOK>(s) | attacks_from<BISHOP>(s)
        : StepAttacksBB[Pt][s];
}

template<>
inline Bitboard Position::attacks_from<PAWN>(Square s, Color c) const {
  return StepAttacksBB[make_piece(c, PAWN)][s];
}

inline Bitboard Position::attacks_from(Piece p, Square s) const {
  return attacks_bb(p, s, byTypeBB[ALL_PIECES]);
}

inline Bitboard Position::attackers_to(Square s) const {
  return attackers_to(s, byTypeBB[ALL_PIECES]);
}

inline Bitboard Position::checkers() const {
  return st->checkersBB;
}

inline Bitboard Position::discovered_check_candidates() const {
  return check_blockers(sideToMove, ~sideToMove);
}

inline Bitboard Position::pinned_pieces(Color c) const {
  return check_blockers(c, c);
}

inline bool Position::pawn_passed(Color c, Square s) const {
  return !(pieces(~c, PAWN) & passed_pawn_mask(c, s));
}

inline bool Position::advanced_pawn_push(Move m) const {
  return   type_of(moved_piece(m)) == PAWN
        && relative_rank(sideToMove, from_sq(m)) > RANK_4;
}

inline Key Position::key() const {
  return st->key;
}

inline Key Position::pawn_key() const {
  return st->pawnKey;
}

inline Key Position::material_key() const {
  return st->materialKey;
}

inline Score Position::psq_score() const {
  return st->psq;
}

inline Value Position::non_pawn_material(Color c) const {
  return st->npMaterial[c];
}

inline int Position::game_ply() const {
  return gamePly;
}

inline bool Position::opposite_bishops() const {

  return   pieceCount[WHITE][BISHOP] == 1
        && pieceCount[BLACK][BISHOP] == 1
        && opposite_colors(pieceList[WHITE][BISHOP][0], pieceList[BLACK][BISHOP][0]);
}

inline bool Position::bishop_pair(Color c) const {

  return   pieceCount[c][BISHOP] >= 2
        && opposite_colors(pieceList[c][BISHOP][0], pieceList[c][BISHOP][1]);
}

inline bool Position::pawn_on_7th(Color c) const {
  return pieces(c, PAWN) & rank_bb(relative_rank(c, RANK_7));
}

inline bool Position::is_chess960() const {
  return chess960;
}

inline bool Position::capture_or_promotion(Move m) const {

  assert(is_ok(m));
  return type_of(m) != NORMAL ? type_of(m) != CASTLING : !empty(to_sq(m));
}

inline bool Position::capture(Move m) const {

  // Note that castling is encoded as "king captures the rook"
  assert(is_ok(m));
  return (!empty(to_sq(m)) && type_of(m) != CASTLING) || type_of(m) == ENPASSANT;
}

inline PieceType Position::captured_piece_type() const {
  return st->capturedType;
}

inline Thread* Position::this_thread() const {
  return thisThread;
}

inline void Position::put_piece(Square s, Color c, PieceType pt) {

  board[s] = make_piece(c, pt);
  byTypeBB[ALL_PIECES] |= s;
  byTypeBB[pt] |= s;
  byColorBB[c] |= s;
  pieceCount[c][ALL_PIECES]++;
  index[s] = pieceCount[c][pt]++;
  pieceList[c][pt][index[s]] = s;
}

inline void Position::move_piece(Square from, Square to, Color c, PieceType pt) {

  // index[from] is not updated and becomes stale. This works as long
  // as index[] is accessed just by known occupied squares.
  Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
  byTypeBB[ALL_PIECES] ^= from_to_bb;
  byTypeBB[pt] ^= from_to_bb;
  byColorBB[c] ^= from_to_bb;
  board[from] = NO_PIECE;
  board[to] = make_piece(c, pt);
  index[to] = index[from];
  pieceList[c][pt][index[to]] = to;
}

inline void Position::remove_piece(Square s, Color c, PieceType pt) {

  // WARNING: This is not a reversible operation. If we remove a piece in
  // do_move() and then replace it in undo_move() we will put it at the end of
  // the list and not in its original place, it means index[] and pieceList[]
  // are not guaranteed to be invariant to a do_move() + undo_move() sequence.
  byTypeBB[ALL_PIECES] ^= s;
  byTypeBB[pt] ^= s;
  byColorBB[c] ^= s;
  /* board[s] = NO_PIECE; */ // Not needed, will be overwritten by capturing
  pieceCount[c][ALL_PIECES]--;
  Square lastSquare = pieceList[c][pt][--pieceCount[c][pt]];
  index[lastSquare] = index[s];
  pieceList[c][pt][index[lastSquare]] = lastSquare;
  pieceList[c][pt][pieceCount[c][pt]] = SQ_NONE;
}

#endif // #ifndef POSITION_H_INCLUDED