move.cpp

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  Copyright (C) 2008-2009 Marco Costalba

  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/>.
*/


////
//// Includes
////

#include <cassert>

#include "move.h"
#include "piece.h"
#include "position.h"


////
//// Functions
////

/// move_from_string() takes a position and a string as input, and attempts to
/// convert the string to a move, using simple coordinate notation (g1f3,
/// a7a8q, etc.). In order to correctly parse en passant captures and castling
/// moves, we need the position. This function is not robust, and expects that
/// the input move is legal and correctly formatted.

Move move_from_string(const Position& pos, const std::string& str) {

  Square from, to;
  Piece piece;
  Color us = pos.side_to_move();

  if (str.length() < 4)
      return MOVE_NONE;

  // Read the from and to squares
  from = square_from_string(str.substr(0, 2));
  to = square_from_string(str.substr(2, 4));

  // Find the moving piece
  piece = pos.piece_on(from);

  // If the string has more than 4 characters, try to interpret the 5th
  // character as a promotion
  if (type_of_piece(piece) == PAWN && str.length() > 4)
  {
      switch (tolower(str[4])) {
      case 'n':
          return make_promotion_move(from, to, KNIGHT);
      case 'b':
          return make_promotion_move(from, to, BISHOP);
      case 'r':
          return make_promotion_move(from, to, ROOK);
      case 'q':
          return make_promotion_move(from, to, QUEEN);
    }
  }

  if (piece == piece_of_color_and_type(us, KING))
  {
      // Is this a castling move? A king move is assumed to be a castling
      // move if the destination square is occupied by a friendly rook, or
      // if the distance between the source and destination squares is more
      // than 1.
      if (pos.piece_on(to) == piece_of_color_and_type(us, ROOK))
          return make_castle_move(from, to);

      else if (square_distance(from, to) > 1)
      {
          // This is a castling move, but we have to translate it to the
          // internal "king captures rook" representation.
          SquareDelta delta = (to > from ? DELTA_E : DELTA_W);
          Square s = from + delta;
          while (relative_rank(us, s) == RANK_1 && pos.piece_on(s) != piece_of_color_and_type(us, ROOK))
              s += delta;

          return (relative_rank(us, s) == RANK_1 ? make_castle_move(from, s) : MOVE_NONE);
      }
  }
  else if (piece == piece_of_color_and_type(us, PAWN))
  {
      // En passant move? We assume that a pawn move is an en passant move
      // without further testing if the destination square is epSquare.
      if (to == pos.ep_square())
          return make_ep_move(from, to);
  }
  return make_move(from, to);
}


/// move_to_string() converts a move to a string in coordinate notation
/// (g1f3, a7a8q, etc.).  The only special case is castling moves, where we
/// print in the e1g1 notation in normal chess mode, and in e1h1 notation in
/// Chess960 mode.

const std::string move_to_string(Move move) {

  std::string str;
  Square from = move_from(move);
  Square to = move_to(move);

  if (move == MOVE_NONE)
      str = "(none)";
  else if (move == MOVE_NULL)
      str = "0000";
  else
  {
      if (!Chess960)
      {
          if (move_is_short_castle(move))
              return (from == SQ_E1 ? "e1g1" : "e8g8");

          if (move_is_long_castle(move))
              return (from == SQ_E1 ? "e1c1" : "e8c8");
      }
      str = square_to_string(from) + square_to_string(to);
      if (move_is_promotion(move))
          str += piece_type_to_char(move_promotion_piece(move), false);
  }
  return str;
}


/// Overload the << operator, to make it easier to print moves.

std::ostream &operator << (std::ostream& os, Move m) {

  return os << move_to_string(m);
}


/// move_is_ok(), for debugging.

bool move_is_ok(Move m) {

  return square_is_ok(move_from(m)) && square_is_ok(move_to(m));
}