Subversion Repositories Games.Chess Giants

/*

  Stockfish, a UCI chess playing engine derived from Glaurung 2.1

  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)

  Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad

  Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, 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 MOVEPICK_H_INCLUDED

#define MOVEPICK_H_INCLUDED

#include <array>

#include <limits>

#include <type_traits>

#include "movegen.h"

#include "position.h"

#include "types.h"

/// StatsEntry stores the stat table value. It is usually a number but could

/// be a move or even a nested history. We use a class instead of naked value

/// to directly call history update operator<<() on the entry so to use stats

/// tables at caller sites as simple multi-dim arrays.

template<typename T, int D>

class StatsEntry {

  T entry;

public:

  void operator=(const T& v) { entry = v; }

  T* operator&() { return &entry; }

  T* operator->() { return &entry; }

  operator const T&() const { return entry; }

  void operator<<(int bonus) {

    assert(abs(bonus) <= D); // Ensure range is [-D, D]

    static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");

    entry += bonus - entry * abs(bonus) / D;

    assert(abs(entry) <= D);

  }

};

/// Stats is a generic N-dimensional array used to store various statistics.

/// The first template parameter T is the base type of the array, the second

/// template parameter D limits the range of updates in [-D, D] when we update

/// values with the << operator, while the last parameters (Size and Sizes)

/// encode the dimensions of the array.

template <typename T, int D, int Size, int... Sizes>

struct Stats : public std::array<Stats<T, D, Sizes...>, Size>

{

  typedef Stats<T, D, Size, Sizes...> stats;

  void fill(const T& v) {

    // For standard-layout 'this' points to first struct member

    assert(std::is_standard_layout<stats>::value);

    typedef StatsEntry<T, D> entry;

    entry* p = reinterpret_cast<entry*>(this);

    std::fill(p, p + sizeof(*this) / sizeof(entry), v);

  }

};

template <typename T, int D, int Size>

struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {};

/// In stats table, D=0 means that the template parameter is not used

enum StatsParams { NOT_USED = 0 };

/// ButterflyHistory records how often quiet moves have been successful or

/// unsuccessful during the current search, and is used for reduction and move

/// ordering decisions. It uses 2 tables (one for each color) indexed by

/// the move's from and to squares, see chessprogramming.wikispaces.com/Butterfly+Boards

typedef Stats<int16_t, 10692, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;

/// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous

/// move, see chessprogramming.wikispaces.com/Countermove+Heuristic

typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;

/// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]

typedef Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB> CapturePieceToHistory;

/// PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]

typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;

/// ContinuationHistory is the combined history of a given pair of moves, usually

/// the current one given a previous one. The nested history table is based on

/// PieceToHistory instead of ButterflyBoards.

typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;

/// MovePicker class is used to pick one pseudo legal move at a time from the

/// current position. The most important method is next_move(), which returns a

/// new pseudo legal move each time it is called, until there are no moves left,

/// when MOVE_NONE is returned. In order to improve the efficiency of the alpha

/// beta algorithm, MovePicker attempts to return the moves which are most likely

/// to get a cut-off first.

class MovePicker {

  enum PickType { Next, Best };

public:

  MovePicker(const MovePicker&) = delete;

  MovePicker& operator=(const MovePicker&) = delete;

  MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);

  MovePicker(const Position&, Move, Depth, const ButterflyHistory*,

                                           const CapturePieceToHistory*,

                                           const PieceToHistory**,

                                           Square);

  MovePicker(const Position&, Move, Depth, const ButterflyHistory*,

                                           const CapturePieceToHistory*,

                                           const PieceToHistory**,

                                           Move,

                                           Move*);

  Move next_move(bool skipQuiets = false);

private:

  template<PickType T, typename Pred> Move select(Pred);

  template<GenType> void score();

  ExtMove* begin() { return cur; }

  ExtMove* end() { return endMoves; }

  const Position& pos;

  const ButterflyHistory* mainHistory;

  const CapturePieceToHistory* captureHistory;

  const PieceToHistory** continuationHistory;

  Move ttMove;

  ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;

  int stage;

  Move move;

  Square recaptureSquare;

  Value threshold;

  Depth depth;

  ExtMove moves[MAX_MOVES];

};

#endif // #ifndef MOVEPICK_H_INCLUDED