/*
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) 2015-2018 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 "movegen.h"
#include "position.h"
#include "types.h"
/// StatBoards is a generic 2-dimensional array used to store various statistics
template<int Size1, int Size2, typename T = int16_t>
struct StatBoards : public std::array<std::array<T, Size2>, Size1> {
void fill(const T& v) {
T* p = &(*this)[0][0];
std::fill(p, p + sizeof(*this) / sizeof(*p), v);
}
void update(T& entry, int bonus, const int D) {
assert(abs(bonus) <= D); // Ensure range is [-32 * D, 32 * D]
assert(abs(32 * D) < (std::numeric_limits<T>::max)()); // Ensure we don't overflow
entry += bonus * 32 - entry * abs(bonus) / D;
assert(abs(entry) <= 32 * D);
}
};
/// StatCubes is a generic 3-dimensional array used to store various statistics
template<int Size1, int Size2, int Size3, typename T = int16_t>
struct StatCubes : public std::array<std::array<std::array<T, Size3>, Size2>, Size1> {
void fill(const T& v) {
T* p = &(*this)[0][0][0];
std::fill(p, p + sizeof(*this) / sizeof(*p), v);
}
void update(T& entry, int bonus, const int D, const int W) {
assert(abs(bonus) <= D); // Ensure range is [-W * D, W * D]
assert(abs(W * D) < (std::numeric_limits<T>::max)()); // Ensure we don't overflow
entry += bonus * W - entry * abs(bonus) / D;
assert(abs(entry) <= W * D);
}
};
/// ButterflyBoards are 2 tables (one for each color) indexed by the move's from
/// and to squares, see chessprogramming.wikispaces.com/Butterfly+Boards
typedef StatBoards<COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyBoards;
/// PieceToBoards are addressed by a move's [piece][to] information
typedef StatBoards<PIECE_NB, SQUARE_NB> PieceToBoards;
/// CapturePieceToBoards are addressed by a move's [piece][to][captured piece type] information
typedef StatCubes<PIECE_NB, SQUARE_NB, PIECE_TYPE_NB> CapturePieceToBoards;
/// 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 ButterflyBoards as backing store.
struct ButterflyHistory : public ButterflyBoards {
void update(Color c, Move m, int bonus) {
StatBoards::update((*this)[c][from_to(m)], bonus, 324);
}
};
/// PieceToHistory is like ButterflyHistory, but is based on PieceToBoards
struct PieceToHistory : public PieceToBoards {
void update(Piece pc, Square to, int bonus) {
StatBoards::update((*this)[pc][to], bonus, 936);
}
};
/// CapturePieceToHistory is like PieceToHistory, but is based on CapturePieceToBoards
struct CapturePieceToHistory : public CapturePieceToBoards {
void update(Piece pc, Square to, PieceType captured, int bonus) {
StatCubes::update((*this)[pc][to][captured], bonus, 324, 2);
}
};
/// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
/// move, see chessprogramming.wikispaces.com/Countermove+Heuristic
typedef StatBoards<PIECE_NB, SQUARE_NB, Move> CounterMoveHistory;
/// ContinuationHistory is the history of a given pair of moves, usually the
/// current one given a previous one. History table is based on PieceToBoards
/// instead of ButterflyBoards.
typedef StatBoards<PIECE_NB, SQUARE_NB, PieceToHistory> 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 {
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*, Square);
MovePicker(const Position&, Move, Depth, const ButterflyHistory*, const CapturePieceToHistory*, const PieceToHistory**, Move, Move*);
Move next_move(bool skipQuiets = false);
private:
template<GenType> void score();
ExtMove* begin() { return cur; }
ExtMove* end() { return endMoves; }
const Position& pos;
const ButterflyHistory* mainHistory;
const CapturePieceToHistory* captureHistory;
const PieceToHistory** contHistory;
Move ttMove, countermove, killers[2];
ExtMove *cur, *endMoves, *endBadCaptures;
int stage;
Square recaptureSquare;
Value threshold;
Depth depth;
ExtMove moves[MAX_MOVES];
};
#endif // #ifndef MOVEPICK_H_INCLUDED