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) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
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.
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.
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/>.
21 #ifndef MOVEPICK_H_INCLUDED
22 #define MOVEPICK_H_INCLUDED
26 #include <type_traits>
32 /// StatsEntry stores the stat table value. It is usually a number but could
33 /// be a move or even a nested history. We use a class instead of naked value
34 /// to directly call history update operator<<() on the entry so to use stats
35 /// tables at caller sites as simple multi-dim arrays.
36 template<typename T, int D>
39 static const bool IsInt = std::is_integral<T>::value;
40 typedef typename std::conditional<IsInt, int, T>::type TT;
45 T* get() { return &entry; }
46 void operator=(const T& v) { entry = v; }
47 operator TT() const { return entry; }
49 void operator<<(int bonus) {
50 assert(abs(bonus) <= D); // Ensure range is [-D, D]
51 static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
53 entry += bonus - entry * abs(bonus) / D;
55 assert(abs(entry) <= D);
59 /// Stats is a generic N-dimensional array used to store various statistics.
60 /// The first template parameter T is the base type of the array, the second
61 /// template parameter D limits the range of updates in [-D, D] when we update
62 /// values with the << operator, while the last parameters (Size and Sizes)
63 /// encode the dimensions of the array.
64 template <typename T, int D, int Size, int... Sizes>
65 struct Stats : public std::array<Stats<T, D, Sizes...>, Size>
67 T* get() { return this->at(0).get(); }
69 void fill(const T& v) {
71 std::fill(p, p + sizeof(*this) / sizeof(*p), v);
75 template <typename T, int D, int Size>
76 struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {
77 T* get() { return this->at(0).get(); }
80 /// In stats table, D=0 means that the template parameter is not used
81 enum StatsParams { NOT_USED = 0 };
84 /// ButterflyHistory records how often quiet moves have been successful or
85 /// unsuccessful during the current search, and is used for reduction and move
86 /// ordering decisions. It uses 2 tables (one for each color) indexed by
87 /// the move's from and to squares, see chessprogramming.wikispaces.com/Butterfly+Boards
88 typedef Stats<int16_t, 10368, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
90 /// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
91 /// move, see chessprogramming.wikispaces.com/Countermove+Heuristic
92 typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;
94 /// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
95 typedef Stats<int16_t, 10368, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB> CapturePieceToHistory;
97 /// PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]
98 typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;
100 /// ContinuationHistory is the combined history of a given pair of moves, usually
101 /// the current one given a previous one. The nested history table is based on
102 /// PieceToHistory instead of ButterflyBoards.
103 typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;
106 /// MovePicker class is used to pick one pseudo legal move at a time from the
107 /// current position. The most important method is next_move(), which returns a
108 /// new pseudo legal move each time it is called, until there are no moves left,
109 /// when MOVE_NONE is returned. In order to improve the efficiency of the alpha
110 /// beta algorithm, MovePicker attempts to return the moves which are most likely
111 /// to get a cut-off first.
114 enum PickType { Next, Best };
117 MovePicker(const MovePicker&) = delete;
118 MovePicker& operator=(const MovePicker&) = delete;
119 MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
120 MovePicker(const Position&, Move, Depth, const ButterflyHistory*, const CapturePieceToHistory*, Square);
121 MovePicker(const Position&, Move, Depth, const ButterflyHistory*, const CapturePieceToHistory*, const PieceToHistory**, Move, Move*);
122 Move next_move(bool skipQuiets = false);
125 template<PickType T, typename Pred> Move select(Pred);
126 template<GenType> void score();
127 ExtMove* begin() { return cur; }
128 ExtMove* end() { return endMoves; }
131 const ButterflyHistory* mainHistory;
132 const CapturePieceToHistory* captureHistory;
133 const PieceToHistory** contHistory;
135 ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
138 Square recaptureSquare;
141 ExtMove moves[MAX_MOVES];
144 #endif // #ifndef MOVEPICK_H_INCLUDED