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) 2015-2019 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>
42 void operator=(const T& v) { entry = v; }
43 T* operator&() { return &entry; }
44 T* operator->() { return &entry; }
45 operator const T&() const { return entry; }
47 void operator<<(int bonus) {
48 assert(abs(bonus) <= D); // Ensure range is [-D, D]
49 static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
51 entry += bonus - entry * abs(bonus) / D;
53 assert(abs(entry) <= D);
57 /// Stats is a generic N-dimensional array used to store various statistics.
58 /// The first template parameter T is the base type of the array, the second
59 /// template parameter D limits the range of updates in [-D, D] when we update
60 /// values with the << operator, while the last parameters (Size and Sizes)
61 /// encode the dimensions of the array.
62 template <typename T, int D, int Size, int... Sizes>
63 struct Stats : public std::array<Stats<T, D, Sizes...>, Size>
65 typedef Stats<T, D, Size, Sizes...> stats;
67 void fill(const T& v) {
69 // For standard-layout 'this' points to first struct member
70 assert(std::is_standard_layout<stats>::value);
72 typedef StatsEntry<T, D> entry;
73 entry* p = reinterpret_cast<entry*>(this);
74 std::fill(p, p + sizeof(*this) / sizeof(entry), v);
78 template <typename T, int D, int Size>
79 struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {};
81 /// In stats table, D=0 means that the template parameter is not used
82 enum StatsParams { NOT_USED = 0 };
85 /// ButterflyHistory records how often quiet moves have been successful or
86 /// unsuccessful during the current search, and is used for reduction and move
87 /// ordering decisions. It uses 2 tables (one for each color) indexed by
88 /// the move's from and to squares, see www.chessprogramming.org/Butterfly_Boards
89 typedef Stats<int16_t, 10692, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
91 /// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
92 /// move, see www.chessprogramming.org/Countermove_Heuristic
93 typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;
95 /// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
96 typedef Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB> CapturePieceToHistory;
98 /// PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]
99 typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;
101 /// ContinuationHistory is the combined history of a given pair of moves, usually
102 /// the current one given a previous one. The nested history table is based on
103 /// PieceToHistory instead of ButterflyBoards.
104 typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;
107 /// MovePicker class is used to pick one pseudo legal move at a time from the
108 /// current position. The most important method is next_move(), which returns a
109 /// new pseudo legal move each time it is called, until there are no moves left,
110 /// when MOVE_NONE is returned. In order to improve the efficiency of the alpha
111 /// beta algorithm, MovePicker attempts to return the moves which are most likely
112 /// to get a cut-off first.
115 enum PickType { Next, Best };
118 MovePicker(const MovePicker&) = delete;
119 MovePicker& operator=(const MovePicker&) = delete;
120 MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
121 MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
122 const CapturePieceToHistory*,
123 const PieceToHistory**,
125 MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
126 const CapturePieceToHistory*,
127 const PieceToHistory**,
130 Move next_move(bool skipQuiets = false);
133 template<PickType T, typename Pred> Move select(Pred);
134 template<GenType> void score();
135 ExtMove* begin() { return cur; }
136 ExtMove* end() { return endMoves; }
139 const ButterflyHistory* mainHistory;
140 const CapturePieceToHistory* captureHistory;
141 const PieceToHistory** continuationHistory;
143 ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
146 Square recaptureSquare;
149 ExtMove moves[MAX_MOVES];
152 #endif // #ifndef MOVEPICK_H_INCLUDED