2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
19 #ifndef MOVEPICK_H_INCLUDED
20 #define MOVEPICK_H_INCLUDED
24 #include <type_traits>
30 /// StatsEntry stores the stat table value. It is usually a number but could
31 /// be a move or even a nested history. We use a class instead of naked value
32 /// to directly call history update operator<<() on the entry so to use stats
33 /// tables at caller sites as simple multi-dim arrays.
34 template<typename T, int D>
40 void operator=(const T& v) { entry = v; }
41 T* operator&() { return &entry; }
42 T* operator->() { return &entry; }
43 operator const T&() const { return entry; }
45 void operator<<(int bonus) {
46 assert(abs(bonus) <= D); // Ensure range is [-D, D]
47 static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
49 entry += bonus - entry * abs(bonus) / D;
51 assert(abs(entry) <= D);
55 /// Stats is a generic N-dimensional array used to store various statistics.
56 /// The first template parameter T is the base type of the array, the second
57 /// template parameter D limits the range of updates in [-D, D] when we update
58 /// values with the << operator, while the last parameters (Size and Sizes)
59 /// encode the dimensions of the array.
60 template <typename T, int D, int Size, int... Sizes>
61 struct Stats : public std::array<Stats<T, D, Sizes...>, Size>
63 typedef Stats<T, D, Size, Sizes...> stats;
65 void fill(const T& v) {
67 // For standard-layout 'this' points to first struct member
68 assert(std::is_standard_layout<stats>::value);
70 typedef StatsEntry<T, D> entry;
71 entry* p = reinterpret_cast<entry*>(this);
72 std::fill(p, p + sizeof(*this) / sizeof(entry), v);
76 template <typename T, int D, int Size>
77 struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {};
79 /// In stats table, D=0 means that the template parameter is not used
80 enum StatsParams { NOT_USED = 0 };
81 enum StatsType { NoCaptures, Captures };
83 /// ButterflyHistory records how often quiet moves have been successful or
84 /// unsuccessful during the current search, and is used for reduction and move
85 /// ordering decisions. It uses 2 tables (one for each color) indexed by
86 /// the move's from and to squares, see www.chessprogramming.org/Butterfly_Boards
87 typedef Stats<int16_t, 10692, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
89 /// At higher depths LowPlyHistory records successful quiet moves near the root
90 /// and quiet moves which are/were in the PV (ttPv). It is cleared with each new
91 /// search and filled during iterative deepening.
92 constexpr int MAX_LPH = 4;
93 typedef Stats<int16_t, 10692, MAX_LPH, int(SQUARE_NB) * int(SQUARE_NB)> LowPlyHistory;
95 /// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
96 /// move, see www.chessprogramming.org/Countermove_Heuristic
97 typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;
99 /// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
100 typedef Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB> CapturePieceToHistory;
102 /// PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]
103 typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;
105 /// ContinuationHistory is the combined history of a given pair of moves, usually
106 /// the current one given a previous one. The nested history table is based on
107 /// PieceToHistory instead of ButterflyBoards.
108 typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;
111 /// MovePicker class is used to pick one pseudo legal move at a time from the
112 /// current position. The most important method is next_move(), which returns a
113 /// new pseudo legal move each time it is called, until there are no moves left,
114 /// when MOVE_NONE is returned. In order to improve the efficiency of the alpha
115 /// beta algorithm, MovePicker attempts to return the moves which are most likely
116 /// to get a cut-off first.
119 enum PickType { Next, Best };
122 MovePicker(const MovePicker&) = delete;
123 MovePicker& operator=(const MovePicker&) = delete;
124 MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
125 MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
126 const CapturePieceToHistory*,
127 const PieceToHistory**,
129 MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
130 const LowPlyHistory*,
131 const CapturePieceToHistory*,
132 const PieceToHistory**,
136 Move next_move(bool skipQuiets = false);
139 template<PickType T, typename Pred> Move select(Pred);
140 template<GenType> void score();
141 ExtMove* begin() { return cur; }
142 ExtMove* end() { return endMoves; }
145 const ButterflyHistory* mainHistory;
146 const LowPlyHistory* lowPlyHistory;
147 const CapturePieceToHistory* captureHistory;
148 const PieceToHistory** continuationHistory;
150 ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
152 Square recaptureSquare;
156 ExtMove moves[MAX_MOVES];
159 #endif // #ifndef MOVEPICK_H_INCLUDED