2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2023 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
27 #include <type_traits> // IWYU pragma: keep
35 constexpr int PAWN_HISTORY_SIZE = 512; // has to be a power of 2
37 static_assert((PAWN_HISTORY_SIZE & (PAWN_HISTORY_SIZE - 1)) == 0,
38 "PAWN_HISTORY_SIZE has to be a power of 2");
40 inline int pawn_structure(const Position& pos) { return pos.pawn_key() & (PAWN_HISTORY_SIZE - 1); }
42 // StatsEntry stores the stat table value. It is usually a number but could
43 // be a move or even a nested history. We use a class instead of a naked value
44 // to directly call history update operator<<() on the entry so to use stats
45 // tables at caller sites as simple multi-dim arrays.
46 template<typename T, int D>
52 void operator=(const T& v) { entry = v; }
53 T* operator&() { return &entry; }
54 T* operator->() { return &entry; }
55 operator const T&() const { return entry; }
57 void operator<<(int bonus) {
58 assert(abs(bonus) <= D); // Ensure range is [-D, D]
59 static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
61 entry += bonus - entry * abs(bonus) / D;
63 assert(abs(entry) <= D);
67 // Stats is a generic N-dimensional array used to store various statistics.
68 // The first template parameter T is the base type of the array, and the second
69 // template parameter D limits the range of updates in [-D, D] when we update
70 // values with the << operator, while the last parameters (Size and Sizes)
71 // encode the dimensions of the array.
72 template<typename T, int D, int Size, int... Sizes>
73 struct Stats: public std::array<Stats<T, D, Sizes...>, Size> {
74 using stats = Stats<T, D, Size, Sizes...>;
76 void fill(const T& v) {
78 // For standard-layout 'this' points to the first struct member
79 assert(std::is_standard_layout_v<stats>);
81 using entry = StatsEntry<T, D>;
82 entry* p = reinterpret_cast<entry*>(this);
83 std::fill(p, p + sizeof(*this) / sizeof(entry), v);
87 template<typename T, int D, int Size>
88 struct Stats<T, D, Size>: public std::array<StatsEntry<T, D>, Size> {};
90 // In stats table, D=0 means that the template parameter is not used
99 // ButterflyHistory records how often quiet moves have been successful or unsuccessful
100 // during the current search, and is used for reduction and move ordering decisions.
101 // It uses 2 tables (one for each color) indexed by the move's from and to squares,
102 // see www.chessprogramming.org/Butterfly_Boards (~11 elo)
103 using ButterflyHistory = Stats<int16_t, 7183, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)>;
105 // CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
106 // move, see www.chessprogramming.org/Countermove_Heuristic
107 using CounterMoveHistory = Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB>;
109 // CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
110 using CapturePieceToHistory = Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB>;
112 // PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]
113 using PieceToHistory = Stats<int16_t, 29952, PIECE_NB, SQUARE_NB>;
115 // ContinuationHistory is the combined history of a given pair of moves, usually
116 // the current one given a previous one. The nested history table is based on
117 // PieceToHistory instead of ButterflyBoards.
119 using ContinuationHistory = Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB>;
121 // PawnHistory is addressed by the pawn structure and a move's [piece][to]
122 using PawnHistory = Stats<int16_t, 8192, PAWN_HISTORY_SIZE, PIECE_NB, SQUARE_NB>;
124 // MovePicker class is used to pick one pseudo-legal move at a time from the
125 // current position. The most important method is next_move(), which returns a
126 // new pseudo-legal move each time it is called, until there are no moves left,
127 // when MOVE_NONE is returned. In order to improve the efficiency of the
128 // alpha-beta algorithm, MovePicker attempts to return the moves which are most
129 // likely to get a cut-off first.
138 MovePicker(const MovePicker&) = delete;
139 MovePicker& operator=(const MovePicker&) = delete;
140 MovePicker(const Position&,
143 const ButterflyHistory*,
144 const CapturePieceToHistory*,
145 const PieceToHistory**,
149 MovePicker(const Position&,
152 const ButterflyHistory*,
153 const CapturePieceToHistory*,
154 const PieceToHistory**,
157 MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
158 Move next_move(bool skipQuiets = false);
161 template<PickType T, typename Pred>
165 ExtMove* begin() { return cur; }
166 ExtMove* end() { return endMoves; }
169 const ButterflyHistory* mainHistory;
170 const CapturePieceToHistory* captureHistory;
171 const PieceToHistory** continuationHistory;
172 const PawnHistory* pawnHistory;
174 ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
176 Square recaptureSquare;
179 ExtMove moves[MAX_MOVES];
182 } // namespace Stockfish
184 #endif // #ifndef MOVEPICK_H_INCLUDED