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;
37 inline int pawn_structure(const Position& pos) { return pos.pawn_key() & (PAWN_HISTORY_SIZE - 1); }
39 // StatsEntry stores the stat table value. It is usually a number but could
40 // be a move or even a nested history. We use a class instead of a naked value
41 // to directly call history update operator<<() on the entry so to use stats
42 // tables at caller sites as simple multi-dim arrays.
43 template<typename T, int D>
49 void operator=(const T& v) { entry = v; }
50 T* operator&() { return &entry; }
51 T* operator->() { return &entry; }
52 operator const T&() const { return entry; }
54 void operator<<(int bonus) {
55 assert(abs(bonus) <= D); // Ensure range is [-D, D]
56 static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
58 entry += (bonus * D - entry * abs(bonus)) / (D * 5 / 4);
60 assert(abs(entry) <= D);
64 // Stats is a generic N-dimensional array used to store various statistics.
65 // The first template parameter T is the base type of the array, and the second
66 // template parameter D limits the range of updates in [-D, D] when we update
67 // values with the << operator, while the last parameters (Size and Sizes)
68 // encode the dimensions of the array.
69 template<typename T, int D, int Size, int... Sizes>
70 struct Stats: public std::array<Stats<T, D, Sizes...>, Size> {
71 using stats = Stats<T, D, Size, Sizes...>;
73 void fill(const T& v) {
75 // For standard-layout 'this' points to the first struct member
76 assert(std::is_standard_layout_v<stats>);
78 using entry = StatsEntry<T, D>;
79 entry* p = reinterpret_cast<entry*>(this);
80 std::fill(p, p + sizeof(*this) / sizeof(entry), v);
84 template<typename T, int D, int Size>
85 struct Stats<T, D, Size>: public std::array<StatsEntry<T, D>, Size> {};
87 // In stats table, D=0 means that the template parameter is not used
96 // ButterflyHistory records how often quiet moves have been successful or
97 // unsuccessful during the current search, and is used for reduction and move
98 // ordering decisions. It uses 2 tables (one for each color) indexed by
99 // the move's from and to squares, see www.chessprogramming.org/Butterfly_Boards
101 using ButterflyHistory = Stats<int16_t, 7183, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)>;
103 // CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
104 // move, see www.chessprogramming.org/Countermove_Heuristic
105 using CounterMoveHistory = Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB>;
107 // CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
108 using CapturePieceToHistory = Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB>;
110 // PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]
111 using PieceToHistory = Stats<int16_t, 29952, PIECE_NB, SQUARE_NB>;
113 // ContinuationHistory is the combined history of a given pair of moves, usually
114 // the current one given a previous one. The nested history table is based on
115 // PieceToHistory instead of ButterflyBoards.
117 using ContinuationHistory = Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB>;
119 // PawnStructureHistory is addressed by the pawn structure and a move's [piece][to]
120 using PawnHistory = Stats<int16_t, 8192, PAWN_HISTORY_SIZE, PIECE_NB, SQUARE_NB>;
122 // MovePicker class is used to pick one pseudo-legal move at a time from the
123 // current position. The most important method is next_move(), which returns a
124 // new pseudo-legal move each time it is called, until there are no moves left,
125 // when MOVE_NONE is returned. In order to improve the efficiency of the
126 // alpha-beta algorithm, MovePicker attempts to return the moves which are most
127 // likely to get a cut-off first.
136 MovePicker(const MovePicker&) = delete;
137 MovePicker& operator=(const MovePicker&) = delete;
138 MovePicker(const Position&,
141 const ButterflyHistory*,
142 const CapturePieceToHistory*,
143 const PieceToHistory**,
147 MovePicker(const Position&,
150 const ButterflyHistory*,
151 const CapturePieceToHistory*,
152 const PieceToHistory**,
155 MovePicker(const Position&, Move, Value, const CapturePieceToHistory*, const PawnHistory&);
156 Move next_move(bool skipQuiets = false);
159 template<PickType T, typename Pred>
163 ExtMove* begin() { return cur; }
164 ExtMove* end() { return endMoves; }
167 const ButterflyHistory* mainHistory;
168 const CapturePieceToHistory* captureHistory;
169 const PieceToHistory** continuationHistory;
170 const PawnHistory& pawnHistory;
172 ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
174 Square recaptureSquare;
177 ExtMove moves[MAX_MOVES];
180 } // namespace Stockfish
182 #endif // #ifndef MOVEPICK_H_INCLUDED