1/*
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
6
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.
11
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.
16
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/>.
19*/
20
21#ifndef MOVEPICK_H_INCLUDED
22#define MOVEPICK_H_INCLUDED
23
24#include <array>
25#include <limits>
26#include <type_traits>
27
28#include "movegen.h"
29#include "position.h"
30#include "types.h"
31
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.
36template<typename T, int D>
37class StatsEntry {
38
39 T entry;
40
41public:
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; }
46
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");
50
51 entry += bonus - entry * abs(bonus) / D;
52
53 assert(abs(entry) <= D);
54 }
55};
56
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.
62template <typename T, int D, int Size, int... Sizes>
63struct Stats : public std::array<Stats<T, D, Sizes...>, Size>
64{
65 typedef Stats<T, D, Size, Sizes...> stats;
66
67 void fill(const T& v) {
68
69 // For standard-layout 'this' points to first struct member
70 assert(std::is_standard_layout<stats>::value);
71
72 typedef StatsEntry<T, D> entry;
73 entry* p = reinterpret_cast<entry*>(this);
74 std::fill(p, p + sizeof(*this) / sizeof(entry), v);
75 }
76};
77
78template <typename T, int D, int Size>
79struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {};
80
81/// In stats table, D=0 means that the template parameter is not used
82enum StatsParams { NOT_USED = 0 };
83
84
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
89typedef Stats<int16_t, 10692, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
90
91/// CounterMoveHistory stores counter moves indexed by [piece][to] of the previous
92/// move, see www.chessprogramming.org/Countermove_Heuristic
93typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;
94
95/// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
96typedef Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB> CapturePieceToHistory;
97
98/// PieceToHistory is like ButterflyHistory but is addressed by a move's [piece][to]
99typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;
100
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.
104typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;
105
106
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.
113class MovePicker {
114
115 enum PickType { Next, Best };
116
117public:
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**,
124 Square);
125 MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
126 const CapturePieceToHistory*,
127 const PieceToHistory**,
128 Move,
129 Move*);
130 Move next_move(bool skipQuiets = false);
131
132private:
133 template<PickType T, typename Pred> Move select(Pred);
134 template<GenType> void score();
135 ExtMove* begin() { return cur; }
136 ExtMove* end() { return endMoves; }
137
138 const Position& pos;
139 const ButterflyHistory* mainHistory;
140 const CapturePieceToHistory* captureHistory;
141 const PieceToHistory** continuationHistory;
142 Move ttMove;
143 ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
144 int stage;
145 Square recaptureSquare;
146 Value threshold;
147 Depth depth;
148 ExtMove moves[MAX_MOVES];
149};
150
151#endif // #ifndef MOVEPICK_H_INCLUDED
152