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Member "stockfish-11-linux/src/movepick.h" (18 Jan 2020, 5968 Bytes) of package /linux/privat/stockfish-11-linux.zip:


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    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) 2015-2020 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.
   36 template<typename T, int D>
   37 class StatsEntry {
   38 
   39   T entry;
   40 
   41 public:
   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.
   62 template <typename T, int D, int Size, int... Sizes>
   63 struct 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 
   78 template <typename T, int D, int Size>
   79 struct 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
   82 enum StatsParams { NOT_USED = 0 };
   83 enum StatsType { NoCaptures, Captures };
   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
   89 typedef 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
   93 typedef Stats<Move, NOT_USED, PIECE_NB, SQUARE_NB> CounterMoveHistory;
   94 
   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;
   97 
   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;
  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.
  104 typedef 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.
  113 class MovePicker {
  114 
  115   enum PickType { Next, Best };
  116 
  117 public:
  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 
  132 private:
  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