+ void update(T& entry, int bonus, const int D) {
+
+ assert(abs(bonus) <= D); // Ensure range is [-32 * D, 32 * D]
+ assert(abs(32 * D) < INT16_MAX); // Ensure we don't overflow
+
+ entry += bonus * 32 - entry * abs(bonus) / D;
+
+ assert(abs(entry) <= 32 * D);
+ }
+};
+
+/// ButterflyBoards are 2 tables (one for each color) indexed by the move's from
+/// and to squares, see chessprogramming.wikispaces.com/Butterfly+Boards
+typedef StatBoards<COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyBoards;
+
+/// PieceToBoards are addressed by a move's [piece][to] information
+typedef StatBoards<PIECE_NB, SQUARE_NB> PieceToBoards;
+
+/// ButterflyHistory records how often quiet moves have been successful or
+/// unsuccessful during the current search, and is used for reduction and move
+/// ordering decisions. It uses ButterflyBoards as backing store.
+struct ButterflyHistory : public ButterflyBoards {