+/// HistoryStats records how often quiet moves have been successful or unsuccessful
+/// during the current search, and is used for reduction and move ordering decisions.
+struct HistoryStats {
+
+ static const Value Max = Value(1 << 28);
+
+ Value get(Color c, Move m) const { return table[c][from_sq(m)][to_sq(m)]; }
+ void clear() { std::memset(table, 0, sizeof(table)); }
+ void update(Color c, Move m, Value v) {
+
+ if (abs(int(v)) >= 324)
+ return;
+
+ Square from = from_sq(m);
+ Square to = to_sq(m);
+
+ table[c][from][to] -= table[c][from][to] * abs(int(v)) / 324;
+ table[c][from][to] += int(v) * 32;
+ }
+
+private:
+ Value table[COLOR_NB][SQUARE_NB][SQUARE_NB];
+};
+
+
+/// A template struct, used to generate MoveStats and CounterMoveHistoryStats:
+/// MoveStats store the move that refute a previous one.
+/// CounterMoveHistoryStats is like HistoryStats, but with two consecutive moves.
+/// Entries are stored using only the moving piece and destination square, hence
+/// two moves with different origin but same destination and piece will be
+/// considered identical.
+template<typename T, bool CM = false>
+struct Stats {
+ const T* operator[](Piece pc) const { return table[pc]; }
+ T* operator[](Piece pc) { return table[pc]; }
+ void clear() { std::memset(table, 0, sizeof(table)); }
+ void update(Piece pc, Square to, Move m) { table[pc][to] = m; }
+ void update(Piece pc, Square to, Value v) {
+
+ if (abs(int(v)) >= 324)
+ return;
+
+ table[pc][to] -= table[pc][to] * abs(int(v)) / (CM ? 936 : 324);
+ table[pc][to] += int(v) * 32;
+ }
+
+private:
+ T table[PIECE_NB][SQUARE_NB];
+};
+
+typedef Stats<Move> MoveStats;
+typedef Stats<Value, true> CounterMoveStats;
+typedef Stats<CounterMoveStats> CounterMoveHistoryStats;
+
+