+/// 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 int Max = 1 << 28;
+
+ int 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, int v) {
+
+ Square from = from_sq(m);
+ Square to = to_sq(m);
+
+ const int denom = 324;
+
+ assert(abs(int(v)) <= denom); // Needed for stability.
+
+ table[c][from][to] -= table[c][from][to] * abs(int(v)) / denom;
+ table[c][from][to] += int(v) * 32;
+ }
+
+private:
+ int 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>
+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 fill(const int& v) { std::fill(&table[0][0], &table[PIECE_NB-1][SQUARE_NB-1]+1, v); };
+ void update(Piece pc, Square to, Move m) { table[pc][to] = m; }
+ void update(Piece pc, Square to, int v) {
+
+ const int denom = 936;
+
+ assert(abs(int(v)) <= denom); // Needed for stability.
+
+ table[pc][to] -= table[pc][to] * abs(int(v)) / denom;
+ table[pc][to] += int(v) * 32;
+ }
+
+private:
+ T table[PIECE_NB][SQUARE_NB];
+};
+
+typedef Stats<Move> MoveStats;
+typedef Stats<int> CounterMoveStats;
+typedef Stats<CounterMoveStats> CounterMoveHistoryStats;
+
+