+#include "search.h"
+#include "types.h"
+
+
+/// The Stats struct stores moves statistics. According to the template parameter
+/// the class can store History, Gains and Countermoves. History records how often
+/// different moves have been successful or unsuccessful during the current search
+/// and is used for reduction and move ordering decisions. Gains records the move's
+/// best evaluation gain from one ply to the next and is used for pruning decisions.
+/// Countermoves store the move that refute a previous one. 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<bool Gain, typename T>
+struct Stats {
+
+ static const Value Max = Value(2000);
+
+ const T* operator[](Piece pc) const { return table[pc]; }
+ void clear() { std::memset(table, 0, sizeof(table)); }
+
+ void update(Piece pc, Square to, Move m) {
+
+ if (m == table[pc][to].first)
+ return;
+
+ table[pc][to].second = table[pc][to].first;
+ table[pc][to].first = m;
+ }