Clarify stats range

[stockfish] / src / movepick.h

diff --git a/src/movepick.h b/src/movepick.h
index afd573ea459badabd1aa208b5d6dd498d49d455b..db0ba3c465e4e8b5aacc832c6bff57955480ba9d 100644 (file)
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -28,13 +28,23 @@
 #include "types.h"
 
 /// StatBoards is a generic 2-dimensional array used to store various statistics
-template<int Size1, int Size2, typename T = int>
+template<int Size1, int Size2, typename T = int16_t>
 struct StatBoards : public std::array<std::array<T, Size2>, Size1> {
 
   void fill(const T& v) {
     T* p = &(*this)[0][0];
     std::fill(p, p + sizeof(*this) / sizeof(*p), v);
   }
+
+  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
@@ -50,15 +60,7 @@ typedef StatBoards<PIECE_NB, SQUARE_NB> PieceToBoards;
 struct ButterflyHistory : public ButterflyBoards {
 
   void update(Color c, Move m, int bonus) {
-
-    const int D = 324;
-    auto& entry = (*this)[c][from_to(m)];
-
-    assert(abs(bonus) <= D); // Consistency check for below formula
-
-    entry += bonus * 32 - entry * abs(bonus) / D;
-
-    assert(abs(entry) <= 32 * D);
+    StatBoards::update((*this)[c][from_to(m)], bonus, 324);
   }
 };
 
@@ -66,15 +68,7 @@ struct ButterflyHistory : public ButterflyBoards {
 struct PieceToHistory : public PieceToBoards {
 
   void update(Piece pc, Square to, int bonus) {
-
-    const int D = 936;
-    auto& entry = (*this)[pc][to];
-
-    assert(abs(bonus) <= D); // Consistency check for below formula
-
-    entry += bonus * 32 - entry * abs(bonus) / D;
-
-    assert(abs(entry) <= 32 * D);
+    StatBoards::update((*this)[pc][to], bonus, 936);
   }
 };