Revert setting a flag when TT value equals static evaluation

[stockfish] / src / tt.cpp

diff --git a/src/tt.cpp b/src/tt.cpp
index 5c842db85ea3a552a03cae2bf03a04199003bb39..8c5f3e347a5353756868e8a2c0877774015647f6 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -101,7 +101,8 @@ void TranspositionTable::clear() {
 /// the least valuable of the four entries in a cluster.  A TTEntry t1 is
 /// considered to be more valuable than a TTEntry t2 if t1 is from the
 /// current search and t2 is from a previous search, or if the depth of t1
-/// is bigger than the depth of t2.
+/// is bigger than the depth of t2. A TTEntry of type VALUE_TYPE_EVAL
+/// never replaces another entry for the same position.
 
 void TranspositionTable::store(const Position &pos, Value v, Depth d,
                                Move m, ValueType type) {
@@ -112,6 +113,11 @@ void TranspositionTable::store(const Position &pos, Value v, Depth d,
   {
     if (!tte->key() || tte->key() == pos.get_key()) // empty or overwrite old
     {
+        // Do not overwrite position entry when VALUE_TYPE_EVAL
+        if (   tte->key()
+            && type == VALUE_TYPE_EVAL)
+            return;
+
         if (m == MOVE_NONE)
             m = tte->move();