Reintroduce permanent PV entries in TT

We are now ready to release so restore this
improvment before 2.1

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/tt.cpp b/src/tt.cpp
index 14217e8..86b16c8 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -107,7 +107,7 @@ void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d,
 
       // Implement replace strategy
       c1 = (replace->generation() == generation ?  2 : 0);
-      c2 = (tte->generation() == generation ? -2 : 0);
+      c2 = (tte->generation() == generation || tte->type() == VALUE_TYPE_EXACT ? -2 : 0);
       c3 = (tte->depth() < replace->depth() ?  1 : 0);
 
       if (c1 + c2 + c3 > 0)