Avoid permanent PV entries in TT

This patch removes a condition that allows a PV entry to remain
in TT across games for an unlimited time.

Although this produces a nice ELO boost in the long term it
is an artifact that affects tests results bewteen version
with and without this feature.

So remove now and readd before to release because it actually
seems a strong feature.

As example a verification tournament against SF 2.0.1 starting around
+10 ELO after 4K games sligltly climbed to +21 ELO after 14K games !!!

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

diff --git a/src/tt.cpp b/src/tt.cpp
index 773f03ccbac463929faf254ec4cb8e591d42c224..20ac1608e2fee1eb0e1338c3dbbe940275cc9f36 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -122,7 +122,7 @@ void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d,
           continue;
 
       c1 = (replace->generation() == generation ?  2 : 0);
           continue;
 
       c1 = (replace->generation() == generation ?  2 : 0);

-      c2 = (tte->generation() == generation || tte->type() == VALUE_TYPE_EXACT ? -2 : 0);
+      c2 = (tte->generation() == generation ? -2 : 0);

       c3 = (tte->depth() < replace->depth() ?  1 : 0);
 
       if (c1 + c2 + c3 > 0)
       c3 = (tte->depth() < replace->depth() ?  1 : 0);
 
       if (c1 + c2 + c3 > 0)