From: Marco Costalba <mcostalba@gmail.com>
Date: Wed, 16 Feb 2011 07:56:24 +0000 (+0100)
Subject: Avoid permanent PV entries  in TT
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=6a19f5832a0b0f94c6677c4ec6aafc9e1f511baa

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 773f03cc..20ac1608 100644
--- 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);
-      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)