Fix a logic bug in TranspositionTable::store()

[stockfish] / src / tt.cpp

diff --git a/src/tt.cpp b/src/tt.cpp
index 1959693258c3d8e0e6dbad995103ed0ee766cbe2..fb524e303fa3a932be953775c03a64e410c4b39a 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -1,13 +1,14 @@
 /*
-  Glaurung, a UCI chess playing engine.
-  Copyright (C) 2004-2008 Tord Romstad
+  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
+  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
+  Copyright (C) 2008 Marco Costalba
 
-  Glaurung is free software: you can redistribute it and/or modify
+  Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
 
-  Glaurung is distributed in the hope that it will be useful,
+  Stockfish is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
@@ -23,6 +24,7 @@
 
 #include <cassert>
 #include <cmath>
+#include <cstring>
 
 #include "tt.h"
 
@@ -122,12 +124,14 @@ void TranspositionTable::store(const Position &pos, Value v, Depth d,
         *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
         return;
     }
-    if (   i == 0  // already is (replace == tte+i), common case
-        || replace->generation() < (tte+i)->generation())
+    if (i == 0)  // replace would be a no-op in this common case
         continue;
 
-    if (    replace->generation() > (tte+i)->generation()
-        || (tte+i)->depth() < replace->depth())
+    int c1 = (replace->generation() == generation ?  2 : 0);
+    int c2 = ((tte+i)->generation() == generation ? -2 : 0);
+    int c3 = ((tte+i)->depth() < replace->depth() ?  1 : 0);
+
+    if (c1 + c2 + c3 > 0)
         replace = tte+i;
   }
   *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
@@ -143,9 +147,8 @@ const TTEntry* TranspositionTable::retrieve(const Position &pos) const {
 
   TTEntry *tte = first_entry(pos);
 
-  for (int i = 0; i < 4; i++)
+  for (int i = 0; i < 4; i++, tte++)
   {
-      tte += i;
       if (tte->key() == pos.get_key())
           return tte;
   }