An VALUE_TYPE_EVAL score cannot overwrite an entry

[stockfish] / src / tt.cpp

diff --git a/src/tt.cpp b/src/tt.cpp
index 83c9f50f0f6aaafb7abb9f73c4d304e52772a304..82d967cab9bb0e018eb4ea00f0912f1f6b8d4415 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -101,9 +101,10 @@ 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,
+TTEntry* TranspositionTable::store(const Position &pos, Value v, Depth d,
                                Move m, ValueType type) {
   TTEntry *tte, *replace;
 
@@ -112,11 +113,16 @@ 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 NULL;
+
         if (m == MOVE_NONE)
             m = tte->move();
 
         *tte = TTEntry(pos.get_key(), v, type, d, m, generation);
-        return;
+        return tte;
     }
     else if (i == 0)  // replace would be a no-op in this common case
         continue;
@@ -130,6 +136,7 @@ void TranspositionTable::store(const Position &pos, Value v, Depth d,
   }
   *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
   writes++;
+  return replace;
 }
 
 
@@ -137,7 +144,7 @@ void TranspositionTable::store(const Position &pos, Value v, Depth d,
 /// transposition table. Returns a pointer to the TTEntry or NULL
 /// if position is not found.
 
-const TTEntry* TranspositionTable::retrieve(const Position &pos) const {
+TTEntry* TranspositionTable::retrieve(const Position &pos) const {
 
   TTEntry *tte = first_entry(pos);
 
@@ -206,5 +213,5 @@ TTEntry::TTEntry() {
 
 TTEntry::TTEntry(Key k, Value v, ValueType t, Depth d, Move m,
                  int generation) :
-  key_ (k), data((m & 0x7FFFF) | (t << 20) | (generation << 23)),
+  key_ (k), data((m & 0x1FFFF) | (t << 20) | (generation << 23)),
   value_(int16_t(v)), depth_(int16_t(d)) {}