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An VALUE_TYPE_EVAL score cannot overwrite an entry

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If we want to store a value of type VALUE_TYPE_EVAL for
a given position and we found an already exsisting entry
for the same position then we skip.

We don't want to overwrite a more valuable score with a
lesser one. Note that also in case the exsisting entry is
of VALUE_TYPE_EVAL type the overwrite is unuseful because
we would store the same score again.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2009-03-30 09:09:27 +01:00
parent 6a8e46d53e
commit 2c0cd95ecf
1 changed files with 7 additions and 1 deletions
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8
src/tt.cpp
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@@ -101,7 +101,8 @@ void TranspositionTable::clear() {
/// the least valuable of the four entries in a cluster. A TTEntry t1 is /// 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 /// 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 /// 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.
TTEntry* TranspositionTable::store(const Position &pos, Value v, Depth d, TTEntry* TranspositionTable::store(const Position &pos, Value v, Depth d,
Move m, ValueType type) { Move m, ValueType type) {
@@ -112,6 +113,11 @@ TTEntry* TranspositionTable::store(const Position &pos, Value v, Depth d,
{ {
if (!tte->key() || tte->key() == pos.get_key()) // empty or overwrite old 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) if (m == MOVE_NONE)
m = tte->move(); m = tte->move();