Tuned version of TT replacement policy

[stockfish] / src / tt.cpp

diff --git a/src/tt.cpp b/src/tt.cpp
index d0e2d729c8c766e883092277bfc5fd97b2bb58e2..5ebd10d2d6cdfa7657c3d967716e03f8b848961f 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -66,9 +66,9 @@ void TranspositionTable::clear() {
 /// TranspositionTable::probe() looks up the current position in the transposition
 /// table. It returns true and a pointer to the TTEntry if the position is found.
 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
-/// to be replaced later. 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.
+/// to be replaced later. TTEntry t1 is considered more valuable than TTEntry t2 if
+/// both are from the current search and the depth of t1 is greater than the depth of t2,
+/// or if t1 is from a previous search but its depth is at least 8 ply deeper than t2.
 
 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
 
@@ -87,9 +87,8 @@ TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
   // Find an entry to be replaced according to the replacement strategy
   TTEntry* replace = tte;
   for (int i = 1; i < ClusterSize; ++i)
-      if (  ((  tte[i].genBound8 & 0xFC) == generation8 || tte[i].bound() == BOUND_EXACT)
-          - ((replace->genBound8 & 0xFC) == generation8)
-          - (tte[i].depth8 < replace->depth8) < 0)
+      if (  ((  tte[i].genBound8 & 0xFC) == generation8) * 8 * ONE_PLY +   tte[i].depth8
+          < ((replace->genBound8 & 0xFC) == generation8) * 8 * ONE_PLY + replace->depth8)
           replace = &tte[i];
 
   return found = false, replace;