Improve the anti-shuffling policy

[stockfish] / src / tt.h

diff --git a/src/tt.h b/src/tt.h
index 8b70f79787619ca4c1b6326f55cfa456a2dcf04f..76db03dabafd744cb813b82654e3da4a3c129219 100644 (file)
--- a/src/tt.h
+++ b/src/tt.h
@@ -66,6 +66,7 @@ private:
 class TranspositionTable {
 
   static constexpr int ClusterSize = 3;
+  static constexpr int ClustersPerSuperCluster = 256;
 
   struct Cluster {
     TTEntry entry[ClusterSize];
@@ -75,22 +76,28 @@ class TranspositionTable {
   static_assert(sizeof(Cluster) == 32, "Unexpected Cluster size");
 
 public:
- ~TranspositionTable() { free(mem); }
+ ~TranspositionTable() { aligned_ttmem_free(mem); }
   void new_search() { generation8 += 8; } // Lower 3 bits are used by PV flag and Bound
   TTEntry* probe(const Key key, bool& found) const;
   int hashfull() const;
   void resize(size_t mbSize);
   void clear();
 
-  // The 32 lowest order bits of the key are used to get the index of the cluster
   TTEntry* first_entry(const Key key) const {
-    return &table[(uint32_t(key) * uint64_t(clusterCount)) >> 32].entry[0];
+
+    // The index is computed from
+    // Idx = (K48 * SCC) / 2^40, with K48 the 48 lowest bits swizzled.
+
+    const uint64_t firstTerm =  uint32_t(key) * uint64_t(superClusterCount);
+    const uint64_t secondTerm = (uint16_t(key >> 32) * uint64_t(superClusterCount)) >> 16;
+
+    return &table[(firstTerm + secondTerm) >> 24].entry[0];
   }
 
 private:
   friend struct TTEntry;
 
-  size_t clusterCount;
+  size_t superClusterCount;
   Cluster* table;
   void* mem;
   uint8_t generation8; // Size must be not bigger than TTEntry::genBound8