X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Ftt.h;h=76db03dabafd744cb813b82654e3da4a3c129219;hp=98b054d397207525a45978e6bae6a15055e29181;hb=4d657618e956decdd51bceca77c2c5489dfcf6af;hpb=09bef14c76e119103cc1a9404cbde7e249205deb

diff --git a/src/tt.h b/src/tt.h
index 98b054d3..76db03da 100644
--- a/src/tt.h
+++ b/src/tt.h
@@ -41,7 +41,7 @@ struct TTEntry {
   Value value() const { return (Value)value16; }
   Value eval()  const { return (Value)eval16; }
   Depth depth() const { return (Depth)depth8 + DEPTH_OFFSET; }
-  bool is_pv() const { return (bool)(genBound8 & 0x4); }
+  bool is_pv()  const { return (bool)(genBound8 & 0x4); }
   Bound bound() const { return (Bound)(genBound8 & 0x3); }
   void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
 
@@ -57,42 +57,47 @@ private:
 };
 
 
-/// A TranspositionTable consists of a power of 2 number of clusters and each
-/// cluster consists of ClusterSize number of TTEntry. Each non-empty entry
-/// contains information of exactly one position. The size of a cluster should
-/// divide the size of a cache line size, to ensure that clusters never cross
-/// cache lines. This ensures best cache performance, as the cacheline is
-/// prefetched, as soon as possible.
+/// A TranspositionTable is an array of Cluster, of size clusterCount. Each
+/// cluster consists of ClusterSize number of TTEntry. Each non-empty TTEntry
+/// contains information on exactly one position. The size of a Cluster should
+/// divide the size of a cache line for best performance,
+/// as the cacheline is prefetched when possible.
 
 class TranspositionTable {
 
-  static constexpr int CacheLineSize = 64;
   static constexpr int ClusterSize = 3;
+  static constexpr int ClustersPerSuperCluster = 256;
 
   struct Cluster {
     TTEntry entry[ClusterSize];
-    char padding[2]; // Align to a divisor of the cache line size
+    char padding[2]; // Pad to 32 bytes
   };
 
-  static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");
+  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