X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Ftt.h;h=84a4b9faec4701fb4b69b9c246cd01bf0952f267;hp=b2f9e0dcdf68a0c643a121dbc8dc4078faeeb1d2;hb=ed72a1e9ba37a9fa2674da8f46bb0597a1721c2d;hpb=4eb2d8ce095b284a1e55762548d9821a83a19b3b

diff --git a/src/tt.h b/src/tt.h
index b2f9e0dc..84a4b9fa 100644
--- a/src/tt.h
+++ b/src/tt.h
@@ -43,14 +43,22 @@ struct TTEntry {
 
   void save(Key k, Value v, Bound b, Depth d, Move m, Value ev, uint8_t g) {
 
-    if (m || (k >> 48) != key16) // Preserve any existing move for the same position
+    // Preserve any existing move for the same position
+    if (m || (k >> 48) != key16)
         move16 = (uint16_t)m;
 
-    key16     = (uint16_t)(k >> 48);
-    value16   = (int16_t)v;
-    eval16    = (int16_t)ev;
-    genBound8 = (uint8_t)(g | b);
-    depth8    = (int8_t)d;
+    // Don't overwrite more valuable entries
+    if (  (k >> 48) != key16
+        || d > depth8 - 2
+     /* || g != (genBound8 & 0xFC) // Matching non-zero keys are already refreshed by probe() */
+        || b == BOUND_EXACT)
+    {
+        key16     = (uint16_t)(k >> 48);
+        value16   = (int16_t)v;
+        eval16    = (int16_t)ev;
+        genBound8 = (uint8_t)(g | b);
+        depth8    = (int8_t)d;
+    }
   }
 
 private:
@@ -66,26 +74,30 @@ private:
 
 
 /// A TranspositionTable consists of a power of 2 number of clusters and each
-/// cluster consists of TTClusterSize number of TTEntry. Each non-empty entry
+/// cluster consists of ClusterSize number of TTEntry. Each non-empty entry
 /// contains information of exactly one position. The size of a cluster should
-/// not be bigger than a cache line size. In case it is less, it should be padded
-/// to guarantee always aligned accesses.
+/// 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.
 
 class TranspositionTable {
 
   static const int CacheLineSize = 64;
-  static const int TTClusterSize = 3;
+  static const int ClusterSize = 3;
 
-  struct TTCluster {
-    TTEntry entry[TTClusterSize];
-    char padding[2]; // Align to the cache line size
+  struct Cluster {
+    TTEntry entry[ClusterSize];
+    char padding[2]; // Align to a divisor of the cache line size
   };
 
+  static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");
+
 public:
  ~TranspositionTable() { free(mem); }
   void new_search() { generation8 += 4; } // Lower 2 bits are used by Bound
   uint8_t generation() const { return generation8; }
   TTEntry* probe(const Key key, bool& found) const;
+  int hashfull() const;
   void resize(size_t mbSize);
   void clear();
 
@@ -96,7 +108,7 @@ public:
 
 private:
   size_t clusterCount;
-  TTCluster* table;
+  Cluster* table;
   void* mem;
   uint8_t generation8; // Size must be not bigger than TTEntry::genBound8
 };