X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Ftt.h;h=5f9c29e4a389745c38639e984b11b8df61cc4126;hp=48c5638a7d971d1ed3c581a37b7a87529948d462;hb=2af2c67650c4ac2531e6ab2753830f91c0999876;hpb=eaeb63f1d03aa71edf719605a31d121bf086a03d

diff --git a/src/tt.h b/src/tt.h
index 48c5638a..5f9c29e4 100644
--- a/src/tt.h
+++ b/src/tt.h
@@ -2,6 +2,7 @@
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+  Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -38,39 +39,29 @@ struct TTEntry {
   Move  move()  const { return (Move )move16; }
   Value value() const { return (Value)value16; }
   Value eval()  const { return (Value)eval16; }
-  Depth depth() const { return (Depth)depth8; }
+  Depth depth() const { return (Depth)(depth8 * int(ONE_PLY)); }
   Bound bound() const { return (Bound)(genBound8 & 0x3); }
 
   void save(Key k, Value v, Bound b, Depth d, Move m, Value ev, uint8_t g) {
 
-      if (key16 != (k >> 48))
-      {
-          key16     = (uint16_t)(k >> 48);
-          move16    = (uint16_t)m;
-          value16   = (int16_t)v;
-          eval16    = (int16_t)ev;
-          genBound8 = (uint8_t)(g | b);
-          depth8    = (int8_t)d;
-      }
-      else
-      {
-          // Preserve any existing move for the same position
-          if (m)
-              move16 = (uint16_t)m;
-
-          // Don't overwrite more valuable values
-          if (   d + 2 > depth8 
-              || g != (genBound8 & 0xFC) 
-              || b == BOUND_EXACT)
-          {
-              value16   = (int16_t)v;
-              genBound8 = (uint8_t)(g | b);
-              depth8    = (int8_t)d;
-          }
-
-          if (ev != VALUE_NONE)
-              eval16 = (int16_t)ev;
-      }
+    assert(d / ONE_PLY * ONE_PLY == d);
+
+    // Preserve any existing move for the same position
+    if (m || (k >> 48) != key16)
+        move16 = (uint16_t)m;
+
+    // Don't overwrite more valuable entries
+    if (  (k >> 48) != key16
+        || d / ONE_PLY > depth8 - 4
+     /* || 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 / ONE_PLY);
+    }
   }
 
 private:
@@ -88,20 +79,21 @@ 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
-/// 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 ClusterSize = 3;
+  static constexpr int CacheLineSize = 64;
+  static constexpr int ClusterSize = 3;
 
   struct Cluster {
     TTEntry entry[ClusterSize];
-    char padding[2]; // Align to the cache line size
+    char padding[2]; // Align to a divisor of the cache line size
   };
 
-  static_assert(sizeof(Cluster) == CacheLineSize / 2, "Cluster size incorrect");
+  static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");
 
 public:
  ~TranspositionTable() { free(mem); }
@@ -112,9 +104,9 @@ public:
   void resize(size_t mbSize);
   void clear();
 
-  // The lowest order bits of the key are used to get the index of the cluster
+  // 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[(size_t)key & (clusterCount - 1)].entry[0];
+    return &table[(uint32_t(key) * uint64_t(clusterCount)) >> 32].entry[0];
   }
 
 private: