X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Ftt.h;h=70283fca29bff341fd7d06d23ac12bacfdf8a66e;hp=f243a39d483335b61496418bf3f35d9ef03a34ff;hb=29b5842da8d5477c0aea924cfd364c9e619456a2;hpb=ee0371f86e319aa24bc1d32f02d9495eea79aa72

diff --git a/src/tt.h b/src/tt.h
index f243a39d..70283fca 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) 2015-2016 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
@@ -49,8 +50,8 @@ struct TTEntry {
 
     // Don't overwrite more valuable entries
     if (  (k >> 48) != key16
-        || d > depth8 - 2
-        || g != (genBound8 & 0xFC)
+        || d > depth8 - 4
+     /* || g != (genBound8 & 0xFC) // Matching non-zero keys are already refreshed by probe() */
         || b == BOUND_EXACT)
     {
         key16     = (uint16_t)(k >> 48);
@@ -76,8 +77,9 @@ 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 {
 
@@ -86,10 +88,10 @@ class TranspositionTable {
 
   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); }