Slight speep up fetching the endgame table

[stockfish] / src / tt.h

diff --git a/src/tt.h b/src/tt.h
index 32b4036e39dea085974410867b7212facfc6c625..3a5ba5da8ee218c76b4e14a097c76c158cdd0a84 100644 (file)
--- 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) 2015-2019 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
@@ -29,7 +30,8 @@
 /// move       16 bit
 /// value      16 bit
 /// eval value 16 bit
-/// generation  6 bit
+/// generation  5 bit
+/// pv node     1 bit
 /// bound type  2 bit
 /// depth       8 bit
 
@@ -38,20 +40,10 @@ 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)) + DEPTH_OFFSET; }
+  bool is_pv() const { return (bool)(genBound8 & 0x4); }
   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 (m || (k >> 48) != key16) // Preserve any existing move for the same position
-        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;
-  }
+  void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
 
 private:
   friend class TranspositionTable;
@@ -61,43 +53,45 @@ private:
   int16_t  value16;
   int16_t  eval16;
   uint8_t  genBound8;
-  int8_t   depth8;
+  uint8_t  depth8;
 };
 
 
 /// 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); }
-  void new_search() { generation8 += 4; } // Lower 2 bits are used by Bound
-  uint8_t generation() const { return generation8; }
+  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 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:
+  friend struct TTEntry;
+
   size_t clusterCount;
   Cluster* table;
   void* mem;