Avoid searching TT twice for the same key/position during probe() and store().

[stockfish] / src / tt.cpp

diff --git a/src/tt.cpp b/src/tt.cpp
index 41fc33ff9ebba868927ce1de876ab42f512b2618..2979c104aac3020c3798996597b182174b03ad4b 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -28,20 +28,19 @@ TranspositionTable TT; // Our global transposition table
 
 /// TranspositionTable::resize() sets the size of the transposition table,
 /// measured in megabytes. Transposition table consists of a power of 2 number
-/// of clusters and each cluster consists of ClusterSize number of TTEntry.
+/// of clusters and each cluster consists of TTClusterSize number of TTEntry.
 
-void TranspositionTable::resize(uint64_t mbSize) {
+void TranspositionTable::resize(size_t mbSize) {
 
-  assert(msb((mbSize << 20) / sizeof(TTEntry)) < 32);
+  size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(TTCluster));
 
-  uint32_t size = ClusterSize << msb((mbSize << 20) / sizeof(TTEntry[ClusterSize]));
-
-  if (hashMask == size - ClusterSize)
+  if (newClusterCount == clusterCount)
       return;
 
-  hashMask = size - ClusterSize;
+  clusterCount = newClusterCount;
+
   free(mem);
-  mem = calloc(size * sizeof(TTEntry) + CACHE_LINE_SIZE - 1, 1);
+  mem = calloc(clusterCount * sizeof(TTCluster) + CACHE_LINE_SIZE - 1, 1);
 
   if (!mem)
   {
@@ -50,75 +49,50 @@ void TranspositionTable::resize(uint64_t mbSize) {
       exit(EXIT_FAILURE);
   }
 
-  table = (TTEntry*)((uintptr_t(mem) + CACHE_LINE_SIZE - 1) & ~(CACHE_LINE_SIZE - 1));
+  table = (TTCluster*)((uintptr_t(mem) + CACHE_LINE_SIZE - 1) & ~(CACHE_LINE_SIZE - 1));
 }
 
 
 /// TranspositionTable::clear() overwrites the entire transposition table
-/// with zeroes. It is called whenever the table is resized, or when the
+/// with zeros. It is called whenever the table is resized, or when the
 /// user asks the program to clear the table (from the UCI interface).
 
 void TranspositionTable::clear() {
 
-  std::memset(table, 0, (hashMask + ClusterSize) * sizeof(TTEntry));
+  std::memset(table, 0, clusterCount * sizeof(TTCluster));
 }
 
 
 /// TranspositionTable::probe() looks up the current position in the
-/// transposition table. Returns a pointer to the TTEntry or NULL if
-/// position is not found.
-
-const TTEntry* TranspositionTable::probe(const Key key) const {
-
-  TTEntry* tte = first_entry(key);
-  uint32_t key32 = key >> 32;
-
-  for (unsigned i = 0; i < ClusterSize; ++i, ++tte)
-      if (tte->key32 == key32)
-      {
-          tte->generation8 = generation; // Refresh
-          return tte;
-      }
-
-  return NULL;
-}
-
-
-/// TranspositionTable::store() writes a new entry containing position key and
-/// valuable information of current position. The lowest order bits of position
-/// key are used to decide in which cluster the position will be placed.
-/// When a new entry is written and there are no empty entries available in the
-/// cluster, it replaces the least valuable of the entries. A TTEntry t1 is considered
+/// transposition table. It returns true and a pointer to the TTEntry if
+/// the position is found. Otherwise, it returns false and a pointer to an empty or
+/// least valuable TTEntry to be replaced later. A TTEntry t1 is considered
 /// to be more valuable than a TTEntry t2 if t1 is from the current search and t2
 /// is from a previous search, or if the depth of t1 is bigger than the depth of t2.
 
-void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m, Value statV) {
-
-  int c1, c2, c3;
-  TTEntry *tte, *replace;
-  uint32_t key32 = key >> 32; // Use the high 32 bits as key inside the cluster
+TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
 
-  tte = replace = first_entry(key);
+  TTEntry* const tte = first_entry(key);
+  const uint16_t key16 = key >> 48;  // Use the high 16 bits as key inside the cluster
 
-  for (unsigned i = 0; i < ClusterSize; ++i, ++tte)
-  {
-      if (!tte->key32 || tte->key32 == key32) // Empty or overwrite old
+  for (unsigned i = 0; i < TTClusterSize; ++i)
+      if (!tte[i].key16 || tte[i].key16 == key16)
       {
-          if (!m)
-              m = tte->move(); // Preserve any existing ttMove
+          if (tte[i].key16)
+              tte[i].genBound8 = uint8_t(generation | tte[i].bound()); // Refresh
 
-          replace = tte;
-          break;
+          found = (bool)tte[i].key16;
+          return &tte[i];
       }
 
-      // Implement replace strategy
-      c1 = (replace->generation8 == generation ?  2 : 0);
-      c2 = (tte->generation8 == generation || tte->bound() == BOUND_EXACT ? -2 : 0);
-      c3 = (tte->depth16 < replace->depth16 ?  1 : 0);
-
-      if (c1 + c2 + c3 > 0)
-          replace = tte;
-  }
+  // Find an entry to be replaced according to the replacement strategy
+  TTEntry* replace = tte;
+  for (unsigned i = 1; i < TTClusterSize; ++i)
+      if (  ((  tte[i].genBound8 & 0xFC) == generation || tte[i].bound() == BOUND_EXACT)
+          - ((replace->genBound8 & 0xFC) == generation)
+          - (tte[i].depth8 < replace->depth8) < 0)
+          replace = &tte[i];
 
-  replace->save(key32, v, b, d, m, generation, statV);
+  found = false;
+  return replace;
 }