Value value() const { return (Value)value16; }
Value eval() const { return (Value)eval16; }
Depth depth() const { return (Depth)depth8 + DEPTH_OFFSET; }
- bool is_pv() const { return (bool)(genBound8 & 0x4); }
+ bool is_pv() const { return (bool)(genBound8 & 0x4); }
Bound bound() const { return (Bound)(genBound8 & 0x3); }
void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
};
-/// 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
-/// 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.
+/// A TranspositionTable is an array of Cluster, of size clusterCount. Each
+/// cluster consists of ClusterSize number of TTEntry. Each non-empty TTEntry
+/// contains information on exactly one position. The size of a Cluster should
+/// divide the size of a cache line for best performance,
+/// as the cacheline is prefetched when possible.
class TranspositionTable {
- static constexpr int CacheLineSize = 64;
static constexpr int ClusterSize = 3;
+ static constexpr int ClustersPerSuperCluster = 256;
struct Cluster {
TTEntry entry[ClusterSize];
- char padding[2]; // Align to a divisor of the cache line size
+ char padding[2]; // Pad to 32 bytes
};
- static_assert(CacheLineSize % sizeof(Cluster) == 0, "Cluster size incorrect");
+ static_assert(sizeof(Cluster) == 32, "Unexpected Cluster size");
public:
- ~TranspositionTable() { free(mem); }
+ ~TranspositionTable() { aligned_ttmem_free(mem); }
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 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[(uint32_t(key) * uint64_t(clusterCount)) >> 32].entry[0];
+
+ // The index is computed from
+ // Idx = (K48 * SCC) / 2^40, with K48 the 48 lowest bits swizzled.
+
+ const uint64_t firstTerm = uint32_t(key) * uint64_t(superClusterCount);
+ const uint64_t secondTerm = (uint16_t(key >> 32) * uint64_t(superClusterCount)) >> 16;
+
+ return &table[(firstTerm + secondTerm) >> 24].entry[0];
}
private:
friend struct TTEntry;
- size_t clusterCount;
+ size_t superClusterCount;
Cluster* table;
void* mem;
uint8_t generation8; // Size must be not bigger than TTEntry::genBound8