/*
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
+ Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
#include "misc.h"
#include "types.h"
+namespace Stockfish {
+
/// TTEntry struct is the 10 bytes transposition table entry, defined as below:
///
/// key 16 bit
-/// move 16 bit
-/// value 16 bit
-/// eval value 16 bit
+/// depth 8 bit
/// generation 5 bit
/// pv node 1 bit
/// bound type 2 bit
-/// depth 8 bit
+/// move 16 bit
+/// value 16 bit
+/// eval value 16 bit
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 * int(ONE_PLY)) + DEPTH_NONE; }
- bool is_pv() const { return (bool)(genBound8 & 0x4); }
+ Depth depth() const { return (Depth)depth8 + DEPTH_OFFSET; }
+ 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);
friend class TranspositionTable;
uint16_t key16;
+ uint8_t depth8;
+ uint8_t genBound8;
uint16_t move16;
int16_t value16;
int16_t eval16;
- uint8_t genBound8;
- 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
-/// 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;
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");
+
+ // Constants used to refresh the hash table periodically
+ static constexpr unsigned GENERATION_BITS = 3; // nb of bits reserved for other things
+ static constexpr int GENERATION_DELTA = (1 << GENERATION_BITS); // increment for generation field
+ static constexpr int GENERATION_CYCLE = 255 + (1 << GENERATION_BITS); // cycle length
+ static constexpr int GENERATION_MASK = (0xFF << GENERATION_BITS) & 0xFF; // mask to pull out generation number
public:
- ~TranspositionTable() { free(mem); }
- void new_search() { generation8 += 8; } // Lower 3 bits are used by PV flag and Bound
+ ~TranspositionTable() { aligned_large_pages_free(table); }
+ void new_search() { generation8 += GENERATION_DELTA; } // Lower bits are used for other things
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];
+ return &table[mul_hi64(key, clusterCount)].entry[0];
}
private:
size_t clusterCount;
Cluster* table;
- void* mem;
uint8_t generation8; // Size must be not bigger than TTEntry::genBound8
};
extern TranspositionTable TT;
+} // namespace Stockfish
+
#endif // #ifndef TT_H_INCLUDED