/*
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) 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
+/// depth 8 bit
+/// generation 5 bit
+/// pv node 1 bit
+/// bound type 2 bit
/// move 16 bit
/// value 16 bit
/// eval value 16 bit
-/// generation 6 bit
-/// bound type 2 bit
-/// depth 8 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; }
+ 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, 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;
uint16_t key16;
+ uint8_t depth8;
+ uint8_t genBound8;
uint16_t move16;
int16_t value16;
int16_t eval16;
- uint8_t genBound8;
- int8_t depth8;
};
-/// A TranspositionTable consists of a power of 2 number of clusters and each
-/// cluster consists of TTClusterSize 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.
+/// 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 const int CacheLineSize = 64;
- static const int TTClusterSize = 3;
+ static constexpr int ClusterSize = 3;
struct Cluster {
- TTEntry entry[TTClusterSize];
- char padding[2]; // Align to the cache line size
+ TTEntry entry[ClusterSize];
+ char padding[2]; // Pad to 32 bytes
};
+ 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 += 4; } // Lower 2 bits are used by Bound
- uint8_t generation() const { return generation8; }
+ ~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 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[mul_hi64(key, clusterCount)].entry[0];
}
private:
+ friend struct TTEntry;
+
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