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/*
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) 2015-2017 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
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef TT_H_INCLUDED
#define TT_H_INCLUDED
#include "misc.h"
#include "types.h"
/// 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
/// 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 * int(ONE_PLY)); }
Bound bound() const { return (Bound)(genBound8 & 0x3); }
void save(Key k, Value v, Bound b, Depth d, Move m, Value ev, uint8_t g) {
assert(d / ONE_PLY * ONE_PLY == d);
// Preserve any existing move for the same position
if (m || (k >> 48) != key16)
move16 = (uint16_t)m;
// Don't overwrite more valuable entries
if ( (k >> 48) != key16
|| d / ONE_PLY > depth8 - 4
/* || g != (genBound8 & 0xFC) // Matching non-zero keys are already refreshed by probe() */
|| b == BOUND_EXACT)
{
key16 = (uint16_t)(k >> 48);
value16 = (int16_t)v;
eval16 = (int16_t)ev;
genBound8 = (uint8_t)(g | b);
depth8 = (int8_t)(d / ONE_PLY);
}
}
private:
friend class TranspositionTable;
uint16_t key16;
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 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.
class TranspositionTable {
static const int CacheLineSize = 64;
static const int ClusterSize = 3;
struct Cluster {
TTEntry entry[ClusterSize];
char padding[2]; // Align to a divisor of the cache line size
};
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; }
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];
}
private:
size_t clusterCount;
Cluster* table;
void* mem;
uint8_t generation8; // Size must be not bigger than TTEntry::genBound8
};
extern TranspositionTable TT;
#endif // #ifndef TT_H_INCLUDED