/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, 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 .
*/
#include
#include
#include "bitboard.h"
#include "tt.h"
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 TTClusterSize number of TTEntry.
void TranspositionTable::resize(size_t mbSize) {
size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(TTCluster));
if (newClusterCount == clusterCount)
return;
clusterCount = newClusterCount;
free(mem);
mem = calloc(clusterCount * sizeof(TTCluster) + CACHE_LINE_SIZE - 1, 1);
if (!mem)
{
std::cerr << "Failed to allocate " << mbSize
<< "MB for transposition table." << std::endl;
exit(EXIT_FAILURE);
}
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
/// user asks the program to clear the table (from the UCI interface).
void TranspositionTable::clear() {
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* const tte = first_entry(key);
const uint16_t key16 = key >> 48;
for (unsigned i = 0; i < TTClusterSize; ++i)
if (tte[i].key16 == key16)
{
tte[i].genBound8 = uint8_t(generation | tte[i].bound()); // Refresh
return &tte[i];
}
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
/// 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) {
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 < TTClusterSize; ++i)
if (!tte[i].key16 || tte[i].key16 == key16) // Empty or overwrite old
{
// Save preserving any existing ttMove
tte[i].save(key16, v, b, d, m ? m : tte[i].move(), generation, statV);
return;
}
// Implement replace 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(key16, v, b, d, m, generation, statV);
}