2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 TranspositionTable TT; // Our global transposition table
29 /// TranspositionTable::resize() sets the size of the transposition table,
30 /// measured in megabytes. Transposition table consists of a power of 2 number
31 /// of clusters and each cluster consists of TTClusterSize number of TTEntry.
33 void TranspositionTable::resize(size_t mbSize) {
35 size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(TTCluster));
37 if (newClusterCount == clusterCount)
40 clusterCount = newClusterCount;
43 mem = calloc(clusterCount * sizeof(TTCluster) + CACHE_LINE_SIZE - 1, 1);
47 std::cerr << "Failed to allocate " << mbSize
48 << "MB for transposition table." << std::endl;
52 table = (TTCluster*)((uintptr_t(mem) + CACHE_LINE_SIZE - 1) & ~(CACHE_LINE_SIZE - 1));
56 /// TranspositionTable::clear() overwrites the entire transposition table
57 /// with zeroes. It is called whenever the table is resized, or when the
58 /// user asks the program to clear the table (from the UCI interface).
60 void TranspositionTable::clear() {
62 std::memset(table, 0, clusterCount * sizeof(TTCluster));
66 /// TranspositionTable::probe() looks up the current position in the
67 /// transposition table. Returns a pointer to the TTEntry or NULL if
68 /// position is not found.
70 const TTEntry* TranspositionTable::probe(const Key key) const {
72 TTEntry* tte = first_entry(key);
73 uint16_t key16 = key >> 48;
75 for (unsigned i = 0; i < TTClusterSize; ++i, ++tte)
76 if (tte->key16 == key16)
78 tte->genBound8 = generation | tte->bound(); // Refresh
86 /// TranspositionTable::store() writes a new entry containing position key and
87 /// valuable information of current position. The lowest order bits of position
88 /// key are used to decide in which cluster the position will be placed.
89 /// When a new entry is written and there are no empty entries available in the
90 /// cluster, it replaces the least valuable of the entries. A TTEntry t1 is considered
91 /// to be more valuable than a TTEntry t2 if t1 is from the current search and t2
92 /// is from a previous search, or if the depth of t1 is bigger than the depth of t2.
94 void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m, Value statV) {
96 TTEntry *tte, *replace;
97 uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
99 tte = replace = first_entry(key);
101 for (unsigned i = 0; i < TTClusterSize; ++i, ++tte)
103 if (!tte->key16 || tte->key16 == key16) // Empty or overwrite old
106 m = tte->move(); // Preserve any existing ttMove
112 // Implement replace strategy
113 if ( (( tte->genBound8 & 0xFC) == generation || tte->bound() == BOUND_EXACT)
114 - ((replace->genBound8 & 0xFC) == generation)
115 - (tte->depth8 < replace->depth8) < 0)
119 replace->save(key16, v, b, d, m, generation, statV);