2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 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/>.
20 #include <cstring> // For std::memset
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 ClusterSize number of TTEntry.
33 void TranspositionTable::resize(size_t mbSize) {
35 assert(sizeof(Cluster) == CacheLineSize / 2);
37 size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(Cluster));
39 if (newClusterCount == clusterCount)
42 clusterCount = newClusterCount;
45 mem = calloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1, 1);
49 std::cerr << "Failed to allocate " << mbSize
50 << "MB for transposition table." << std::endl;
54 table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
58 /// TranspositionTable::clear() overwrites the entire transposition table
59 /// with zeros. It is called whenever the table is resized, or when the
60 /// user asks the program to clear the table (from the UCI interface).
62 void TranspositionTable::clear() {
64 std::memset(table, 0, clusterCount * sizeof(Cluster));
68 /// TranspositionTable::probe() looks up the current position in the transposition
69 /// table. It returns true and a pointer to the TTEntry if the position is found.
70 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
71 /// to be replaced later. A TTEntry t1 is considered to be more valuable than a
72 /// TTEntry t2 if t1 is from the current search and t2 is from a previous search,
73 /// or if the depth of t1 is bigger than the depth of t2.
75 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
77 TTEntry* const tte = first_entry(key);
78 const uint16_t key16 = key >> 48; // Use the high 16 bits as key inside the cluster
80 for (int i = 0; i < ClusterSize; ++i)
81 if (!tte[i].key16 || tte[i].key16 == key16)
84 tte[i].genBound8 = uint8_t(generation8 | tte[i].bound()); // Refresh
86 return found = (bool)tte[i].key16, &tte[i];
89 // Find an entry to be replaced according to the replacement strategy
90 TTEntry* replace = tte;
91 for (int i = 1; i < ClusterSize; ++i)
92 if ( (( tte[i].genBound8 & 0xFC) == generation8 || tte[i].bound() == BOUND_EXACT)
93 - ((replace->genBound8 & 0xFC) == generation8)
94 - (tte[i].depth8 < replace->depth8) < 0)
97 return found = false, replace;
101 /// Returns an approximation of the hashtable occupation during a search. The
102 /// hash is x permill full, as per UCI protocol.
104 int TranspositionTable::hashfull() const
107 for (int i = 0; i < 1000 / ClusterSize; i++)
109 const TTEntry* tte = &table[i].entry[0];
110 for (int j = 0; j < ClusterSize; j++)
111 if ((tte[j].genBound8 & 0xFC) == generation8)