2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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
28 TranspositionTable::TranspositionTable() {
30 size = generation = 0;
34 TranspositionTable::~TranspositionTable() {
40 /// TranspositionTable::set_size() sets the size of the transposition table,
41 /// measured in megabytes. Transposition table consists of a power of 2 number of
42 /// TTCluster and each cluster consists of ClusterSize number of TTEntries. Each
43 /// non-empty entry contains information of exactly one position.
45 void TranspositionTable::set_size(size_t mbSize) {
47 size_t newSize = 1ULL << msb((mbSize << 20) / sizeof(TTCluster));
54 entries = new (std::nothrow) TTCluster[size];
58 std::cerr << "Failed to allocate " << mbSize
59 << "MB for transposition table." << std::endl;
63 clear(); // Operator new is not guaranteed to initialize memory to zero
67 /// TranspositionTable::clear() overwrites the entire transposition table
68 /// with zeroes. It is called whenever the table is resized, or when the
69 /// user asks the program to clear the table (from the UCI interface).
71 void TranspositionTable::clear() {
73 memset(entries, 0, size * sizeof(TTCluster));
77 /// TranspositionTable::store() writes a new entry containing position key and
78 /// valuable information of current position. The lowest order bits of position
79 /// key are used to decide on which cluster the position will be placed.
80 /// When a new entry is written and there are no empty entries available in cluster,
81 /// it replaces the least valuable of entries. A TTEntry t1 is considered to be
82 /// more valuable than a TTEntry t2 if t1 is from the current search and t2 is from
83 /// a previous search, or if the depth of t1 is bigger than the depth of t2.
85 void TranspositionTable::store(const Key posKey, Value v, Bound t, Depth d, Move m, Value statV, Value kingD) {
88 TTEntry *tte, *replace;
89 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key inside the cluster
91 tte = replace = first_entry(posKey);
93 for (int i = 0; i < ClusterSize; i++, tte++)
95 if (!tte->key() || tte->key() == posKey32) // Empty or overwrite old
97 // Preserve any existing ttMove
101 tte->save(posKey32, v, t, d, m, generation, statV, kingD);
105 // Implement replace strategy
106 c1 = (replace->generation() == generation ? 2 : 0);
107 c2 = (tte->generation() == generation || tte->type() == BOUND_EXACT ? -2 : 0);
108 c3 = (tte->depth() < replace->depth() ? 1 : 0);
110 if (c1 + c2 + c3 > 0)
113 replace->save(posKey32, v, t, d, m, generation, statV, kingD);
117 /// TranspositionTable::probe() looks up the current position in the
118 /// transposition table. Returns a pointer to the TTEntry or NULL if
119 /// position is not found.
121 TTEntry* TranspositionTable::probe(const Key posKey) const {
123 uint32_t posKey32 = posKey >> 32;
124 TTEntry* tte = first_entry(posKey);
126 for (int i = 0; i < ClusterSize; i++, tte++)
127 if (tte->key() == posKey32)
134 /// TranspositionTable::new_search() is called at the beginning of every new
135 /// search. It increments the "generation" variable, which is used to
136 /// distinguish transposition table entries from previous searches from
137 /// entries from the current search.
139 void TranspositionTable::new_search() {