2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
31 // The main transposition table
32 TranspositionTable TT;
38 TranspositionTable::TranspositionTable() {
45 TranspositionTable::~TranspositionTable() {
51 /// TranspositionTable::set_size sets the size of the transposition table,
52 /// measured in megabytes.
54 void TranspositionTable::set_size(size_t mbSize) {
56 size_t newSize = 1024;
58 // We store a cluster of ClusterSize number of TTEntry for each position
59 // and newSize is the maximum number of storable positions.
60 while ((2 * newSize) * sizeof(TTCluster) <= (mbSize << 20))
67 entries = new TTCluster[size];
70 std::cerr << "Failed to allocate " << mbSize
71 << " MB for transposition table." << std::endl;
72 Application::exit_with_failure();
78 /// TranspositionTable::clear overwrites the entire transposition table
79 /// with zeroes. It is called whenever the table is resized, or when the
80 /// user asks the program to clear the table (from the UCI interface).
81 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
83 void TranspositionTable::clear() {
85 memset(entries, 0, size * sizeof(TTCluster));
89 /// TranspositionTable::store writes a new entry containing a position,
90 /// a value, a value type, a search depth, and a best move to the
91 /// transposition table. Transposition table is organized in clusters of
92 /// four TTEntry objects, and when a new entry is written, it replaces
93 /// the least valuable of the four entries in a cluster. A TTEntry t1 is
94 /// considered to be more valuable than a TTEntry t2 if t1 is from the
95 /// current search and t2 is from a previous search, or if the depth of t1
96 /// is bigger than the depth of t2. A TTEntry of type VALUE_TYPE_EVAL
97 /// never replaces another entry for the same position.
99 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m, Value statV, Value kingD) {
102 TTEntry *tte, *replace;
103 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key
105 tte = replace = first_entry(posKey);
106 for (int i = 0; i < ClusterSize; i++, tte++)
108 if (!tte->key() || tte->key() == posKey32) // empty or overwrite old
110 // Preserve any exsisting ttMove
114 tte->save(posKey32, v, t, d, m, generation, statV, kingD);
118 if (i == 0) // replace would be a no-op in this common case
121 c1 = (replace->generation() == generation ? 2 : 0);
122 c2 = (tte->generation() == generation ? -2 : 0);
123 c3 = (tte->depth() < replace->depth() ? 1 : 0);
125 if (c1 + c2 + c3 > 0)
128 replace->save(posKey32, v, t, d, m, generation, statV, kingD);
132 /// TranspositionTable::retrieve looks up the current position in the
133 /// transposition table. Returns a pointer to the TTEntry or NULL
134 /// if position is not found.
136 TTEntry* TranspositionTable::retrieve(const Key posKey) const {
138 uint32_t posKey32 = posKey >> 32;
139 TTEntry* tte = first_entry(posKey);
141 for (int i = 0; i < ClusterSize; i++, tte++)
142 if (tte->key() == posKey32)
149 /// TranspositionTable::new_search() is called at the beginning of every new
150 /// search. It increments the "generation" variable, which is used to
151 /// distinguish transposition table entries from previous searches from
152 /// entries from the current search.
154 void TranspositionTable::new_search() {
159 /// TranspositionTable::insert_pv() is called at the end of a search
160 /// iteration, and inserts the PV back into the PV. This makes sure
161 /// the old PV moves are searched first, even if the old TT entries
162 /// have been overwritten.
164 void TranspositionTable::insert_pv(const Position& pos, Move pv[]) {
167 Position p(pos, pos.thread());
169 for (int i = 0; pv[i] != MOVE_NONE; i++)
171 TTEntry *tte = retrieve(p.get_key());
172 if (!tte || tte->move() != pv[i])
173 store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, Depth(-127*OnePly), pv[i], VALUE_NONE, VALUE_NONE);
174 p.do_move(pv[i], st);
179 /// TranspositionTable::extract_pv() builds a PV by adding moves from the
180 /// transposition table. We consider also failing high nodes and not only
181 /// VALUE_TYPE_EXACT nodes. This allow to always have a ponder move even
182 /// when we fail high at root and also a long PV to print that is important
183 /// for position analysis.
185 void TranspositionTable::extract_pv(const Position& pos, Move bestMove, Move pv[], const int PLY_MAX) {
189 Position p(pos, pos.thread());
192 assert(bestMove != MOVE_NONE);
195 p.do_move(pv[ply++], st);
197 while ( (tte = retrieve(p.get_key())) != NULL
198 && tte->move() != MOVE_NONE
199 && move_is_legal(p, tte->move())
200 && (!p.is_draw() || ply < 2)
203 pv[ply] = tte->move();
204 p.do_move(pv[ply++], st);