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/>.
32 // The main transposition table
33 TranspositionTable TT;
39 TranspositionTable::TranspositionTable() {
46 TranspositionTable::~TranspositionTable() {
52 /// TranspositionTable::set_size sets the size of the transposition table,
53 /// measured in megabytes.
55 void TranspositionTable::set_size(size_t mbSize) {
57 size_t newSize = 1024;
59 // We store a cluster of ClusterSize number of TTEntry for each position
60 // and newSize is the maximum number of storable positions.
61 while ((2 * newSize) * sizeof(TTCluster) <= (mbSize << 20))
68 entries = new TTCluster[size];
71 std::cerr << "Failed to allocate " << mbSize
72 << " MB for transposition table." << std::endl;
73 Application::exit_with_failure();
80 /// TranspositionTable::clear overwrites the entire transposition table
81 /// with zeroes. It is called whenever the table is resized, or when the
82 /// user asks the program to clear the table (from the UCI interface).
83 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
85 void TranspositionTable::clear() {
87 memset(entries, 0, size * sizeof(TTCluster));
91 /// TranspositionTable::store writes a new entry containing a position,
92 /// a value, a value type, a search depth, and a best move to the
93 /// transposition table. Transposition table is organized in clusters of
94 /// four TTEntry objects, and when a new entry is written, it replaces
95 /// the least valuable of the four entries in a cluster. A TTEntry t1 is
96 /// considered to be more valuable than a TTEntry t2 if t1 is from the
97 /// current search and t2 is from a previous search, or if the depth of t1
98 /// is bigger than the depth of t2. A TTEntry of type VALUE_TYPE_EVAL
99 /// never replaces another entry for the same position.
101 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m, Value statV, Value kingD) {
103 TTEntry *tte, *replace;
104 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key
106 tte = replace = first_entry(posKey);
107 for (int i = 0; i < ClusterSize; i++, tte++)
109 if (!tte->key() || tte->key() == posKey32) // empty or overwrite old
111 // Preserve any exsisting ttMove
115 tte->save(posKey32, v, t, d, m, generation, statV, kingD);
118 else if (i == 0) // replace would be a no-op in this common case
121 int c1 = (replace->generation() == generation ? 2 : 0);
122 int c2 = (tte->generation() == generation ? -2 : 0);
123 int c3 = (tte->depth() < replace->depth() ? 1 : 0);
125 if (c1 + c2 + c3 > 0)
128 replace->save(posKey32, v, t, d, m, generation, statV, kingD);
133 /// TranspositionTable::retrieve looks up the current position in the
134 /// transposition table. Returns a pointer to the TTEntry or NULL
135 /// if position is not found.
137 TTEntry* TranspositionTable::retrieve(const Key posKey) const {
139 uint32_t posKey32 = posKey >> 32;
140 TTEntry* tte = first_entry(posKey);
142 for (int i = 0; i < ClusterSize; i++, tte++)
143 if (tte->key() == posKey32)
150 /// TranspositionTable::new_search() is called at the beginning of every new
151 /// search. It increments the "generation" variable, which is used to
152 /// distinguish transposition table entries from previous searches from
153 /// entries from the current search.
155 void TranspositionTable::new_search() {
162 /// TranspositionTable::insert_pv() is called at the end of a search
163 /// iteration, and inserts the PV back into the PV. This makes sure
164 /// the old PV moves are searched first, even if the old TT entries
165 /// have been overwritten.
167 void TranspositionTable::insert_pv(const Position& pos, Move pv[]) {
170 Position p(pos, pos.thread());
172 for (int i = 0; pv[i] != MOVE_NONE; i++)
174 TTEntry *tte = retrieve(p.get_key());
175 if (!tte || tte->move() != pv[i])
176 store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, Depth(-127*OnePly), pv[i], VALUE_NONE, VALUE_NONE);
177 p.do_move(pv[i], st);
182 /// TranspositionTable::extract_pv() extends a PV by adding moves from the
183 /// transposition table at the end. This should ensure that the PV is almost
184 /// always at least two plies long, which is important, because otherwise we
185 /// will often get single-move PVs when the search stops while failing high,
186 /// and a single-move PV means that we don't have a ponder move.
188 void TranspositionTable::extract_pv(const Position& pos, Move pv[], const int PLY_MAX) {
192 Position p(pos, pos.thread());
195 // Update position to the end of current PV
196 while (pv[ply] != MOVE_NONE)
197 p.do_move(pv[ply++], st);
199 // Try to add moves from TT while possible
200 while ( (tte = retrieve(p.get_key())) != NULL
201 && tte->move() != MOVE_NONE
202 && move_is_legal(p, tte->move())
203 && (!p.is_draw() || ply < 2)
206 pv[ply] = tte->move();
207 p.do_move(pv[ply++], st);
213 /// TranspositionTable::full() returns the permill of all transposition table
214 /// entries which have received at least one write during the current search.
215 /// It is used to display the "info hashfull ..." information in UCI.
217 int TranspositionTable::full() const {
219 double N = double(size) * ClusterSize;
220 return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));