2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
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/>.
36 TranspositionTable::TranspositionTable() {
43 TranspositionTable::~TranspositionTable() {
49 /// TranspositionTable::set_size sets the size of the transposition table,
50 /// measured in megabytes.
52 void TranspositionTable::set_size(unsigned mbSize) {
54 assert(mbSize >= 4 && mbSize <= 4096);
56 unsigned newSize = 1024;
58 // We store a cluster of 4 TTEntry for each position and newSize is
59 // the maximum number of storable positions
60 while ((2 * newSize) * 4 * (sizeof(TTEntry)) <= (mbSize << 20))
67 entries = new TTEntry[size * 4];
70 std::cerr << "Failed to allocate " << mbSize
71 << " MB for transposition table." << std::endl;
72 Application::exit_with_failure();
79 /// TranspositionTable::clear overwrites the entire transposition table
80 /// with zeroes. It is called whenever the table is resized, or when the
81 /// user asks the program to clear the table (from the UCI interface).
82 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
84 void TranspositionTable::clear() {
86 memset(entries, 0, size * 4 * sizeof(TTEntry));
90 /// TranspositionTable::store writes a new entry containing a position,
91 /// a value, a value type, a search depth, and a best move to the
92 /// transposition table. Transposition table is organized in clusters of
93 /// four TTEntry objects, and when a new entry is written, it replaces
94 /// the least valuable of the four entries in a cluster. A TTEntry t1 is
95 /// considered to be more valuable than a TTEntry t2 if t1 is from the
96 /// current search and t2 is from a previous search, or if the depth of t1
97 /// is bigger than the depth of t2. A TTEntry of type VALUE_TYPE_EVAL
98 /// never replaces another entry for the same position.
100 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m) {
102 TTEntry *tte, *replace;
104 tte = replace = first_entry(posKey);
105 for (int i = 0; i < 4; i++, tte++)
107 if (!tte->key() || tte->key() == posKey) // empty or overwrite old
109 // Do not overwrite when new type is VALUE_TYPE_EVAL
110 if (tte->key() && t == VALUE_TYPE_EVAL)
116 *tte = TTEntry(posKey, v, t, d, m, generation);
119 else if (i == 0) // replace would be a no-op in this common case
122 int c1 = (replace->generation() == generation ? 2 : 0);
123 int c2 = (tte->generation() == generation ? -2 : 0);
124 int c3 = (tte->depth() < replace->depth() ? 1 : 0);
126 if (c1 + c2 + c3 > 0)
129 *replace = TTEntry(posKey, v, t, d, m, generation);
134 /// TranspositionTable::retrieve looks up the current position in the
135 /// transposition table. Returns a pointer to the TTEntry or NULL
136 /// if position is not found.
138 TTEntry* TranspositionTable::retrieve(const Key posKey) const {
140 TTEntry *tte = first_entry(posKey);
142 for (int i = 0; i < 4; i++, tte++)
143 if (tte->key() == posKey)
150 /// TranspositionTable::first_entry returns a pointer to the first
151 /// entry of a cluster given a position.
153 inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {
155 return entries + (int(posKey & (size - 1)) << 2);
158 /// TranspositionTable::new_search() is called at the beginning of every new
159 /// search. It increments the "generation" variable, which is used to
160 /// distinguish transposition table entries from previous searches from
161 /// entries from the current search.
163 void TranspositionTable::new_search() {
170 /// TranspositionTable::insert_pv() is called at the end of a search
171 /// iteration, and inserts the PV back into the PV. This makes sure
172 /// the old PV moves are searched first, even if the old TT entries
173 /// have been overwritten.
175 void TranspositionTable::insert_pv(const Position& pos, Move pv[]) {
180 for (int i = 0; pv[i] != MOVE_NONE; i++)
182 store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, Depth(-127*OnePly), pv[i]);
183 p.do_move(pv[i], st);
188 /// TranspositionTable::full() returns the permill of all transposition table
189 /// entries which have received at least one write during the current search.
190 /// It is used to display the "info hashfull ..." information in UCI.
192 int TranspositionTable::full() const {
194 double N = double(size) * 4.0;
195 return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));