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/>.
29 # include <xmmintrin.h>
35 // The main transposition table
36 TranspositionTable TT;
42 TranspositionTable::TranspositionTable() {
49 TranspositionTable::~TranspositionTable() {
55 /// TranspositionTable::set_size sets the size of the transposition table,
56 /// measured in megabytes.
58 void TranspositionTable::set_size(size_t mbSize) {
60 size_t newSize = 1024;
62 // We store a cluster of ClusterSize number of TTEntry for each position
63 // and newSize is the maximum number of storable positions.
64 while ((2 * newSize) * sizeof(TTCluster) <= (mbSize << 20))
71 entries = new TTCluster[size];
74 std::cerr << "Failed to allocate " << mbSize
75 << " MB for transposition table." << std::endl;
76 Application::exit_with_failure();
83 /// TranspositionTable::clear overwrites the entire transposition table
84 /// with zeroes. It is called whenever the table is resized, or when the
85 /// user asks the program to clear the table (from the UCI interface).
86 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
88 void TranspositionTable::clear() {
90 memset(entries, 0, size * sizeof(TTCluster));
94 /// TranspositionTable::first_entry returns a pointer to the first
95 /// entry of a cluster given a position. The low 32 bits of the key
96 /// are used to get the index in the table.
98 inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {
100 return entries[uint32_t(posKey) & (size - 1)].data;
104 /// TranspositionTable::store writes a new entry containing a position,
105 /// a value, a value type, a search depth, and a best move to the
106 /// transposition table. Transposition table is organized in clusters of
107 /// four TTEntry objects, and when a new entry is written, it replaces
108 /// the least valuable of the four entries in a cluster. A TTEntry t1 is
109 /// considered to be more valuable than a TTEntry t2 if t1 is from the
110 /// current search and t2 is from a previous search, or if the depth of t1
111 /// is bigger than the depth of t2. A TTEntry of type VALUE_TYPE_EVAL
112 /// never replaces another entry for the same position.
114 void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m) {
116 TTEntry *tte, *replace;
117 uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key
119 tte = replace = first_entry(posKey);
120 for (int i = 0; i < ClusterSize; i++, tte++)
122 if (!tte->key() || tte->key() == posKey32) // empty or overwrite old
124 // Do not overwrite when new type is VALUE_TYPE_EV_LO
125 if (tte->key() && t == VALUE_TYPE_EV_LO)
128 // Preserve any exsisting ttMove
132 *tte = TTEntry(posKey32, v, t, d, m, generation);
135 else if (i == 0) // replace would be a no-op in this common case
138 int c1 = (replace->generation() == generation ? 2 : 0);
139 int c2 = (tte->generation() == generation ? -2 : 0);
140 int c3 = (tte->depth() < replace->depth() ? 1 : 0);
142 if (c1 + c2 + c3 > 0)
145 *replace = TTEntry(posKey32, v, t, d, m, generation);
150 /// TranspositionTable::retrieve looks up the current position in the
151 /// transposition table. Returns a pointer to the TTEntry or NULL
152 /// if position is not found.
154 TTEntry* TranspositionTable::retrieve(const Key posKey) const {
156 uint32_t posKey32 = posKey >> 32;
157 TTEntry* tte = first_entry(posKey);
159 for (int i = 0; i < ClusterSize; i++, tte++)
160 if (tte->key() == posKey32)
167 /// TranspositionTable::prefetch looks up the current position in the
168 /// transposition table and load it in L1/L2 cache. This is a non
169 /// blocking function and do not stalls the CPU waiting for data
170 /// to be loaded from RAM, that can be very slow. When we will
171 /// subsequently call retrieve() the TT data will be already
172 /// quickly accessible in L1/L2 CPU cache.
174 void TranspositionTable::prefetch(const Key) const {} // Not supported on HP UX
177 void TranspositionTable::prefetch(const Key posKey) const {
179 #if defined(__INTEL_COMPILER) || defined(__ICL)
180 // This hack prevents prefetches to be optimized away by
181 // Intel compiler. Both MSVC and gcc seems not affected.
185 char const* addr = (char*)first_entry(posKey);
186 _mm_prefetch(addr, _MM_HINT_T2);
187 _mm_prefetch(addr+64, _MM_HINT_T2); // 64 bytes ahead
192 /// TranspositionTable::new_search() is called at the beginning of every new
193 /// search. It increments the "generation" variable, which is used to
194 /// distinguish transposition table entries from previous searches from
195 /// entries from the current search.
197 void TranspositionTable::new_search() {
204 /// TranspositionTable::insert_pv() is called at the end of a search
205 /// iteration, and inserts the PV back into the PV. This makes sure
206 /// the old PV moves are searched first, even if the old TT entries
207 /// have been overwritten.
209 void TranspositionTable::insert_pv(const Position& pos, Move pv[]) {
214 for (int i = 0; pv[i] != MOVE_NONE; i++)
216 TTEntry *tte = retrieve(p.get_key());
217 if (!tte || tte->move() != pv[i])
218 store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, Depth(-127*OnePly), pv[i]);
219 p.do_move(pv[i], st);
224 /// TranspositionTable::extract_pv() extends a PV by adding moves from the
225 /// transposition table at the end. This should ensure that the PV is almost
226 /// always at least two plies long, which is important, because otherwise we
227 /// will often get single-move PVs when the search stops while failing high,
228 /// and a single-move PV means that we don't have a ponder move.
230 void TranspositionTable::extract_pv(const Position& pos, Move pv[], const int PLY_MAX) {
237 // Update position to the end of current PV
238 while (pv[ply] != MOVE_NONE)
239 p.do_move(pv[ply++], st);
241 // Try to add moves from TT while possible
242 while ( (tte = retrieve(p.get_key())) != NULL
243 && tte->move() != MOVE_NONE
244 && move_is_legal(p, tte->move())
245 && (!p.is_draw() || ply < 2)
248 pv[ply] = tte->move();
249 p.do_move(pv[ply++], st);
255 /// TranspositionTable::full() returns the permill of all transposition table
256 /// entries which have received at least one write during the current search.
257 /// It is used to display the "info hashfull ..." information in UCI.
259 int TranspositionTable::full() const {
261 double N = double(size) * ClusterSize;
262 return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));