2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
19 #include <cstring> // For std::memset
29 TranspositionTable TT; // Our global transposition table
31 /// TTEntry::save() populates the TTEntry with a new node's data, possibly
32 /// overwriting an old position. Update is not atomic and can be racy.
34 void TTEntry::save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev) {
36 // Preserve any existing move for the same position
37 if (m || (uint16_t)k != key16)
40 // Overwrite less valuable entries (cheapest checks first)
42 || (uint16_t)k != key16
43 || d - DEPTH_OFFSET > depth8 - 4)
45 assert(d > DEPTH_OFFSET);
46 assert(d < 256 + DEPTH_OFFSET);
49 depth8 = (uint8_t)(d - DEPTH_OFFSET);
50 genBound8 = (uint8_t)(TT.generation8 | uint8_t(pv) << 2 | b);
57 /// TranspositionTable::resize() sets the size of the transposition table,
58 /// measured in megabytes. Transposition table consists of a power of 2 number
59 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
61 void TranspositionTable::resize(size_t mbSize) {
63 Threads.main()->wait_for_search_finished();
65 aligned_ttmem_free(mem);
67 clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
68 table = static_cast<Cluster*>(aligned_ttmem_alloc(clusterCount * sizeof(Cluster), mem));
71 std::cerr << "Failed to allocate " << mbSize
72 << "MB for transposition table." << std::endl;
80 /// TranspositionTable::clear() initializes the entire transposition table to zero,
81 // in a multi-threaded way.
83 void TranspositionTable::clear() {
85 std::vector<std::thread> threads;
87 for (size_t idx = 0; idx < Options["Threads"]; ++idx)
89 threads.emplace_back([this, idx]() {
91 // Thread binding gives faster search on systems with a first-touch policy
92 if (Options["Threads"] > 8)
93 WinProcGroup::bindThisThread(idx);
95 // Each thread will zero its part of the hash table
96 const size_t stride = size_t(clusterCount / Options["Threads"]),
97 start = size_t(stride * idx),
98 len = idx != Options["Threads"] - 1 ?
99 stride : clusterCount - start;
101 std::memset(&table[start], 0, len * sizeof(Cluster));
105 for (std::thread& th : threads)
110 /// TranspositionTable::probe() looks up the current position in the transposition
111 /// table. It returns true and a pointer to the TTEntry if the position is found.
112 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
113 /// to be replaced later. The replace value of an entry is calculated as its depth
114 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
115 /// TTEntry t2 if its replace value is greater than that of t2.
117 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
119 TTEntry* const tte = first_entry(key);
120 const uint16_t key16 = (uint16_t)key; // Use the low 16 bits as key inside the cluster
122 for (int i = 0; i < ClusterSize; ++i)
123 if (tte[i].key16 == key16 || !tte[i].depth8)
125 tte[i].genBound8 = uint8_t(generation8 | (tte[i].genBound8 & 0x7)); // Refresh
127 return found = (bool)tte[i].depth8, &tte[i];
130 // Find an entry to be replaced according to the replacement strategy
131 TTEntry* replace = tte;
132 for (int i = 1; i < ClusterSize; ++i)
133 // Due to our packed storage format for generation and its cyclic
134 // nature we add 263 (256 is the modulus plus 7 to keep the unrelated
135 // lowest three bits from affecting the result) to calculate the entry
136 // age correctly even after generation8 overflows into the next cycle.
137 if ( replace->depth8 - ((263 + generation8 - replace->genBound8) & 0xF8)
138 > tte[i].depth8 - ((263 + generation8 - tte[i].genBound8) & 0xF8))
141 return found = false, replace;
145 /// TranspositionTable::hashfull() returns an approximation of the hashtable
146 /// occupation during a search. The hash is x permill full, as per UCI protocol.
148 int TranspositionTable::hashfull() const {
151 for (int i = 0; i < 1000; ++i)
152 for (int j = 0; j < ClusterSize; ++j)
153 cnt += table[i].entry[j].depth8 && (table[i].entry[j].genBound8 & 0xF8) == generation8;
155 return cnt / ClusterSize;