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Member "stockfish-11-linux/src/tt.cpp" (18 Jan 2020, 5539 Bytes) of package /linux/privat/stockfish-11-linux.zip:


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    1 /*
    2   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
    3   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
    4   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
    5   Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
    6 
    7   Stockfish is free software: you can redistribute it and/or modify
    8   it under the terms of the GNU General Public License as published by
    9   the Free Software Foundation, either version 3 of the License, or
   10   (at your option) any later version.
   11 
   12   Stockfish is distributed in the hope that it will be useful,
   13   but WITHOUT ANY WARRANTY; without even the implied warranty of
   14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   15   GNU General Public License for more details.
   16 
   17   You should have received a copy of the GNU General Public License
   18   along with this program.  If not, see <http://www.gnu.org/licenses/>.
   19 */
   20 
   21 #include <cstring>   // For std::memset
   22 #include <iostream>
   23 #include <thread>
   24 
   25 #include "bitboard.h"
   26 #include "misc.h"
   27 #include "thread.h"
   28 #include "tt.h"
   29 #include "uci.h"
   30 
   31 TranspositionTable TT; // Our global transposition table
   32 
   33 /// TTEntry::save populates the TTEntry with a new node's data, possibly
   34 /// overwriting an old position. Update is not atomic and can be racy.
   35 
   36 void TTEntry::save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev) {
   37 
   38   // Preserve any existing move for the same position
   39   if (m || (k >> 48) != key16)
   40       move16 = (uint16_t)m;
   41 
   42   // Overwrite less valuable entries
   43   if (  (k >> 48) != key16
   44       || d - DEPTH_OFFSET > depth8 - 4
   45       || b == BOUND_EXACT)
   46   {
   47       assert(d >= DEPTH_OFFSET);
   48 
   49       key16     = (uint16_t)(k >> 48);
   50       value16   = (int16_t)v;
   51       eval16    = (int16_t)ev;
   52       genBound8 = (uint8_t)(TT.generation8 | uint8_t(pv) << 2 | b);
   53       depth8    = (uint8_t)(d - DEPTH_OFFSET);
   54   }
   55 }
   56 
   57 
   58 /// TranspositionTable::resize() sets the size of the transposition table,
   59 /// measured in megabytes. Transposition table consists of a power of 2 number
   60 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
   61 
   62 void TranspositionTable::resize(size_t mbSize) {
   63 
   64   Threads.main()->wait_for_search_finished();
   65 
   66   clusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
   67 
   68   free(mem);
   69   mem = malloc(clusterCount * sizeof(Cluster) + CacheLineSize - 1);
   70 
   71   if (!mem)
   72   {
   73       std::cerr << "Failed to allocate " << mbSize
   74                 << "MB for transposition table." << std::endl;
   75       exit(EXIT_FAILURE);
   76   }
   77 
   78   table = (Cluster*)((uintptr_t(mem) + CacheLineSize - 1) & ~(CacheLineSize - 1));
   79   clear();
   80 }
   81 
   82 
   83 /// TranspositionTable::clear() initializes the entire transposition table to zero,
   84 //  in a multi-threaded way.
   85 
   86 void TranspositionTable::clear() {
   87 
   88   std::vector<std::thread> threads;
   89 
   90   for (size_t idx = 0; idx < Options["Threads"]; ++idx)
   91   {
   92       threads.emplace_back([this, idx]() {
   93 
   94           // Thread binding gives faster search on systems with a first-touch policy
   95           if (Options["Threads"] > 8)
   96               WinProcGroup::bindThisThread(idx);
   97 
   98           // Each thread will zero its part of the hash table
   99           const size_t stride = clusterCount / Options["Threads"],
  100                        start  = stride * idx,
  101                        len    = idx != Options["Threads"] - 1 ?
  102                                 stride : clusterCount - start;
  103 
  104           std::memset(&table[start], 0, len * sizeof(Cluster));
  105       });
  106   }
  107 
  108   for (std::thread& th: threads)
  109       th.join();
  110 }
  111 
  112 /// TranspositionTable::probe() looks up the current position in the transposition
  113 /// table. It returns true and a pointer to the TTEntry if the position is found.
  114 /// Otherwise, it returns false and a pointer to an empty or least valuable TTEntry
  115 /// to be replaced later. The replace value of an entry is calculated as its depth
  116 /// minus 8 times its relative age. TTEntry t1 is considered more valuable than
  117 /// TTEntry t2 if its replace value is greater than that of t2.
  118 
  119 TTEntry* TranspositionTable::probe(const Key key, bool& found) const {
  120 
  121   TTEntry* const tte = first_entry(key);
  122   const uint16_t key16 = key >> 48;  // Use the high 16 bits as key inside the cluster
  123 
  124   for (int i = 0; i < ClusterSize; ++i)
  125       if (!tte[i].key16 || tte[i].key16 == key16)
  126       {
  127           tte[i].genBound8 = uint8_t(generation8 | (tte[i].genBound8 & 0x7)); // Refresh
  128 
  129           return found = (bool)tte[i].key16, &tte[i];
  130       }
  131 
  132   // Find an entry to be replaced according to the replacement strategy
  133   TTEntry* replace = tte;
  134   for (int i = 1; i < ClusterSize; ++i)
  135       // Due to our packed storage format for generation and its cyclic
  136       // nature we add 263 (256 is the modulus plus 7 to keep the unrelated
  137       // lowest three bits from affecting the result) to calculate the entry
  138       // age correctly even after generation8 overflows into the next cycle.
  139       if (  replace->depth8 - ((263 + generation8 - replace->genBound8) & 0xF8)
  140           >   tte[i].depth8 - ((263 + generation8 -   tte[i].genBound8) & 0xF8))
  141           replace = &tte[i];
  142 
  143   return found = false, replace;
  144 }
  145 
  146 
  147 /// TranspositionTable::hashfull() returns an approximation of the hashtable
  148 /// occupation during a search. The hash is x permill full, as per UCI protocol.
  149 
  150 int TranspositionTable::hashfull() const {
  151 
  152   int cnt = 0;
  153   for (int i = 0; i < 1000 / ClusterSize; ++i)
  154       for (int j = 0; j < ClusterSize; ++j)
  155           cnt += (table[i].entry[j].genBound8 & 0xF8) == generation8;
  156 
  157   return cnt * 1000 / (ClusterSize * (1000 / ClusterSize));
  158 }