src/tt.cpp

   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 Marco Costalba
   5
   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.
  10
  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.
  15
  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/>.
  18 */
  19
  20
  21 ////
  22 //// Includes
  23 ////
  24
  25 #include <cassert>
  26 #include <cmath>
  27 #include <cstring>
  28
  29 #include "tt.h"
  30
  31
  32 ////
  33 //// Functions
  34 ////
  35
  36 /// Constructor
  37
  38 TranspositionTable::TranspositionTable(unsigned mbSize) {
  39
  40   size = 0;
  41   generation = 0;
  42   writes = 0;
  43   entries = 0;
  44   set_size(mbSize);
  45 }
  46
  47
  48 /// Destructor
  49
  50 TranspositionTable::~TranspositionTable() {
  51
  52   delete [] entries;
  53 }
  54
  55
  56 /// TranspositionTable::set_size sets the size of the transposition table,
  57 /// measured in megabytes.
  58
  59 void TranspositionTable::set_size(unsigned mbSize) {
  60
  61   assert(mbSize >= 4 && mbSize <= 1024);
  62
  63   unsigned newSize = 1024;
  64
  65   // We store a cluster of 4 TTEntry for each position and newSize is
  66   // the maximum number of storable positions
  67   for ( ; newSize * 4 * (sizeof(TTEntry)) <= (mbSize << 20); newSize *= 2);
  68   newSize /= 2;
  69   if (newSize != size)
  70   {
  71     size = newSize;
  72     delete [] entries;
  73     entries = new TTEntry[size * 4];
  74     if (!entries)
  75     {
  76       std::cerr << "Failed to allocate " << mbSize
  77                 << " MB for transposition table."
  78                 << std::endl;
  79       exit(EXIT_FAILURE);
  80     }
  81     clear();
  82   }
  83 }
  84
  85
  86 /// TranspositionTable::clear overwrites the entire transposition table
  87 /// with zeroes.  It is called whenever the table is resized, or when the
  88 /// user asks the program to clear the table (from the UCI interface).
  89 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
  90
  91 void TranspositionTable::clear() {
  92
  93   memset(entries, 0, size * 4 * sizeof(TTEntry));
  94 }
  95
  96
  97 /// TranspositionTable::store writes a new entry containing a position,
  98 /// a value, a value type, a search depth, and a best move to the
  99 /// transposition table.  The transposition table is organized in clusters
 100 /// of four TTEntry objects, and when a new entry is written, it replaces
 101 /// the least valuable of the four entries in a cluster.  A TTEntry t1 is
 102 /// considered to be more valuable than a TTEntry t2 if t1 is from the
 103 /// current search and t2 is from a previous search, or if the depth of t1
 104 /// is bigger than the depth of t2.
 105
 106 void TranspositionTable::store(const Position &pos, Value v, Depth d,
 107                                Move m, ValueType type) {
 108   TTEntry *tte, *replace;
 109
 110   tte = replace = first_entry(pos);
 111   for (int i = 0; i < 4; i++, tte++)
 112   {
 113     if (!tte->key() || tte->key() == pos.get_key()) // empty or overwrite old
 114     {
 115         if (m == MOVE_NONE)
 116             m = tte->move();
 117
 118         *tte = TTEntry(pos.get_key(), v, type, d, m, generation);
 119         return;
 120     }
 121     else if (i == 0)  // replace would be a no-op in this common case
 122         continue;
 123
 124     int c1 = (replace->generation() == generation ?  2 : 0);
 125     int c2 = (tte->generation() == generation ? -2 : 0);
 126     int c3 = (tte->depth() < replace->depth() ?  1 : 0);
 127
 128     if (c1 + c2 + c3 > 0)
 129         replace = tte;
 130   }
 131   *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
 132   writes++;
 133 }
 134
 135
 136 /// TranspositionTable::retrieve looks up the current position in the
 137 /// transposition table. Returns a pointer to the TTEntry or NULL
 138 /// if position is not found.
 139
 140 TTEntry* TranspositionTable::retrieve(const Position &pos) const {
 141
 142   TTEntry *tte = first_entry(pos);
 143
 144   for (int i = 0; i < 4; i++, tte++)
 145   {
 146       if (tte->key() == pos.get_key())
 147           return tte;
 148   }
 149   return NULL;
 150 }
 151
 152
 153 /// TranspositionTable::first_entry returns a pointer to the first
 154 /// entry of a cluster given a position.
 155
 156 inline TTEntry* TranspositionTable::first_entry(const Position &pos) const {
 157
 158   return entries + (int(pos.get_key() & (size - 1)) << 2);
 159 }
 160
 161 /// TranspositionTable::new_search() is called at the beginning of every new
 162 /// search.  It increments the "generation" variable, which is used to
 163 /// distinguish transposition table entries from previous searches from
 164 /// entries from the current search.
 165
 166 void TranspositionTable::new_search() {
 167
 168   generation++;
 169   writes = 0;
 170 }
 171
 172
 173 /// TranspositionTable::insert_pv() is called at the end of a search
 174 /// iteration, and inserts the PV back into the PV.  This makes sure the
 175 /// old PV moves are searched first, even if the old TT entries have been
 176 /// overwritten.
 177
 178 void TranspositionTable::insert_pv(const Position &pos, Move pv[]) {
 179
 180   StateInfo st;
 181   Position p(pos);
 182
 183   for (int i = 0; pv[i] != MOVE_NONE; i++)
 184   {
 185     store(p, VALUE_NONE, Depth(-127*OnePly), pv[i], VALUE_TYPE_NONE);
 186     p.do_move(pv[i], st);
 187   }
 188 }
 189
 190
 191 /// TranspositionTable::full() returns the permill of all transposition table
 192 /// entries which have received at least one write during the current search.
 193 /// It is used to display the "info hashfull ..." information in UCI.
 194
 195 int TranspositionTable::full() {
 196
 197   double N = double(size) * 4.0;
 198   return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));
 199 }
 200
 201
 202 /// Constructors
 203
 204 TTEntry::TTEntry() {
 205 }
 206
 207 TTEntry::TTEntry(Key k, Value v, ValueType t, Depth d, Move m,
 208                  int generation) :
 209   key_ (k), data((m & 0x1FFFF) | (t << 20) | (generation << 23)),
 210   value_(int16_t(v)), depth_(int16_t(d)) {}