src/tt.cpp

   1 /*
   2   Glaurung, a UCI chess playing engine.
   3   Copyright (C) 2004-2008 Tord Romstad
   4
   5   Glaurung 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.
   9
  10   Glaurung 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.
  14
  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/>.
  17 */
  18
  19
  20 ////
  21 //// Includes
  22 ////
  23
  24 #include <cassert>
  25 #include <cmath>
  26
  27 #include "tt.h"
  28
  29
  30 ////
  31 //// Functions
  32 ////
  33
  34 /// Constructor
  35
  36 TranspositionTable::TranspositionTable(unsigned mbSize) {
  37
  38   size = 0;
  39   generation = 0;
  40   writes = 0;
  41   entries = 0;
  42   set_size(mbSize);
  43 }
  44
  45
  46 /// Destructor
  47
  48 TranspositionTable::~TranspositionTable() {
  49
  50   delete [] entries;
  51 }
  52
  53
  54 /// TranspositionTable::set_size sets the size of the transposition table,
  55 /// measured in megabytes.
  56
  57 void TranspositionTable::set_size(unsigned mbSize) {
  58
  59   assert(mbSize >= 4 && mbSize <= 1024);
  60
  61   unsigned newSize = 1024;
  62
  63   // We store a cluster of 4 TTEntry for each position and newSize is
  64   // the maximum number of storable positions
  65   for ( ; newSize * 4 * (sizeof(TTEntry)) <= (mbSize << 20); newSize *= 2);
  66   newSize /= 2;
  67   if (newSize != size)
  68   {
  69     size = newSize;
  70     delete [] entries;
  71     entries = new TTEntry[size * 4];
  72     if (!entries)
  73     {
  74       std::cerr << "Failed to allocate " << mbSize
  75                 << " MB for transposition table."
  76                 << std::endl;
  77       exit(EXIT_FAILURE);
  78     }
  79     clear();
  80   }
  81 }
  82
  83
  84 /// TranspositionTable::clear overwrites the entire transposition table
  85 /// with zeroes.  It is called whenever the table is resized, or when the
  86 /// user asks the program to clear the table (from the UCI interface).
  87 /// Perhaps we should also clear it when the "ucinewgame" command is recieved?
  88
  89 void TranspositionTable::clear() {
  90
  91   memset(entries, 0, size * 4 * sizeof(TTEntry));
  92 }
  93
  94
  95 /// TranspositionTable::store writes a new entry containing a position,
  96 /// a value, a value type, a search depth, and a best move to the
  97 /// transposition table.  The transposition table is organized in clusters
  98 /// of four TTEntry objects, and when a new entry is written, it replaces
  99 /// the least valuable of the four entries in a cluster.  A TTEntry t1 is
 100 /// considered to be more valuable than a TTEntry t2 if t1 is from the
 101 /// current search and t2 is from a previous search, or if the depth of t1
 102 /// is bigger than the depth of t2.
 103
 104 void TranspositionTable::store(const Position &pos, Value v, Depth d,
 105                                Move m, ValueType type) {
 106   TTEntry *tte, *replace;
 107
 108   tte = replace = first_entry(pos);
 109   for (int i = 0; i < 4; i++)
 110   {
 111     if (!(tte+i)->key()) // still empty
 112     {
 113         *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
 114         writes++;
 115         return;
 116     }
 117     if ((tte+i)->key() == pos.get_key()) // overwrite old
 118     {
 119         if (m == MOVE_NONE)
 120             m = (tte+i)->move();
 121
 122         *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
 123         return;
 124     }
 125     if (   i == 0  // already is (replace == tte+i), common case
 126         || replace->generation() < (tte+i)->generation())
 127         continue;
 128
 129     if (    replace->generation() > (tte+i)->generation()
 130         || (tte+i)->depth() < replace->depth())
 131         replace = tte+i;
 132   }
 133   *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
 134   writes++;
 135 }
 136
 137
 138 /// TranspositionTable::retrieve looks up the current position in the
 139 /// transposition table. Returns a pointer to the TTEntry or NULL
 140 /// if position is not found.
 141
 142 const TTEntry* TranspositionTable::retrieve(const Position &pos) const {
 143
 144   TTEntry *tte = first_entry(pos);
 145
 146   for (int i = 0; i < 4; i++)
 147   {
 148       tte += i;
 149       if (tte->key() == pos.get_key())
 150           return tte;
 151   }
 152   return NULL;
 153 }
 154
 155
 156 /// TranspositionTable::first_entry returns a pointer to the first
 157 /// entry of a cluster given a position.
 158
 159 inline TTEntry* TranspositionTable::first_entry(const Position &pos) const {
 160
 161   return entries + (int(pos.get_key() & (size - 1)) << 2);
 162 }
 163
 164 /// TranspositionTable::new_search() is called at the beginning of every new
 165 /// search.  It increments the "generation" variable, which is used to
 166 /// distinguish transposition table entries from previous searches from
 167 /// entries from the current search.
 168
 169 void TranspositionTable::new_search() {
 170
 171   generation++;
 172   writes = 0;
 173 }
 174
 175
 176 /// TranspositionTable::insert_pv() is called at the end of a search
 177 /// iteration, and inserts the PV back into the PV.  This makes sure the
 178 /// old PV moves are searched first, even if the old TT entries have been
 179 /// overwritten.
 180
 181 void TranspositionTable::insert_pv(const Position &pos, Move pv[]) {
 182
 183   UndoInfo u;
 184   Position p(pos);
 185
 186   for (int i = 0; pv[i] != MOVE_NONE; i++)
 187   {
 188     store(p, VALUE_NONE, Depth(0), pv[i], VALUE_TYPE_NONE);
 189     p.do_move(pv[i], u);
 190   }
 191 }
 192
 193
 194 /// TranspositionTable::full() returns the permill of all transposition table
 195 /// entries which have received at least one write during the current search.
 196 /// It is used to display the "info hashfull ..." information in UCI.
 197
 198 int TranspositionTable::full() {
 199
 200   double N = double(size) * 4.0;
 201   return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));
 202 }
 203
 204
 205 /// Constructors
 206
 207 TTEntry::TTEntry() {
 208 }
 209
 210 TTEntry::TTEntry(Key k, Value v, ValueType t, Depth d, Move m,
 211                  int generation) :
 212   key_ (k), data((m & 0x7FFFF) | (t << 20) | (generation << 23)),
 213   value_(v), depth_(int16_t(d)) {}
 214
 215
 216