ginac/remember.cpp

   1 /** @file remember.cpp
   2  *
   3  *  Implementation of helper classes for using the remember option
   4  *  in GiNaC functions */
   5
   6 /*
   7  *  GiNaC Copyright (C) 1999-2001 Johannes Gutenberg University Mainz, Germany
   8  *
   9  *  This program is free software; you can redistribute it and/or modify
  10  *  it under the terms of the GNU General Public License as published by
  11  *  the Free Software Foundation; either version 2 of the License, or
  12  *  (at your option) any later version.
  13  *
  14  *  This program is distributed in the hope that it will be useful,
  15  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  *  GNU General Public License for more details.
  18  *
  19  *  You should have received a copy of the GNU General Public License
  20  *  along with this program; if not, write to the Free Software
  21  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  22  */
  23
  24 #include <stdexcept>
  25
  26 #include "function.h"
  27 #include "utils.h"
  28 #include "remember.h"
  29
  30 namespace GiNaC {
  31
  32 //////////
  33 // class remember_table_entry
  34 //////////
  35
  36 remember_table_entry::remember_table_entry(function const & f, ex const & r)
  37   : hashvalue(f.gethash()), seq(f.seq), result(r)
  38 {
  39         ++last_access = access_counter;
  40         successful_hits = 0;
  41 }
  42
  43 bool remember_table_entry::is_equal(function const & f) const
  44 {
  45         GINAC_ASSERT(f.seq.size()==seq.size());
  46         if (f.gethash()!=hashvalue) return false;
  47         for (unsigned i=0; i<seq.size(); ++i)
  48                 if (!seq[i].is_equal(f.seq[i])) return false;
  49         ++last_access = access_counter;
  50         ++successful_hits;
  51         return true;
  52 }
  53
  54 unsigned long remember_table_entry::access_counter = 0;
  55
  56 //////////
  57 // class remember_table_list
  58 //////////
  59
  60 remember_table_list::remember_table_list(unsigned as, unsigned strat)
  61 {
  62         max_assoc_size = as;
  63         remember_strategy = strat;
  64 }
  65
  66
  67 void remember_table_list::add_entry(function const & f, ex const & result)
  68 {
  69         if ((max_assoc_size!=0) &&
  70                 (remember_strategy!=remember_strategies::delete_never) &&
  71                 (size()>=max_assoc_size)) {
  72                 // table is full, we must delete an older entry
  73                 GINAC_ASSERT(size()>0); // there must be at least one entry
  74
  75                 switch (remember_strategy) {
  76                 case remember_strategies::delete_cyclic: {
  77                         // delete oldest entry (first in list)
  78                         erase(begin());
  79                         break;
  80                 }
  81                 case remember_strategies::delete_lru: {
  82                         // delete least recently used entry
  83                         iterator it = begin();
  84                         iterator lowest_access_it = it;
  85                         unsigned long lowest_access = (*it).get_last_access();
  86                         ++it;
  87                         while (it!=end()) {
  88                                 if ((*it).get_last_access()<lowest_access) {
  89                                         lowest_access = (*it).get_last_access();
  90                                         lowest_access_it = it;
  91                                 }
  92                                 ++it;
  93                         }
  94                         erase(lowest_access_it);
  95                         break;
  96                 }
  97                 case remember_strategies::delete_lfu: {
  98                         // delete least frequently used entry
  99                         iterator it = begin();
 100                         iterator lowest_hits_it = it;
 101                         unsigned lowest_hits = (*it).get_successful_hits();
 102                         ++it;
 103                         while (it!=end()) {
 104                                 if ((*it).get_successful_hits()<lowest_hits) {
 105                                         lowest_hits = (*it).get_successful_hits();
 106                                         lowest_hits_it = it;
 107                                 }
 108                                 ++it;
 109                         }
 110                         erase(lowest_hits_it);
 111                         break;
 112                 }
 113                 default:
 114                         throw(std::logic_error("remember_table_list::add_entry(): invalid remember_strategy"));
 115         }
 116                 GINAC_ASSERT(size()==max_assoc_size-1);
 117         }
 118         push_back(remember_table_entry(f,result));
 119 }
 120
 121 bool remember_table_list::lookup_entry(function const & f, ex & result) const
 122 {
 123         for (const_iterator cit=begin(); cit!=end(); ++cit) {
 124                 if ((*cit).is_equal(f)) {
 125                         result = (*cit).get_result();
 126                         return true;
 127                 }
 128         }
 129         return false;
 130 }
 131
 132 //////////
 133 // class remember_table
 134 //////////
 135
 136 remember_table::remember_table()
 137 {
 138         table_size=0;
 139         max_assoc_size=0;
 140         remember_strategy=remember_strategies::delete_never;
 141 }
 142
 143 remember_table::remember_table(unsigned s, unsigned as, unsigned strat)
 144   : max_assoc_size(as), remember_strategy(strat)
 145 {
 146         // we keep max_assoc_size and remember_strategy if we need to clear
 147         // all entries
 148
 149         // use some power of 2 next to s
 150         table_size = 1 << log2(s);
 151         init_table();
 152 }
 153
 154 bool remember_table::lookup_entry(function const & f, ex & result) const
 155 {
 156         unsigned entry = f.gethash() & (table_size-1);
 157         GINAC_ASSERT(entry<size());
 158         return operator[](entry).lookup_entry(f,result);
 159 }
 160
 161 void remember_table::add_entry(function const & f, ex const & result)
 162 {
 163         unsigned entry = f.gethash() & (table_size-1);
 164         GINAC_ASSERT(entry<size());
 165         operator[](entry).add_entry(f,result);
 166 }
 167
 168 void remember_table::clear_all_entries(void)
 169 {
 170         clear();
 171         init_table();
 172 }
 173
 174 void remember_table::init_table(void)
 175 {
 176         reserve(table_size);
 177         for (unsigned i=0; i<table_size; ++i)
 178                 push_back(remember_table_list(max_assoc_size,remember_strategy));
 179 }
 180
 181 std::vector<remember_table> & remember_table::remember_tables(void)
 182 {
 183         static std::vector<remember_table> * rt = new std::vector<remember_table>;
 184         return *rt;
 185 }
 186
 187 } // namespace GiNaC