remember.cpp

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/*
 *  GiNaC Copyright (C) 1999-2026 Johannes Gutenberg University Mainz, Germany
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#include "function.h"
#include "utils.h"
#include "remember.h"
 
#include <stdexcept>
 
namespace GiNaC {
 
// class remember_table_entry
 
remember_table_entry::remember_table_entry(function const & f, ex const & r)
  : hashvalue(f.gethash()), seq(f.seq), result(r)
{
    ++last_access = access_counter;
    successful_hits = 0;
}
 
bool remember_table_entry::is_equal(function const & f) const
{
    GINAC_ASSERT(f.seq.size()==seq.size());
    if (f.gethash()!=hashvalue) return false;
    size_t num = seq.size();
    for (size_t i=0; i<num; ++i)
        if (!seq[i].is_equal(f.seq[i])) return false;
    ++last_access = access_counter;
    ++successful_hits;
    return true;
}
 
unsigned long remember_table_entry::access_counter = 0;
 
// class remember_table_list
 
remember_table_list::remember_table_list(unsigned as, unsigned strat)
{
    max_assoc_size = as;
    remember_strategy = strat;
}
 
 
void remember_table_list::add_entry(function const & f, ex const & result)
{
    if ((max_assoc_size!=0) &&
        (remember_strategy!=remember_strategies::delete_never) &&
        (size()>=max_assoc_size)) {
        // table is full, we must delete an older entry
        GINAC_ASSERT(size()>0); // there must be at least one entry
        
        switch (remember_strategy) {
        case remember_strategies::delete_cyclic: {
            // delete oldest entry (first in list)
            erase(begin());
            break;
        }
        case remember_strategies::delete_lru: {
            // delete least recently used entry
            auto it = begin();
            auto lowest_access_it = it;
            unsigned long lowest_access = (*it).get_last_access();
            ++it;
            while (it!=end()) {
                if ((*it).get_last_access()<lowest_access) {
                    lowest_access = (*it).get_last_access();
                    lowest_access_it = it;
                }
                ++it;
            }
            erase(lowest_access_it);
            break;
        }
        case remember_strategies::delete_lfu: {
            // delete least frequently used entry
            auto it = begin();
            auto lowest_hits_it = it;
            unsigned lowest_hits = (*it).get_successful_hits();
            ++it;
            while (it!=end()) {
                if ((*it).get_successful_hits()<lowest_hits) {
                    lowest_hits = (*it).get_successful_hits();
                    lowest_hits_it = it;
                }
                ++it;
            }
            erase(lowest_hits_it);
            break;
        }
        default:
            throw(std::logic_error("remember_table_list::add_entry(): invalid remember_strategy"));
    }
        GINAC_ASSERT(size()==max_assoc_size-1);
    }
    push_back(remember_table_entry(f,result));
}
 
bool remember_table_list::lookup_entry(function const & f, ex & result) const
{
    auto i = begin(), iend = end();
    while (i != iend) {
        if (i->is_equal(f)) {
            result = i->get_result();
            return true;
        }
        ++i;
    }
    return false;
}
 
// class remember_table
 
remember_table::remember_table()
{
    table_size=0;
    max_assoc_size=0;
    remember_strategy=remember_strategies::delete_never;
}
 
remember_table::remember_table(unsigned s, unsigned as, unsigned strat)
  : max_assoc_size(as), remember_strategy(strat)
{
    // we keep max_assoc_size and remember_strategy if we need to clear
    // all entries
    
    // use some power of 2 next to s
    table_size = 1 << log2(s);
    init_table();
}
 
bool remember_table::lookup_entry(function const & f, ex & result) const
{
    unsigned entry = f.gethash() & (table_size-1);
    GINAC_ASSERT(entry<size());
    return operator[](entry).lookup_entry(f,result);
}
 
void remember_table::add_entry(function const & f, ex const & result)
{
    unsigned entry = f.gethash() & (table_size-1);
    GINAC_ASSERT(entry<size());
    operator[](entry).add_entry(f,result);
}        
 
void remember_table::clear_all_entries()
{
    clear();
    init_table();
}
 
void remember_table::init_table()
{
    reserve(table_size);
    for (unsigned i=0; i<table_size; ++i)
        push_back(remember_table_list(max_assoc_size,remember_strategy));
}
 
std::vector<remember_table> & remember_table::remember_tables()
{
    static std::vector<remember_table> rt = std::vector<remember_table>();
    return rt;
}
 
} // namespace GiNaC