list_update_policy.hpp revision 1.11
1// -*- C++ -*- 2 3// Copyright (C) 2005-2020 Free Software Foundation, Inc. 4// 5// This file is part of the GNU ISO C++ Library. This library is free 6// software; you can redistribute it and/or modify it under the terms 7// of the GNU General Public License as published by the Free Software 8// Foundation; either version 3, or (at your option) any later 9// version. 10 11// This library is distributed in the hope that it will be useful, but 12// WITHOUT ANY WARRANTY; without even the implied warranty of 13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14// General Public License for more details. 15 16// Under Section 7 of GPL version 3, you are granted additional 17// permissions described in the GCC Runtime Library Exception, version 18// 3.1, as published by the Free Software Foundation. 19 20// You should have received a copy of the GNU General Public License and 21// a copy of the GCC Runtime Library Exception along with this program; 22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23// <http://www.gnu.org/licenses/>. 24 25// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL. 26 27// Permission to use, copy, modify, sell, and distribute this software 28// is hereby granted without fee, provided that the above copyright 29// notice appears in all copies, and that both that copyright notice 30// and this permission notice appear in supporting documentation. None 31// of the above authors, nor IBM Haifa Research Laboratories, make any 32// representation about the suitability of this software for any 33// purpose. It is provided "as is" without express or implied 34// warranty. 35 36/** 37 * @file list_update_policy.hpp 38 * Contains policies for list update containers. 39 */ 40 41#ifndef PB_DS_LU_POLICY_HPP 42#define PB_DS_LU_POLICY_HPP 43 44#include <bits/c++config.h> 45#include <cstdlib> 46#include <ext/pb_ds/detail/types_traits.hpp> 47#include <ext/pb_ds/detail/list_update_policy/lu_counter_metadata.hpp> 48#include <ext/pb_ds/tag_and_trait.hpp> 49 50namespace __gnu_pbds 51{ 52 /** 53 * A list-update policy that unconditionally moves elements to the 54 * front of the list. A null type means that each link in a 55 * list-based container does not actually need metadata. 56 */ 57 template<typename _Alloc = std::allocator<char> > 58 class lu_move_to_front_policy 59 { 60 public: 61 typedef _Alloc allocator_type; 62 63 /// Metadata on which this functor operates. 64 typedef null_type metadata_type; 65 66 public: 67 /// Reference to metadata on which this functor operates. 68 typedef typename detail::rebind_traits<_Alloc, metadata_type>::reference 69 metadata_reference; 70 71 /// Creates a metadata object. 72 metadata_type 73 operator()() const 74 { return s_metadata; } 75 76 /// Decides whether a metadata object should be moved to the front 77 /// of the list. 78 inline bool 79 operator()(metadata_reference r_metadata) const 80 { return true; } 81 82 private: 83 static null_type s_metadata; 84 }; 85 86 /** 87 * A list-update policy that moves elements to the front of the 88 * list based on the counter algorithm. 89 */ 90 template<std::size_t Max_Count = 5, typename _Alloc = std::allocator<char> > 91 class lu_counter_policy 92 : private detail::lu_counter_policy_base<typename _Alloc::size_type> 93 { 94 public: 95 typedef _Alloc allocator_type; 96 typedef typename allocator_type::size_type size_type; 97 98 enum 99 { 100 /// When some element is accessed this number of times, it 101 /// will be moved to the front of the list. 102 max_count = Max_Count 103 }; 104 105 /// Metadata on which this functor operates. 106 typedef detail::lu_counter_metadata<size_type> metadata_type; 107 108 private: 109 typedef detail::lu_counter_policy_base<size_type> base_type; 110 111 public: 112 /// Reference to metadata on which this functor operates. 113 typedef typename detail::rebind_traits<_Alloc, metadata_type>::reference 114 metadata_reference; 115 116 /// Creates a metadata object. 117 metadata_type 118 operator()() const 119 { return base_type::operator()(max_count); } 120 121 /// Decides whether a metadata object should be moved to the front 122 /// of the list. 123 bool 124 operator()(metadata_reference r_data) const 125 { return base_type::operator()(r_data, max_count); } 126 }; 127} // namespace __gnu_pbds 128 129#endif 130