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