libstdc++
list_update_policy.hpp
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26 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
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36 
37 /**
38  * @file list_update_policy.hpp
39  * Contains policies for list update containers.
40  */
41 
42 #ifndef PB_DS_LU_POLICY_HPP
43 #define PB_DS_LU_POLICY_HPP
44 
45 #include <bits/c++config.h>
46 #include <cstdlib>
49 
50 namespace __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> >
59  {
60  public:
61  typedef _Alloc allocator_type;
62 
63  /// Metadata on which this functor operates.
65 
66  private:
67  typedef typename _Alloc::template rebind<metadata_type> __rebind_m;
68 
69  public:
70  /// Reference to metadata on which this functor operates.
71  typedef typename __rebind_m::other::reference metadata_reference;
72 
73  /// Creates a metadata object.
75  operator()() const
76  { return s_metadata; }
77 
78  /// Decides whether a metadata object should be moved to the front
79  /// of the list.
80  inline bool
81  operator()(metadata_reference r_metadata) const
82  { return true; }
83 
84  private:
85  static null_type s_metadata;
86  };
87 
88  /**
89  * A list-update policy that moves elements to the front of the
90  * list based on the counter algorithm.
91  */
92  template<std::size_t Max_Count = 5, typename _Alloc = std::allocator<char> >
94  : private detail::lu_counter_policy_base<typename _Alloc::size_type>
95  {
96  public:
97  typedef _Alloc allocator_type;
98  typedef typename allocator_type::size_type size_type;
99 
100  enum
101  {
102  /// When some element is accessed this number of times, it
103  /// will be moved to the front of the list.
104  max_count = Max_Count
105  };
106 
107  /// Metadata on which this functor operates.
109 
110  private:
112  typedef typename _Alloc::template rebind<metadata_type> __rebind_m;
113 
114  public:
115  /// Reference to metadata on which this functor operates.
116  typedef typename __rebind_m::other::reference metadata_reference;
117 
118  /// Creates a metadata object.
120  operator()() const
121  { return base_type::operator()(max_count); }
122 
123  /// Decides whether a metadata object should be moved to the front
124  /// of the list.
125  bool
127  { return base_type::operator()(r_data, max_count); }
128  };
129 } // namespace __gnu_pbds
130 
131 #endif