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     1	// -*- C++ -*-
     2	
     3	// Copyright (C) 2005-2021 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	
    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> >
    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