path: root/libstdc++-v3/include/bits/hashtable_policy.h

// Internal policy header for unordered_set and unordered_map -*- C++ -*-

// Copyright (C) 2010, 2011 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library 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 3, or (at your option)
// any later version.

// This library 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file bits/hashtable_policy.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly.
 *  @headername{unordered_map,unordered_set}
 */

#ifndef _HASHTABLE_POLICY_H
#define _HASHTABLE_POLICY_H 1

namespace std _GLIBCXX_VISIBILITY(default)
{
namespace __detail
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // Helper function: return distance(first, last) for forward
  // iterators, or 0 for input iterators.
  template<class _Iterator>
    inline typename std::iterator_traits<_Iterator>::difference_type
    __distance_fw(_Iterator __first, _Iterator __last,
		  std::input_iterator_tag)
    { return 0; }

  template<class _Iterator>
    inline typename std::iterator_traits<_Iterator>::difference_type
    __distance_fw(_Iterator __first, _Iterator __last,
		  std::forward_iterator_tag)
    { return std::distance(__first, __last); }

  template<class _Iterator>
    inline typename std::iterator_traits<_Iterator>::difference_type
    __distance_fw(_Iterator __first, _Iterator __last)
    {
      typedef typename std::iterator_traits<_Iterator>::iterator_category _Tag;
      return __distance_fw(__first, __last, _Tag());
    }

  // Auxiliary types used for all instantiations of _Hashtable: nodes
  // and iterators.

  // Nodes, used to wrap elements stored in the hash table.  A policy
  // template parameter of class template _Hashtable controls whether
  // nodes also store a hash code. In some cases (e.g. strings) this
  // may be a performance win.
  template<typename _Value, bool __cache_hash_code>
    struct _Hash_node;

  template<typename _Value>
    struct _Hash_node<_Value, true>
    {
      _Value       _M_v;
      std::size_t  _M_hash_code;
      _Hash_node*  _M_next;

      template<typename... _Args>
	_Hash_node(_Args&&... __args)
	: _M_v(std::forward<_Args>(__args)...),
	  _M_hash_code(), _M_next() { }
    };

  template<typename _Value>
    struct _Hash_node<_Value, false>
    {
      _Value       _M_v;
      _Hash_node*  _M_next;

      template<typename... _Args>
	_Hash_node(_Args&&... __args)
	: _M_v(std::forward<_Args>(__args)...),
	  _M_next() { }
    };

  // Local iterators, used to iterate within a bucket but not between
  // buckets.
  template<typename _Value, bool __cache>
    struct _Node_iterator_base
    {
      _Node_iterator_base(_Hash_node<_Value, __cache>* __p)
      : _M_cur(__p) { }

      void
      _M_incr()
      { _M_cur = _M_cur->_M_next; }

      _Hash_node<_Value, __cache>*  _M_cur;
    };

  template<typename _Value, bool __cache>
    inline bool
    operator==(const _Node_iterator_base<_Value, __cache>& __x,
	       const _Node_iterator_base<_Value, __cache>& __y)
    { return __x._M_cur == __y._M_cur; }

  template<typename _Value, bool __cache>
    inline bool
    operator!=(const _Node_iterator_base<_Value, __cache>& __x,
	       const _Node_iterator_base<_Value, __cache>& __y)
    { return __x._M_cur != __y._M_cur; }

  template<typename _Value, bool __constant_iterators, bool __cache>
    struct _Node_iterator
    : public _Node_iterator_base<_Value, __cache>
    {
      typedef _Value                                   value_type;
      typedef typename std::conditional<__constant_iterators,
					const _Value*, _Value*>::type
						       pointer;
      typedef typename std::conditional<__constant_iterators,
					const _Value&, _Value&>::type
						       reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      _Node_iterator()
      : _Node_iterator_base<_Value, __cache>(0) { }

      explicit
      _Node_iterator(_Hash_node<_Value, __cache>* __p)
      : _Node_iterator_base<_Value, __cache>(__p) { }

      reference
      operator*() const
      { return this->_M_cur->_M_v; }

      pointer
      operator->() const
      { return std::__addressof(this->_M_cur->_M_v); }

      _Node_iterator&
      operator++()
      {
	this->_M_incr();
	return *this;
      }

      _Node_iterator
      operator++(int)
      {
	_Node_iterator __tmp(*this);
	this->_M_incr();
	return __tmp;
      }
    };

  template<typename _Value, bool __constant_iterators, bool __cache>
    struct _Node_const_iterator
    : public _Node_iterator_base<_Value, __cache>
    {
      typedef _Value                                   value_type;
      typedef const _Value*                            pointer;
      typedef const _Value&                            reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      _Node_const_iterator()
      : _Node_iterator_base<_Value, __cache>(0) { }

      explicit
      _Node_const_iterator(_Hash_node<_Value, __cache>* __p)
      : _Node_iterator_base<_Value, __cache>(__p) { }

      _Node_const_iterator(const _Node_iterator<_Value, __constant_iterators,
			   __cache>& __x)
      : _Node_iterator_base<_Value, __cache>(__x._M_cur) { }

      reference
      operator*() const
      { return this->_M_cur->_M_v; }

      pointer
      operator->() const
      { return std::__addressof(this->_M_cur->_M_v); }

      _Node_const_iterator&
      operator++()
      {
	this->_M_incr();
	return *this;
      }

      _Node_const_iterator
      operator++(int)
      {
	_Node_const_iterator __tmp(*this);
	this->_M_incr();
	return __tmp;
      }
    };

  template<typename _Value, bool __cache>
    struct _Hashtable_iterator_base
    {
      _Hashtable_iterator_base(_Hash_node<_Value, __cache>* __node,
			       _Hash_node<_Value, __cache>** __bucket)
      : _M_cur_node(__node), _M_cur_bucket(__bucket) { }

      void
      _M_incr()
      {
	_M_cur_node = _M_cur_node->_M_next;
	if (!_M_cur_node)
	  _M_incr_bucket();
      }

      void
      _M_incr_bucket();

      _Hash_node<_Value, __cache>*   _M_cur_node;
      _Hash_node<_Value, __cache>**  _M_cur_bucket;
    };

  // Global iterators, used for arbitrary iteration within a hash
  // table.  Larger and more expensive than local iterators.
  template<typename _Value, bool __cache>
    void
    _Hashtable_iterator_base<_Value, __cache>::
    _M_incr_bucket()
    {
      ++_M_cur_bucket;

      // This loop requires the bucket array to have a non-null sentinel.
      while (!*_M_cur_bucket)
	++_M_cur_bucket;
      _M_cur_node = *_M_cur_bucket;
    }

  template<typename _Value, bool __cache>
    inline bool
    operator==(const _Hashtable_iterator_base<_Value, __cache>& __x,
	       const _Hashtable_iterator_base<_Value, __cache>& __y)
    { return __x._M_cur_node == __y._M_cur_node; }

  template<typename _Value, bool __cache>
    inline bool
    operator!=(const _Hashtable_iterator_base<_Value, __cache>& __x,
	       const _Hashtable_iterator_base<_Value, __cache>& __y)
    { return __x._M_cur_node != __y._M_cur_node; }

  template<typename _Value, bool __constant_iterators, bool __cache>
    struct _Hashtable_iterator
    : public _Hashtable_iterator_base<_Value, __cache>
    {
      typedef _Value                                   value_type;
      typedef typename std::conditional<__constant_iterators,
					const _Value*, _Value*>::type
						       pointer;
      typedef typename std::conditional<__constant_iterators,
					const _Value&, _Value&>::type
						       reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      _Hashtable_iterator()
      : _Hashtable_iterator_base<_Value, __cache>(0, 0) { }

      _Hashtable_iterator(_Hash_node<_Value, __cache>* __p,
			  _Hash_node<_Value, __cache>** __b)
      : _Hashtable_iterator_base<_Value, __cache>(__p, __b) { }

      explicit
      _Hashtable_iterator(_Hash_node<_Value, __cache>** __b)
      : _Hashtable_iterator_base<_Value, __cache>(*__b, __b) { }

      reference
      operator*() const
      { return this->_M_cur_node->_M_v; }

      pointer
      operator->() const
      { return std::__addressof(this->_M_cur_node->_M_v); }

      _Hashtable_iterator&
      operator++()
      {
	this->_M_incr();
	return *this;
      }

      _Hashtable_iterator
      operator++(int)
      {
	_Hashtable_iterator __tmp(*this);
	this->_M_incr();
	return __tmp;
      }
    };

  template<typename _Value, bool __constant_iterators, bool __cache>
    struct _Hashtable_const_iterator
    : public _Hashtable_iterator_base<_Value, __cache>
    {
      typedef _Value                                   value_type;
      typedef const _Value*                            pointer;
      typedef const _Value&                            reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      _Hashtable_const_iterator()
      : _Hashtable_iterator_base<_Value, __cache>(0, 0) { }

      _Hashtable_const_iterator(_Hash_node<_Value, __cache>* __p,
				_Hash_node<_Value, __cache>** __b)
      : _Hashtable_iterator_base<_Value, __cache>(__p, __b) { }

      explicit
      _Hashtable_const_iterator(_Hash_node<_Value, __cache>** __b)
      : _Hashtable_iterator_base<_Value, __cache>(*__b, __b) { }

      _Hashtable_const_iterator(const _Hashtable_iterator<_Value,
				__constant_iterators, __cache>& __x)
      : _Hashtable_iterator_base<_Value, __cache>(__x._M_cur_node,
						  __x._M_cur_bucket) { }

      reference
      operator*() const
      { return this->_M_cur_node->_M_v; }

      pointer
      operator->() const
      { return std::__addressof(this->_M_cur_node->_M_v); }

      _Hashtable_const_iterator&
      operator++()
      {
	this->_M_incr();
	return *this;
      }

      _Hashtable_const_iterator
      operator++(int)
      {
	_Hashtable_const_iterator __tmp(*this);
	this->_M_incr();
	return __tmp;
      }
    };


  // Many of class template _Hashtable's template parameters are policy
  // classes.  These are defaults for the policies.

  // Default range hashing function: use division to fold a large number
  // into the range [0, N).
  struct _Mod_range_hashing
  {
    typedef std::size_t first_argument_type;
    typedef std::size_t second_argument_type;
    typedef std::size_t result_type;

    result_type
    operator()(first_argument_type __num, second_argument_type __den) const
    { return __num % __den; }
  };

  // Default ranged hash function H.  In principle it should be a
  // function object composed from objects of type H1 and H2 such that
  // h(k, N) = h2(h1(k), N), but that would mean making extra copies of
  // h1 and h2.  So instead we'll just use a tag to tell class template
  // hashtable to do that composition.
  struct _Default_ranged_hash { };

  // Default value for rehash policy.  Bucket size is (usually) the
  // smallest prime that keeps the load factor small enough.
  struct _Prime_rehash_policy
  {
    _Prime_rehash_policy(float __z = 1.0)
    : _M_max_load_factor(__z), _M_growth_factor(2.f), _M_next_resize(0) { }

    float
    max_load_factor() const
    { return _M_max_load_factor; }

    // Return a bucket size no smaller than n.
    std::size_t
    _M_next_bkt(std::size_t __n) const;

    // Return a bucket count appropriate for n elements
    std::size_t
    _M_bkt_for_elements(std::size_t __n) const;

    // __n_bkt is current bucket count, __n_elt is current element count,
    // and __n_ins is number of elements to be inserted.  Do we need to
    // increase bucket count?  If so, return make_pair(true, n), where n
    // is the new bucket count.  If not, return make_pair(false, 0).
    std::pair<bool, std::size_t>
    _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
		   std::size_t __n_ins) const;

    enum { _S_n_primes = sizeof(unsigned long) != 8 ? 256 : 256 + 48 };

    float                _M_max_load_factor;
    float                _M_growth_factor;
    mutable std::size_t  _M_next_resize;
  };

  extern const unsigned long __prime_list[];

  // XXX This is a hack.  There's no good reason for any of
  // _Prime_rehash_policy's member functions to be inline.

  // Return a prime no smaller than n.
  inline std::size_t
  _Prime_rehash_policy::
  _M_next_bkt(std::size_t __n) const
  {
    const unsigned long* __p = std::lower_bound(__prime_list, __prime_list
						+ _S_n_primes, __n);
    _M_next_resize =
      static_cast<std::size_t>(__builtin_ceil(*__p * _M_max_load_factor));
    return *__p;
  }

  // Return the smallest prime p such that alpha p >= n, where alpha
  // is the load factor.
  inline std::size_t
  _Prime_rehash_policy::
  _M_bkt_for_elements(std::size_t __n) const
  {
    const float __min_bkts = __n / _M_max_load_factor;
    const unsigned long* __p = std::lower_bound(__prime_list, __prime_list
						+ _S_n_primes, __min_bkts);
    _M_next_resize =
      static_cast<std::size_t>(__builtin_ceil(*__p * _M_max_load_factor));
    return *__p;
  }

  // Finds the smallest prime p such that alpha p > __n_elt + __n_ins.
  // If p > __n_bkt, return make_pair(true, p); otherwise return
  // make_pair(false, 0).  In principle this isn't very different from
  // _M_bkt_for_elements.

  // The only tricky part is that we're caching the element count at
  // which we need to rehash, so we don't have to do a floating-point
  // multiply for every insertion.

  inline std::pair<bool, std::size_t>
  _Prime_rehash_policy::
  _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
		 std::size_t __n_ins) const
  {
    if (__n_elt + __n_ins > _M_next_resize)
      {
	float __min_bkts = ((float(__n_ins) + float(__n_elt))
			    / _M_max_load_factor);
	if (__min_bkts > __n_bkt)
	  {
	    __min_bkts = std::max(__min_bkts, _M_growth_factor * __n_bkt);
	    const unsigned long* __p =
	      std::lower_bound(__prime_list, __prime_list + _S_n_primes,
			       __min_bkts);
	    _M_next_resize = static_cast<std::size_t>
	      (__builtin_ceil(*__p * _M_max_load_factor));
	    return std::make_pair(true, *__p);
	  }
	else
	  {
	    _M_next_resize = static_cast<std::size_t>
	      (__builtin_ceil(__n_bkt * _M_max_load_factor));
	    return std::make_pair(false, 0);
	  }
      }
    else
      return std::make_pair(false, 0);
  }

  // Base classes for std::_Hashtable.  We define these base classes
  // because in some cases we want to do different things depending
  // on the value of a policy class.  In some cases the policy class
  // affects which member functions and nested typedefs are defined;
  // we handle that by specializing base class templates.  Several of
  // the base class templates need to access other members of class
  // template _Hashtable, so we use the "curiously recurring template
  // pattern" for them.

  // class template _Map_base.  If the hashtable has a value type of
  // the form pair<T1, T2> and a key extraction policy that returns the
  // first part of the pair, the hashtable gets a mapped_type typedef.
  // If it satisfies those criteria and also has unique keys, then it
  // also gets an operator[].
  template<typename _Key, typename _Value, typename _Ex, bool __unique,
	   typename _Hashtable>
    struct _Map_base { };

  template<typename _Key, typename _Pair, typename _Hashtable>
    struct _Map_base<_Key, _Pair, std::_Select1st<_Pair>, false, _Hashtable>
    {
      typedef typename _Pair::second_type mapped_type;
    };

  template<typename _Key, typename _Pair, typename _Hashtable>
    struct _Map_base<_Key, _Pair, std::_Select1st<_Pair>, true, _Hashtable>
    {
      typedef typename _Pair::second_type mapped_type;

      mapped_type&
      operator[](const _Key& __k);

      mapped_type&
      operator[](_Key&& __k);

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // DR 761. unordered_map needs an at() member function.
      mapped_type&
      at(const _Key& __k);

      const mapped_type&
      at(const _Key& __k) const;
    };

  template<typename _Key, typename _Pair, typename _Hashtable>
    typename _Map_base<_Key, _Pair, std::_Select1st<_Pair>,
		       true, _Hashtable>::mapped_type&
    _Map_base<_Key, _Pair, std::_Select1st<_Pair>, true, _Hashtable>::
    operator[](const _Key& __k)
    {
      _Hashtable* __h = static_cast<_Hashtable*>(this);
      typename _Hashtable::_Hash_code_type __code = __h->_M_hash_code(__k);
      std::size_t __n = __h->_M_bucket_index(__k, __code,
					     __h->_M_bucket_count);

      typename _Hashtable::_Node* __p =
	__h->_M_find_node(__h->_M_buckets[__n], __k, __code);
      if (!__p)
	return __h->_M_insert_bucket(std::make_pair(__k, mapped_type()),
				     __n, __code)->second;
      return (__p->_M_v).second;
    }

  template<typename _Key, typename _Pair, typename _Hashtable>
    typename _Map_base<_Key, _Pair, std::_Select1st<_Pair>,
		       true, _Hashtable>::mapped_type&
    _Map_base<_Key, _Pair, std::_Select1st<_Pair>, true, _Hashtable>::
    operator[](_Key&& __k)
    {
      _Hashtable* __h = static_cast<_Hashtable*>(this);
      typename _Hashtable::_Hash_code_type __code = __h->_M_hash_code(__k);
      std::size_t __n = __h->_M_bucket_index(__k, __code,
					     __h->_M_bucket_count);

      typename _Hashtable::_Node* __p =
	__h->_M_find_node(__h->_M_buckets[__n], __k, __code);
      if (!__p)
	return __h->_M_insert_bucket(std::make_pair(std::move(__k),
						    mapped_type()),
				     __n, __code)->second;
      return (__p->_M_v).second;
    }

  template<typename _Key, typename _Pair, typename _Hashtable>
    typename _Map_base<_Key, _Pair, std::_Select1st<_Pair>,
		       true, _Hashtable>::mapped_type&
    _Map_base<_Key, _Pair, std::_Select1st<_Pair>, true, _Hashtable>::
    at(const _Key& __k)
    {
      _Hashtable* __h = static_cast<_Hashtable*>(this);
      typename _Hashtable::_Hash_code_type __code = __h->_M_hash_code(__k);
      std::size_t __n = __h->_M_bucket_index(__k, __code,
					     __h->_M_bucket_count);

      typename _Hashtable::_Node* __p =
	__h->_M_find_node(__h->_M_buckets[__n], __k, __code);
      if (!__p)
	__throw_out_of_range(__N("_Map_base::at"));
      return (__p->_M_v).second;
    }

  template<typename _Key, typename _Pair, typename _Hashtable>
    const typename _Map_base<_Key, _Pair, std::_Select1st<_Pair>,
			     true, _Hashtable>::mapped_type&
    _Map_base<_Key, _Pair, std::_Select1st<_Pair>, true, _Hashtable>::
    at(const _Key& __k) const
    {
      const _Hashtable* __h = static_cast<const _Hashtable*>(this);
      typename _Hashtable::_Hash_code_type __code = __h->_M_hash_code(__k);
      std::size_t __n = __h->_M_bucket_index(__k, __code,
					     __h->_M_bucket_count);

      typename _Hashtable::_Node* __p =
	__h->_M_find_node(__h->_M_buckets[__n], __k, __code);
      if (!__p)
	__throw_out_of_range(__N("_Map_base::at"));
      return (__p->_M_v).second;
    }

  // class template _Rehash_base.  Give hashtable the max_load_factor
  // functions and reserve iff the rehash policy is _Prime_rehash_policy.
  template<typename _RehashPolicy, typename _Hashtable>
    struct _Rehash_base { };

  template<typename _Hashtable>
    struct _Rehash_base<_Prime_rehash_policy, _Hashtable>
    {
      float
      max_load_factor() const
      {
	const _Hashtable* __this = static_cast<const _Hashtable*>(this);
	return __this->__rehash_policy().max_load_factor();
      }

      void
      max_load_factor(float __z)
      {
	_Hashtable* __this = static_cast<_Hashtable*>(this);
	__this->__rehash_policy(_Prime_rehash_policy(__z));
      }

      void
      reserve(std::size_t __n)
      {
	_Hashtable* __this = static_cast<_Hashtable*>(this);
	__this->rehash(__builtin_ceil(__n / max_load_factor()));
      }
    };

  // Class template _Hash_code_base.  Encapsulates two policy issues that
  // aren't quite orthogonal.
  //   (1) the difference between using a ranged hash function and using
  //       the combination of a hash function and a range-hashing function.
  //       In the former case we don't have such things as hash codes, so
  //       we have a dummy type as placeholder.
  //   (2) Whether or not we cache hash codes.  Caching hash codes is
  //       meaningless if we have a ranged hash function.
  // We also put the key extraction and equality comparison function
  // objects here, for convenience.

  // Primary template: unused except as a hook for specializations.
  template<typename _Key, typename _Value,
	   typename _ExtractKey, typename _Equal,
	   typename _H1, typename _H2, typename _Hash,
	   bool __cache_hash_code>
    struct _Hash_code_base;

  // Specialization: ranged hash function, no caching hash codes.  H1
  // and H2 are provided but ignored.  We define a dummy hash code type.
  template<typename _Key, typename _Value,
	   typename _ExtractKey, typename _Equal,
	   typename _H1, typename _H2, typename _Hash>
    struct _Hash_code_base<_Key, _Value, _ExtractKey, _Equal, _H1, _H2,
			   _Hash, false>
    {
    protected:
      _Hash_code_base(const _ExtractKey& __ex, const _Equal& __eq,
		      const _H1&, const _H2&, const _Hash& __h)
      : _M_extract(__ex), _M_eq(__eq), _M_ranged_hash(__h) { }

      typedef void* _Hash_code_type;

      _Hash_code_type
      _M_hash_code(const _Key& __key) const
      { return 0; }

      std::size_t
      _M_bucket_index(const _Key& __k, _Hash_code_type,
		      std::size_t __n) const
      { return _M_ranged_hash(__k, __n); }

      std::size_t
      _M_bucket_index(const _Hash_node<_Value, false>* __p,
		      std::size_t __n) const
      { return _M_ranged_hash(_M_extract(__p->_M_v), __n); }

      bool
      _M_compare(const _Key& __k, _Hash_code_type,
		 _Hash_node<_Value, false>* __n) const
      { return _M_eq(__k, _M_extract(__n->_M_v)); }

      void
      _M_store_code(_Hash_node<_Value, false>*, _Hash_code_type) const
      { }

      void
      _M_copy_code(_Hash_node<_Value, false>*,
		   const _Hash_node<_Value, false>*) const
      { }

      void
      _M_swap(_Hash_code_base& __x)
      {
	std::swap(_M_extract, __x._M_extract);
	std::swap(_M_eq, __x._M_eq);
	std::swap(_M_ranged_hash, __x._M_ranged_hash);
      }

    protected:
      _ExtractKey  _M_extract;
      _Equal       _M_eq;
      _Hash        _M_ranged_hash;
    };


  // No specialization for ranged hash function while caching hash codes.
  // That combination is meaningless, and trying to do it is an error.


  // Specialization: ranged hash function, cache hash codes.  This
  // combination is meaningless, so we provide only a declaration
  // and no definition.
  template<typename _Key, typename _Value,
	   typename _ExtractKey, typename _Equal,
	   typename _H1, typename _H2, typename _Hash>
    struct _Hash_code_base<_Key, _Value, _ExtractKey, _Equal, _H1, _H2,
			   _Hash, true>;

  // Specialization: hash function and range-hashing function, no
  // caching of hash codes.  H is provided but ignored.  Provides
  // typedef and accessor required by TR1.
  template<typename _Key, typename _Value,
	   typename _ExtractKey, typename _Equal,
	   typename _H1, typename _H2>
    struct _Hash_code_base<_Key, _Value, _ExtractKey, _Equal, _H1, _H2,
			   _Default_ranged_hash, false>
    {
      typedef _H1 hasher;

      hasher
      hash_function() const
      { return _M_h1; }

    protected:
      _Hash_code_base(const _ExtractKey& __ex, const _Equal& __eq,
		      const _H1& __h1, const _H2& __h2,
		      const _Default_ranged_hash&)
      : _M_extract(__ex), _M_eq(__eq), _M_h1(__h1), _M_h2(__h2) { }

      typedef std::size_t _Hash_code_type;

      _Hash_code_type
      _M_hash_code(const _Key& __k) const
      { return _M_h1(__k); }

      std::size_t
      _M_bucket_index(const _Key&, _Hash_code_type __c,
		      std::size_t __n) const
      { return _M_h2(__c, __n); }

      std::size_t
      _M_bucket_index(const _Hash_node<_Value, false>* __p,
		      std::size_t __n) const
      { return _M_h2(_M_h1(_M_extract(__p->_M_v)), __n); }

      bool
      _M_compare(const _Key& __k, _Hash_code_type,
		 _Hash_node<_Value, false>* __n) const
      { return _M_eq(__k, _M_extract(__n->_M_v)); }

      void
      _M_store_code(_Hash_node<_Value, false>*, _Hash_code_type) const
      { }

      void
      _M_copy_code(_Hash_node<_Value, false>*,
		   const _Hash_node<_Value, false>*) const
      { }

      void
      _M_swap(_Hash_code_base& __x)
      {
	std::swap(_M_extract, __x._M_extract);
	std::swap(_M_eq, __x._M_eq);
	std::swap(_M_h1, __x._M_h1);
	std::swap(_M_h2, __x._M_h2);
      }

    protected:
      _ExtractKey  _M_extract;
      _Equal       _M_eq;
      _H1          _M_h1;
      _H2          _M_h2;
    };

  // Specialization: hash function and range-hashing function,
  // caching hash codes.  H is provided but ignored.  Provides
  // typedef and accessor required by TR1.
  template<typename _Key, typename _Value,
	   typename _ExtractKey, typename _Equal,
	   typename _H1, typename _H2>
    struct _Hash_code_base<_Key, _Value, _ExtractKey, _Equal, _H1, _H2,
			   _Default_ranged_hash, true>
    {
      typedef _H1 hasher;

      hasher
      hash_function() const
      { return _M_h1; }

    protected:
      _Hash_code_base(const _ExtractKey& __ex, const _Equal& __eq,
		      const _H1& __h1, const _H2& __h2,
		      const _Default_ranged_hash&)
      : _M_extract(__ex), _M_eq(__eq), _M_h1(__h1), _M_h2(__h2) { }

      typedef std::size_t _Hash_code_type;

      _Hash_code_type
      _M_hash_code(const _Key& __k) const
      { return _M_h1(__k); }

      std::size_t
      _M_bucket_index(const _Key&, _Hash_code_type __c,
		      std::size_t __n) const
      { return _M_h2(__c, __n); }

      std::size_t
      _M_bucket_index(const _Hash_node<_Value, true>* __p,
		      std::size_t __n) const
      { return _M_h2(__p->_M_hash_code, __n); }

      bool
      _M_compare(const _Key& __k, _Hash_code_type __c,
		 _Hash_node<_Value, true>* __n) const
      { return __c == __n->_M_hash_code && _M_eq(__k, _M_extract(__n->_M_v)); }

      void
      _M_store_code(_Hash_node<_Value, true>* __n, _Hash_code_type __c) const
      { __n->_M_hash_code = __c; }

      void
      _M_copy_code(_Hash_node<_Value, true>* __to,
		   const _Hash_node<_Value, true>* __from) const
      { __to->_M_hash_code = __from->_M_hash_code; }

      void
      _M_swap(_Hash_code_base& __x)
      {
	std::swap(_M_extract, __x._M_extract);
	std::swap(_M_eq, __x._M_eq);
	std::swap(_M_h1, __x._M_h1);
	std::swap(_M_h2, __x._M_h2);
      }

    protected:
      _ExtractKey  _M_extract;
      _Equal       _M_eq;
      _H1          _M_h1;
      _H2          _M_h2;
    };


  // Class template _Equality_base.  This is for implementing equality
  // comparison for unordered containers, per N3068, by John Lakos and
  // Pablo Halpern.  Algorithmically, we follow closely the reference
  // implementations therein.
  template<typename _ExtractKey, bool __unique_keys,
	   typename _Hashtable>
    struct _Equality_base;

  template<typename _ExtractKey, typename _Hashtable>
    struct _Equality_base<_ExtractKey, true, _Hashtable>
    {
      bool _M_equal(const _Hashtable&) const;
    };

  template<typename _ExtractKey, typename _Hashtable>
    bool
    _Equality_base<_ExtractKey, true, _Hashtable>::
    _M_equal(const _Hashtable& __other) const
    {
      const _Hashtable* __this = static_cast<const _Hashtable*>(this);

      if (__this->size() != __other.size())
	return false;

      for (auto __itx = __this->begin(); __itx != __this->end(); ++__itx)
	{
	  const auto __ity = __other.find(_ExtractKey()(*__itx));
	  if (__ity == __other.end() || !bool(*__ity == *__itx))
	    return false;
	}
      return true;
    }

  template<typename _ExtractKey, typename _Hashtable>
    struct _Equality_base<_ExtractKey, false, _Hashtable>
    {
      bool _M_equal(const _Hashtable&) const;

    private:
      template<typename _Uiterator>
	static bool
	_S_is_permutation(_Uiterator, _Uiterator, _Uiterator);
    };

  // See std::is_permutation in N3068.
  template<typename _ExtractKey, typename _Hashtable>
    template<typename _Uiterator>
      bool
      _Equality_base<_ExtractKey, false, _Hashtable>::
      _S_is_permutation(_Uiterator __first1, _Uiterator __last1,
			_Uiterator __first2)
      {
	for (; __first1 != __last1; ++__first1, ++__first2)
	  if (!(*__first1 == *__first2))
	    break;

	if (__first1 == __last1)
	  return true;

	_Uiterator __last2 = __first2;
	std::advance(__last2, std::distance(__first1, __last1));

	for (_Uiterator __it1 = __first1; __it1 != __last1; ++__it1)
	  {
	    _Uiterator __tmp =  __first1;
	    while (__tmp != __it1 && !bool(*__tmp == *__it1))
	      ++__tmp;

	    // We've seen this one before.
	    if (__tmp != __it1)
	      continue;

	    std::ptrdiff_t __n2 = 0;
	    for (__tmp = __first2; __tmp != __last2; ++__tmp)
	      if (*__tmp == *__it1)
		++__n2;

	    if (!__n2)
	      return false;

	    std::ptrdiff_t __n1 = 0;
	    for (__tmp = __it1; __tmp != __last1; ++__tmp)
	      if (*__tmp == *__it1)
		++__n1;

	    if (__n1 != __n2)
	      return false;
	  }
	return true;
      }

  template<typename _ExtractKey, typename _Hashtable>
    bool
    _Equality_base<_ExtractKey, false, _Hashtable>::
    _M_equal(const _Hashtable& __other) const
    {
      const _Hashtable* __this = static_cast<const _Hashtable*>(this);

      if (__this->size() != __other.size())
	return false;

      for (auto __itx = __this->begin(); __itx != __this->end();)
	{
	  const auto __xrange = __this->equal_range(_ExtractKey()(*__itx));
	  const auto __yrange = __other.equal_range(_ExtractKey()(*__itx));

	  if (std::distance(__xrange.first, __xrange.second)
	      != std::distance(__yrange.first, __yrange.second))
	    return false;

	  if (!_S_is_permutation(__xrange.first,
				 __xrange.second,
				 __yrange.first))
	    return false;

	  __itx = __xrange.second;
	}
      return true;
    }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace __detail
} // namespace std

#endif // _HASHTABLE_POLICY_H