libstdc++-v3/include/bits/hashtable_policy.h

   1 // Internal policy header for unordered_set and unordered_map -*- C++ -*-
   2
   3 // Copyright (C) 2010-2014 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
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU 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 /** @file bits/hashtable_policy.h
  26  *  This is an internal header file, included by other library headers.
  27  *  Do not attempt to use it directly.
  28  *  @headername{unordered_map,unordered_set}
  29  */
  30
  31 #ifndef _HASHTABLE_POLICY_H
  32 #define _HASHTABLE_POLICY_H 1
  33
  34 namespace std _GLIBCXX_VISIBILITY(default)
  35 {
  36 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  37
  38   template<typename _Key, typename _Value, typename _Alloc,
  39            typename _ExtractKey, typename _Equal,
  40            typename _H1, typename _H2, typename _Hash,
  41            typename _RehashPolicy, typename _Traits>
  42     class _Hashtable;
  43
  44 _GLIBCXX_END_NAMESPACE_VERSION
  45
  46 namespace __detail
  47 {
  48 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  49
  50   /**
  51    *  @defgroup hashtable-detail Base and Implementation Classes
  52    *  @ingroup unordered_associative_containers
  53    *  @{
  54    */
  55   template<typename _Key, typename _Value,
  56            typename _ExtractKey, typename _Equal,
  57            typename _H1, typename _H2, typename _Hash, typename _Traits>
  58     struct _Hashtable_base;
  59
  60   // Helper function: return distance(first, last) for forward
  61   // iterators, or 0 for input iterators.
  62   template<class _Iterator>
  63     inline typename std::iterator_traits<_Iterator>::difference_type
  64     __distance_fw(_Iterator __first, _Iterator __last,
  65                   std::input_iterator_tag)
  66     { return 0; }
  67
  68   template<class _Iterator>
  69     inline typename std::iterator_traits<_Iterator>::difference_type
  70     __distance_fw(_Iterator __first, _Iterator __last,
  71                   std::forward_iterator_tag)
  72     { return std::distance(__first, __last); }
  73
  74   template<class _Iterator>
  75     inline typename std::iterator_traits<_Iterator>::difference_type
  76     __distance_fw(_Iterator __first, _Iterator __last)
  77     {
  78       typedef typename std::iterator_traits<_Iterator>::iterator_category _Tag;
  79       return __distance_fw(__first, __last, _Tag());
  80     }
  81
  82   // Helper type used to detect whether the hash functor is noexcept.
  83   template <typename _Key, typename _Hash>
  84     struct __is_noexcept_hash : std::integral_constant<bool,
  85         noexcept(declval<const _Hash&>()(declval<const _Key&>()))>
  86     { };
  87
  88   struct _Identity
  89   {
  90     template<typename _Tp>
  91       _Tp&&
  92       operator()(_Tp&& __x) const
  93       { return std::forward<_Tp>(__x); }
  94   };
  95
  96   struct _Select1st
  97   {
  98     template<typename _Tp>
  99       auto
 100       operator()(_Tp&& __x) const
 101       -> decltype(std::get<0>(std::forward<_Tp>(__x)))
 102       { return std::get<0>(std::forward<_Tp>(__x)); }
 103   };
 104
 105   template<typename _NodeAlloc>
 106     struct _Hashtable_alloc;
 107
 108   // Functor recycling a pool of nodes and using allocation once the pool is
 109   // empty.
 110   template<typename _NodeAlloc>
 111     struct _ReuseOrAllocNode
 112     {
 113     private:
 114       using __node_alloc_type = _NodeAlloc;
 115       using __hashtable_alloc = _Hashtable_alloc<__node_alloc_type>;
 116       using __value_alloc_type = typename __hashtable_alloc::__value_alloc_type;
 117       using __value_alloc_traits =
 118         typename __hashtable_alloc::__value_alloc_traits;
 119       using __node_alloc_traits =
 120         typename __hashtable_alloc::__node_alloc_traits;
 121       using __node_type = typename __hashtable_alloc::__node_type;
 122
 123     public:
 124       _ReuseOrAllocNode(__node_type* __nodes, __hashtable_alloc& __h)
 125         : _M_nodes(__nodes), _M_h(__h) { }
 126       _ReuseOrAllocNode(const _ReuseOrAllocNode&) = delete;
 127
 128       ~_ReuseOrAllocNode()
 129       { _M_h._M_deallocate_nodes(_M_nodes); }
 130
 131       template<typename _Arg>
 132         __node_type*
 133         operator()(_Arg&& __arg) const
 134         {
 135           if (_M_nodes)
 136             {
 137               __node_type* __node = _M_nodes;
 138               _M_nodes = _M_nodes->_M_next();
 139               __node->_M_nxt = nullptr;
 140               __value_alloc_type __a(_M_h._M_node_allocator());
 141               __value_alloc_traits::destroy(__a, __node->_M_valptr());
 142               __try
 143                 {
 144                   __value_alloc_traits::construct(__a, __node->_M_valptr(),
 145                                                   std::forward<_Arg>(__arg));
 146                 }
 147               __catch(...)
 148                 {
 149                   __node->~__node_type();
 150                   __node_alloc_traits::deallocate(_M_h._M_node_allocator(),
 151                                                   __node, 1);
 152                   __throw_exception_again;
 153                 }
 154               return __node;
 155             }
 156           return _M_h._M_allocate_node(std::forward<_Arg>(__arg));
 157         }
 158
 159     private:
 160       mutable __node_type* _M_nodes;
 161       __hashtable_alloc& _M_h;
 162     };
 163
 164   // Functor similar to the previous one but without any pool of nodes to
 165   // recycle.
 166   template<typename _NodeAlloc>
 167     struct _AllocNode
 168     {
 169     private:
 170       using __hashtable_alloc = _Hashtable_alloc<_NodeAlloc>;
 171       using __node_type = typename __hashtable_alloc::__node_type;
 172
 173     public:
 174       _AllocNode(__hashtable_alloc& __h)
 175         : _M_h(__h) { }
 176
 177       template<typename _Arg>
 178         __node_type*
 179         operator()(_Arg&& __arg) const
 180         { return _M_h._M_allocate_node(std::forward<_Arg>(__arg)); }
 181
 182     private:
 183       __hashtable_alloc& _M_h;
 184     };
 185
 186   // Auxiliary types used for all instantiations of _Hashtable nodes
 187   // and iterators.
 188
 189   /**
 190    *  struct _Hashtable_traits
 191    *
 192    *  Important traits for hash tables.
 193    *
 194    *  @tparam _Cache_hash_code  Boolean value. True if the value of
 195    *  the hash function is stored along with the value. This is a
 196    *  time-space tradeoff.  Storing it may improve lookup speed by
 197    *  reducing the number of times we need to call the _Equal
 198    *  function.
 199    *
 200    *  @tparam _Constant_iterators  Boolean value. True if iterator and
 201    *  const_iterator are both constant iterator types. This is true
 202    *  for unordered_set and unordered_multiset, false for
 203    *  unordered_map and unordered_multimap.
 204    *
 205    *  @tparam _Unique_keys  Boolean value. True if the return value
 206    *  of _Hashtable::count(k) is always at most one, false if it may
 207    *  be an arbitrary number. This is true for unordered_set and
 208    *  unordered_map, false for unordered_multiset and
 209    *  unordered_multimap.
 210    */
 211   template<bool _Cache_hash_code, bool _Constant_iterators, bool _Unique_keys>
 212     struct _Hashtable_traits
 213     {
 214       template<bool _Cond>
 215         using __bool_constant = integral_constant<bool, _Cond>;
 216
 217       using __hash_cached = __bool_constant<_Cache_hash_code>;
 218       using __constant_iterators = __bool_constant<_Constant_iterators>;
 219       using __unique_keys = __bool_constant<_Unique_keys>;
 220     };
 221
 222   /**
 223    *  struct _Hash_node_base
 224    *
 225    *  Nodes, used to wrap elements stored in the hash table.  A policy
 226    *  template parameter of class template _Hashtable controls whether
 227    *  nodes also store a hash code. In some cases (e.g. strings) this
 228    *  may be a performance win.
 229    */
 230   struct _Hash_node_base
 231   {
 232     _Hash_node_base* _M_nxt;
 233
 234     _Hash_node_base() noexcept : _M_nxt() { }
 235
 236     _Hash_node_base(_Hash_node_base* __next) noexcept : _M_nxt(__next) { }
 237   };
 238
 239   /**
 240    *  struct _Hash_node_value_base
 241    *
 242    *  Node type with the value to store.
 243    */
 244   template<typename _Value>
 245     struct _Hash_node_value_base : _Hash_node_base
 246     {
 247       typedef _Value value_type;
 248
 249       __gnu_cxx::__aligned_buffer<_Value> _M_storage;
 250
 251       _Value*
 252       _M_valptr() noexcept
 253       { return _M_storage._M_ptr(); }
 254
 255       const _Value*
 256       _M_valptr() const noexcept
 257       { return _M_storage._M_ptr(); }
 258
 259       _Value&
 260       _M_v() noexcept
 261       { return *_M_valptr(); }
 262
 263       const _Value&
 264       _M_v() const noexcept
 265       { return *_M_valptr(); }
 266     };
 267
 268   /**
 269    *  Primary template struct _Hash_node.
 270    */
 271   template<typename _Value, bool _Cache_hash_code>
 272     struct _Hash_node;
 273
 274   /**
 275    *  Specialization for nodes with caches, struct _Hash_node.
 276    *
 277    *  Base class is __detail::_Hash_node_value_base.
 278    */
 279   template<typename _Value>
 280     struct _Hash_node<_Value, true> : _Hash_node_value_base<_Value>
 281     {
 282       std::size_t  _M_hash_code;
 283
 284       _Hash_node*
 285       _M_next() const noexcept
 286       { return static_cast<_Hash_node*>(this->_M_nxt); }
 287     };
 288
 289   /**
 290    *  Specialization for nodes without caches, struct _Hash_node.
 291    *
 292    *  Base class is __detail::_Hash_node_value_base.
 293    */
 294   template<typename _Value>
 295     struct _Hash_node<_Value, false> : _Hash_node_value_base<_Value>
 296     {
 297       _Hash_node*
 298       _M_next() const noexcept
 299       { return static_cast<_Hash_node*>(this->_M_nxt); }
 300     };
 301
 302   /// Base class for node iterators.
 303   template<typename _Value, bool _Cache_hash_code>
 304     struct _Node_iterator_base
 305     {
 306       using __node_type = _Hash_node<_Value, _Cache_hash_code>;
 307
 308       __node_type*  _M_cur;
 309
 310       _Node_iterator_base(__node_type* __p) noexcept
 311       : _M_cur(__p) { }
 312
 313       void
 314       _M_incr() noexcept
 315       { _M_cur = _M_cur->_M_next(); }
 316     };
 317
 318   template<typename _Value, bool _Cache_hash_code>
 319     inline bool
 320     operator==(const _Node_iterator_base<_Value, _Cache_hash_code>& __x,
 321                const _Node_iterator_base<_Value, _Cache_hash_code >& __y)
 322     noexcept
 323     { return __x._M_cur == __y._M_cur; }
 324
 325   template<typename _Value, bool _Cache_hash_code>
 326     inline bool
 327     operator!=(const _Node_iterator_base<_Value, _Cache_hash_code>& __x,
 328                const _Node_iterator_base<_Value, _Cache_hash_code>& __y)
 329     noexcept
 330     { return __x._M_cur != __y._M_cur; }
 331
 332   /// Node iterators, used to iterate through all the hashtable.
 333   template<typename _Value, bool __constant_iterators, bool __cache>
 334     struct _Node_iterator
 335     : public _Node_iterator_base<_Value, __cache>
 336     {
 337     private:
 338       using __base_type = _Node_iterator_base<_Value, __cache>;
 339       using __node_type = typename __base_type::__node_type;
 340
 341     public:
 342       typedef _Value                                    value_type;
 343       typedef std::ptrdiff_t                            difference_type;
 344       typedef std::forward_iterator_tag                 iterator_category;
 345
 346       using pointer = typename std::conditional<__constant_iterators,
 347                                                 const _Value*, _Value*>::type;
 348
 349       using reference = typename std::conditional<__constant_iterators,
 350                                                   const _Value&, _Value&>::type;
 351
 352       _Node_iterator() noexcept
 353       : __base_type(0) { }
 354
 355       explicit
 356       _Node_iterator(__node_type* __p) noexcept
 357       : __base_type(__p) { }
 358
 359       reference
 360       operator*() const noexcept
 361       { return this->_M_cur->_M_v(); }
 362
 363       pointer
 364       operator->() const noexcept
 365       { return this->_M_cur->_M_valptr(); }
 366
 367       _Node_iterator&
 368       operator++() noexcept
 369       {
 370         this->_M_incr();
 371         return *this;
 372       }
 373
 374       _Node_iterator
 375       operator++(int) noexcept
 376       {
 377         _Node_iterator __tmp(*this);
 378         this->_M_incr();
 379         return __tmp;
 380       }
 381     };
 382
 383   /// Node const_iterators, used to iterate through all the hashtable.
 384   template<typename _Value, bool __constant_iterators, bool __cache>
 385     struct _Node_const_iterator
 386     : public _Node_iterator_base<_Value, __cache>
 387     {
 388     private:
 389       using __base_type = _Node_iterator_base<_Value, __cache>;
 390       using __node_type = typename __base_type::__node_type;
 391
 392     public:
 393       typedef _Value                                    value_type;
 394       typedef std::ptrdiff_t                            difference_type;
 395       typedef std::forward_iterator_tag                 iterator_category;
 396
 397       typedef const _Value*                             pointer;
 398       typedef const _Value&                             reference;
 399
 400       _Node_const_iterator() noexcept
 401       : __base_type(0) { }
 402
 403       explicit
 404       _Node_const_iterator(__node_type* __p) noexcept
 405       : __base_type(__p) { }
 406
 407       _Node_const_iterator(const _Node_iterator<_Value, __constant_iterators,
 408                            __cache>& __x) noexcept
 409       : __base_type(__x._M_cur) { }
 410
 411       reference
 412       operator*() const noexcept
 413       { return this->_M_cur->_M_v(); }
 414
 415       pointer
 416       operator->() const noexcept
 417       { return this->_M_cur->_M_valptr(); }
 418
 419       _Node_const_iterator&
 420       operator++() noexcept
 421       {
 422         this->_M_incr();
 423         return *this;
 424       }
 425
 426       _Node_const_iterator
 427       operator++(int) noexcept
 428       {
 429         _Node_const_iterator __tmp(*this);
 430         this->_M_incr();
 431         return __tmp;
 432       }
 433     };
 434
 435   // Many of class template _Hashtable's template parameters are policy
 436   // classes.  These are defaults for the policies.
 437
 438   /// Default range hashing function: use division to fold a large number
 439   /// into the range [0, N).
 440   struct _Mod_range_hashing
 441   {
 442     typedef std::size_t first_argument_type;
 443     typedef std::size_t second_argument_type;
 444     typedef std::size_t result_type;
 445
 446     result_type
 447     operator()(first_argument_type __num,
 448                second_argument_type __den) const noexcept
 449     { return __num % __den; }
 450   };
 451
 452   /// Default ranged hash function H.  In principle it should be a
 453   /// function object composed from objects of type H1 and H2 such that
 454   /// h(k, N) = h2(h1(k), N), but that would mean making extra copies of
 455   /// h1 and h2.  So instead we'll just use a tag to tell class template
 456   /// hashtable to do that composition.
 457   struct _Default_ranged_hash { };
 458
 459   /// Default value for rehash policy.  Bucket size is (usually) the
 460   /// smallest prime that keeps the load factor small enough.
 461   struct _Prime_rehash_policy
 462   {
 463     _Prime_rehash_policy(float __z = 1.0)
 464     : _M_max_load_factor(__z), _M_next_resize(0) { }
 465
 466     float
 467     max_load_factor() const noexcept
 468     { return _M_max_load_factor; }
 469
 470     // Return a bucket size no smaller than n.
 471     std::size_t
 472     _M_next_bkt(std::size_t __n) const;
 473
 474     // Return a bucket count appropriate for n elements
 475     std::size_t
 476     _M_bkt_for_elements(std::size_t __n) const
 477     { return __builtin_ceil(__n / (long double)_M_max_load_factor); }
 478
 479     // __n_bkt is current bucket count, __n_elt is current element count,
 480     // and __n_ins is number of elements to be inserted.  Do we need to
 481     // increase bucket count?  If so, return make_pair(true, n), where n
 482     // is the new bucket count.  If not, return make_pair(false, 0).
 483     std::pair<bool, std::size_t>
 484     _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
 485                    std::size_t __n_ins) const;
 486
 487     typedef std::size_t _State;
 488
 489     _State
 490     _M_state() const
 491     { return _M_next_resize; }
 492
 493     void
 494     _M_reset() noexcept
 495     { _M_next_resize = 0; }
 496
 497     void
 498     _M_reset(_State __state)
 499     { _M_next_resize = __state; }
 500
 501     enum { _S_n_primes = sizeof(unsigned long) != 8 ? 256 : 256 + 48 };
 502
 503     static const std::size_t _S_growth_factor = 2;
 504
 505     float               _M_max_load_factor;
 506     mutable std::size_t _M_next_resize;
 507   };
 508
 509   // Base classes for std::_Hashtable.  We define these base classes
 510   // because in some cases we want to do different things depending on
 511   // the value of a policy class.  In some cases the policy class
 512   // affects which member functions and nested typedefs are defined;
 513   // we handle that by specializing base class templates.  Several of
 514   // the base class templates need to access other members of class
 515   // template _Hashtable, so we use a variant of the "Curiously
 516   // Recurring Template Pattern" (CRTP) technique.
 517
 518   /**
 519    *  Primary class template _Map_base.
 520    *
 521    *  If the hashtable has a value type of the form pair<T1, T2> and a
 522    *  key extraction policy (_ExtractKey) that returns the first part
 523    *  of the pair, the hashtable gets a mapped_type typedef.  If it
 524    *  satisfies those criteria and also has unique keys, then it also
 525    *  gets an operator[].
 526    */
 527   template<typename _Key, typename _Value, typename _Alloc,
 528            typename _ExtractKey, typename _Equal,
 529            typename _H1, typename _H2, typename _Hash,
 530            typename _RehashPolicy, typename _Traits,
 531            bool _Unique_keys = _Traits::__unique_keys::value>
 532     struct _Map_base { };
 533
 534   /// Partial specialization, __unique_keys set to false.
 535   template<typename _Key, typename _Pair, typename _Alloc, typename _Equal,
 536            typename _H1, typename _H2, typename _Hash,
 537            typename _RehashPolicy, typename _Traits>
 538     struct _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 539                      _H1, _H2, _Hash, _RehashPolicy, _Traits, false>
 540     {
 541       using mapped_type = typename std::tuple_element<1, _Pair>::type;
 542     };
 543
 544   /// Partial specialization, __unique_keys set to true.
 545   template<typename _Key, typename _Pair, typename _Alloc, typename _Equal,
 546            typename _H1, typename _H2, typename _Hash,
 547            typename _RehashPolicy, typename _Traits>
 548     struct _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 549                      _H1, _H2, _Hash, _RehashPolicy, _Traits, true>
 550     {
 551     private:
 552       using __hashtable_base = __detail::_Hashtable_base<_Key, _Pair,
 553                                                          _Select1st,
 554                                                         _Equal, _H1, _H2, _Hash,
 555                                                           _Traits>;
 556
 557       using __hashtable = _Hashtable<_Key, _Pair, _Alloc,
 558                                      _Select1st, _Equal,
 559                                      _H1, _H2, _Hash, _RehashPolicy, _Traits>;
 560
 561       using __hash_code = typename __hashtable_base::__hash_code;
 562       using __node_type = typename __hashtable_base::__node_type;
 563
 564     public:
 565       using key_type = typename __hashtable_base::key_type;
 566       using iterator = typename __hashtable_base::iterator;
 567       using mapped_type = typename std::tuple_element<1, _Pair>::type;
 568
 569       mapped_type&
 570       operator[](const key_type& __k);
 571
 572       mapped_type&
 573       operator[](key_type&& __k);
 574
 575       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 576       // DR 761. unordered_map needs an at() member function.
 577       mapped_type&
 578       at(const key_type& __k);
 579
 580       const mapped_type&
 581       at(const key_type& __k) const;
 582     };
 583
 584   template<typename _Key, typename _Pair, typename _Alloc, typename _Equal,
 585            typename _H1, typename _H2, typename _Hash,
 586            typename _RehashPolicy, typename _Traits>
 587     typename _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 588                        _H1, _H2, _Hash, _RehashPolicy, _Traits, true>
 589                        ::mapped_type&
 590     _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 591               _H1, _H2, _Hash, _RehashPolicy, _Traits, true>::
 592     operator[](const key_type& __k)
 593     {
 594       __hashtable* __h = static_cast<__hashtable*>(this);
 595       __hash_code __code = __h->_M_hash_code(__k);
 596       std::size_t __n = __h->_M_bucket_index(__k, __code);
 597       __node_type* __p = __h->_M_find_node(__n, __k, __code);
 598
 599       if (!__p)
 600         {
 601           __p = __h->_M_allocate_node(std::piecewise_construct,
 602                                       std::tuple<const key_type&>(__k),
 603                                       std::tuple<>());
 604           return __h->_M_insert_unique_node(__n, __code, __p)->second;
 605         }
 606
 607       return __p->_M_v().second;
 608     }
 609
 610   template<typename _Key, typename _Pair, typename _Alloc, typename _Equal,
 611            typename _H1, typename _H2, typename _Hash,
 612            typename _RehashPolicy, typename _Traits>
 613     typename _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 614                        _H1, _H2, _Hash, _RehashPolicy, _Traits, true>
 615                        ::mapped_type&
 616     _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 617               _H1, _H2, _Hash, _RehashPolicy, _Traits, true>::
 618     operator[](key_type&& __k)
 619     {
 620       __hashtable* __h = static_cast<__hashtable*>(this);
 621       __hash_code __code = __h->_M_hash_code(__k);
 622       std::size_t __n = __h->_M_bucket_index(__k, __code);
 623       __node_type* __p = __h->_M_find_node(__n, __k, __code);
 624
 625       if (!__p)
 626         {
 627           __p = __h->_M_allocate_node(std::piecewise_construct,
 628                                       std::forward_as_tuple(std::move(__k)),
 629                                       std::tuple<>());
 630           return __h->_M_insert_unique_node(__n, __code, __p)->second;
 631         }
 632
 633       return __p->_M_v().second;
 634     }
 635
 636   template<typename _Key, typename _Pair, typename _Alloc, typename _Equal,
 637            typename _H1, typename _H2, typename _Hash,
 638            typename _RehashPolicy, typename _Traits>
 639     typename _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 640                        _H1, _H2, _Hash, _RehashPolicy, _Traits, true>
 641                        ::mapped_type&
 642     _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 643               _H1, _H2, _Hash, _RehashPolicy, _Traits, true>::
 644     at(const key_type& __k)
 645     {
 646       __hashtable* __h = static_cast<__hashtable*>(this);
 647       __hash_code __code = __h->_M_hash_code(__k);
 648       std::size_t __n = __h->_M_bucket_index(__k, __code);
 649       __node_type* __p = __h->_M_find_node(__n, __k, __code);
 650
 651       if (!__p)
 652         __throw_out_of_range(__N("_Map_base::at"));
 653       return __p->_M_v().second;
 654     }
 655
 656   template<typename _Key, typename _Pair, typename _Alloc, typename _Equal,
 657            typename _H1, typename _H2, typename _Hash,
 658            typename _RehashPolicy, typename _Traits>
 659     const typename _Map_base<_Key, _Pair, _Alloc, _Select1st,
 660                              _Equal, _H1, _H2, _Hash, _RehashPolicy,
 661                              _Traits, true>::mapped_type&
 662     _Map_base<_Key, _Pair, _Alloc, _Select1st, _Equal,
 663               _H1, _H2, _Hash, _RehashPolicy, _Traits, true>::
 664     at(const key_type& __k) const
 665     {
 666       const __hashtable* __h = static_cast<const __hashtable*>(this);
 667       __hash_code __code = __h->_M_hash_code(__k);
 668       std::size_t __n = __h->_M_bucket_index(__k, __code);
 669       __node_type* __p = __h->_M_find_node(__n, __k, __code);
 670
 671       if (!__p)
 672         __throw_out_of_range(__N("_Map_base::at"));
 673       return __p->_M_v().second;
 674     }
 675
 676   /**
 677    *  Primary class template _Insert_base.
 678    *
 679    *  insert member functions appropriate to all _Hashtables.
 680    */
 681   template<typename _Key, typename _Value, typename _Alloc,
 682            typename _ExtractKey, typename _Equal,
 683            typename _H1, typename _H2, typename _Hash,
 684            typename _RehashPolicy, typename _Traits>
 685     struct _Insert_base
 686     {
 687     protected:
 688       using __hashtable = _Hashtable<_Key, _Value, _Alloc, _ExtractKey,
 689                                      _Equal, _H1, _H2, _Hash,
 690                                      _RehashPolicy, _Traits>;
 691
 692       using __hashtable_base = _Hashtable_base<_Key, _Value, _ExtractKey,
 693                                                _Equal, _H1, _H2, _Hash,
 694                                                _Traits>;
 695
 696       using value_type = typename __hashtable_base::value_type;
 697       using iterator = typename __hashtable_base::iterator;
 698       using const_iterator =  typename __hashtable_base::const_iterator;
 699       using size_type = typename __hashtable_base::size_type;
 700
 701       using __unique_keys = typename __hashtable_base::__unique_keys;
 702       using __ireturn_type = typename __hashtable_base::__ireturn_type;
 703       using __node_type = _Hash_node<_Value, _Traits::__hash_cached::value>;
 704       using __node_alloc_type = __alloc_rebind<_Alloc, __node_type>;
 705       using __node_gen_type = _AllocNode<__node_alloc_type>;
 706
 707       __hashtable&
 708       _M_conjure_hashtable()
 709       { return *(static_cast<__hashtable*>(this)); }
 710
 711       template<typename _InputIterator, typename _NodeGetter>
 712         void
 713         _M_insert_range(_InputIterator __first, _InputIterator __last,
 714                         const _NodeGetter&);
 715
 716     public:
 717       __ireturn_type
 718       insert(const value_type& __v)
 719       {
 720         __hashtable& __h = _M_conjure_hashtable();
 721         __node_gen_type __node_gen(__h);
 722         return __h._M_insert(__v, __node_gen, __unique_keys());
 723       }
 724
 725       iterator
 726       insert(const_iterator __hint, const value_type& __v)
 727       {
 728         __hashtable& __h = _M_conjure_hashtable();
 729         __node_gen_type __node_gen(__h);
 730         return __h._M_insert(__hint, __v, __node_gen, __unique_keys());
 731       }
 732
 733       void
 734       insert(initializer_list<value_type> __l)
 735       { this->insert(__l.begin(), __l.end()); }
 736
 737       template<typename _InputIterator>
 738         void
 739         insert(_InputIterator __first, _InputIterator __last)
 740         {
 741           __hashtable& __h = _M_conjure_hashtable();
 742           __node_gen_type __node_gen(__h);
 743           return _M_insert_range(__first, __last, __node_gen);
 744         }
 745     };
 746
 747   template<typename _Key, typename _Value, typename _Alloc,
 748            typename _ExtractKey, typename _Equal,
 749            typename _H1, typename _H2, typename _Hash,
 750            typename _RehashPolicy, typename _Traits>
 751     template<typename _InputIterator, typename _NodeGetter>
 752       void
 753       _Insert_base<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash,
 754                     _RehashPolicy, _Traits>::
 755       _M_insert_range(_InputIterator __first, _InputIterator __last,
 756                       const _NodeGetter& __node_gen)
 757       {
 758         using __rehash_type = typename __hashtable::__rehash_type;
 759         using __rehash_state = typename __hashtable::__rehash_state;
 760         using pair_type = std::pair<bool, std::size_t>;
 761
 762         size_type __n_elt = __detail::__distance_fw(__first, __last);
 763
 764         __hashtable& __h = _M_conjure_hashtable();
 765         __rehash_type& __rehash = __h._M_rehash_policy;
 766         const __rehash_state& __saved_state = __rehash._M_state();
 767         pair_type __do_rehash = __rehash._M_need_rehash(__h._M_bucket_count,
 768                                                         __h._M_element_count,
 769                                                         __n_elt);
 770
 771         if (__do_rehash.first)
 772           __h._M_rehash(__do_rehash.second, __saved_state);
 773
 774         for (; __first != __last; ++__first)
 775           __h._M_insert(*__first, __node_gen, __unique_keys());
 776       }
 777
 778   /**
 779    *  Primary class template _Insert.
 780    *
 781    *  Select insert member functions appropriate to _Hashtable policy choices.
 782    */
 783   template<typename _Key, typename _Value, typename _Alloc,
 784            typename _ExtractKey, typename _Equal,
 785            typename _H1, typename _H2, typename _Hash,
 786            typename _RehashPolicy, typename _Traits,
 787            bool _Constant_iterators = _Traits::__constant_iterators::value,
 788            bool _Unique_keys = _Traits::__unique_keys::value>
 789     struct _Insert;
 790
 791   /// Specialization.
 792   template<typename _Key, typename _Value, typename _Alloc,
 793            typename _ExtractKey, typename _Equal,
 794            typename _H1, typename _H2, typename _Hash,
 795            typename _RehashPolicy, typename _Traits>
 796     struct _Insert<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash,
 797                    _RehashPolicy, _Traits, true, true>
 798     : public _Insert_base<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 799                            _H1, _H2, _Hash, _RehashPolicy, _Traits>
 800     {
 801       using __base_type = _Insert_base<_Key, _Value, _Alloc, _ExtractKey,
 802                                         _Equal, _H1, _H2, _Hash,
 803                                         _RehashPolicy, _Traits>;
 804       using value_type = typename __base_type::value_type;
 805       using iterator = typename __base_type::iterator;
 806       using const_iterator =  typename __base_type::const_iterator;
 807
 808       using __unique_keys = typename __base_type::__unique_keys;
 809       using __hashtable = typename __base_type::__hashtable;
 810       using __node_gen_type = typename __base_type::__node_gen_type;
 811
 812       using __base_type::insert;
 813
 814       std::pair<iterator, bool>
 815       insert(value_type&& __v)
 816       {
 817         __hashtable& __h = this->_M_conjure_hashtable();
 818         __node_gen_type __node_gen(__h);
 819         return __h._M_insert(std::move(__v), __node_gen, __unique_keys());
 820       }
 821
 822       iterator
 823       insert(const_iterator __hint, value_type&& __v)
 824       {
 825         __hashtable& __h = this->_M_conjure_hashtable();
 826         __node_gen_type __node_gen(__h);
 827         return __h._M_insert(__hint, std::move(__v), __node_gen,
 828                              __unique_keys());
 829       }
 830     };
 831
 832   /// Specialization.
 833   template<typename _Key, typename _Value, typename _Alloc,
 834            typename _ExtractKey, typename _Equal,
 835            typename _H1, typename _H2, typename _Hash,
 836            typename _RehashPolicy, typename _Traits>
 837     struct _Insert<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash,
 838                    _RehashPolicy, _Traits, true, false>
 839     : public _Insert_base<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 840                            _H1, _H2, _Hash, _RehashPolicy, _Traits>
 841     {
 842       using __base_type = _Insert_base<_Key, _Value, _Alloc, _ExtractKey,
 843                                         _Equal, _H1, _H2, _Hash,
 844                                         _RehashPolicy, _Traits>;
 845       using value_type = typename __base_type::value_type;
 846       using iterator = typename __base_type::iterator;
 847       using const_iterator =  typename __base_type::const_iterator;
 848
 849       using __unique_keys = typename __base_type::__unique_keys;
 850       using __hashtable = typename __base_type::__hashtable;
 851       using __node_gen_type = typename __base_type::__node_gen_type;
 852
 853       using __base_type::insert;
 854
 855       iterator
 856       insert(value_type&& __v)
 857       {
 858         __hashtable& __h = this->_M_conjure_hashtable();
 859         __node_gen_type __node_gen(__h);
 860         return __h._M_insert(std::move(__v), __node_gen, __unique_keys());
 861       }
 862
 863       iterator
 864       insert(const_iterator __hint, value_type&& __v)
 865       {
 866         __hashtable& __h = this->_M_conjure_hashtable();
 867         __node_gen_type __node_gen(__h);
 868         return __h._M_insert(__hint, std::move(__v), __node_gen,
 869                              __unique_keys());
 870       }
 871     };
 872
 873   /// Specialization.
 874   template<typename _Key, typename _Value, typename _Alloc,
 875            typename _ExtractKey, typename _Equal,
 876            typename _H1, typename _H2, typename _Hash,
 877            typename _RehashPolicy, typename _Traits, bool _Unique_keys>
 878     struct _Insert<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash,
 879                    _RehashPolicy, _Traits, false, _Unique_keys>
 880     : public _Insert_base<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 881                            _H1, _H2, _Hash, _RehashPolicy, _Traits>
 882     {
 883       using __base_type = _Insert_base<_Key, _Value, _Alloc, _ExtractKey,
 884                                        _Equal, _H1, _H2, _Hash,
 885                                        _RehashPolicy, _Traits>;
 886       using value_type = typename __base_type::value_type;
 887       using iterator = typename __base_type::iterator;
 888       using const_iterator =  typename __base_type::const_iterator;
 889
 890       using __unique_keys = typename __base_type::__unique_keys;
 891       using __hashtable = typename __base_type::__hashtable;
 892       using __ireturn_type = typename __base_type::__ireturn_type;
 893
 894       using __base_type::insert;
 895
 896       template<typename _Pair>
 897         using __is_cons = std::is_constructible<value_type, _Pair&&>;
 898
 899       template<typename _Pair>
 900         using _IFcons = std::enable_if<__is_cons<_Pair>::value>;
 901
 902       template<typename _Pair>
 903         using _IFconsp = typename _IFcons<_Pair>::type;
 904
 905       template<typename _Pair, typename = _IFconsp<_Pair>>
 906         __ireturn_type
 907         insert(_Pair&& __v)
 908         {
 909           __hashtable& __h = this->_M_conjure_hashtable();
 910           return __h._M_emplace(__unique_keys(), std::forward<_Pair>(__v));
 911         }
 912
 913       template<typename _Pair, typename = _IFconsp<_Pair>>
 914         iterator
 915         insert(const_iterator __hint, _Pair&& __v)
 916         {
 917           __hashtable& __h = this->_M_conjure_hashtable();
 918           return __h._M_emplace(__hint, __unique_keys(),
 919                                 std::forward<_Pair>(__v));
 920         }
 921    };
 922
 923   /**
 924    *  Primary class template  _Rehash_base.
 925    *
 926    *  Give hashtable the max_load_factor functions and reserve iff the
 927    *  rehash policy is _Prime_rehash_policy.
 928   */
 929   template<typename _Key, typename _Value, typename _Alloc,
 930            typename _ExtractKey, typename _Equal,
 931            typename _H1, typename _H2, typename _Hash,
 932            typename _RehashPolicy, typename _Traits>
 933     struct _Rehash_base;
 934
 935   /// Specialization.
 936   template<typename _Key, typename _Value, typename _Alloc,
 937            typename _ExtractKey, typename _Equal,
 938            typename _H1, typename _H2, typename _Hash, typename _Traits>
 939     struct _Rehash_base<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 940                         _H1, _H2, _Hash, _Prime_rehash_policy, _Traits>
 941     {
 942       using __hashtable = _Hashtable<_Key, _Value, _Alloc, _ExtractKey,
 943                                      _Equal, _H1, _H2, _Hash,
 944                                      _Prime_rehash_policy, _Traits>;
 945
 946       float
 947       max_load_factor() const noexcept
 948       {
 949         const __hashtable* __this = static_cast<const __hashtable*>(this);
 950         return __this->__rehash_policy().max_load_factor();
 951       }
 952
 953       void
 954       max_load_factor(float __z)
 955       {
 956         __hashtable* __this = static_cast<__hashtable*>(this);
 957         __this->__rehash_policy(_Prime_rehash_policy(__z));
 958       }
 959
 960       void
 961       reserve(std::size_t __n)
 962       {
 963         __hashtable* __this = static_cast<__hashtable*>(this);
 964         __this->rehash(__builtin_ceil(__n / max_load_factor()));
 965       }
 966     };
 967
 968   /**
 969    *  Primary class template _Hashtable_ebo_helper.
 970    *
 971    *  Helper class using EBO when it is not forbidden (the type is not
 972    *  final) and when it is worth it (the type is empty.)
 973    */
 974   template<int _Nm, typename _Tp,
 975            bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
 976     struct _Hashtable_ebo_helper;
 977
 978   /// Specialization using EBO.
 979   template<int _Nm, typename _Tp>
 980     struct _Hashtable_ebo_helper<_Nm, _Tp, true>
 981     : private _Tp
 982     {
 983       _Hashtable_ebo_helper() = default;
 984
 985       template<typename _OtherTp>
 986         _Hashtable_ebo_helper(_OtherTp&& __tp)
 987           : _Tp(std::forward<_OtherTp>(__tp))
 988         { }
 989
 990       static const _Tp&
 991       _S_cget(const _Hashtable_ebo_helper& __eboh)
 992       { return static_cast<const _Tp&>(__eboh); }
 993
 994       static _Tp&
 995       _S_get(_Hashtable_ebo_helper& __eboh)
 996       { return static_cast<_Tp&>(__eboh); }
 997     };
 998
 999   /// Specialization not using EBO.
1000   template<int _Nm, typename _Tp>
1001     struct _Hashtable_ebo_helper<_Nm, _Tp, false>
1002     {
1003       _Hashtable_ebo_helper() = default;
1004
1005       template<typename _OtherTp>
1006         _Hashtable_ebo_helper(_OtherTp&& __tp)
1007           : _M_tp(std::forward<_OtherTp>(__tp))
1008         { }
1009
1010       static const _Tp&
1011       _S_cget(const _Hashtable_ebo_helper& __eboh)
1012       { return __eboh._M_tp; }
1013
1014       static _Tp&
1015       _S_get(_Hashtable_ebo_helper& __eboh)
1016       { return __eboh._M_tp; }
1017
1018     private:
1019       _Tp _M_tp;
1020     };
1021
1022   /**
1023    *  Primary class template _Local_iterator_base.
1024    *
1025    *  Base class for local iterators, used to iterate within a bucket
1026    *  but not between buckets.
1027    */
1028   template<typename _Key, typename _Value, typename _ExtractKey,
1029            typename _H1, typename _H2, typename _Hash,
1030            bool __cache_hash_code>
1031     struct _Local_iterator_base;
1032
1033   /**
1034    *  Primary class template _Hash_code_base.
1035    *
1036    *  Encapsulates two policy issues that aren't quite orthogonal.
1037    *   (1) the difference between using a ranged hash function and using
1038    *       the combination of a hash function and a range-hashing function.
1039    *       In the former case we don't have such things as hash codes, so
1040    *       we have a dummy type as placeholder.
1041    *   (2) Whether or not we cache hash codes.  Caching hash codes is
1042    *       meaningless if we have a ranged hash function.
1043    *
1044    *  We also put the key extraction objects here, for convenience.
1045    *  Each specialization derives from one or more of the template
1046    *  parameters to benefit from Ebo. This is important as this type
1047    *  is inherited in some cases by the _Local_iterator_base type used
1048    *  to implement local_iterator and const_local_iterator. As with
1049    *  any iterator type we prefer to make it as small as possible.
1050    *
1051    *  Primary template is unused except as a hook for specializations.
1052    */
1053   template<typename _Key, typename _Value, typename _ExtractKey,
1054            typename _H1, typename _H2, typename _Hash,
1055            bool __cache_hash_code>
1056     struct _Hash_code_base;
1057
1058   /// Specialization: ranged hash function, no caching hash codes.  H1
1059   /// and H2 are provided but ignored.  We define a dummy hash code type.
1060   template<typename _Key, typename _Value, typename _ExtractKey,
1061            typename _H1, typename _H2, typename _Hash>
1062     struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash, false>
1063     : private _Hashtable_ebo_helper<0, _ExtractKey>,
1064       private _Hashtable_ebo_helper<1, _Hash>
1065     {
1066     private:
1067       using __ebo_extract_key = _Hashtable_ebo_helper<0, _ExtractKey>;
1068       using __ebo_hash = _Hashtable_ebo_helper<1, _Hash>;
1069
1070     protected:
1071       typedef void*                                     __hash_code;
1072       typedef _Hash_node<_Value, false>                 __node_type;
1073
1074       // We need the default constructor for the local iterators.
1075       _Hash_code_base() = default;
1076
1077       _Hash_code_base(const _ExtractKey& __ex, const _H1&, const _H2&,
1078                       const _Hash& __h)
1079       : __ebo_extract_key(__ex), __ebo_hash(__h) { }
1080
1081       __hash_code
1082       _M_hash_code(const _Key& __key) const
1083       { return 0; }
1084
1085       std::size_t
1086       _M_bucket_index(const _Key& __k, __hash_code, std::size_t __n) const
1087       { return _M_ranged_hash()(__k, __n); }
1088
1089       std::size_t
1090       _M_bucket_index(const __node_type* __p, std::size_t __n) const
1091         noexcept( noexcept(declval<const _Hash&>()(declval<const _Key&>(),
1092                                                    (std::size_t)0)) )
1093       { return _M_ranged_hash()(_M_extract()(__p->_M_v()), __n); }
1094
1095       void
1096       _M_store_code(__node_type*, __hash_code) const
1097       { }
1098
1099       void
1100       _M_copy_code(__node_type*, const __node_type*) const
1101       { }
1102
1103       void
1104       _M_swap(_Hash_code_base& __x)
1105       {
1106         std::swap(_M_extract(), __x._M_extract());
1107         std::swap(_M_ranged_hash(), __x._M_ranged_hash());
1108       }
1109
1110       const _ExtractKey&
1111       _M_extract() const { return __ebo_extract_key::_S_cget(*this); }
1112
1113       _ExtractKey&
1114       _M_extract() { return __ebo_extract_key::_S_get(*this); }
1115
1116       const _Hash&
1117       _M_ranged_hash() const { return __ebo_hash::_S_cget(*this); }
1118
1119       _Hash&
1120       _M_ranged_hash() { return __ebo_hash::_S_get(*this); }
1121     };
1122
1123   // No specialization for ranged hash function while caching hash codes.
1124   // That combination is meaningless, and trying to do it is an error.
1125
1126   /// Specialization: ranged hash function, cache hash codes.  This
1127   /// combination is meaningless, so we provide only a declaration
1128   /// and no definition.
1129   template<typename _Key, typename _Value, typename _ExtractKey,
1130            typename _H1, typename _H2, typename _Hash>
1131     struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash, true>;
1132
1133   /// Specialization: hash function and range-hashing function, no
1134   /// caching of hash codes.
1135   /// Provides typedef and accessor required by C++ 11.
1136   template<typename _Key, typename _Value, typename _ExtractKey,
1137            typename _H1, typename _H2>
1138     struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2,
1139                            _Default_ranged_hash, false>
1140     : private _Hashtable_ebo_helper<0, _ExtractKey>,
1141       private _Hashtable_ebo_helper<1, _H1>,
1142       private _Hashtable_ebo_helper<2, _H2>
1143     {
1144     private:
1145       using __ebo_extract_key = _Hashtable_ebo_helper<0, _ExtractKey>;
1146       using __ebo_h1 = _Hashtable_ebo_helper<1, _H1>;
1147       using __ebo_h2 = _Hashtable_ebo_helper<2, _H2>;
1148
1149       // Gives the local iterator implementation access to _M_bucket_index().
1150       friend struct _Local_iterator_base<_Key, _Value, _ExtractKey, _H1, _H2,
1151                                          _Default_ranged_hash, false>;
1152
1153     public:
1154       typedef _H1                                       hasher;
1155
1156       hasher
1157       hash_function() const
1158       { return _M_h1(); }
1159
1160     protected:
1161       typedef std::size_t                               __hash_code;
1162       typedef _Hash_node<_Value, false>                 __node_type;
1163
1164       // We need the default constructor for the local iterators.
1165       _Hash_code_base() = default;
1166
1167       _Hash_code_base(const _ExtractKey& __ex,
1168                       const _H1& __h1, const _H2& __h2,
1169                       const _Default_ranged_hash&)
1170       : __ebo_extract_key(__ex), __ebo_h1(__h1), __ebo_h2(__h2) { }
1171
1172       __hash_code
1173       _M_hash_code(const _Key& __k) const
1174       { return _M_h1()(__k); }
1175
1176       std::size_t
1177       _M_bucket_index(const _Key&, __hash_code __c, std::size_t __n) const
1178       { return _M_h2()(__c, __n); }
1179
1180       std::size_t
1181       _M_bucket_index(const __node_type* __p, std::size_t __n) const
1182         noexcept( noexcept(declval<const _H1&>()(declval<const _Key&>()))
1183                   && noexcept(declval<const _H2&>()((__hash_code)0,
1184                                                     (std::size_t)0)) )
1185       { return _M_h2()(_M_h1()(_M_extract()(__p->_M_v())), __n); }
1186
1187       void
1188       _M_store_code(__node_type*, __hash_code) const
1189       { }
1190
1191       void
1192       _M_copy_code(__node_type*, const __node_type*) const
1193       { }
1194
1195       void
1196       _M_swap(_Hash_code_base& __x)
1197       {
1198         std::swap(_M_extract(), __x._M_extract());
1199         std::swap(_M_h1(), __x._M_h1());
1200         std::swap(_M_h2(), __x._M_h2());
1201       }
1202
1203       const _ExtractKey&
1204       _M_extract() const { return __ebo_extract_key::_S_cget(*this); }
1205
1206       _ExtractKey&
1207       _M_extract() { return __ebo_extract_key::_S_get(*this); }
1208
1209       const _H1&
1210       _M_h1() const { return __ebo_h1::_S_cget(*this); }
1211
1212       _H1&
1213       _M_h1() { return __ebo_h1::_S_get(*this); }
1214
1215       const _H2&
1216       _M_h2() const { return __ebo_h2::_S_cget(*this); }
1217
1218       _H2&
1219       _M_h2() { return __ebo_h2::_S_get(*this); }
1220     };
1221
1222   /// Specialization: hash function and range-hashing function,
1223   /// caching hash codes.  H is provided but ignored.  Provides
1224   /// typedef and accessor required by C++ 11.
1225   template<typename _Key, typename _Value, typename _ExtractKey,
1226            typename _H1, typename _H2>
1227     struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2,
1228                            _Default_ranged_hash, true>
1229     : private _Hashtable_ebo_helper<0, _ExtractKey>,
1230       private _Hashtable_ebo_helper<1, _H1>,
1231       private _Hashtable_ebo_helper<2, _H2>
1232     {
1233     private:
1234       // Gives the local iterator implementation access to _M_h2().
1235       friend struct _Local_iterator_base<_Key, _Value, _ExtractKey, _H1, _H2,
1236                                          _Default_ranged_hash, true>;
1237
1238       using __ebo_extract_key = _Hashtable_ebo_helper<0, _ExtractKey>;
1239       using __ebo_h1 = _Hashtable_ebo_helper<1, _H1>;
1240       using __ebo_h2 = _Hashtable_ebo_helper<2, _H2>;
1241
1242     public:
1243       typedef _H1                                       hasher;
1244
1245       hasher
1246       hash_function() const
1247       { return _M_h1(); }
1248
1249     protected:
1250       typedef std::size_t                               __hash_code;
1251       typedef _Hash_node<_Value, true>                  __node_type;
1252
1253       _Hash_code_base(const _ExtractKey& __ex,
1254                       const _H1& __h1, const _H2& __h2,
1255                       const _Default_ranged_hash&)
1256       : __ebo_extract_key(__ex), __ebo_h1(__h1), __ebo_h2(__h2) { }
1257
1258       __hash_code
1259       _M_hash_code(const _Key& __k) const
1260       { return _M_h1()(__k); }
1261
1262       std::size_t
1263       _M_bucket_index(const _Key&, __hash_code __c,
1264                       std::size_t __n) const
1265       { return _M_h2()(__c, __n); }
1266
1267       std::size_t
1268       _M_bucket_index(const __node_type* __p, std::size_t __n) const
1269         noexcept( noexcept(declval<const _H2&>()((__hash_code)0,
1270                                                  (std::size_t)0)) )
1271       { return _M_h2()(__p->_M_hash_code, __n); }
1272
1273       void
1274       _M_store_code(__node_type* __n, __hash_code __c) const
1275       { __n->_M_hash_code = __c; }
1276
1277       void
1278       _M_copy_code(__node_type* __to, const __node_type* __from) const
1279       { __to->_M_hash_code = __from->_M_hash_code; }
1280
1281       void
1282       _M_swap(_Hash_code_base& __x)
1283       {
1284         std::swap(_M_extract(), __x._M_extract());
1285         std::swap(_M_h1(), __x._M_h1());
1286         std::swap(_M_h2(), __x._M_h2());
1287       }
1288
1289       const _ExtractKey&
1290       _M_extract() const { return __ebo_extract_key::_S_cget(*this); }
1291
1292       _ExtractKey&
1293       _M_extract() { return __ebo_extract_key::_S_get(*this); }
1294
1295       const _H1&
1296       _M_h1() const { return __ebo_h1::_S_cget(*this); }
1297
1298       _H1&
1299       _M_h1() { return __ebo_h1::_S_get(*this); }
1300
1301       const _H2&
1302       _M_h2() const { return __ebo_h2::_S_cget(*this); }
1303
1304       _H2&
1305       _M_h2() { return __ebo_h2::_S_get(*this); }
1306     };
1307
1308   /**
1309    *  Primary class template _Equal_helper.
1310    *
1311    */
1312   template <typename _Key, typename _Value, typename _ExtractKey,
1313             typename _Equal, typename _HashCodeType,
1314             bool __cache_hash_code>
1315   struct _Equal_helper;
1316
1317   /// Specialization.
1318   template<typename _Key, typename _Value, typename _ExtractKey,
1319            typename _Equal, typename _HashCodeType>
1320   struct _Equal_helper<_Key, _Value, _ExtractKey, _Equal, _HashCodeType, true>
1321   {
1322     static bool
1323     _S_equals(const _Equal& __eq, const _ExtractKey& __extract,
1324               const _Key& __k, _HashCodeType __c, _Hash_node<_Value, true>* __n)
1325     { return __c == __n->_M_hash_code && __eq(__k, __extract(__n->_M_v())); }
1326   };
1327
1328   /// Specialization.
1329   template<typename _Key, typename _Value, typename _ExtractKey,
1330            typename _Equal, typename _HashCodeType>
1331   struct _Equal_helper<_Key, _Value, _ExtractKey, _Equal, _HashCodeType, false>
1332   {
1333     static bool
1334     _S_equals(const _Equal& __eq, const _ExtractKey& __extract,
1335               const _Key& __k, _HashCodeType, _Hash_node<_Value, false>* __n)
1336     { return __eq(__k, __extract(__n->_M_v())); }
1337   };
1338
1339
1340   /// Partial specialization used when nodes contain a cached hash code.
1341   template<typename _Key, typename _Value, typename _ExtractKey,
1342            typename _H1, typename _H2, typename _Hash>
1343     struct _Local_iterator_base<_Key, _Value, _ExtractKey,
1344                                 _H1, _H2, _Hash, true>
1345     : private _Hashtable_ebo_helper<0, _H2>
1346     {
1347     protected:
1348       using __base_type = _Hashtable_ebo_helper<0, _H2>;
1349       using __hash_code_base = _Hash_code_base<_Key, _Value, _ExtractKey,
1350                                                _H1, _H2, _Hash, true>;
1351
1352       _Local_iterator_base() = default;
1353       _Local_iterator_base(const __hash_code_base& __base,
1354                            _Hash_node<_Value, true>* __p,
1355                            std::size_t __bkt, std::size_t __bkt_count)
1356       : __base_type(__base._M_h2()),
1357         _M_cur(__p), _M_bucket(__bkt), _M_bucket_count(__bkt_count) { }
1358
1359       void
1360       _M_incr()
1361       {
1362         _M_cur = _M_cur->_M_next();
1363         if (_M_cur)
1364           {
1365             std::size_t __bkt
1366               = __base_type::_S_get(*this)(_M_cur->_M_hash_code,
1367                                            _M_bucket_count);
1368             if (__bkt != _M_bucket)
1369               _M_cur = nullptr;
1370           }
1371       }
1372
1373       _Hash_node<_Value, true>*  _M_cur;
1374       std::size_t _M_bucket;
1375       std::size_t _M_bucket_count;
1376
1377     public:
1378       const void*
1379       _M_curr() const { return _M_cur; }  // for equality ops
1380
1381       std::size_t
1382       _M_get_bucket() const { return _M_bucket; }  // for debug mode
1383     };
1384
1385   // Uninitialized storage for a _Hash_code_base.
1386   // This type is DefaultConstructible and Assignable even if the
1387   // _Hash_code_base type isn't, so that _Local_iterator_base<..., false>
1388   // can be DefaultConstructible and Assignable.
1389   template<typename _Tp, bool _IsEmpty = std::is_empty<_Tp>::value>
1390     struct _Hash_code_storage
1391     {
1392       __gnu_cxx::__aligned_buffer<_Tp> _M_storage;
1393
1394       _Tp*
1395       _M_h() { return _M_storage._M_ptr(); }
1396
1397       const _Tp*
1398       _M_h() const { return _M_storage._M_ptr(); }
1399     };
1400
1401   // Empty partial specialization for empty _Hash_code_base types.
1402   template<typename _Tp>
1403     struct _Hash_code_storage<_Tp, true>
1404     {
1405       static_assert( std::is_empty<_Tp>::value, "Type must be empty" );
1406
1407       // As _Tp is an empty type there will be no bytes written/read through
1408       // the cast pointer, so no strict-aliasing violation.
1409       _Tp*
1410       _M_h() { return reinterpret_cast<_Tp*>(this); }
1411
1412       const _Tp*
1413       _M_h() const { return reinterpret_cast<const _Tp*>(this); }
1414     };
1415
1416   template<typename _Key, typename _Value, typename _ExtractKey,
1417            typename _H1, typename _H2, typename _Hash>
1418     using __hash_code_for_local_iter
1419       = _Hash_code_storage<_Hash_code_base<_Key, _Value, _ExtractKey,
1420                                            _H1, _H2, _Hash, false>>;
1421
1422   // Partial specialization used when hash codes are not cached
1423   template<typename _Key, typename _Value, typename _ExtractKey,
1424            typename _H1, typename _H2, typename _Hash>
1425     struct _Local_iterator_base<_Key, _Value, _ExtractKey,
1426                                 _H1, _H2, _Hash, false>
1427     : __hash_code_for_local_iter<_Key, _Value, _ExtractKey, _H1, _H2, _Hash>
1428     {
1429     protected:
1430       using __hash_code_base = _Hash_code_base<_Key, _Value, _ExtractKey,
1431                                                _H1, _H2, _Hash, false>;
1432
1433       _Local_iterator_base() : _M_bucket_count(-1) { }
1434
1435       _Local_iterator_base(const __hash_code_base& __base,
1436                            _Hash_node<_Value, false>* __p,
1437                            std::size_t __bkt, std::size_t __bkt_count)
1438       : _M_cur(__p), _M_bucket(__bkt), _M_bucket_count(__bkt_count)
1439       { _M_init(__base); }
1440
1441       ~_Local_iterator_base()
1442       {
1443         if (_M_bucket_count != -1)
1444           _M_destroy();
1445       }
1446
1447       _Local_iterator_base(const _Local_iterator_base& __iter)
1448       : _M_cur(__iter._M_cur), _M_bucket(__iter._M_bucket),
1449         _M_bucket_count(__iter._M_bucket_count)
1450       {
1451         if (_M_bucket_count != -1)
1452           _M_init(*__iter._M_h());
1453       }
1454
1455       _Local_iterator_base&
1456       operator=(const _Local_iterator_base& __iter)
1457       {
1458         if (_M_bucket_count != -1)
1459           _M_destroy();
1460         _M_cur = __iter._M_cur;
1461         _M_bucket = __iter._M_bucket;
1462         _M_bucket_count = __iter._M_bucket_count;
1463         if (_M_bucket_count != -1)
1464           _M_init(*__iter._M_h());
1465         return *this;
1466       }
1467
1468       void
1469       _M_incr()
1470       {
1471         _M_cur = _M_cur->_M_next();
1472         if (_M_cur)
1473           {
1474             std::size_t __bkt = this->_M_h()->_M_bucket_index(_M_cur,
1475                                                               _M_bucket_count);
1476             if (__bkt != _M_bucket)
1477               _M_cur = nullptr;
1478           }
1479       }
1480
1481       _Hash_node<_Value, false>*  _M_cur;
1482       std::size_t _M_bucket;
1483       std::size_t _M_bucket_count;
1484
1485       void
1486       _M_init(const __hash_code_base& __base)
1487       { ::new(this->_M_h()) __hash_code_base(__base); }
1488
1489       void
1490       _M_destroy() { this->_M_h()->~__hash_code_base(); }
1491
1492     public:
1493       const void*
1494       _M_curr() const { return _M_cur; }  // for equality ops and debug mode
1495
1496       std::size_t
1497       _M_get_bucket() const { return _M_bucket; }  // for debug mode
1498     };
1499
1500   template<typename _Key, typename _Value, typename _ExtractKey,
1501            typename _H1, typename _H2, typename _Hash, bool __cache>
1502     inline bool
1503     operator==(const _Local_iterator_base<_Key, _Value, _ExtractKey,
1504                                           _H1, _H2, _Hash, __cache>& __x,
1505                const _Local_iterator_base<_Key, _Value, _ExtractKey,
1506                                           _H1, _H2, _Hash, __cache>& __y)
1507     { return __x._M_curr() == __y._M_curr(); }
1508
1509   template<typename _Key, typename _Value, typename _ExtractKey,
1510            typename _H1, typename _H2, typename _Hash, bool __cache>
1511     inline bool
1512     operator!=(const _Local_iterator_base<_Key, _Value, _ExtractKey,
1513                                           _H1, _H2, _Hash, __cache>& __x,
1514                const _Local_iterator_base<_Key, _Value, _ExtractKey,
1515                                           _H1, _H2, _Hash, __cache>& __y)
1516     { return __x._M_curr() != __y._M_curr(); }
1517
1518   /// local iterators
1519   template<typename _Key, typename _Value, typename _ExtractKey,
1520            typename _H1, typename _H2, typename _Hash,
1521            bool __constant_iterators, bool __cache>
1522     struct _Local_iterator
1523     : public _Local_iterator_base<_Key, _Value, _ExtractKey,
1524                                   _H1, _H2, _Hash, __cache>
1525     {
1526     private:
1527       using __base_type = _Local_iterator_base<_Key, _Value, _ExtractKey,
1528                                                _H1, _H2, _Hash, __cache>;
1529       using __hash_code_base = typename __base_type::__hash_code_base;
1530     public:
1531       typedef _Value                                    value_type;
1532       typedef typename std::conditional<__constant_iterators,
1533                                         const _Value*, _Value*>::type
1534                                                        pointer;
1535       typedef typename std::conditional<__constant_iterators,
1536                                         const _Value&, _Value&>::type
1537                                                        reference;
1538       typedef std::ptrdiff_t                            difference_type;
1539       typedef std::forward_iterator_tag                 iterator_category;
1540
1541       _Local_iterator() = default;
1542
1543       _Local_iterator(const __hash_code_base& __base,
1544                       _Hash_node<_Value, __cache>* __p,
1545                       std::size_t __bkt, std::size_t __bkt_count)
1546         : __base_type(__base, __p, __bkt, __bkt_count)
1547       { }
1548
1549       reference
1550       operator*() const
1551       { return this->_M_cur->_M_v(); }
1552
1553       pointer
1554       operator->() const
1555       { return this->_M_cur->_M_valptr(); }
1556
1557       _Local_iterator&
1558       operator++()
1559       {
1560         this->_M_incr();
1561         return *this;
1562       }
1563
1564       _Local_iterator
1565       operator++(int)
1566       {
1567         _Local_iterator __tmp(*this);
1568         this->_M_incr();
1569         return __tmp;
1570       }
1571     };
1572
1573   /// local const_iterators
1574   template<typename _Key, typename _Value, typename _ExtractKey,
1575            typename _H1, typename _H2, typename _Hash,
1576            bool __constant_iterators, bool __cache>
1577     struct _Local_const_iterator
1578     : public _Local_iterator_base<_Key, _Value, _ExtractKey,
1579                                   _H1, _H2, _Hash, __cache>
1580     {
1581     private:
1582       using __base_type = _Local_iterator_base<_Key, _Value, _ExtractKey,
1583                                                _H1, _H2, _Hash, __cache>;
1584       using __hash_code_base = typename __base_type::__hash_code_base;
1585
1586     public:
1587       typedef _Value                                    value_type;
1588       typedef const _Value*                             pointer;
1589       typedef const _Value&                             reference;
1590       typedef std::ptrdiff_t                            difference_type;
1591       typedef std::forward_iterator_tag                 iterator_category;
1592
1593       _Local_const_iterator() = default;
1594
1595       _Local_const_iterator(const __hash_code_base& __base,
1596                             _Hash_node<_Value, __cache>* __p,
1597                             std::size_t __bkt, std::size_t __bkt_count)
1598         : __base_type(__base, __p, __bkt, __bkt_count)
1599       { }
1600
1601       _Local_const_iterator(const _Local_iterator<_Key, _Value, _ExtractKey,
1602                                                   _H1, _H2, _Hash,
1603                                                   __constant_iterators,
1604                                                   __cache>& __x)
1605         : __base_type(__x)
1606       { }
1607
1608       reference
1609       operator*() const
1610       { return this->_M_cur->_M_v(); }
1611
1612       pointer
1613       operator->() const
1614       { return this->_M_cur->_M_valptr(); }
1615
1616       _Local_const_iterator&
1617       operator++()
1618       {
1619         this->_M_incr();
1620         return *this;
1621       }
1622
1623       _Local_const_iterator
1624       operator++(int)
1625       {
1626         _Local_const_iterator __tmp(*this);
1627         this->_M_incr();
1628         return __tmp;
1629       }
1630     };
1631
1632   /**
1633    *  Primary class template _Hashtable_base.
1634    *
1635    *  Helper class adding management of _Equal functor to
1636    *  _Hash_code_base type.
1637    *
1638    *  Base class templates are:
1639    *    - __detail::_Hash_code_base
1640    *    - __detail::_Hashtable_ebo_helper
1641    */
1642   template<typename _Key, typename _Value,
1643            typename _ExtractKey, typename _Equal,
1644            typename _H1, typename _H2, typename _Hash, typename _Traits>
1645   struct _Hashtable_base
1646   : public _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash,
1647                            _Traits::__hash_cached::value>,
1648     private _Hashtable_ebo_helper<0, _Equal>
1649   {
1650   public:
1651     typedef _Key                                        key_type;
1652     typedef _Value                                      value_type;
1653     typedef _Equal                                      key_equal;
1654     typedef std::size_t                                 size_type;
1655     typedef std::ptrdiff_t                              difference_type;
1656
1657     using __traits_type = _Traits;
1658     using __hash_cached = typename __traits_type::__hash_cached;
1659     using __constant_iterators = typename __traits_type::__constant_iterators;
1660     using __unique_keys = typename __traits_type::__unique_keys;
1661
1662     using __hash_code_base = _Hash_code_base<_Key, _Value, _ExtractKey,
1663                                              _H1, _H2, _Hash,
1664                                              __hash_cached::value>;
1665
1666     using __hash_code = typename __hash_code_base::__hash_code;
1667     using __node_type = typename __hash_code_base::__node_type;
1668
1669     using iterator = __detail::_Node_iterator<value_type,
1670                                               __constant_iterators::value,
1671                                               __hash_cached::value>;
1672
1673     using const_iterator = __detail::_Node_const_iterator<value_type,
1674                                                    __constant_iterators::value,
1675                                                    __hash_cached::value>;
1676
1677     using local_iterator = __detail::_Local_iterator<key_type, value_type,
1678                                                   _ExtractKey, _H1, _H2, _Hash,
1679                                                   __constant_iterators::value,
1680                                                      __hash_cached::value>;
1681
1682     using const_local_iterator = __detail::_Local_const_iterator<key_type,
1683                                                                  value_type,
1684                                         _ExtractKey, _H1, _H2, _Hash,
1685                                         __constant_iterators::value,
1686                                         __hash_cached::value>;
1687
1688     using __ireturn_type = typename std::conditional<__unique_keys::value,
1689                                                      std::pair<iterator, bool>,
1690                                                      iterator>::type;
1691   private:
1692     using _EqualEBO = _Hashtable_ebo_helper<0, _Equal>;
1693     using _EqualHelper =  _Equal_helper<_Key, _Value, _ExtractKey, _Equal,
1694                                         __hash_code, __hash_cached::value>;
1695
1696   protected:
1697     _Hashtable_base(const _ExtractKey& __ex, const _H1& __h1, const _H2& __h2,
1698                     const _Hash& __hash, const _Equal& __eq)
1699     : __hash_code_base(__ex, __h1, __h2, __hash), _EqualEBO(__eq)
1700     { }
1701
1702     bool
1703     _M_equals(const _Key& __k, __hash_code __c, __node_type* __n) const
1704     {
1705       return _EqualHelper::_S_equals(_M_eq(), this->_M_extract(),
1706                                      __k, __c, __n);
1707     }
1708
1709     void
1710     _M_swap(_Hashtable_base& __x)
1711     {
1712       __hash_code_base::_M_swap(__x);
1713       std::swap(_M_eq(), __x._M_eq());
1714     }
1715
1716     const _Equal&
1717     _M_eq() const { return _EqualEBO::_S_cget(*this); }
1718
1719     _Equal&
1720     _M_eq() { return _EqualEBO::_S_get(*this); }
1721   };
1722
1723   /**
1724    *  struct _Equality_base.
1725    *
1726    *  Common types and functions for class _Equality.
1727    */
1728   struct _Equality_base
1729   {
1730   protected:
1731     template<typename _Uiterator>
1732       static bool
1733       _S_is_permutation(_Uiterator, _Uiterator, _Uiterator);
1734   };
1735
1736   // See std::is_permutation in N3068.
1737   template<typename _Uiterator>
1738     bool
1739     _Equality_base::
1740     _S_is_permutation(_Uiterator __first1, _Uiterator __last1,
1741                       _Uiterator __first2)
1742     {
1743       for (; __first1 != __last1; ++__first1, ++__first2)
1744         if (!(*__first1 == *__first2))
1745           break;
1746
1747       if (__first1 == __last1)
1748         return true;
1749
1750       _Uiterator __last2 = __first2;
1751       std::advance(__last2, std::distance(__first1, __last1));
1752
1753       for (_Uiterator __it1 = __first1; __it1 != __last1; ++__it1)
1754         {
1755           _Uiterator __tmp =  __first1;
1756           while (__tmp != __it1 && !bool(*__tmp == *__it1))
1757             ++__tmp;
1758
1759           // We've seen this one before.
1760           if (__tmp != __it1)
1761             continue;
1762
1763           std::ptrdiff_t __n2 = 0;
1764           for (__tmp = __first2; __tmp != __last2; ++__tmp)
1765             if (*__tmp == *__it1)
1766               ++__n2;
1767
1768           if (!__n2)
1769             return false;
1770
1771           std::ptrdiff_t __n1 = 0;
1772           for (__tmp = __it1; __tmp != __last1; ++__tmp)
1773             if (*__tmp == *__it1)
1774               ++__n1;
1775
1776           if (__n1 != __n2)
1777             return false;
1778         }
1779       return true;
1780     }
1781
1782   /**
1783    *  Primary class template  _Equality.
1784    *
1785    *  This is for implementing equality comparison for unordered
1786    *  containers, per N3068, by John Lakos and Pablo Halpern.
1787    *  Algorithmically, we follow closely the reference implementations
1788    *  therein.
1789    */
1790   template<typename _Key, typename _Value, typename _Alloc,
1791            typename _ExtractKey, typename _Equal,
1792            typename _H1, typename _H2, typename _Hash,
1793            typename _RehashPolicy, typename _Traits,
1794            bool _Unique_keys = _Traits::__unique_keys::value>
1795     struct _Equality;
1796
1797   /// Specialization.
1798   template<typename _Key, typename _Value, typename _Alloc,
1799            typename _ExtractKey, typename _Equal,
1800            typename _H1, typename _H2, typename _Hash,
1801            typename _RehashPolicy, typename _Traits>
1802     struct _Equality<_Key, _Value, _Alloc, _ExtractKey, _Equal,
1803                      _H1, _H2, _Hash, _RehashPolicy, _Traits, true>
1804     {
1805       using __hashtable = _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
1806                                      _H1, _H2, _Hash, _RehashPolicy, _Traits>;
1807
1808       bool
1809       _M_equal(const __hashtable&) const;
1810     };
1811
1812   template<typename _Key, typename _Value, typename _Alloc,
1813            typename _ExtractKey, typename _Equal,
1814            typename _H1, typename _H2, typename _Hash,
1815            typename _RehashPolicy, typename _Traits>
1816     bool
1817     _Equality<_Key, _Value, _Alloc, _ExtractKey, _Equal,
1818               _H1, _H2, _Hash, _RehashPolicy, _Traits, true>::
1819     _M_equal(const __hashtable& __other) const
1820     {
1821       const __hashtable* __this = static_cast<const __hashtable*>(this);
1822
1823       if (__this->size() != __other.size())
1824         return false;
1825
1826       for (auto __itx = __this->begin(); __itx != __this->end(); ++__itx)
1827         {
1828           const auto __ity = __other.find(_ExtractKey()(*__itx));
1829           if (__ity == __other.end() || !bool(*__ity == *__itx))
1830             return false;
1831         }
1832       return true;
1833     }
1834
1835   /// Specialization.
1836   template<typename _Key, typename _Value, typename _Alloc,
1837            typename _ExtractKey, typename _Equal,
1838            typename _H1, typename _H2, typename _Hash,
1839            typename _RehashPolicy, typename _Traits>
1840     struct _Equality<_Key, _Value, _Alloc, _ExtractKey, _Equal,
1841                      _H1, _H2, _Hash, _RehashPolicy, _Traits, false>
1842     : public _Equality_base
1843     {
1844       using __hashtable = _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
1845                                      _H1, _H2, _Hash, _RehashPolicy, _Traits>;
1846
1847       bool
1848       _M_equal(const __hashtable&) const;
1849     };
1850
1851   template<typename _Key, typename _Value, typename _Alloc,
1852            typename _ExtractKey, typename _Equal,
1853            typename _H1, typename _H2, typename _Hash,
1854            typename _RehashPolicy, typename _Traits>
1855     bool
1856     _Equality<_Key, _Value, _Alloc, _ExtractKey, _Equal,
1857               _H1, _H2, _Hash, _RehashPolicy, _Traits, false>::
1858     _M_equal(const __hashtable& __other) const
1859     {
1860       const __hashtable* __this = static_cast<const __hashtable*>(this);
1861
1862       if (__this->size() != __other.size())
1863         return false;
1864
1865       for (auto __itx = __this->begin(); __itx != __this->end();)
1866         {
1867           const auto __xrange = __this->equal_range(_ExtractKey()(*__itx));
1868           const auto __yrange = __other.equal_range(_ExtractKey()(*__itx));
1869
1870           if (std::distance(__xrange.first, __xrange.second)
1871               != std::distance(__yrange.first, __yrange.second))
1872             return false;
1873
1874           if (!_S_is_permutation(__xrange.first, __xrange.second,
1875                                  __yrange.first))
1876             return false;
1877
1878           __itx = __xrange.second;
1879         }
1880       return true;
1881     }
1882
1883   /**
1884    * This type deals with all allocation and keeps an allocator instance through
1885    * inheritance to benefit from EBO when possible.
1886    */
1887   template<typename _NodeAlloc>
1888     struct _Hashtable_alloc : private _Hashtable_ebo_helper<0, _NodeAlloc>
1889     {
1890     private:
1891       using __ebo_node_alloc = _Hashtable_ebo_helper<0, _NodeAlloc>;
1892     public:
1893       using __node_type = typename _NodeAlloc::value_type;
1894       using __node_alloc_type = _NodeAlloc;
1895       // Use __gnu_cxx to benefit from _S_always_equal and al.
1896       using __node_alloc_traits = __gnu_cxx::__alloc_traits<__node_alloc_type>;
1897
1898       using __value_type = typename __node_type::value_type;
1899       using __value_alloc_type =
1900         __alloc_rebind<__node_alloc_type, __value_type>;
1901       using __value_alloc_traits = std::allocator_traits<__value_alloc_type>;
1902
1903       using __node_base = __detail::_Hash_node_base;
1904       using __bucket_type = __node_base*;
1905       using __bucket_alloc_type =
1906         __alloc_rebind<__node_alloc_type, __bucket_type>;
1907       using __bucket_alloc_traits = std::allocator_traits<__bucket_alloc_type>;
1908
1909       _Hashtable_alloc(const _Hashtable_alloc&) = default;
1910       _Hashtable_alloc(_Hashtable_alloc&&) = default;
1911
1912       template<typename _Alloc>
1913         _Hashtable_alloc(_Alloc&& __a)
1914           : __ebo_node_alloc(std::forward<_Alloc>(__a))
1915         { }
1916
1917       __node_alloc_type&
1918       _M_node_allocator()
1919       { return __ebo_node_alloc::_S_get(*this); }
1920
1921       const __node_alloc_type&
1922       _M_node_allocator() const
1923       { return __ebo_node_alloc::_S_cget(*this); }
1924
1925       template<typename... _Args>
1926         __node_type*
1927         _M_allocate_node(_Args&&... __args);
1928
1929       void
1930       _M_deallocate_node(__node_type* __n);
1931
1932       // Deallocate the linked list of nodes pointed to by __n
1933       void
1934       _M_deallocate_nodes(__node_type* __n);
1935
1936       __bucket_type*
1937       _M_allocate_buckets(std::size_t __n);
1938
1939       void
1940       _M_deallocate_buckets(__bucket_type*, std::size_t __n);
1941     };
1942
1943   // Definitions of class template _Hashtable_alloc's out-of-line member
1944   // functions.
1945   template<typename _NodeAlloc>
1946     template<typename... _Args>
1947       typename _Hashtable_alloc<_NodeAlloc>::__node_type*
1948       _Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&&... __args)
1949       {
1950         auto __nptr = __node_alloc_traits::allocate(_M_node_allocator(), 1);
1951         __node_type* __n = std::__addressof(*__nptr);
1952         __try
1953           {
1954             __value_alloc_type __a(_M_node_allocator());
1955             ::new ((void*)__n) __node_type;
1956             __value_alloc_traits::construct(__a, __n->_M_valptr(),
1957                                             std::forward<_Args>(__args)...);
1958             return __n;
1959           }
1960         __catch(...)
1961           {
1962             __node_alloc_traits::deallocate(_M_node_allocator(), __nptr, 1);
1963             __throw_exception_again;
1964           }
1965       }
1966
1967   template<typename _NodeAlloc>
1968     void
1969     _Hashtable_alloc<_NodeAlloc>::_M_deallocate_node(__node_type* __n)
1970     {
1971       typedef typename __node_alloc_traits::pointer _Ptr;
1972       auto __ptr = std::pointer_traits<_Ptr>::pointer_to(*__n);
1973       __value_alloc_type __a(_M_node_allocator());
1974       __value_alloc_traits::destroy(__a, __n->_M_valptr());
1975       __n->~__node_type();
1976       __node_alloc_traits::deallocate(_M_node_allocator(), __ptr, 1);
1977     }
1978
1979   template<typename _NodeAlloc>
1980     void
1981     _Hashtable_alloc<_NodeAlloc>::_M_deallocate_nodes(__node_type* __n)
1982     {
1983       while (__n)
1984         {
1985           __node_type* __tmp = __n;
1986           __n = __n->_M_next();
1987           _M_deallocate_node(__tmp);
1988         }
1989     }
1990
1991   template<typename _NodeAlloc>
1992     typename _Hashtable_alloc<_NodeAlloc>::__bucket_type*
1993     _Hashtable_alloc<_NodeAlloc>::_M_allocate_buckets(std::size_t __n)
1994     {
1995       __bucket_alloc_type __alloc(_M_node_allocator());
1996
1997       auto __ptr = __bucket_alloc_traits::allocate(__alloc, __n);
1998       __bucket_type* __p = std::__addressof(*__ptr);
1999       __builtin_memset(__p, 0, __n * sizeof(__bucket_type));
2000       return __p;
2001     }
2002
2003   template<typename _NodeAlloc>
2004     void
2005     _Hashtable_alloc<_NodeAlloc>::_M_deallocate_buckets(__bucket_type* __bkts,
2006                                                         std::size_t __n)
2007     {
2008       typedef typename __bucket_alloc_traits::pointer _Ptr;
2009       auto __ptr = std::pointer_traits<_Ptr>::pointer_to(*__bkts);
2010       __bucket_alloc_type __alloc(_M_node_allocator());
2011       __bucket_alloc_traits::deallocate(__alloc, __ptr, __n);
2012     }
2013
2014  //@} hashtable-detail
2015 _GLIBCXX_END_NAMESPACE_VERSION
2016 } // namespace __detail
2017 } // namespace std
2018
2019 #endif // _HASHTABLE_POLICY_H