Filename: //usr/include/c++/10///tr1/hashtable_policy.h

// Internal policy header for TR1 unordered_set and unordered_map -*- C++ -*- // Copyright (C) 2010-2020 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 tr1/hashtable_policy.h * This is an internal header file, included by other library headers. * Do not attempt to use it directly. * @headername{tr1/unordered_map, tr1/unordered_set} */ namespace std _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION namespace tr1 { namespace __detail { // 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 _Value> struct _Hash_node<_Value, false> { _Value _M_v; _Hash_node* _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 __gnu_cxx::__conditional_type<__constant_iterators, const _Value*, _Value*>::__type pointer; typedef typename __gnu_cxx::__conditional_type<__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 __gnu_cxx::__conditional_type<__constant_iterators, const _Value*, _Value*>::__type pointer; typedef typename __gnu_cxx::__conditional_type<__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 { // Don't include the last prime in the search, so that anything // higher than the second-to-last prime returns a past-the-end // iterator that can be dereferenced to get the last prime. const unsigned long* __p = std::lower_bound(__prime_list, __prime_list + _S_n_primes - 1, __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; return _M_next_bkt(__builtin_ceil(__min_bkts)); } // 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); return std::make_pair(true, _M_next_bkt(__builtin_ceil(__min_bkts))); } 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::tr1::_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); }; 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; } // class template _Rehash_base. Give hashtable the max_load_factor // functions 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)); } }; // 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; }; } // namespace __detail } _GLIBCXX_END_NAMESPACE_VERSION }

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