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1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___CXX03___ITERATOR_ALIASING_ITERATOR_H
10#define _LIBCPP___CXX03___ITERATOR_ALIASING_ITERATOR_H
11
12#include <__cxx03/__config>
13#include <__cxx03/__iterator/iterator_traits.h>
14#include <__cxx03/__memory/pointer_traits.h>
15#include <__cxx03/__type_traits/is_trivial.h>
16#include <__cxx03/cstddef>
17
18#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19# pragma GCC system_header
20#endif
21
22// This iterator wrapper is used to type-pun an iterator to return a different type. This is done without UB by not
23// actually punning the type, but instead inspecting the object representation of the base type and copying that into
24// an instance of the alias type. For that reason the alias type has to be trivial. The alias is returned as a prvalue
25// when derferencing the iterator, since it is temporary storage. This wrapper is used to vectorize some algorithms.
26
27_LIBCPP_BEGIN_NAMESPACE_STD
28
29template <class _BaseIter, class _Alias>
30struct __aliasing_iterator_wrapper {
31 class __iterator {
32 _BaseIter __base_ = nullptr;
33
34 using __iter_traits = iterator_traits<_BaseIter>;
35 using __base_value_type = typename __iter_traits::value_type;
36
37 static_assert(__has_random_access_iterator_category<_BaseIter>::value,
38 "The base iterator has to be a random access iterator!");
39
40 public:
41 using iterator_category = random_access_iterator_tag;
42 using value_type = _Alias;
43 using difference_type = ptrdiff_t;
44 using reference = value_type&;
45 using pointer = value_type*;
46
47 static_assert(is_trivial<value_type>::value);
48 static_assert(sizeof(__base_value_type) == sizeof(value_type));
49
50 _LIBCPP_HIDE_FROM_ABI __iterator() = default;
51 _LIBCPP_HIDE_FROM_ABI __iterator(_BaseIter __base) _NOEXCEPT : __base_(__base) {}
52
53 _LIBCPP_HIDE_FROM_ABI __iterator& operator++() _NOEXCEPT {
54 ++__base_;
55 return *this;
56 }
57
58 _LIBCPP_HIDE_FROM_ABI __iterator operator++(int) _NOEXCEPT {
59 __iterator __tmp(*this);
60 ++__base_;
61 return __tmp;
62 }
63
64 _LIBCPP_HIDE_FROM_ABI __iterator& operator--() _NOEXCEPT {
65 --__base_;
66 return *this;
67 }
68
69 _LIBCPP_HIDE_FROM_ABI __iterator operator--(int) _NOEXCEPT {
70 __iterator __tmp(*this);
71 --__base_;
72 return __tmp;
73 }
74
75 _LIBCPP_HIDE_FROM_ABI friend __iterator operator+(__iterator __iter, difference_type __n) _NOEXCEPT {
76 return __iterator(__iter.__base_ + __n);
77 }
78
79 _LIBCPP_HIDE_FROM_ABI friend __iterator operator+(difference_type __n, __iterator __iter) _NOEXCEPT {
80 return __iterator(__n + __iter.__base_);
81 }
82
83 _LIBCPP_HIDE_FROM_ABI __iterator& operator+=(difference_type __n) _NOEXCEPT {
84 __base_ += __n;
85 return *this;
86 }
87
88 _LIBCPP_HIDE_FROM_ABI friend __iterator operator-(__iterator __iter, difference_type __n) _NOEXCEPT {
89 return __iterator(__iter.__base_ - __n);
90 }
91
92 _LIBCPP_HIDE_FROM_ABI friend difference_type operator-(__iterator __lhs, __iterator __rhs) _NOEXCEPT {
93 return __lhs.__base_ - __rhs.__base_;
94 }
95
96 _LIBCPP_HIDE_FROM_ABI __iterator& operator-=(difference_type __n) _NOEXCEPT {
97 __base_ -= __n;
98 return *this;
99 }
100
101 _LIBCPP_HIDE_FROM_ABI _BaseIter __base() const _NOEXCEPT { return __base_; }
102
103 _LIBCPP_HIDE_FROM_ABI _Alias operator*() const _NOEXCEPT {
104 _Alias __val;
105 __builtin_memcpy(&__val, std::__to_address(__base_), sizeof(value_type));
106 return __val;
107 }
108
109 _LIBCPP_HIDE_FROM_ABI value_type operator[](difference_type __n) const _NOEXCEPT { return *(*this + __n); }
110
111 _LIBCPP_HIDE_FROM_ABI friend bool operator==(const __iterator& __lhs, const __iterator& __rhs) _NOEXCEPT {
112 return __lhs.__base_ == __rhs.__base_;
113 }
114
115 _LIBCPP_HIDE_FROM_ABI friend bool operator!=(const __iterator& __lhs, const __iterator& __rhs) _NOEXCEPT {
116 return __lhs.__base_ != __rhs.__base_;
117 }
118 };
119};
120
121// This is required to avoid ADL instantiations on _BaseT
122template <class _BaseT, class _Alias>
123using __aliasing_iterator = typename __aliasing_iterator_wrapper<_BaseT, _Alias>::__iterator;
124
125_LIBCPP_END_NAMESPACE_STD
126
127#endif // _LIBCPP___CXX03___ITERATOR_ALIASING_ITERATOR_H
128

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source code of libcxx/include/__cxx03/__iterator/aliasing_iterator.h