1// -*- C++ -*-
2//===----------------------------------------------------------------------===//
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef _LIBCPP___ITERATOR_BOUNDED_ITER_H
11#define _LIBCPP___ITERATOR_BOUNDED_ITER_H
12
13#include <__assert>
14#include <__compare/ordering.h>
15#include <__compare/three_way_comparable.h>
16#include <__config>
17#include <__iterator/iterator_traits.h>
18#include <__memory/pointer_traits.h>
19#include <__type_traits/conjunction.h>
20#include <__type_traits/disjunction.h>
21#include <__type_traits/enable_if.h>
22#include <__type_traits/integral_constant.h>
23#include <__type_traits/is_convertible.h>
24#include <__type_traits/is_same.h>
25#include <__type_traits/make_const_lvalue_ref.h>
26#include <__utility/move.h>
27
28#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
29# pragma GCC system_header
30#endif
31
32_LIBCPP_PUSH_MACROS
33#include <__undef_macros>
34
35_LIBCPP_BEGIN_NAMESPACE_STD
36
37// Iterator wrapper that carries the valid range it is allowed to access.
38//
39// This is a simple iterator wrapper for contiguous iterators that points
40// within a [begin, end] range and carries these bounds with it. The iterator
41// ensures that it is pointing within [begin, end) range when it is
42// dereferenced. It also ensures that it is never iterated outside of
43// [begin, end]. This is important for two reasons:
44//
45// 1. It allows `operator*` and `operator++` bounds checks to be `iter != end`.
46// This is both less for the optimizer to prove, and aligns with how callers
47// typically use iterators.
48//
49// 2. Advancing an iterator out of bounds is undefined behavior (see the table
50// in [input.iterators]). In particular, when the underlying iterator is a
51// pointer, it is undefined at the language level (see [expr.add]). If
52// bounded iterators exhibited this undefined behavior, we risk compiler
53// optimizations deleting non-redundant bounds checks.
54template <class _Iterator>
55struct __bounded_iter {
56 static_assert(__libcpp_is_contiguous_iterator<_Iterator>::value,
57 "Only contiguous iterators can be adapted by __bounded_iter.");
58
59 using value_type = typename iterator_traits<_Iterator>::value_type;
60 using difference_type = typename iterator_traits<_Iterator>::difference_type;
61 using pointer = typename iterator_traits<_Iterator>::pointer;
62 using reference = typename iterator_traits<_Iterator>::reference;
63 using iterator_category = typename iterator_traits<_Iterator>::iterator_category;
64#if _LIBCPP_STD_VER >= 20
65 using iterator_concept = contiguous_iterator_tag;
66#endif
67
68 // Create a singular iterator.
69 //
70 // Such an iterator points past the end of an empty range, so it is not dereferenceable.
71 // Operations like comparison and assignment are valid.
72 _LIBCPP_HIDE_FROM_ABI __bounded_iter() = default;
73
74 _LIBCPP_HIDE_FROM_ABI __bounded_iter(__bounded_iter const&) = default;
75 _LIBCPP_HIDE_FROM_ABI __bounded_iter(__bounded_iter&&) = default;
76
77 template <class _OtherIterator,
78 __enable_if_t<
79 _And<is_convertible<const _OtherIterator&, _Iterator>,
80 _Or<is_same<reference, __iterator_reference<_OtherIterator> >,
81 is_same<reference, __make_const_lvalue_ref<__iterator_reference<_OtherIterator> > > > >::value,
82 int> = 0>
83 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __bounded_iter(__bounded_iter<_OtherIterator> const& __other) _NOEXCEPT
84 : __current_(__other.__current_),
85 __begin_(__other.__begin_),
86 __end_(__other.__end_) {}
87
88 // Assign a bounded iterator to another one, rebinding the bounds of the iterator as well.
89 _LIBCPP_HIDE_FROM_ABI __bounded_iter& operator=(__bounded_iter const&) = default;
90 _LIBCPP_HIDE_FROM_ABI __bounded_iter& operator=(__bounded_iter&&) = default;
91
92private:
93 // Create an iterator wrapping the given iterator, and whose bounds are described
94 // by the provided [begin, end] range.
95 //
96 // The constructor does not check whether the resulting iterator is within its bounds. It is a
97 // responsibility of the container to ensure that the given bounds are valid.
98 //
99 // Since it is non-standard for iterators to have this constructor, __bounded_iter must
100 // be created via `std::__make_bounded_iter`.
101 _LIBCPP_HIDE_FROM_ABI
102 _LIBCPP_CONSTEXPR_SINCE_CXX14 explicit __bounded_iter(_Iterator __current, _Iterator __begin, _Iterator __end)
103 : __current_(__current), __begin_(__begin), __end_(__end) {
104 _LIBCPP_ASSERT_INTERNAL(
105 __begin <= __current, "__bounded_iter(current, begin, end): current and begin are inconsistent");
106 _LIBCPP_ASSERT_INTERNAL(
107 __current <= __end, "__bounded_iter(current, begin, end): current and end are inconsistent");
108 }
109
110 template <class _It>
111 friend _LIBCPP_CONSTEXPR __bounded_iter<_It> __make_bounded_iter(_It, _It, _It);
112
113public:
114 // Dereference and indexing operations.
115 //
116 // These operations check that the iterator is dereferenceable. Since the class invariant is
117 // that the iterator is always within `[begin, end]`, we only need to check it's not pointing to
118 // `end`. This is easier for the optimizer because it aligns with the `iter != container.end()`
119 // checks that typical callers already use (see https://llvm.org/PR78829).
120 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference operator*() const _NOEXCEPT {
121 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
122 __current_ != __end_, "__bounded_iter::operator*: Attempt to dereference an iterator at the end");
123 return *__current_;
124 }
125
126 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pointer operator->() const _NOEXCEPT {
127 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
128 __current_ != __end_, "__bounded_iter::operator->: Attempt to dereference an iterator at the end");
129 return std::__to_address(__current_);
130 }
131
132 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference operator[](difference_type __n) const _NOEXCEPT {
133 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
134 __n >= __begin_ - __current_, "__bounded_iter::operator[]: Attempt to index an iterator past the start");
135 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
136 __n < __end_ - __current_, "__bounded_iter::operator[]: Attempt to index an iterator at or past the end");
137 return __current_[__n];
138 }
139
140 // Arithmetic operations.
141 //
142 // These operations check that the iterator remains within `[begin, end]`.
143 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __bounded_iter& operator++() _NOEXCEPT {
144 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
145 __current_ != __end_, "__bounded_iter::operator++: Attempt to advance an iterator past the end");
146 ++__current_;
147 return *this;
148 }
149 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __bounded_iter operator++(int) _NOEXCEPT {
150 __bounded_iter __tmp(*this);
151 ++*this;
152 return __tmp;
153 }
154
155 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __bounded_iter& operator--() _NOEXCEPT {
156 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
157 __current_ != __begin_, "__bounded_iter::operator--: Attempt to rewind an iterator past the start");
158 --__current_;
159 return *this;
160 }
161 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __bounded_iter operator--(int) _NOEXCEPT {
162 __bounded_iter __tmp(*this);
163 --*this;
164 return __tmp;
165 }
166
167 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __bounded_iter& operator+=(difference_type __n) _NOEXCEPT {
168 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
169 __n >= __begin_ - __current_, "__bounded_iter::operator+=: Attempt to rewind an iterator past the start");
170 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
171 __n <= __end_ - __current_, "__bounded_iter::operator+=: Attempt to advance an iterator past the end");
172 __current_ += __n;
173 return *this;
174 }
175 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __bounded_iter
176 operator+(__bounded_iter const& __self, difference_type __n) _NOEXCEPT {
177 __bounded_iter __tmp(__self);
178 __tmp += __n;
179 return __tmp;
180 }
181 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __bounded_iter
182 operator+(difference_type __n, __bounded_iter const& __self) _NOEXCEPT {
183 __bounded_iter __tmp(__self);
184 __tmp += __n;
185 return __tmp;
186 }
187
188 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __bounded_iter& operator-=(difference_type __n) _NOEXCEPT {
189 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
190 __n <= __current_ - __begin_, "__bounded_iter::operator-=: Attempt to rewind an iterator past the start");
191 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
192 __n >= __current_ - __end_, "__bounded_iter::operator-=: Attempt to advance an iterator past the end");
193 __current_ -= __n;
194 return *this;
195 }
196 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __bounded_iter
197 operator-(__bounded_iter const& __self, difference_type __n) _NOEXCEPT {
198 __bounded_iter __tmp(__self);
199 __tmp -= __n;
200 return __tmp;
201 }
202 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend difference_type
203 operator-(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
204 return __x.__current_ - __y.__current_;
205 }
206
207 // Comparison operations.
208 //
209 // These operations do not check whether the iterators are within their bounds.
210 // The valid range for each iterator is also not considered as part of the comparison,
211 // i.e. two iterators pointing to the same location will be considered equal even
212 // if they have different validity ranges.
213 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
214 operator==(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
215 return __x.__current_ == __y.__current_;
216 }
217
218#if _LIBCPP_STD_VER <= 17
219 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
220 operator!=(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
221 return __x.__current_ != __y.__current_;
222 }
223
224 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
225 operator<(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
226 return __x.__current_ < __y.__current_;
227 }
228 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
229 operator>(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
230 return __x.__current_ > __y.__current_;
231 }
232 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
233 operator<=(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
234 return __x.__current_ <= __y.__current_;
235 }
236 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
237 operator>=(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
238 return __x.__current_ >= __y.__current_;
239 }
240
241#else
242 _LIBCPP_HIDE_FROM_ABI constexpr friend strong_ordering
243 operator<=>(__bounded_iter const& __x, __bounded_iter const& __y) noexcept {
244 if constexpr (three_way_comparable<_Iterator, strong_ordering>) {
245 return __x.__current_ <=> __y.__current_;
246 } else {
247 if (__x.__current_ < __y.__current_)
248 return strong_ordering::less;
249
250 if (__x.__current_ == __y.__current_)
251 return strong_ordering::equal;
252
253 return strong_ordering::greater;
254 }
255 }
256#endif // _LIBCPP_STD_VER >= 20
257
258private:
259 template <class>
260 friend struct pointer_traits;
261 template <class>
262 friend struct __bounded_iter;
263 _Iterator __current_; // current iterator
264 _Iterator __begin_, __end_; // valid range represented as [begin, end]
265};
266
267template <class _It>
268_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __bounded_iter<_It> __make_bounded_iter(_It __it, _It __begin, _It __end) {
269 return __bounded_iter<_It>(std::move(__it), std::move(__begin), std::move(__end));
270}
271
272#if _LIBCPP_STD_VER <= 17
273template <class _Iterator>
274struct __libcpp_is_contiguous_iterator<__bounded_iter<_Iterator> > : true_type {};
275#endif
276
277template <class _Iterator>
278struct pointer_traits<__bounded_iter<_Iterator> > {
279 using pointer = __bounded_iter<_Iterator>;
280 using element_type = typename pointer_traits<_Iterator>::element_type;
281 using difference_type = typename pointer_traits<_Iterator>::difference_type;
282
283 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static element_type* to_address(pointer __it) _NOEXCEPT {
284 return std::__to_address(__it.__current_);
285 }
286};
287
288_LIBCPP_END_NAMESPACE_STD
289
290_LIBCPP_POP_MACROS
291
292#endif // _LIBCPP___ITERATOR_BOUNDED_ITER_H
293