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_PREV_H
11#define _LIBCPP___ITERATOR_PREV_H
12
13#include <__assert>
14#include <__config>
15#include <__iterator/advance.h>
16#include <__iterator/concepts.h>
17#include <__iterator/incrementable_traits.h>
18#include <__iterator/iterator_traits.h>
19#include <__type_traits/enable_if.h>
20
21#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
22#  pragma GCC system_header
23#endif
24
25_LIBCPP_BEGIN_NAMESPACE_STD
26
27template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>
28inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter
29prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) {
30  // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation.
31  // Note that this check duplicates the similar check in `std::advance`.
32  _LIBCPP_ASSERT_PEDANTIC(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value,
33                          "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
34  std::advance(__x, -__n);
35  return __x;
36}
37
38#if _LIBCPP_STD_VER >= 20
39
40// [range.iter.op.prev]
41
42namespace ranges {
43namespace __prev {
44
45struct __fn {
46  template <bidirectional_iterator _Ip>
47  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
48    --__x;
49    return __x;
50  }
51
52  template <bidirectional_iterator _Ip>
53  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
54    ranges::advance(__x, -__n);
55    return __x;
56  }
57
58  template <bidirectional_iterator _Ip>
59  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
60    ranges::advance(__x, -__n, __bound_iter);
61    return __x;
62  }
63};
64
65} // namespace __prev
66
67inline namespace __cpo {
68inline constexpr auto prev = __prev::__fn{};
69} // namespace __cpo
70} // namespace ranges
71
72#endif // _LIBCPP_STD_VER >= 20
73
74_LIBCPP_END_NAMESPACE_STD
75
76#endif // _LIBCPP___ITERATOR_PREV_H
77