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___ALGORITHM_SHIFT_LEFT_H
10#define _LIBCPP___ALGORITHM_SHIFT_LEFT_H
11
12#include <__algorithm/iterator_operations.h>
13#include <__algorithm/move.h>
14#include <__assert>
15#include <__config>
16#include <__iterator/concepts.h>
17#include <__iterator/iterator_traits.h>
18#include <__utility/move.h>
19#include <__utility/pair.h>
20
21#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
22# pragma GCC system_header
23#endif
24
25_LIBCPP_PUSH_MACROS
26#include <__undef_macros>
27
28_LIBCPP_BEGIN_NAMESPACE_STD
29
30#if _LIBCPP_STD_VER >= 20
31
32template <class _AlgPolicy, class _Iter, class _Sent>
33_LIBCPP_HIDE_FROM_ABI constexpr pair<_Iter, _Iter>
34__shift_left(_Iter __first, _Sent __last, typename _IterOps<_AlgPolicy>::template __difference_type<_Iter> __n) {
35 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n >= 0, "n must be greater than or equal to 0");
36
37 if (__n == 0) {
38 _Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
39 return {std::move(__first), std::move(__end)};
40 }
41
42 _Iter __m = __first;
43 if constexpr (sized_sentinel_for<_Sent, _Iter>) {
44 auto __size = _IterOps<_AlgPolicy>::distance(__first, __last);
45 if (__n >= __size) {
46 return {__first, std::move(__first)};
47 }
48 _IterOps<_AlgPolicy>::advance(__m, __n);
49 } else {
50 for (; __n > 0; --__n) {
51 if (__m == __last) {
52 return {__first, std::move(__first)};
53 }
54 ++__m;
55 }
56 }
57
58 _Iter __result = std::__move<_AlgPolicy>(__m, __last, __first).second;
59 return {std::move(__first), std::move(__result)};
60}
61
62template <class _ForwardIterator>
63_LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator
64shift_left(_ForwardIterator __first,
65 _ForwardIterator __last,
66 typename iterator_traits<_ForwardIterator>::difference_type __n) {
67 return std::__shift_left<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __n).second;
68}
69
70#endif // _LIBCPP_STD_VER >= 20
71
72_LIBCPP_END_NAMESPACE_STD
73
74_LIBCPP_POP_MACROS
75
76#endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H
77