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/move.h>
13#include <__config>
14#include <__iterator/iterator_traits.h>
15
16#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17# pragma GCC system_header
18#endif
19
20_LIBCPP_PUSH_MACROS
21#include <__undef_macros>
22
23_LIBCPP_BEGIN_NAMESPACE_STD
24
25#if _LIBCPP_STD_VER >= 20
26
27template <class _ForwardIterator>
28inline _LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator
29shift_left(_ForwardIterator __first,
30 _ForwardIterator __last,
31 typename iterator_traits<_ForwardIterator>::difference_type __n) {
32 if (__n == 0) {
33 return __last;
34 }
35
36 _ForwardIterator __m = __first;
37 if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) {
38 if (__n >= __last - __first) {
39 return __first;
40 }
41 __m += __n;
42 } else {
43 for (; __n > 0; --__n) {
44 if (__m == __last) {
45 return __first;
46 }
47 ++__m;
48 }
49 }
50 return std::move(__m, __last, __first);
51}
52
53#endif // _LIBCPP_STD_VER >= 20
54
55_LIBCPP_END_NAMESPACE_STD
56
57_LIBCPP_POP_MACROS
58
59#endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H
60