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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
#define _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
#include <__config>
#include <__algorithm/move.h>
#include <__algorithm/move_backward.h>
#include <__algorithm/swap_ranges.h>
#include <__iterator/iterator_traits.h>
#include <type_traits> // swap
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
#if _LIBCPP_STD_VER > 17
template <class _ForwardIterator>
inline _LIBCPP_INLINE_VISIBILITY constexpr
_ForwardIterator
shift_right(_ForwardIterator __first, _ForwardIterator __last,
typename iterator_traits<_ForwardIterator>::difference_type __n)
{
if (__n == 0) {
return __first;
}
if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) {
decltype(__n) __d = __last - __first;
if (__n >= __d) {
return __last;
}
_ForwardIterator __m = __first + (__d - __n);
return _VSTD::move_backward(__first, __m, __last);
} else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) {
_ForwardIterator __m = __last;
for (; __n > 0; --__n) {
if (__m == __first) {
return __last;
}
--__m;
}
return _VSTD::move_backward(__first, __m, __last);
} else {
_ForwardIterator __ret = __first;
for (; __n > 0; --__n) {
if (__ret == __last) {
return __last;
}
++__ret;
}
// We have an __n-element scratch space from __first to __ret.
// Slide an __n-element window [__trail, __lead) from left to right.
// We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
// over and over; but once __lead reaches __last we needn't bother
// to save the values of elements [__trail, __last).
auto __trail = __first;
auto __lead = __ret;
while (__trail != __ret) {
if (__lead == __last) {
_VSTD::move(__first, __trail, __ret);
return __ret;
}
++__trail;
++__lead;
}
_ForwardIterator __mid = __first;
while (true) {
if (__lead == __last) {
__trail = _VSTD::move(__mid, __ret, __trail);
_VSTD::move(__first, __mid, __trail);
return __ret;
}
swap(*__mid, *__trail);
++__mid;
++__trail;
++__lead;
if (__mid == __ret) {
__mid = __first;
}
}
}
}
#endif // _LIBCPP_STD_VER > 17
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
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