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