d7a24d30f6
Implement the `ranges::shift_right` algorithm from [P2440R1](https://wg21.link/P2440R1). Fixes #134062 Fixes #105184
132 lines
4.5 KiB
C++
132 lines
4.5 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 <__algorithm/iterator_operations.h>
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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 <__assert>
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#include <__concepts/derived_from.h>
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#include <__config>
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#include <__iterator/concepts.h>
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#include <__iterator/iterator_traits.h>
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#include <__utility/move.h>
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#include <__utility/pair.h>
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#include <__utility/swap.h>
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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_PUSH_MACROS
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#include <__undef_macros>
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if _LIBCPP_STD_VER >= 20
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template <class _AlgPolicy, class _Iter, class _Sent>
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_LIBCPP_HIDE_FROM_ABI constexpr pair<_Iter, _Iter>
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__shift_right(_Iter __first, _Sent __last, typename _IterOps<_AlgPolicy>::template __difference_type<_Iter> __n) {
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_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n >= 0, "Providing a negative shift amount to shift_right is UB");
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if (__n == 0) {
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_Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
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return pair<_Iter, _Iter>(std::move(__first), std::move(__end));
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}
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using _IterCategory = typename _IterOps<_AlgPolicy>::template __iterator_category<_Iter>;
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if constexpr (derived_from<_IterCategory, random_access_iterator_tag>) {
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_Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
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auto __size = __end - __first;
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if (__n >= __size) {
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return pair<_Iter, _Iter>(__end, std::move(__end));
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}
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_Iter __m = __first;
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_IterOps<_AlgPolicy>::advance(__m, (__size - __n));
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auto __ret = std::__move_backward<_AlgPolicy>(std::move(__first), std::move(__m), __end);
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return pair<_Iter, _Iter>(std::move(__ret.second), std::move(__end));
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} else if constexpr (derived_from<_IterCategory, bidirectional_iterator_tag>) {
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_Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
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if constexpr (sized_sentinel_for<_Sent, _Iter>) {
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if (__n >= ranges::distance(__first, __last)) {
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return pair<_Iter, _Iter>(__end, std::move(__end));
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}
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}
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_Iter __m = __end;
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for (; __n > 0; --__n) {
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if (__m == __first) {
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return pair<_Iter, _Iter>(__end, std::move(__end));
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}
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--__m;
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}
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auto __ret = std::__move_backward<_AlgPolicy>(std::move(__first), std::move(__m), __end);
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return pair<_Iter, _Iter>(std::move(__ret.second), std::move(__end));
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} else {
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_Iter __ret = __first;
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for (; __n > 0; --__n) {
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if (__ret == __last) {
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return pair<_Iter, _Iter>(__ret, std::move(__ret));
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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 __end we needn't bother
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// to save the values of elements [__trail, __end).
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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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std::__move<_AlgPolicy>(std::move(__first), std::move(__trail), __ret);
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return pair<_Iter, _Iter>(__ret, std::move(__lead));
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}
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++__trail;
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++__lead;
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}
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_Iter __mid = __first;
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while (true) {
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if (__lead == __last) {
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__trail = std::__move<_AlgPolicy>(__mid, __ret, __trail).second;
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std::__move<_AlgPolicy>(std::move(__first), std::move(__mid), std::move(__trail));
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return pair<_Iter, _Iter>(__ret, std::move(__lead));
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}
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_IterOps<_AlgPolicy>::iter_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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template <class _ForwardIterator>
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_LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator
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shift_right(_ForwardIterator __first,
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_ForwardIterator __last,
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typename iterator_traits<_ForwardIterator>::difference_type __n) {
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return std::__shift_right<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __n).first;
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}
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#endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_END_NAMESPACE_STD
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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
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