9311996261
Implement the `ranges::shift_left` algorithm from [P2440R1](https://wg21.link/P2440R1). Closes: #134061 --------- Co-authored-by: Hui Xie <hui.xie1990@gmail.com> Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
77 lines
2.3 KiB
C++
77 lines
2.3 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_LEFT_H
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#define _LIBCPP___ALGORITHM_SHIFT_LEFT_H
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#include <__algorithm/iterator_operations.h>
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#include <__algorithm/move.h>
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#include <__assert>
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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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#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_left(_Iter __first, _Sent __last, typename _IterOps<_AlgPolicy>::template __difference_type<_Iter> __n) {
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_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n >= 0, "n must be greater than or equal to 0");
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if (__n == 0) {
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_Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
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return {std::move(__first), std::move(__end)};
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}
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_Iter __m = __first;
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if constexpr (sized_sentinel_for<_Sent, _Iter>) {
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auto __size = _IterOps<_AlgPolicy>::distance(__first, __last);
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if (__n >= __size) {
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return {__first, std::move(__first)};
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}
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_IterOps<_AlgPolicy>::advance(__m, __n);
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} else {
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for (; __n > 0; --__n) {
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if (__m == __last) {
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return {__first, std::move(__first)};
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}
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++__m;
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}
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}
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_Iter __result = std::__move<_AlgPolicy>(__m, __last, __first).second;
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return {std::move(__first), std::move(__result)};
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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_left(_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_left<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __n).second;
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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_LEFT_H
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