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80643d9366
We plan to add concepts for checking that iterators actually provide what they claim to. This is to avoid people thinking that these type traits actually check the iterator requirements in more detail. Reviewed By: ldionne, #libc Spies: Mordante, libcxx-commits, wenlei Differential Revision: https://reviews.llvm.org/D150801
56 lines
1.5 KiB
C++
56 lines
1.5 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_LEFT_H
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#define _LIBCPP___ALGORITHM_SHIFT_LEFT_H
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#include <__algorithm/move.h>
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#include <__config>
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#include <__iterator/iterator_traits.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_BEGIN_NAMESPACE_STD
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#if _LIBCPP_STD_VER >= 20
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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_left(_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 __last;
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}
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_ForwardIterator __m = __first;
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if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) {
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if (__n >= __last - __first) {
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return __first;
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}
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__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;
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}
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++__m;
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}
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}
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return _VSTD::move(__m, __last, __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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#endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H
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