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https://github.com/jart/cosmopolitan.git
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76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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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___ITERATOR_PREV_H
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#define _LIBCPP___ITERATOR_PREV_H
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#include <__assert>
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#include <__config>
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#include <__iterator/advance.h>
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#include <__iterator/concepts.h>
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#include <__iterator/incrementable_traits.h>
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#include <__iterator/iterator_traits.h>
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#include <__type_traits/enable_if.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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template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>
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inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter
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prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) {
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// Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation.
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// Note that this check duplicates the similar check in `std::advance`.
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_LIBCPP_ASSERT_PEDANTIC(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value,
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"Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
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std::advance(__x, -__n);
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return __x;
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}
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#if _LIBCPP_STD_VER >= 20
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// [range.iter.op.prev]
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namespace ranges {
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namespace __prev {
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struct __fn {
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template <bidirectional_iterator _Ip>
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_LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
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--__x;
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return __x;
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}
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template <bidirectional_iterator _Ip>
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_LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
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ranges::advance(__x, -__n);
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return __x;
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}
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template <bidirectional_iterator _Ip>
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_LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
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ranges::advance(__x, -__n, __bound_iter);
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return __x;
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}
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};
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} // namespace __prev
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inline namespace __cpo {
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inline constexpr auto prev = __prev::__fn{};
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} // namespace __cpo
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} // namespace ranges
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#endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ITERATOR_PREV_H
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