forked from OSchip/llvm-project
128 lines
4.1 KiB
C++
128 lines
4.1 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___RANGES_DROP_VIEW_H
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#define _LIBCPP___RANGES_DROP_VIEW_H
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#include <__config>
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#include <__debug>
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#include <__iterator/concepts.h>
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#include <__iterator/iterator_traits.h>
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#include <__iterator/next.h>
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#include <__ranges/access.h>
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#include <__ranges/all.h>
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#include <__ranges/concepts.h>
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#include <__ranges/enable_borrowed_range.h>
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#include <__ranges/non_propagating_cache.h>
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#include <__ranges/size.h>
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#include <__ranges/view_interface.h>
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#include <__utility/move.h>
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#include <concepts>
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#include <type_traits>
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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 !defined(_LIBCPP_HAS_NO_RANGES)
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namespace ranges {
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template<view _View>
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class drop_view
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: public view_interface<drop_view<_View>>
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{
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// We cache begin() whenever ranges::next is not guaranteed O(1) to provide an
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// amortized O(1) begin() method. If this is an input_range, then we cannot cache
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// begin because begin is not equality preserving.
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// Note: drop_view<input-range>::begin() is still trivially amortized O(1) because
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// one can't call begin() on it more than once.
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static constexpr bool _UseCache = forward_range<_View> && !(random_access_range<_View> && sized_range<_View>);
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using _Cache = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
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[[no_unique_address]] _Cache __cached_begin_ = _Cache();
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range_difference_t<_View> __count_ = 0;
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_View __base_ = _View();
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public:
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drop_view() requires default_initializable<_View> = default;
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_LIBCPP_HIDE_FROM_ABI
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constexpr drop_view(_View __base, range_difference_t<_View> __count)
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: __count_(__count)
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, __base_(_VSTD::move(__base))
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{
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_LIBCPP_ASSERT(__count_ >= 0, "count must be greater than or equal to zero.");
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}
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_LIBCPP_HIDE_FROM_ABI constexpr _View base() const& requires copy_constructible<_View> { return __base_; }
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_LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return _VSTD::move(__base_); }
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto begin()
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requires (!(__simple_view<_View> &&
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random_access_range<const _View> && sized_range<const _View>))
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{
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if constexpr (_UseCache)
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if (__cached_begin_.__has_value())
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return *__cached_begin_;
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auto __tmp = ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
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if constexpr (_UseCache)
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__cached_begin_.__emplace(__tmp);
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return __tmp;
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}
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto begin() const
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requires random_access_range<const _View> && sized_range<const _View>
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{
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return ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
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}
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto end()
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requires (!__simple_view<_View>)
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{ return ranges::end(__base_); }
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto end() const
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requires range<const _View>
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{ return ranges::end(__base_); }
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_LIBCPP_HIDE_FROM_ABI
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static constexpr auto __size(auto& __self) {
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const auto __s = ranges::size(__self.__base_);
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const auto __c = static_cast<decltype(__s)>(__self.__count_);
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return __s < __c ? 0 : __s - __c;
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}
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto size()
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requires sized_range<_View>
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{ return __size(*this); }
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto size() const
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requires sized_range<const _View>
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{ return __size(*this); }
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};
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template<class _Range>
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drop_view(_Range&&, range_difference_t<_Range>) -> drop_view<views::all_t<_Range>>;
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template<class _Tp>
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inline constexpr bool enable_borrowed_range<drop_view<_Tp>> = enable_borrowed_range<_Tp>;
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} // namespace ranges
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#endif // !defined(_LIBCPP_HAS_NO_RANGES)
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___RANGES_DROP_VIEW_H
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