85 lines
2.7 KiB
C++
85 lines
2.7 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_UNWRAP_ITER_H
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#define _LIBCPP___ALGORITHM_UNWRAP_ITER_H
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#include <__config>
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#include <__memory/pointer_traits.h>
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#include <iterator>
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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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// The job of __unwrap_iter is to lower contiguous iterators (such as
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// vector<T>::iterator) into pointers, to reduce the number of template
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// instantiations and to enable pointer-based optimizations e.g. in std::copy.
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// For iterators that are not contiguous, it must be a no-op.
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// In debug mode, we don't do this.
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//
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// __unwrap_iter is non-constexpr for user-defined iterators whose
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// `to_address` and/or `operator->` is non-constexpr. This is okay; but we
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// try to avoid doing __unwrap_iter in constant-evaluated contexts anyway.
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//
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// Some algorithms (e.g. std::copy, but not std::sort) need to convert an
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// "unwrapped" result back into a contiguous iterator. Since contiguous iterators
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// are random-access, we can do this portably using iterator arithmetic; this
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// is the job of __rewrap_iter.
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template <class _Iter, bool = __is_cpp17_contiguous_iterator<_Iter>::value>
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struct __unwrap_iter_impl {
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static _LIBCPP_CONSTEXPR _Iter
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__apply(_Iter __i) _NOEXCEPT {
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return __i;
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}
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};
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#if _LIBCPP_DEBUG_LEVEL < 2
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template <class _Iter>
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struct __unwrap_iter_impl<_Iter, true> {
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static _LIBCPP_CONSTEXPR decltype(_VSTD::__to_address(declval<_Iter>()))
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__apply(_Iter __i) _NOEXCEPT {
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return _VSTD::__to_address(__i);
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}
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};
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#endif // _LIBCPP_DEBUG_LEVEL < 2
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template<class _Iter, class _Impl = __unwrap_iter_impl<_Iter> >
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inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
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decltype(_Impl::__apply(declval<_Iter>()))
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__unwrap_iter(_Iter __i) _NOEXCEPT
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{
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return _Impl::__apply(__i);
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}
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template<class _OrigIter>
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_LIBCPP_HIDE_FROM_ABI
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_OrigIter __rewrap_iter(_OrigIter, _OrigIter __result)
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{
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return __result;
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}
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template<class _OrigIter, class _UnwrappedIter>
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_LIBCPP_HIDE_FROM_ABI
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_OrigIter __rewrap_iter(_OrigIter __first, _UnwrappedIter __result)
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{
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// Precondition: __result is reachable from __first
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// Precondition: _OrigIter is a contiguous iterator
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return __first + (__result - _VSTD::__unwrap_iter(__first));
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ALGORITHM_UNWRAP_ITER_H
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