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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP___ALGORITHM_SIFT_DOWN_H
#define _LIBCPP___ALGORITHM_SIFT_DOWN_H
#include <__config>
#include <__iterator/iterator_traits.h>
#include <__utility/move.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
template <class _Compare, class _RandomAccessIterator>
_LIBCPP_CONSTEXPR_AFTER_CXX11 void
__sift_down(_RandomAccessIterator __first, _Compare __comp,
typename iterator_traits<_RandomAccessIterator>::difference_type __len,
_RandomAccessIterator __start)
{
typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
// left-child of __start is at 2 * __start + 1
// right-child of __start is at 2 * __start + 2
difference_type __child = __start - __first;
if (__len < 2 || (__len - 2) / 2 < __child)
return;
__child = 2 * __child + 1;
_RandomAccessIterator __child_i = __first + __child;
if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
// right-child exists and is greater than left-child
++__child_i;
++__child;
}
// check if we are in heap-order
if (__comp(*__child_i, *__start))
// we are, __start is larger than its largest child
return;
value_type __top(_VSTD::move(*__start));
do
{
// we are not in heap-order, swap the parent with its largest child
*__start = _VSTD::move(*__child_i);
__start = __child_i;
if ((__len - 2) / 2 < __child)
break;
// recompute the child based off of the updated parent
__child = 2 * __child + 1;
__child_i = __first + __child;
if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
// right-child exists and is greater than left-child
++__child_i;
++__child;
}
// check if we are in heap-order
} while (!__comp(*__child_i, __top));
*__start = _VSTD::move(__top);
}
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H
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