forked from OSchip/llvm-project
85 lines
2.6 KiB
C++
85 lines
2.6 KiB
C++
//===----------------------------------------------------------------------===//
|
|
//
|
|
// 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_PUSH_MACROS
|
|
#include <__undef_macros>
|
|
|
|
_LIBCPP_BEGIN_NAMESPACE_STD
|
|
|
|
template <class _Compare, class _RandomAccessIterator>
|
|
_LIBCPP_CONSTEXPR_AFTER_CXX11 void
|
|
__sift_down(_RandomAccessIterator __first, _RandomAccessIterator /*__last*/,
|
|
_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 + 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 it's 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 + 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
|
|
|
|
_LIBCPP_POP_MACROS
|
|
|
|
#endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H
|