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1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___ALGORITHM_SIFT_DOWN_H
10#define _LIBCPP___ALGORITHM_SIFT_DOWN_H
11
12#include <__algorithm/iterator_operations.h>
13#include <__assert>
14#include <__config>
15#include <__iterator/iterator_traits.h>
16#include <__utility/move.h>
17
18#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19# pragma GCC system_header
20#endif
21
22_LIBCPP_PUSH_MACROS
23#include <__undef_macros>
24
25_LIBCPP_BEGIN_NAMESPACE_STD
26
27template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
28_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
29__sift_down(_RandomAccessIterator __first,
30 _Compare&& __comp,
31 typename iterator_traits<_RandomAccessIterator>::difference_type __len,
32 _RandomAccessIterator __start) {
33 using _Ops = _IterOps<_AlgPolicy>;
34
35 typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
36 typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
37 // left-child of __start is at 2 * __start + 1
38 // right-child of __start is at 2 * __start + 2
39 difference_type __child = __start - __first;
40
41 if (__len < 2 || (__len - 2) / 2 < __child)
42 return;
43
44 __child = 2 * __child + 1;
45 _RandomAccessIterator __child_i = __first + __child;
46
47 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
48 // right-child exists and is greater than left-child
49 ++__child_i;
50 ++__child;
51 }
52
53 // check if we are in heap-order
54 if (__comp(*__child_i, *__start))
55 // we are, __start is larger than its largest child
56 return;
57
58 value_type __top(_Ops::__iter_move(__start));
59 do {
60 // we are not in heap-order, swap the parent with its largest child
61 *__start = _Ops::__iter_move(__child_i);
62 __start = __child_i;
63
64 if ((__len - 2) / 2 < __child)
65 break;
66
67 // recompute the child based off of the updated parent
68 __child = 2 * __child + 1;
69 __child_i = __first + __child;
70
71 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
72 // right-child exists and is greater than left-child
73 ++__child_i;
74 ++__child;
75 }
76
77 // check if we are in heap-order
78 } while (!__comp(*__child_i, __top));
79 *__start = std::move(__top);
80}
81
82template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
83_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _RandomAccessIterator __floyd_sift_down(
84 _RandomAccessIterator __first,
85 _Compare&& __comp,
86 typename iterator_traits<_RandomAccessIterator>::difference_type __len) {
87 using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type;
88 _LIBCPP_ASSERT_INTERNAL(__len >= 2, "shouldn't be called unless __len >= 2");
89
90 _RandomAccessIterator __hole = __first;
91 _RandomAccessIterator __child_i = __first;
92 difference_type __child = 0;
93
94 while (true) {
95 __child_i += difference_type(__child + 1);
96 __child = 2 * __child + 1;
97
98 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
99 // right-child exists and is greater than left-child
100 ++__child_i;
101 ++__child;
102 }
103
104 // swap __hole with its largest child
105 *__hole = _IterOps<_AlgPolicy>::__iter_move(__child_i);
106 __hole = __child_i;
107
108 // if __hole is now a leaf, we're done
109 if (__child > (__len - 2) / 2)
110 return __hole;
111 }
112}
113
114_LIBCPP_END_NAMESPACE_STD
115
116_LIBCPP_POP_MACROS
117
118#endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H