Run DCE after a LoopFlatten test to reduce spurious output [nfc]
[llvm-project.git] / libcxx / include / __algorithm / sift_down.h
blob20f0b0275dd9569995701a95512e6118b91a8328
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 //===----------------------------------------------------------------------===//
9 #ifndef _LIBCPP___ALGORITHM_SIFT_DOWN_H
10 #define _LIBCPP___ALGORITHM_SIFT_DOWN_H
12 #include <__algorithm/iterator_operations.h>
13 #include <__assert>
14 #include <__config>
15 #include <__iterator/iterator_traits.h>
16 #include <__utility/move.h>
18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19 # pragma GCC system_header
20 #endif
22 _LIBCPP_PUSH_MACROS
23 #include <__undef_macros>
25 _LIBCPP_BEGIN_NAMESPACE_STD
27 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
28 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
29 __sift_down(_RandomAccessIterator __first, _Compare&& __comp,
30 typename iterator_traits<_RandomAccessIterator>::difference_type __len,
31 _RandomAccessIterator __start)
33 using _Ops = _IterOps<_AlgPolicy>;
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;
41 if (__len < 2 || (__len - 2) / 2 < __child)
42 return;
44 __child = 2 * __child + 1;
45 _RandomAccessIterator __child_i = __first + __child;
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;
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;
58 value_type __top(_Ops::__iter_move(__start));
61 // we are not in heap-order, swap the parent with its largest child
62 *__start = _Ops::__iter_move(__child_i);
63 __start = __child_i;
65 if ((__len - 2) / 2 < __child)
66 break;
68 // recompute the child based off of the updated parent
69 __child = 2 * __child + 1;
70 __child_i = __first + __child;
72 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
73 // right-child exists and is greater than left-child
74 ++__child_i;
75 ++__child;
78 // check if we are in heap-order
79 } while (!__comp(*__child_i, __top));
80 *__start = _VSTD::move(__top);
83 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
84 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _RandomAccessIterator
85 __floyd_sift_down(_RandomAccessIterator __first, _Compare&& __comp,
86 typename iterator_traits<_RandomAccessIterator>::difference_type __len)
88 using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type;
89 _LIBCPP_ASSERT_UNCATEGORIZED(__len >= 2, "shouldn't be called unless __len >= 2");
91 _RandomAccessIterator __hole = __first;
92 _RandomAccessIterator __child_i = __first;
93 difference_type __child = 0;
95 while (true) {
96 __child_i += difference_type(__child + 1);
97 __child = 2 * __child + 1;
99 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
100 // right-child exists and is greater than left-child
101 ++__child_i;
102 ++__child;
105 // swap __hole with its largest child
106 *__hole = _IterOps<_AlgPolicy>::__iter_move(__child_i);
107 __hole = __child_i;
109 // if __hole is now a leaf, we're done
110 if (__child > (__len - 2) / 2)
111 return __hole;
115 _LIBCPP_END_NAMESPACE_STD
117 _LIBCPP_POP_MACROS
119 #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H