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_BEGIN_NAMESPACE_STD 23 24 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator> 25 _LIBCPP_CONSTEXPR_AFTER_CXX11 void 26 __sift_down(_RandomAccessIterator __first, _Compare&& __comp, 27 typename iterator_traits<_RandomAccessIterator>::difference_type __len, 28 _RandomAccessIterator __start) 29 { 30 using _Ops = _IterOps<_AlgPolicy>; 31 32 typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type; 33 typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type; 34 // left-child of __start is at 2 * __start + 1 35 // right-child of __start is at 2 * __start + 2 36 difference_type __child = __start - __first; 37 38 if (__len < 2 || (__len - 2) / 2 < __child) 39 return; 40 41 __child = 2 * __child + 1; 42 _RandomAccessIterator __child_i = __first + __child; 43 44 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 45 // right-child exists and is greater than left-child 46 ++__child_i; 47 ++__child; 48 } 49 50 // check if we are in heap-order 51 if (__comp(*__child_i, *__start)) 52 // we are, __start is larger than its largest child 53 return; 54 55 value_type __top(_Ops::__iter_move(__start)); 56 do 57 { 58 // we are not in heap-order, swap the parent with its largest child 59 *__start = _Ops::__iter_move(__child_i); 60 __start = __child_i; 61 62 if ((__len - 2) / 2 < __child) 63 break; 64 65 // recompute the child based off of the updated parent 66 __child = 2 * __child + 1; 67 __child_i = __first + __child; 68 69 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 70 // right-child exists and is greater than left-child 71 ++__child_i; 72 ++__child; 73 } 74 75 // check if we are in heap-order 76 } while (!__comp(*__child_i, __top)); 77 *__start = _VSTD::move(__top); 78 } 79 80 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator> 81 _LIBCPP_CONSTEXPR_AFTER_CXX11 _RandomAccessIterator 82 __floyd_sift_down(_RandomAccessIterator __first, _Compare&& __comp, 83 typename iterator_traits<_RandomAccessIterator>::difference_type __len) 84 { 85 using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type; 86 _LIBCPP_ASSERT(__len >= 2, "shouldn't be called unless __len >= 2"); 87 88 _RandomAccessIterator __hole = __first; 89 _RandomAccessIterator __child_i = __first; 90 difference_type __child = 0; 91 92 while (true) { 93 __child_i += difference_type(__child + 1); 94 __child = 2 * __child + 1; 95 96 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 97 // right-child exists and is greater than left-child 98 ++__child_i; 99 ++__child; 100 } 101 102 // swap __hole with its largest child 103 *__hole = _IterOps<_AlgPolicy>::__iter_move(__child_i); 104 __hole = __child_i; 105 106 // if __hole is now a leaf, we're done 107 if (__child > (__len - 2) / 2) 108 return __hole; 109 } 110 } 111 112 _LIBCPP_END_NAMESPACE_STD 113 114 #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H 115