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 <__assert> 13 #include <__config> 14 #include <__iterator/iterator_traits.h> 15 #include <__utility/move.h> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 # pragma GCC system_header 19 #endif 20 21 _LIBCPP_BEGIN_NAMESPACE_STD 22 23 template <class _Compare, class _RandomAccessIterator> 24 _LIBCPP_CONSTEXPR_AFTER_CXX11 void 25 __sift_down(_RandomAccessIterator __first, _Compare __comp, 26 typename iterator_traits<_RandomAccessIterator>::difference_type __len, 27 _RandomAccessIterator __start) 28 { 29 typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type; 30 typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type; 31 // left-child of __start is at 2 * __start + 1 32 // right-child of __start is at 2 * __start + 2 33 difference_type __child = __start - __first; 34 35 if (__len < 2 || (__len - 2) / 2 < __child) 36 return; 37 38 __child = 2 * __child + 1; 39 _RandomAccessIterator __child_i = __first + __child; 40 41 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 42 // right-child exists and is greater than left-child 43 ++__child_i; 44 ++__child; 45 } 46 47 // check if we are in heap-order 48 if (__comp(*__child_i, *__start)) 49 // we are, __start is larger than its largest child 50 return; 51 52 value_type __top(_VSTD::move(*__start)); 53 do 54 { 55 // we are not in heap-order, swap the parent with its largest child 56 *__start = _VSTD::move(*__child_i); 57 __start = __child_i; 58 59 if ((__len - 2) / 2 < __child) 60 break; 61 62 // recompute the child based off of the updated parent 63 __child = 2 * __child + 1; 64 __child_i = __first + __child; 65 66 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 67 // right-child exists and is greater than left-child 68 ++__child_i; 69 ++__child; 70 } 71 72 // check if we are in heap-order 73 } while (!__comp(*__child_i, __top)); 74 *__start = _VSTD::move(__top); 75 } 76 77 template <class _Compare, class _RandomAccessIterator> 78 _LIBCPP_CONSTEXPR_AFTER_CXX11 _RandomAccessIterator 79 __floyd_sift_down(_RandomAccessIterator __first, _Compare __comp, 80 typename iterator_traits<_RandomAccessIterator>::difference_type __len) 81 { 82 using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type; 83 _LIBCPP_ASSERT(__len >= 2, "shouldn't be called unless __len >= 2"); 84 85 _RandomAccessIterator __hole = __first; 86 _RandomAccessIterator __child_i = __first; 87 difference_type __child = 0; 88 89 while (true) { 90 __child_i += difference_type(__child + 1); 91 __child = 2 * __child + 1; 92 93 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 94 // right-child exists and is greater than left-child 95 ++__child_i; 96 ++__child; 97 } 98 99 // swap __hole with its largest child 100 *__hole = std::move(*__child_i); 101 __hole = __child_i; 102 103 // if __hole is now a leaf, we're done 104 if (__child > (__len - 2) / 2) 105 return __hole; 106 } 107 } 108 109 _LIBCPP_END_NAMESPACE_STD 110 111 #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H 112