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 27 template <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 82 template <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 119