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 <__config> 13 #include <__iterator/iterator_traits.h> 14 #include <__utility/move.h> 15 16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 17 #pragma GCC system_header 18 #endif 19 20 _LIBCPP_PUSH_MACROS 21 #include <__undef_macros> 22 23 _LIBCPP_BEGIN_NAMESPACE_STD 24 25 template <class _Compare, class _RandomAccessIterator> 26 _LIBCPP_CONSTEXPR_AFTER_CXX11 void 27 __sift_down(_RandomAccessIterator __first, _RandomAccessIterator /*__last*/, 28 _Compare __comp, 29 typename iterator_traits<_RandomAccessIterator>::difference_type __len, 30 _RandomAccessIterator __start) 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 + 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 it's largest child 53 return; 54 55 value_type __top(_VSTD::move(*__start)); 56 do 57 { 58 // we are not in heap-order, swap the parent with its largest child 59 *__start = _VSTD::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 + 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 _LIBCPP_END_NAMESPACE_STD 81 82 _LIBCPP_POP_MACROS 83 84 #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H 85