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_BEGIN_NAMESPACE_STD 21 22 template <class _Compare, class _RandomAccessIterator> 23 _LIBCPP_CONSTEXPR_AFTER_CXX11 void 24 __sift_down(_RandomAccessIterator __first, _Compare __comp, 25 typename iterator_traits<_RandomAccessIterator>::difference_type __len, 26 _RandomAccessIterator __start) 27 { 28 typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type; 29 typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type; 30 // left-child of __start is at 2 * __start + 1 31 // right-child of __start is at 2 * __start + 2 32 difference_type __child = __start - __first; 33 34 if (__len < 2 || (__len - 2) / 2 < __child) 35 return; 36 37 __child = 2 * __child + 1; 38 _RandomAccessIterator __child_i = __first + __child; 39 40 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 41 // right-child exists and is greater than left-child 42 ++__child_i; 43 ++__child; 44 } 45 46 // check if we are in heap-order 47 if (__comp(*__child_i, *__start)) 48 // we are, __start is larger than its largest child 49 return; 50 51 value_type __top(_VSTD::move(*__start)); 52 do 53 { 54 // we are not in heap-order, swap the parent with its largest child 55 *__start = _VSTD::move(*__child_i); 56 __start = __child_i; 57 58 if ((__len - 2) / 2 < __child) 59 break; 60 61 // recompute the child based off of the updated parent 62 __child = 2 * __child + 1; 63 __child_i = __first + __child; 64 65 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { 66 // right-child exists and is greater than left-child 67 ++__child_i; 68 ++__child; 69 } 70 71 // check if we are in heap-order 72 } while (!__comp(*__child_i, __top)); 73 *__start = _VSTD::move(__top); 74 } 75 76 _LIBCPP_END_NAMESPACE_STD 77 78 #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H 79