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> 15 #include <type_traits> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 #pragma GCC system_header 19 #endif 20 21 _LIBCPP_PUSH_MACROS 22 #include <__undef_macros> 23 24 _LIBCPP_BEGIN_NAMESPACE_STD 25 26 template <class _Compare, class _RandomAccessIterator> 27 _LIBCPP_CONSTEXPR_AFTER_CXX11 void 28 __sift_down(_RandomAccessIterator __first, _RandomAccessIterator /*__last*/, 29 _Compare __comp, 30 typename iterator_traits<_RandomAccessIterator>::difference_type __len, 31 _RandomAccessIterator __start) 32 { 33 typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type; 34 typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type; 35 // left-child of __start is at 2 * __start + 1 36 // right-child of __start is at 2 * __start + 2 37 difference_type __child = __start - __first; 38 39 if (__len < 2 || (__len - 2) / 2 < __child) 40 return; 41 42 __child = 2 * __child + 1; 43 _RandomAccessIterator __child_i = __first + __child; 44 45 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + 1))) { 46 // right-child exists and is greater than left-child 47 ++__child_i; 48 ++__child; 49 } 50 51 // check if we are in heap-order 52 if (__comp(*__child_i, *__start)) 53 // we are, __start is larger than it's largest child 54 return; 55 56 value_type __top(_VSTD::move(*__start)); 57 do 58 { 59 // we are not in heap-order, swap the parent with its largest child 60 *__start = _VSTD::move(*__child_i); 61 __start = __child_i; 62 63 if ((__len - 2) / 2 < __child) 64 break; 65 66 // recompute the child based off of the updated parent 67 __child = 2 * __child + 1; 68 __child_i = __first + __child; 69 70 if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + 1))) { 71 // right-child exists and is greater than left-child 72 ++__child_i; 73 ++__child; 74 } 75 76 // check if we are in heap-order 77 } while (!__comp(*__child_i, __top)); 78 *__start = _VSTD::move(__top); 79 } 80 81 _LIBCPP_END_NAMESPACE_STD 82 83 _LIBCPP_POP_MACROS 84 85 #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H 86