| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef _LIBCPP___ALGORITHM_SIFT_DOWN_H |
| #define _LIBCPP___ALGORITHM_SIFT_DOWN_H |
| |
| #include <__assert> |
| #include <__config> |
| #include <__iterator/iterator_traits.h> |
| #include <__utility/move.h> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| # pragma GCC system_header |
| #endif |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| template <class _Compare, class _RandomAccessIterator> |
| _LIBCPP_CONSTEXPR_AFTER_CXX11 void |
| __sift_down(_RandomAccessIterator __first, _Compare __comp, |
| typename iterator_traits<_RandomAccessIterator>::difference_type __len, |
| _RandomAccessIterator __start) |
| { |
| typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type; |
| typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type; |
| // left-child of __start is at 2 * __start + 1 |
| // right-child of __start is at 2 * __start + 2 |
| difference_type __child = __start - __first; |
| |
| if (__len < 2 || (__len - 2) / 2 < __child) |
| return; |
| |
| __child = 2 * __child + 1; |
| _RandomAccessIterator __child_i = __first + __child; |
| |
| if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { |
| // right-child exists and is greater than left-child |
| ++__child_i; |
| ++__child; |
| } |
| |
| // check if we are in heap-order |
| if (__comp(*__child_i, *__start)) |
| // we are, __start is larger than its largest child |
| return; |
| |
| value_type __top(_VSTD::move(*__start)); |
| do |
| { |
| // we are not in heap-order, swap the parent with its largest child |
| *__start = _VSTD::move(*__child_i); |
| __start = __child_i; |
| |
| if ((__len - 2) / 2 < __child) |
| break; |
| |
| // recompute the child based off of the updated parent |
| __child = 2 * __child + 1; |
| __child_i = __first + __child; |
| |
| if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { |
| // right-child exists and is greater than left-child |
| ++__child_i; |
| ++__child; |
| } |
| |
| // check if we are in heap-order |
| } while (!__comp(*__child_i, __top)); |
| *__start = _VSTD::move(__top); |
| } |
| |
| template <class _Compare, class _RandomAccessIterator> |
| _LIBCPP_CONSTEXPR_AFTER_CXX11 _RandomAccessIterator |
| __floyd_sift_down(_RandomAccessIterator __first, _Compare __comp, |
| typename iterator_traits<_RandomAccessIterator>::difference_type __len) |
| { |
| using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type; |
| _LIBCPP_ASSERT(__len >= 2, "shouldn't be called unless __len >= 2"); |
| |
| _RandomAccessIterator __hole = __first; |
| _RandomAccessIterator __child_i = __first; |
| difference_type __child = 0; |
| |
| while (true) { |
| __child_i += difference_type(__child + 1); |
| __child = 2 * __child + 1; |
| |
| if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) { |
| // right-child exists and is greater than left-child |
| ++__child_i; |
| ++__child; |
| } |
| |
| // swap __hole with its largest child |
| *__hole = std::move(*__child_i); |
| __hole = __child_i; |
| |
| // if __hole is now a leaf, we're done |
| if (__child > (__len - 2) / 2) |
| return __hole; |
| } |
| } |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| #endif // _LIBCPP___ALGORITHM_SIFT_DOWN_H |