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