NonCopyingSort.h   [plain text]

/*
 * Copyright (C) 2010 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
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 */

#ifndef WTF_NonCopyingSort_h
#define WTF_NonCopyingSort_h

namespace WTF {

using std::swap;

template<typename RandomAccessIterator, typename Predicate>
inline void siftDown(RandomAccessIterator array, ptrdiff_t start, ptrdiff_t end, Predicate compareLess) 
{
    ptrdiff_t root = start;

    while (root * 2 + 1 <= end) {
        ptrdiff_t child = root * 2 + 1;
        if (child < end && compareLess(array[child], array[child + 1]))
            child++;
        
        if (compareLess(array[root], array[child])) {
            swap(array[root], array[child]);
            root = child;
        } else
            return;
    }
}

template<typename RandomAccessIterator, typename Predicate>
inline void heapify(RandomAccessIterator array, ptrdiff_t count, Predicate compareLess) 
{
    ptrdiff_t start = (count - 2) / 2;
     
    while (start >= 0) {
        siftDown(array, start, count - 1, compareLess);
        start--;
    }
}

template<typename RandomAccessIterator, typename Predicate>
void heapSort(RandomAccessIterator start, RandomAccessIterator end, Predicate compareLess)
{
    ptrdiff_t count = end - start;
    heapify(start, count, compareLess);

    ptrdiff_t endIndex = count - 1;
    while (endIndex > 0) {
        swap(start[endIndex], start[0]);
        siftDown(start, 0, endIndex - 1, compareLess);
        endIndex--;
    }
}

template<typename RandomAccessIterator, typename Predicate>
inline void nonCopyingSort(RandomAccessIterator start, RandomAccessIterator end, Predicate compareLess)
{
    // heapsort happens to use only swaps, not copies, but the essential thing about
    // this function is the fact that it does not copy, not the specific algorithm
    heapSort(start, end, compareLess);
}

} // namespace WTF

using WTF::nonCopyingSort;

#endif // WTF_NonCopyingSort_h