wtf/NonCopyingSort.h

   1 /*
   2  * Copyright (C) 2010 Apple Inc. All Rights Reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  *
  25  */
  26
  27 #ifndef WTF_NonCopyingSort_h
  28 #define WTF_NonCopyingSort_h
  29
  30 namespace WTF {
  31
  32 using std::swap;
  33
  34 template<typename RandomAccessIterator, typename Predicate>
  35 inline void siftDown(RandomAccessIterator array, ptrdiff_t start, ptrdiff_t end, Predicate compareLess)
  36 {
  37     ptrdiff_t root = start;
  38
  39     while (root * 2 + 1 <= end) {
  40         ptrdiff_t child = root * 2 + 1;
  41         if (child < end && compareLess(array[child], array[child + 1]))
  42             child++;
  43
  44         if (compareLess(array[root], array[child])) {
  45             swap(array[root], array[child]);
  46             root = child;
  47         } else
  48             return;
  49     }
  50 }
  51
  52 template<typename RandomAccessIterator, typename Predicate>
  53 inline void heapify(RandomAccessIterator array, ptrdiff_t count, Predicate compareLess)
  54 {
  55     ptrdiff_t start = (count - 2) / 2;
  56
  57     while (start >= 0) {
  58         siftDown(array, start, count - 1, compareLess);
  59         start--;
  60     }
  61 }
  62
  63 template<typename RandomAccessIterator, typename Predicate>
  64 void heapSort(RandomAccessIterator start, RandomAccessIterator end, Predicate compareLess)
  65 {
  66     ptrdiff_t count = end - start;
  67     heapify(start, count, compareLess);
  68
  69     ptrdiff_t endIndex = count - 1;
  70     while (endIndex > 0) {
  71         swap(start[endIndex], start[0]);
  72         siftDown(start, 0, endIndex - 1, compareLess);
  73         endIndex--;
  74     }
  75 }
  76
  77 template<typename RandomAccessIterator, typename Predicate>
  78 inline void nonCopyingSort(RandomAccessIterator start, RandomAccessIterator end, Predicate compareLess)
  79 {
  80     // heapsort happens to use only swaps, not copies, but the essential thing about
  81     // this function is the fact that it does not copy, not the specific algorithm
  82     heapSort(start, end, compareLess);
  83 }
  84
  85 } // namespace WTF
  86
  87 using WTF::nonCopyingSort;
  88
  89 #endif // WTF_NonCopyingSort_h