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/* IBM_PROLOG_BEGIN_TAG */
/* This is an automatically generated prolog. */
/* */
/* $Source: import/chips/p9/procedures/ppe/include/std/util/impl/qsort.H $ */
/* */
/* OpenPOWER sbe Project */
/* */
/* Contributors Listed Below - COPYRIGHT 2016 */
/* [+] International Business Machines Corp. */
/* */
/* */
/* Licensed under the Apache License, Version 2.0 (the "License"); */
/* you may not use this file except in compliance with the License. */
/* You may obtain a copy of the License at */
/* */
/* http://www.apache.org/licenses/LICENSE-2.0 */
/* */
/* Unless required by applicable law or agreed to in writing, software */
/* distributed under the License is distributed on an "AS IS" BASIS, */
/* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or */
/* implied. See the License for the specific language governing */
/* permissions and limitations under the License. */
/* */
/* IBM_PROLOG_END_TAG */
#ifndef __UTIL_IMPL_QSORT_H
#define __UTIL_IMPL_QSORT_H
/** @file qsort.H
*
* Contains the internal implementation details of std::sort implemented as
* quick-sort.
*/
#include <iterator>
// Forward declaration due to 'swap' being defined in <algorithm> which is
// including this file itself.
namespace std
{
template <typename T> void swap(T& a, T& b);
};
namespace Util
{
namespace __Util_QSort_Impl
{
template <typename RandomAccessIterator>
void sort(RandomAccessIterator first, RandomAccessIterator last)
{
size_t length = std::distance(first, last);
// A range of length 0 or 1 is already sort.
if ((length == 0) || (length == 1))
{
return;
}
// A range of length 2 has a trivial sort.
if (length == 2)
{
RandomAccessIterator next = first;
std::advance(next, 1);
if (*next < *first)
{
std::swap(*first, *next);
}
return;
}
// Choose pivot as middle and move pivot to end.
// This is done to eliminate the O(n^2) behavior when the
// range is already sorted.
RandomAccessIterator pivot = first;
std::advance(pivot, length - 1);
RandomAccessIterator middle = first;
std::advance(middle, length / 2);
std::swap(*pivot, *middle);
// Perform partitioning...
// Division points to the first element greater than the pivot or
// else the farthest point partitioned if no elements greater than
// the pivot have been found yet.
RandomAccessIterator division = first;
RandomAccessIterator pos = first;
while(pos != pivot)
{
// Element less than the pivot is found, so move it to the
// "less than" side of the division line.
if (*pos < *pivot)
{
if (pos != division)
{
std::swap(*pos, *division);
}
++division;
}
++pos;
}
// Move the pivot down to the division line, which is its sorted
// position in the range.
if (pivot != division)
{
std::swap(*pivot, *division);
}
// Sort each partition
__Util_QSort_Impl::sort(first, division);
std::advance(division, 1);
__Util_QSort_Impl::sort(division, last);
};
template <typename RandomAccessIterator, typename StrictWeakOrdering>
void sort(RandomAccessIterator first, RandomAccessIterator last,
StrictWeakOrdering pred)
{
size_t length = std::distance(first, last);
// A range of length 0 or 1 is already sort.
if ((length == 0) || (length == 1))
{
return;
}
// A range of length 2 has a trivial sort.
if (length == 2)
{
RandomAccessIterator next = first;
std::advance(next, 1);
if (pred(*next, *first))
{
std::swap(*first, *next);
}
return;
}
// Choose pivot as middle and move pivot to end.
// This is done to eliminate the O(n^2) behavior when the
// range is already sorted.
RandomAccessIterator pivot = first;
std::advance(pivot, length - 1);
RandomAccessIterator middle = first;
std::advance(middle, length / 2);
std::swap(*pivot, *middle);
// Perform partitioning...
// Division points to the first element greater than the pivot or
// else the farthest point partitioned if no elements greater than
// the pivot have been found yet.
RandomAccessIterator division = first;
RandomAccessIterator pos = first;
while(pos != pivot)
{
// Element less than the pivot is found, so move it to the
// "less than" side of the division line.
if (pred(*pos, *pivot))
{
if (pos != division)
{
std::swap(*pos, *division);
}
++division;
}
++pos;
}
// Move the pivot down to the division line, which is its sorted
// position in the range.
if (pivot != division)
{
std::swap(*pivot, *division);
}
// Sort each partition.
__Util_QSort_Impl::sort(first, division, pred);
std::advance(division, 1);
__Util_QSort_Impl::sort(division, last, pred);
};
};
};
#endif
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