parallel_sort.h

/*
    Copyright 2005-2009 Intel Corporation.  All Rights Reserved.

    The source code contained or described herein and all documents related
    to the source code ("Material") are owned by Intel Corporation or its
    suppliers or licensors.  Title to the Material remains with Intel
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    Material may be used, copied, reproduced, modified, published, uploaded,
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    No license under any patent, copyright, trade secret or other
    intellectual property right is granted to or conferred upon you by
    disclosure or delivery of the Materials, either expressly, by
    implication, inducement, estoppel or otherwise.  Any license under such
    intellectual property rights must be express and approved by Intel in
    writing.
*/

#ifndef __TBB_parallel_sort_H
#define __TBB_parallel_sort_H

#include "parallel_for.h"
#include "blocked_range.h"
#include <algorithm>
#include <iterator>
#include <functional>

namespace tbb {

namespace internal {


template<typename RandomAccessIterator, typename Compare>
class quick_sort_range: private no_assign {

    inline size_t median_of_three(const RandomAccessIterator &array, size_t l, size_t m, size_t r) const {
        return comp(array[l], array[m]) ? ( comp(array[m], array[r]) ? m : ( comp( array[l], array[r]) ? r : l ) ) 
                                        : ( comp(array[r], array[m]) ? m : ( comp( array[r], array[l] ) ? r : l ) );
    }

    inline size_t pseudo_median_of_nine( const RandomAccessIterator &array, const quick_sort_range &range ) const {
        size_t offset = range.size/8u;
        return median_of_three(array, 
                               median_of_three(array, 0, offset, offset*2),
                               median_of_three(array, offset*3, offset*4, offset*5),
                               median_of_three(array, offset*6, offset*7, range.size - 1) );

    }

public:

    static const size_t grainsize = 500;
    const Compare &comp;
    RandomAccessIterator begin;
    size_t size;

    quick_sort_range( RandomAccessIterator begin_, size_t size_, const Compare &comp_ ) :
        comp(comp_), begin(begin_), size(size_) {}

    bool empty() const {return size==0;}
    bool is_divisible() const {return size>=grainsize;}

    quick_sort_range( quick_sort_range& range, split ) : comp(range.comp) {
        RandomAccessIterator array = range.begin;
        RandomAccessIterator key0 = range.begin; 
        size_t m = pseudo_median_of_nine(array, range);
        if (m) std::swap ( array[0], array[m] );

        size_t i=0;
        size_t j=range.size;
        // Partition interval [i+1,j-1] with key *key0.
        for(;;) {
            __TBB_ASSERT( i<j, NULL );
            // Loop must terminate since array[l]==*key0.
            do {
                --j;
                __TBB_ASSERT( i<=j, "bad ordering relation?" );
            } while( comp( *key0, array[j] ));
            do {
                __TBB_ASSERT( i<=j, NULL );
                if( i==j ) goto partition;
                ++i;
            } while( comp( array[i],*key0 ));
            if( i==j ) goto partition;
            std::swap( array[i], array[j] );
        }
partition:
        // Put the partition key were it belongs
        std::swap( array[j], *key0 );
        // array[l..j) is less or equal to key.
        // array(j..r) is greater or equal to key.
        // array[j] is equal to key
        i=j+1;
        begin = array+i;
        size = range.size-i;
        range.size = j;
    }
};


template<typename RandomAccessIterator, typename Compare>
class quick_sort_pretest_body : internal::no_assign {
    const Compare &comp;

public:
    quick_sort_pretest_body(const Compare &_comp) : comp(_comp) {}

    void operator()( const blocked_range<RandomAccessIterator>& range ) const {
        task &my_task = task::self();
        RandomAccessIterator my_end = range.end();

        int i = 0;
        for (RandomAccessIterator k = range.begin(); k != my_end; ++k, ++i) {
            if ( i%64 == 0 && my_task.is_cancelled() ) break;
          
            // The k-1 is never out-of-range because the first chunk starts at begin+serial_cutoff+1
            if ( comp( *(k), *(k-1) ) ) {
                my_task.cancel_group_execution();
                break;
            }
        }
    }

};


template<typename RandomAccessIterator, typename Compare>
struct quick_sort_body {
    void operator()( const quick_sort_range<RandomAccessIterator,Compare>& range ) const {
        //SerialQuickSort( range.begin, range.size, range.comp );
        std::sort( range.begin, range.begin + range.size, range.comp );
    }
};


template<typename RandomAccessIterator, typename Compare>
void parallel_quick_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp ) {
    task_group_context my_context;
    const int serial_cutoff = 9;

    __TBB_ASSERT( begin + serial_cutoff < end, "min_parallel_size is smaller than serial cutoff?" );
    RandomAccessIterator k;
    for ( k = begin ; k != begin + serial_cutoff; ++k ) {
        if ( comp( *(k+1), *k ) ) {
            goto do_parallel_quick_sort;
        }
    }

    parallel_for( blocked_range<RandomAccessIterator>(k+1, end),
                  quick_sort_pretest_body<RandomAccessIterator,Compare>(comp),
                  auto_partitioner(),
                  my_context);

    if (my_context.is_group_execution_cancelled())
do_parallel_quick_sort:
        parallel_for( quick_sort_range<RandomAccessIterator,Compare>(begin, end-begin, comp ), 
                      quick_sort_body<RandomAccessIterator,Compare>(),
                      auto_partitioner() );
}

} // namespace internal



template<typename RandomAccessIterator, typename Compare>
void parallel_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp) { 
    const int min_parallel_size = 500; 
    if( end > begin ) {
        if (end - begin < min_parallel_size) { 
            std::sort(begin, end, comp);
        } else {
            internal::parallel_quick_sort(begin, end, comp);
        }
    }
}


template<typename RandomAccessIterator>
inline void parallel_sort( RandomAccessIterator begin, RandomAccessIterator end ) { 
    parallel_sort( begin, end, std::less< typename std::iterator_traits<RandomAccessIterator>::value_type >() );
}


template<typename T>
inline void parallel_sort( T * begin, T * end ) {
    parallel_sort( begin, end, std::less< T >() );
}   


} // namespace tbb

#endif

---

Copyright © 2005-2009 Intel Corporation. All Rights Reserved.

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