blocked_range.h

/*
    Copyright 2005-2016 Intel Corporation.  All Rights Reserved.

    This file is part of Threading Building Blocks. Threading Building Blocks is free software;
    you can redistribute it and/or modify it under the terms of the GNU General Public License
    version 2  as  published  by  the  Free Software Foundation.  Threading Building Blocks is
    distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
    implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    See  the GNU General Public License for more details.   You should have received a copy of
    the  GNU General Public License along with Threading Building Blocks; if not, write to the
    Free Software Foundation, Inc.,  51 Franklin St,  Fifth Floor,  Boston,  MA 02110-1301 USA

    As a special exception,  you may use this file  as part of a free software library without
    restriction.  Specifically,  if other files instantiate templates  or use macros or inline
    functions from this file, or you compile this file and link it with other files to produce
    an executable,  this file does not by itself cause the resulting executable to be covered
    by the GNU General Public License. This exception does not however invalidate any other
    reasons why the executable file might be covered by the GNU General Public License.
*/

#ifndef __TBB_blocked_range_H
#define __TBB_blocked_range_H

#include "tbb_stddef.h"

namespace tbb {


template<typename Value>
class blocked_range {
public:

    typedef Value const_iterator;

    typedef std::size_t size_type;


    blocked_range() : my_end(), my_begin() {}

    blocked_range( Value begin_, Value end_, size_type grainsize_=1 ) :
        my_end(end_), my_begin(begin_), my_grainsize(grainsize_)
    {
        __TBB_ASSERT( my_grainsize>0, "grainsize must be positive" );
    }

    const_iterator begin() const {return my_begin;}

    const_iterator end() const {return my_end;}


    size_type size() const {
        __TBB_ASSERT( !(end()<begin()), "size() unspecified if end()<begin()" );
        return size_type(my_end-my_begin);
    }

    size_type grainsize() const {return my_grainsize;}

    //------------------------------------------------------------------------
    // Methods that implement Range concept
    //------------------------------------------------------------------------

    bool empty() const {return !(my_begin<my_end);}


    bool is_divisible() const {return my_grainsize<size();}


    blocked_range( blocked_range& r, split ) :
        my_end(r.my_end),
        my_begin(do_split(r, split())),
        my_grainsize(r.my_grainsize)
    {
        // only comparison 'less than' is required from values of blocked_range objects
        __TBB_ASSERT( !(my_begin < r.my_end) && !(r.my_end < my_begin), "blocked_range has been split incorrectly" );
    }

#if __TBB_USE_PROPORTIONAL_SPLIT_IN_BLOCKED_RANGES
    static const bool is_splittable_in_proportion = true;


    blocked_range( blocked_range& r, proportional_split& proportion ) :
        my_end(r.my_end),
        my_begin(do_split(r, proportion)),
        my_grainsize(r.my_grainsize)
    {
        // only comparison 'less than' is required from values of blocked_range objects
        __TBB_ASSERT( !(my_begin < r.my_end) && !(r.my_end < my_begin), "blocked_range has been split incorrectly" );
    }
#endif /* __TBB_USE_PROPORTIONAL_SPLIT_IN_BLOCKED_RANGES */

private:
    Value my_end;
    Value my_begin;
    size_type my_grainsize;


    static Value do_split( blocked_range& r, split )
    {
        __TBB_ASSERT( r.is_divisible(), "cannot split blocked_range that is not divisible" );
        Value middle = r.my_begin + (r.my_end - r.my_begin) / 2u;
        r.my_end = middle;
        return middle;
    }

#if __TBB_USE_PROPORTIONAL_SPLIT_IN_BLOCKED_RANGES
    static Value do_split( blocked_range& r, proportional_split& proportion )
    {
        __TBB_ASSERT( r.is_divisible(), "cannot split blocked_range that is not divisible" );

        // usage of 32-bit floating point arithmetic is not enough to handle ranges of
        // more than 2^24 iterations accurately. However, even on ranges with 2^64
        // iterations the computational error approximately equals to 0.000001% which
        // makes small impact on uniform distribution of such range's iterations (assuming
        // all iterations take equal time to complete). See 'test_partitioner_whitebox'
        // for implementation of an exact split algorithm
        size_type right_part = size_type(float(r.size()) * float(proportion.right())
                                         / float(proportion.left() + proportion.right()) + 0.5f);
        return r.my_end = Value(r.my_end - right_part);
    }
#endif /* __TBB_USE_PROPORTIONAL_SPLIT_IN_BLOCKED_RANGES */

    template<typename RowValue, typename ColValue>
    friend class blocked_range2d;

    template<typename RowValue, typename ColValue, typename PageValue>
    friend class blocked_range3d;
};

} // namespace tbb

#endif /* __TBB_blocked_range_H */