blocked_range2d

[algorithms.blocked_range2d]

Class template that represents a recursively divisible two-dimensional half-open interval.

A blocked_range2d represents a half-open two-dimensional range [i0,j0)×[i1,j1). Each axis of the range has its own splitting threshold. A blocked_range2d is divisible if either axis is divisible.

A blocked_range2d meets the Range requirements.

// Defined in header <oneapi/tbb/blocked_range2d.h>

namespace oneapi {
    namespace tbb {

        template<typename RowValue, typename ColValue=RowValue>
        class blocked_range2d {
        public:
            // Types
            using row_range_type = blocked_range<RowValue>;
            using col_range_type = blocked_range<ColValue>;

            // Constructors
            blocked_range2d(
                RowValue row_begin, RowValue row_end,
                typename row_range_type::size_type row_grainsize,
                ColValue col_begin, ColValue col_end,
                typename col_range_type::size_type col_grainsize);
            blocked_range2d( RowValue row_begin, RowValue row_end,
                            ColValue col_begin, ColValue col_end );
            // Splitting constructors
            blocked_range2d( blocked_range2d& r, split );
            blocked_range2d( blocked_range2d& r, proportional_split proportion );

            // Capacity
            bool empty() const;

            // Access
            bool is_divisible() const;
            const row_range_type& rows() const;
            const col_range_type& cols() const;
        };

    } // namespace tbb
} // namespace oneapi

Requirements:

• The RowValue and ColValue must meet the blocked_range requirements

Member types

using row_range_type = blocked_range<RowValue>;

The type of the row values.

using col_range_type = blocked_range<ColValue>;

The type of the column values.

Member functions

blocked_range2d(
    RowValue row_begin, RowValue row_end,
    typename row_range_type::size_type row_grainsize,
    ColValue col_begin, ColValue col_end,
    typename col_range_type::size_type col_grainsize);

Effects: Constructs a blocked_range2d representing a two-dimensional space of values. The space is the half-open Cartesian product [row_begin, row_end) x [col_begin, col_end), with the given grain sizes for the rows and columns.

Example: The statement blocked_range2d<char,int> r('a', 'z'+1, 3, 0, 10, 2 ); constructs a two-dimensional space that contains all value pairs of the form (i, j), where i ranges from 'a' to 'z' with a grain size of 3, and j ranges from 0 to 9 with a grain size of 2.

blocked_range2d(RowValue row_begin, RowValue row_end,
                ColValue col_begin, ColValue col_end);

Same as blocked_range2d(row_begin,row_end,1,col_begin,col_end,1).

blocked_range2d(blocked_range2d& range, split);

Basic splitting constructor.

Requirements: is_divisible() is true.

Effects: Partitions range into two subranges. The newly constructed blocked_range2d is approximately the second half of the original range, and range is updated to be the remainder. Each subrange has the same grain size as the original range. Splitting is done either by rows or columns. The choice of which axis to split is intended to cause, after repeated splitting, the subranges to approach the aspect ratio of the respective row and column grain sizes.

blocked_range2d(blocked_range2d& range, proportional_split proportion);

Proportional splitting constructor.

Requirements: is_divisible() is true.

Effects: Partitions range into two subranges in the given proportion across one of its axes. The choice of which axis to split is made in the same way as for the basic splitting constructor; then, proportional splitting is done for the chosen axis. The second axis and the grain sizes for each subrange remain the same as in the original range.

bool empty() const;

Effects: Determines if range is empty.

Returns: rows().empty()||cols().empty()

bool is_divisible() const;

Effects: Determines if range can be split into subranges.

Returns: rows().is_divisible()||cols().is_divisible()

const row_range_type& rows() const;

Returns: Range containing the rows of the value space.

const col_range_type& cols() const;

Returns: Range containing the columns of the value space.

See also:

• blocked_range