.. SPDX-FileCopyrightText: 2019-2021 Intel Corporation
..
.. SPDX-License-Identifier: CC-BY-4.0

===============
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 :doc:`Range requirements <../../named_requirements/algorithms/range>`.

.. code:: cpp

    // 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 :doc:`blocked_range requirements <../../named_requirements/algorithms/blocked_range_val>`

Member types
------------

.. code:: cpp

    using row_range_type = blocked_range<RowValue>;

The type of the row values.

.. code:: cpp

    using col_range_type = blocked_range<ColValue>;

The type of the column values.

Member functions
----------------

.. code:: cpp

    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.

.. code:: cpp

    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)``.

.. code:: cpp

    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.

.. code:: cpp

    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.

.. code:: cpp

    bool empty() const;

**Effects**: Determines if range is empty.

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

.. code:: cpp

    bool is_divisible() const;

**Effects**: Determines if range can be split into subranges.

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

.. code:: cpp

    const row_range_type& rows() const;

**Returns:**  Range containing the rows of the value space.

.. code:: cpp

    const col_range_type& cols() const;

**Returns:**  Range containing the columns of the value space.

See also:

* :doc:`blocked_range <blocked_range_cls>`