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<h1 class="topictitle1">blocked_range2d Template Class</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
Template class that represents recursively
divisible two-dimensional half-open interval.
</div>
<div class="section"><h2 class="sectiontitle"> Header</h2>
<p>
<pre>#include "tbb/blocked_range2d.h"</pre>
</p>
</div>
<div class="section"><h2 class="sectiontitle"> Syntax</h2>
<pre>template<typename RowValue, typename ColValue> class blocked_range2d;</pre>
</div>
<div class="section"><h2 class="sectiontitle"> Description</h2>
<p>A
<samp class="codeph">blocked_range2d<<em>RowValue</em> ,<em>ColValue</em>
></samp> represents a half-open two dimensional range<samp class="codeph"> [<em>i</em>
<sub>0</sub>,<em>j</em>
<sub>0</sub>)×[<em>i</em>
<sub>1</sub>,<em>j</em>
<sub>1</sub>)</samp>. Each axis of the range has its own splitting
threshold. The
<em>RowValue</em> and
<em>ColValue</em> must meet the requirements in the table in the
blocked_range Template Class section. A
<samp class="codeph">blocked_range</samp> is splittable if either axis is
splittable. A<samp class="codeph"> blocked_range</samp> models the Range concept.
</p>
</div>
<div class="section"><h2 class="sectiontitle"> Members</h2>
<pre>
namespace tbb {
template<typename RowValue, typename ColValue=RowValue>
class blocked_range2d {
public:
// Types
typedef blocked_range<RowValue> row_range_type;
typedef blocked_range<ColValue> col_range_type;
// 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);
blocked_range2d( blocked_range2d& r, split );
// Capacity
bool empty() const;
// Access
bool is_divisible() const;
const row_range_type& rows() const;
const col_range_type& cols() const;
};
}
</pre>
</div>
<div class="section"><h2 class="sectiontitle"> Example</h2>
<p>The code that follows shows a serial matrix
multiply, and the corresponding parallel matrix multiply that uses a
<samp class="codeph">blocked_range2d</samp> to specify the iteration space.
</p>
<pre>
const size_t L = 150;
const size_t M = 225;
const size_t N = 300;
void SerialMatrixMultiply( float c[M][N], float a[M][L], float b[L][N] ) {
for( size_t i=0; i<M; ++i ) {
for( size_t j=0; j<N; ++j ) {
float sum = 0;
for( size_t k=0; k<L; ++k )
sum += a[i][k]*b[k][j];
c[i][j] = sum;
}
}
}
</pre>
<pre>
#include "tbb/parallel_for.h"
#include "tbb/blocked_range2d.h"
using namespace tbb;
const size_t L = 150;
const size_t M = 225;
const size_t N = 300;
class MatrixMultiplyBody2D {
float (*my_a)[L];
float (*my_b)[N];
float (*my_c)[N];
public:
void operator()( const blocked_range2d<size_t>& r ) const {
float (*a)[L] = my_a;
float (*b)[N] = my_b;
float (*c)[N] = my_c;
for( size_t i=r.rows().begin(); i!=r.rows().end(); ++i ){
for( size_t j=r.cols().begin(); j!=r.cols().end(); ++j ) {
float sum = 0;
for( size_t k=0; k<L; ++k )
sum += a[i][k]*b[k][j];
c[i][j] = sum;
}
}
}
MatrixMultiplyBody2D( float c[M][N], float a[M][L], float b[L][N] ) :
my_a(a), my_b(b), my_c(c)
{}
};
void ParallelMatrixMultiply(float c[M][N], float a[M][L], float b[L][N]){
parallel_for( blocked_range2d<size_t>(0, M, 16, 0, N, 32),
MatrixMultiplyBody2D(c,a,b) );
}
</pre>
<p>The<samp class="codeph"> blocked_range2d</samp> enables the
two outermost loops of the serial version to become parallel loops. The<samp class="codeph">
parallel_for</samp> recursively splits the
<samp class="codeph">blocked_range2d
</samp>until the pieces are no larger than 16x32. It invokes
<samp class="codeph">MatrixMultiplyBody2D::operator(</samp>) on each piece.
</p>
<p>
<div class="tablenoborder"><table cellpadding="4" summary="" frame="border" border="1" cellspacing="0" rules="all"><span class="tabledesc">The following table provides additional information on the
members of this template class.
</span><thead align="left">
<tr>
<th class="cellrowborder" valign="top" width="33.89830508474576%" id="d13569e170">Member
</th>
<th class="cellrowborder" valign="top" width="66.10169491525423%" id="d13569e173">Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">row_range_type</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p> A
<samp class="codeph">blocked_range<RowValue></samp>. That is, the
type of the row values.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">col_range_type</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p>A<samp class="codeph">
blocked_range<ColValue></samp>. That is, the type of the column values.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">blocked_range2d<RowValue,ColValue>( 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 )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p><strong>Effects:
</strong> Constructs a
<samp class="codeph">blocked_range2d</samp> representing a two
dimensional space of values. The space is the half-open Cartesian
product<samp class="codeph"> [ row_begin, row_end) x [ col_begin, col_end)</samp>, with
the given grain sizes for the rows and columns.
</p>
<p>
<strong>Example:
</strong> The statement
<samp class="codeph">" blocked_range2d<char,int> r('a', 'z'+1, 3, 0,
10, 2 );"</samp> constructs a two-dimensional space that contains all value
pairs of the form
<samp class="codeph">(i, j)</samp>, where<samp class="codeph"> i
</samp>ranges from
<samp class="codeph">'a</samp>' to
<samp class="codeph">'z</samp>' with a grain size of 3, and<samp class="codeph">
j</samp> ranges from 0 to 9 with a grain size of 2.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">blocked_range2d<RowValue,ColValue>( RowValue
row_begin, RowValue row_end, ColValue col_begin, ColValue col_end )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">Same as
<samp class="codeph">blocked_range2d(row_begin,row_end,1,col_begin,col_end,1)</samp>.
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">blocked_range2d<RowValue,ColValue> (
blocked_range2d& range, split )</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">Partitions range into two subranges. The
newly constructed
<samp class="codeph">blocked_range2d</samp> is approximately the second
half of the original
<samp class="codeph">range</samp>, and
<samp class="codeph">range</samp> is updated to be the remainder. Each
subrange has the same grain size as the original
<samp class="codeph">range</samp>. The split is 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. For example, if the
<samp class="codeph">row_grainsize</samp> is twice
<samp class="codeph">col_grainsize</samp>, the subranges will tend towards
having twice as many rows as columns.
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">bool empty() const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p> Determines if range is empty.
</p>
<p><strong>Returns:
</strong>
<samp class="codeph"> rows().empty()||cols().empty()</samp>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">bool is_divisible()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p> Determines if range can be split into subranges..
</p>
<p><strong>Returns:</strong>
<samp class="codeph">
rows().is_divisible()||cols().is_divisible()</samp>
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">const row_range_type& rows()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p><strong>Returns:
</strong> Range containing the rows of the value space.
</p>
</td>
</tr>
<tr>
<td class="cellrowborder" valign="top" width="33.89830508474576%" headers="d13569e170 "><span class="keyword">const col_range_type& cols()
const</span>
</td>
<td class="cellrowborder" valign="top" width="66.10169491525423%" headers="d13569e173 ">
<p><strong>Returns:
</strong> Range containing the columns of the value space.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</p>
</div>
</div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="../../../reference/algorithms/range_concept.htm">Range Concept</a></div>
</div>
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