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<h1 class="topictitle1">Range Concept</h1>
<div>
<div class="section"><h2 class="sectiontitle">Summary</h2>
<p>Requirements for type representing a recursively divisible set of
values.
</p>
</div>
<div class="section"><h2 class="sectiontitle">Requirements</h2>
<p>The following table lists the requirements for a
Range type
<samp class="codeph">R</samp>.
</p>
<div class="tablenoborder"><a name="tbl8"><!-- --></a><table cellpadding="4" summary="" id="tbl8" width="100%" frame="hsides" border="1" rules="all"><caption><span class="tablecap">Range Concept</span></caption>
<thead align="left">
<tr>
<th class="cellrowborder" valign="top" id="d12945e60">
<p>Pseudo-Signature
</p>
</th>
<th class="row-nocellborder" valign="top" id="d12945e66">
<p>Semantics
</p>
</th>
</tr>
</thead>
<tbody>
<tr valign="top">
<td class="cellrowborder" valign="top" headers="d12945e60 ">
<p><samp class="codeph"> R::R( const R& )</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" headers="d12945e66 ">
<p> Copy constructor.
</p>
</td>
</tr>
<tr valign="top">
<td class="cellrowborder" valign="top" headers="d12945e60 ">
<p><samp class="codeph"> R::~R()</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" headers="d12945e66 ">
<p> Destructor.
</p>
</td>
</tr>
<tr valign="top">
<td class="cellrowborder" valign="top" headers="d12945e60 ">
<p><samp class="codeph"> bool R::empty() const</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" headers="d12945e66 ">
<p> True if range is empty.
</p>
</td>
</tr>
<tr valign="top">
<td class="cellrowborder" valign="top" headers="d12945e60 ">
<p><samp class="codeph"> bool R::is_divisible()
const</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" headers="d12945e66 ">
<p> True if range can be partitioned into two
subranges.
</p>
</td>
</tr>
<tr valign="top">
<td class="cellrowborder" valign="top" headers="d12945e60 ">
<p><samp class="codeph"> R::R( R& r, split )</samp>
</p>
</td>
<td class="row-nocellborder" valign="top" headers="d12945e66 ">
<p> Split
<samp class="codeph">r</samp> into two subranges.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section"><h2 class="sectiontitle"> Description</h2>
<p>A Range can be recursively subdivided into two parts. It is
recommended that the division be into nearly equal parts, but it is not
required. Splitting as evenly as possible typically yields the best
parallelism. Ideally, a range is recursively splittable until the parts
represent portions of work that are more efficient to execute serially rather
than split further. The amount of work represented by a Range typically depends
upon higher level context, hence a typical type that models a Range should
provide a way to control the degree of splitting. For example, the template
class
<samp class="codeph">blocked_range</samp> has a
<em>grainsize</em> parameter that specifies the biggest range considered
indivisible.
</p>
<p>The constructor that implements splitting is called a
<em>splitting constructor</em>. If the set of values has a sense of
direction, then by convention the splitting constructor should construct the
second part of the range, and update the argument to be the first half.
Following this convention causes the<samp class="codeph">parallel_for</samp>,
<samp class="codeph">parallel_reduce</samp> and <samp class="codeph">parallel_scan</samp> algorithms,
when running sequentially, to work across a range in the increasing order typical
of an ordinary sequential loop.
</p>
</div>
<div class="section"><h2 class="sectiontitle"> Example</h2>
<p>The following code defines a type
<samp class="codeph">TrivialIntegerRange</samp> that models the Range concept. It
represents a half-open interval [lower,upper) that is divisible down to a
single integer.
</p>
<pre>
struct TrivialIntegerRange {
int lower;
int upper;
bool empty() const {return lower==upper;}
bool is_divisible() const {return upper>lower+1;}
TrivialIntegerRange( TrivialIntegerRange& r, split ) {
int m = (r.lower+r.upper)/2;
lower = m;
upper = r.upper;
r.upper = m;
}
};
</pre>
<p>
<samp class="codeph">TrivialIntegerRange</samp> is for demonstration and not very
practical, because it lacks a grainsize parameter. Use the library class
<samp class="codeph">blocked_range</samp> instead.
</p>
</div>
<div class="section"><h2 class="sectiontitle"> Model Types</h2>
<p>Type
<samp class="codeph">blocked_range</samp> models a one-dimensional range.
</p>
<p>Type
<samp class="codeph">blocked_range2</samp>d models a two-dimensional range.
</p>
<p>Type
<samp class="codeph">blocked_range3d</samp> models a three-dimensional range.
</p>
<p>The Container Range Concept models a container as a range.
</p>
</div>
</div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="../../reference/algorithms.htm">Algorithms</a></div>
</div>
<div class="See Also">
<ul class="ullinks">
<li class="ulchildlink"><a href="../../reference/algorithms/range_concept/blocked_range_cls.htm">blocked_range Template Class</a><br>
</li>
<li class="ulchildlink"><a href="../../reference/algorithms/range_concept/blocked_range2d_cls.htm">blocked_range2d Template Class</a><br>
</li>
<li class="ulchildlink"><a href="../../reference/algorithms/range_concept/blocked_range3d_cls.htm">blocked_range3d Template Class</a><br>
</li>
</ul>
<h2>See Also</h2>
<div class="linklist">
<div><a href="parallel_for_func.htm#parallel_for_func">parallel_for Template Function
</a></div>
<div><a href="parallel_reduce_func.htm#parallel_reduce_func">parallel_reduce Template Function
</a></div>
<div><a href="parallel_scan_func.htm#parallel_scan_func">parallel_scan Template Function
</a></div>
<div><a href="../containers_overview/container_range_concept.htm#container_range_concept">Container Range Concept
</a></div></div>
</div>
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