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<a name="boost_compute.tutorial"></a><a class="link" href="tutorial.html" title="Tutorial">Tutorial</a>
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<div class="toc"><dl>
<dt><span class="section"><a href="tutorial.html#boost_compute.tutorial.hello_world">Hello World</a></span></dt>
<dt><span class="section"><a href="tutorial.html#boost_compute.tutorial.transferring_data">Transferring
Data</a></span></dt>
<dt><span class="section"><a href="tutorial.html#boost_compute.tutorial.transforming_data">Transforming
Data</a></span></dt>
<dt><span class="section"><a href="tutorial.html#boost_compute.tutorial.vector_data_types">Vector Data
Types</a></span></dt>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_compute.tutorial.hello_world"></a><a class="link" href="tutorial.html#boost_compute.tutorial.hello_world" title="Hello World">Hello World</a>
</h3></div></div></div>
<p>
The hello world example gives a simple application that prints the name of
the default GPU compute device on the system.
</p>
<p>
Compute devices are represented with the <code class="computeroutput"><a class="link" href="../boost/compute/device.html" title="Class device">device</a></code>
class.
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">compute</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// get the default device</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">device</span> <span class="identifier">device</span> <span class="special">=</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">default_device</span><span class="special">();</span>
<span class="comment">// print the device's name</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"hello from "</span> <span class="special">&lt;&lt;</span> <span class="identifier">device</span><span class="special">.</span><span class="identifier">name</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_compute.tutorial.transferring_data"></a><a class="link" href="tutorial.html#boost_compute.tutorial.transferring_data" title="Transferring Data">Transferring
Data</a>
</h3></div></div></div>
<p>
Before any computation occurs, data must be transferred from the host to
the compute device. The generic <code class="computeroutput"><a class="link" href="../boost/compute/copy.html" title="Function template copy">copy()</a></code>
function provides a simple interface for transfering data and the generic
<code class="computeroutput"><a class="link" href="../boost/compute/vector.html" title="Class template vector">vector&lt;T&gt;</a></code> class
provides a container for storing data on a compute device.
</p>
<p>
The following example shows how to transfer data from an array on the host
to a <code class="computeroutput"><a class="link" href="../boost/compute/vector.html" title="Class template vector">vector&lt;T&gt;</a></code>
on the device and then back to a separate <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
on the host. At the end of the example both <code class="computeroutput"><span class="identifier">host_array</span></code>
and <code class="computeroutput"><span class="identifier">host_vector</span></code> contain the
same values which were copied through the memory on the compute device.
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">compute</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// create data array on host</span>
<span class="keyword">int</span> <span class="identifier">host_data</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span> <span class="number">1</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="number">5</span><span class="special">,</span> <span class="number">7</span><span class="special">,</span> <span class="number">9</span> <span class="special">};</span>
<span class="comment">// create vector on device</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">device_vector</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
<span class="comment">// copy from host to device</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span><span class="identifier">host_data</span><span class="special">,</span>
<span class="identifier">host_data</span> <span class="special">+</span> <span class="number">5</span><span class="special">,</span>
<span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
<span class="comment">// create vector on host</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">host_vector</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
<span class="comment">// copy data back to host</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span><span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<span class="identifier">host_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_compute.tutorial.transforming_data"></a><a class="link" href="tutorial.html#boost_compute.tutorial.transforming_data" title="Transforming Data">Transforming
Data</a>
</h3></div></div></div>
<p>
The following example shows how to calculate the square-root of a vector
of <code class="computeroutput"><span class="keyword">float</span></code>s on a compute device
using the <code class="computeroutput"><a class="link" href="../boost/compute/transform_idp8766528.html" title="Function template transform">transform()</a></code>
function.
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">algorithm</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">compute</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// generate random data on the host</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">&gt;</span> <span class="identifier">host_vector</span><span class="special">(</span><span class="number">10000</span><span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">generate</span><span class="special">(</span><span class="identifier">host_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">host_vector</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">rand</span><span class="special">);</span>
<span class="comment">// create a vector on the device and transfer data from the host</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">&gt;</span> <span class="identifier">device_vector</span> <span class="special">=</span> <span class="identifier">host_vector</span><span class="special">;</span>
<span class="comment">// calculate sqrt of each element in-place</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">sqrt</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">&gt;());</span>
<span class="comment">// copy values back to the host</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span><span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">device_vector</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<span class="identifier">host_vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_compute.tutorial.vector_data_types"></a><a class="link" href="tutorial.html#boost_compute.tutorial.vector_data_types" title="Vector Data Types">Vector Data
Types</a>
</h3></div></div></div>
<p>
In addition to the built-in scalar types (e.g. <code class="computeroutput"><span class="keyword">int</span></code>
and <code class="computeroutput"><span class="keyword">float</span></code>), OpenCL also provides
vector data types (e.g. <code class="computeroutput"><span class="identifier">int2</span></code>
and <code class="computeroutput"><span class="identifier">vector4</span></code>). These can be
used with the Boost Compute library on both the host and device.
</p>
<p>
Boost.Compute provides typedefs for these types which take the form: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">scalarN_</span></code> where <code class="computeroutput"><span class="identifier">scalar</span></code>
is a scalar data type (e.g. <code class="computeroutput"><span class="keyword">int</span></code>,
<code class="computeroutput"><span class="keyword">float</span></code>, <code class="computeroutput"><span class="keyword">char</span></code>)
and <code class="computeroutput"><span class="identifier">N</span></code> is the size of the
vector. Supported vector sizes are: 2, 4, 8, and 16.
</p>
<p>
The following example shows how to transfer a set of 3D points stored as
an array of <code class="computeroutput"><span class="keyword">float</span></code>s on the host
the device and then calculate the sum of the point coordinates using the
<code class="computeroutput"><a class="link" href="../boost/compute/accumulate_idp7997392.html" title="Function template accumulate">accumulate()</a></code>
function. The sum is transferred to the host and the centroid computed by
dividing by the total number of points.
</p>
<p>
Note that even though the points are in 3D, they are stored as <code class="computeroutput"><span class="identifier">float4</span></code> due to OpenCL's alignment requirements.
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">compute</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="comment">// the point centroid example calculates and displays the</span>
<span class="comment">// centroid of a set of 3D points stored as float4's</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">float4_</span><span class="special">;</span>
<span class="comment">// point coordinates</span>
<span class="keyword">float</span> <span class="identifier">points</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span> <span class="number">1.0f</span><span class="special">,</span> <span class="number">2.0f</span><span class="special">,</span> <span class="number">3.0f</span><span class="special">,</span> <span class="number">0.0f</span><span class="special">,</span>
<span class="special">-</span><span class="number">2.0f</span><span class="special">,</span> <span class="special">-</span><span class="number">3.0f</span><span class="special">,</span> <span class="number">4.0f</span><span class="special">,</span> <span class="number">0.0f</span><span class="special">,</span>
<span class="number">1.0f</span><span class="special">,</span> <span class="special">-</span><span class="number">2.0f</span><span class="special">,</span> <span class="number">2.5f</span><span class="special">,</span> <span class="number">0.0f</span><span class="special">,</span>
<span class="special">-</span><span class="number">7.0f</span><span class="special">,</span> <span class="special">-</span><span class="number">3.0f</span><span class="special">,</span> <span class="special">-</span><span class="number">2.0f</span><span class="special">,</span> <span class="number">0.0f</span><span class="special">,</span>
<span class="number">3.0f</span><span class="special">,</span> <span class="number">4.0f</span><span class="special">,</span> <span class="special">-</span><span class="number">5.0f</span><span class="special">,</span> <span class="number">0.0f</span> <span class="special">};</span>
<span class="comment">// create vector for five points</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">float4_</span><span class="special">&gt;</span> <span class="identifier">vector</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
<span class="comment">// copy point data to the device</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span>
<span class="keyword">reinterpret_cast</span><span class="special">&lt;</span><span class="identifier">float4_</span> <span class="special">*&gt;(</span><span class="identifier">points</span><span class="special">),</span>
<span class="keyword">reinterpret_cast</span><span class="special">&lt;</span><span class="identifier">float4_</span> <span class="special">*&gt;(</span><span class="identifier">points</span><span class="special">)</span> <span class="special">+</span> <span class="number">5</span><span class="special">,</span>
<span class="identifier">vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()</span>
<span class="special">);</span>
<span class="comment">// calculate sum</span>
<span class="identifier">float4_</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">compute</span><span class="special">::</span><span class="identifier">accumulate</span><span class="special">(</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">vector</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span>
<span class="identifier">float4_</span><span class="special">(</span><span class="number">0</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="number">0</span><span class="special">));</span>
<span class="comment">// calculate centroid</span>
<span class="identifier">float4_</span> <span class="identifier">centroid</span><span class="special">;</span>
<span class="keyword">for</span><span class="special">(</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="number">3</span><span class="special">;</span> <span class="identifier">i</span><span class="special">++){</span>
<span class="identifier">centroid</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">sum</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">/</span> <span class="number">5.0f</span><span class="special">;</span>
<span class="special">}</span>
<span class="comment">// print centroid</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"centroid: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">centroid</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
</pre>
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</p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2013 Kyle Lutz<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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