<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
<!-- saved from url=(0013)about:internet -->
<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" xmlns:xlink="http://www.w3.org/1999/xlink" pref:renderer="mathplayer-dl">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <style xmlns="" type="text/css">
    /* This style sets a margin around the entire page */
        html, body {
            margin: 10px;
        }

        p {
            font: normal 16px verdana, sans-serif;
            margin: 0;
            padding-bottom:12px;
        }

        h1 {
            font: bold 25px verdana, sans-serif;
            margin-top: 0;
            margin-bottom: 3px;
            padding-top: 0;
            padding-bottom: 0;
        }

        h2 {
            font: bold 19px verdana, sans-serif;
            margin-top: 28px;
            margin-bottom: 3px;
            padding-top: 0;
            padding-bottom: 0;
        }

        h3 {
            font: bold 19px verdana, sans-serif !important;
            margin-top: 28px;
            margin-bottom: 3px;
            padding-top: 0;
            padding-bottom: 0;
        }

        li {
            font: normal 16px verdana, sans-serif;
            margin-top: 0;
            margin-bottom: 18px;
            padding-top: 0;
            padding-bottom: 0;
        }

        .pdparam {
            font: italic 16px verdana, sans-serif;
        }

                .term {
                        font: italic 16px verdana, sans-serif;
                        font-weight: normal;
                }

                .type {
                        font: normal 16px verdana, sans-serif !important;
                }

                .parameter {
                        font-style: italic;
                        }

        a:link, a:visited {
            color: blue;
            text-decoration: none;
            font: normal 16px;
        }

        a:hover {
            background-color: #FFFF99;
            font: normal 16px;
        }

        div.funcsynopsis {
            text-align: left;
            background-color: #e6e6e6;
            font: normal 16px verdana, sans-serif;
                        padding-top: 10px;
                        padding-bottom: 10px;
        }

        div.funcsynopsis table {
            border-collapse: separate;
            font: normal 16px verdana, sans-serif;
        }

        div.funcsynopsis td {
            background-color: #e6e6e6;
            border: 0 solid #000;
            padding: 1px;
            font: normal 16px verdana, sans-serif;
        }

        div.refsect1 {
            font-family: verdana, sans-serif;
            font-size: 16px;
        }

        code.constant {
            font: normal 16px courier new, monospace !important;
        }

                span.errorname {
            font: normal 16px verdana, sans-serif !important;
        }

        code.function {
            font: bold 16px verdana, sans-serif !important;
        }

        b.fsfunc {
            font: bold 16px verdana, sans-serif !important;
        }

        code.varname {
            font: italic 16px verdana, sans-serif;
        }

        code.replaceable {
            font: italic 16px courier new, monospace;
        }

        code.funcdef {
            font: normal 16px verdana, sans-serif !important;
        }

        .citerefentry {
            font: normal 16px verdana, sans-serif !important;
        }

        .parameter {
            font-style: italic;
        }

        code.fsfunc {
            font: normal 16px verdana, sans-serif !important;
        }

        /* PARAMETER: This style controls spacing between the terms in Parameter section */
        dt {
            margin-top: 15px;
        }

        /* TABLES: These styles apply to all tables OTHER than the Synopsis and Example tables */
        div.refsect1 table {
            width: 100%;
                        margin-top: 10px;
            background-color: #FFF;
                        border-collapse: collapse;
                        border-color: #000;
            border-width: 1px;
                        font: normal 16px verdana, sans-serif;
        }

        div.refsect1 th {
                        border-collapse: collapse;
                        border-color: #000;
            border-width: 1px;
            font: bold 16px verdana, sans-serif;
        }

        div.refsect1 td {
            background-color: #FFF;
            padding: 5px;
            vertical-align: text-top;
                        border-collapse: collapse;
                        border-color: #000;
            border-width: 1px;
            font: normal 16px verdana, sans-serif;
        }

                  div.refsect1 p{
            font: normal 16px verdana, sans-serif;
            margin-top: 8px;
            margin-bottom: 8px;
            padding-top: 0;
            padding-bottom: 0;
        }


        /* EXAMPLE: These styles apply only to the Example section */
        div.refsect2 {
            font: normal 16px courier new, monospace !important;
        }

        div.refsect2 table {
            margin-top: 0;
            background-color: #e6e6e6;
            width: 100%;
            border: 0 solid #000;
            padding: 2px;
            font: normal 16px courier new, monospace !important;
        }

        div.refsect2 td {
            background-color: #e6e6e6;
            font: normal 16px courier new, monospace !important;
                        white-space:pre;
        }

        /* COPYRIGHT: This style formats the text of the copyright statement at the bottom of the page */
        div.refsect3 {
            font: normal 11px verdana, sans-serif;
            margin-top: 50px;
            margin-bottom: 20px;
            padding-top: 0;
            padding-bottom: 0;
        }

</style>
    <title>Specifying Attribute For Unrolling Loops</title>
    <meta name="generator" content="DocBook XSL Stylesheets V1.78.1" />
    <meta name="keywords" content="Specifying Attribute For Unrolling Loops" />
  </head>
  <body>
    <div class="refentry">
      <a id="id-1"></a>
      <div class="titlepage"></div>
      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="AttributesofBlocksandControl-Flow-Statements"></a>
        <h1>Specifying Attribute For Unrolling Loops</h1>
        <p>
            Specifying Attribute For Unrolling Loops.
        </p>
      </div>
      <div class="refsect2">
        <a id="synopsis"></a>
        <h3>
        </h3>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint))
                        </td>
              </tr>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint(n)))
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
            The <code class="code">__attribute__((opencl_unroll_hint))</code> 
            and <code class="code">__attribute__((opencl_unroll_hint(n)))</code> 
            attribute qualifiers can be used to specify that a loop 
            (<code class="code">for</code>, <code class="code">while</code> and <code class="code">do</code> loops)
            can be unrolled. This attribute qualifier can be 
            used to specify full unrolling or partial unrolling 
            by a specified amount. This is a compiler hint 
            and the compiler may ignore this directive.
        </p>
        <p>
            <code class="code">n</code> is the loop unrolling factor and must 
            be a positive integral compile time constant expression. 
            An unroll factor of 1 disables unrolling. If 
            <code class="code">n</code> is not specified, the compiler determines the 
            unrolling factor for the loop.
        </p>
        <p>
            NOTE: The <code class="code">__attribute__((opencl_unroll_hint(n)))</code> 
            attribute qualifier must 
            appear immediately before the loop to be affected.
        </p>
      </div>
      <div class="refsect2">
        <a id="example1"></a>
        <h3>
            Examples
        </h3>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint(2)))
while (*s != 0)
    *p++ = *s++;
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
            This tells the compiler to unroll the above while loop by a factor of 2.
        </p>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint))
for (int i=0; i&lt;2; i++)
{
    …
}
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
            In the example above, the compiler will determine how much to unroll the loop.
        </p>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint(1)))
for (int i=0; i&lt;32; i++)
{
    …
}
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
            The above is an example where the loop should not be unrolled.
        </p>
        <p>
            Below are some examples of invalid usage of 
            <code class="code">__attribute__((opencl_unroll_hint(n)))</code>.
        </p>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint(-1)))
while (…)
{
    …
}
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
            The above example is an invalid usage of the loop unroll 
            factor as the loop unroll factor is negative.
        </p>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
__attribute__((opencl_unroll_hint))
if (…)
{
    …
}
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
            The above example is invalid because the unroll 
            attribute qualifier is used on a non-loop 
            construct.
        </p>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
kernel void
my_kernel( … )
{
    int x;
    __attribute__((opencl_unroll_hint(x))
    for (int i=0; i&lt;x; i++)
    {
        …
    }
}
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
            The above example is invalid because the loop unroll 
            factor is not a compile-time constant expression.
        </p>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />

            <a href="https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#page=61" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="attribute.html"><span class="citerefentry"><span class="refentrytitle">__attribute__</span></span></a>,
            <a class="citerefentry" href="attributes-types.html"><span class="citerefentry"><span class="refentrytitle">Type Attributes</span></span></a>,
            <a class="citerefentry" href="attributes-variables.html"><span class="citerefentry"><span class="refentrytitle">Variable Attributes</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2013 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.
</div>
    </div>
  </body>
</html>