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| <title>work_group_scan_exclusive</title> |
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| <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="work_group_scan_exclusive"></a> |
| <h1>work_group_scan_exclusive_<op></h1> |
| <p> |
| Do an exclusive prefix-sum operation of all values in work-items in the work-group |
| </p> |
| </div> |
| <div class="refsynopsisdiv"> |
| <h2></h2> |
| <div class="funcsynopsis"> |
| <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"> |
| <tr valign="bottom"> |
| <td> |
| <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef"> |
| gentype |
| <strong class="fsfunc"> |
| work_group_scan_exclusive_<op> |
| </strong> |
| (</code> |
| <td>gentype <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">x</var><code>)</code></td> |
| </td> |
| </tr> |
| </table> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="description"></a> |
| <h2>Description</h2> |
| <p> |
| Do an exclusive scan operation specified |
| by <span class="emphasis"><em><op></em></span> of all values specified by work-items |
| in the work-group. The scan results are |
| returned for each work-item. |
| </p> |
| <p> |
| The scan order is defined by increasing |
| 1D linear global ID within the work-group. |
| </p> |
| <h4><a id="id-1.5.4"></a>General information about work-group functions</h4> |
| <p> |
| This built-in function must be encountered by |
| all work-items in a |
| work-group executing the kernel. We use the |
| generic type name gentype to indicate the |
| built-in data types <span class="type">half</span> (if the |
| <a class="citerefentry" href="cl_khr_fp16.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_fp16</span></span></a> |
| extension is supported), |
| <span class="type">int</span>, <span class="type">uint</span>, <span class="type">long</span>, |
| <span class="type">ulong</span>, <span class="type">float</span> or <span class="type">double</span> |
| (if double precision is supported) as the type |
| for the arguments. |
| </p> |
| <p> |
| The <span class="emphasis"><em><op></em></span> in |
| <code class="function">work_group_reduce_<span class="emphasis"><em><op></em></span></code>, |
| <code class="function">work_group_scan_exclusive_<span class="emphasis"><em><op></em></span></code> and |
| <code class="function">work_group_scan_inclusive_<span class="emphasis"><em><op></em></span></code> |
| defines the operator and can be <code class="code">add</code>, <code class="code">min</code> or <code class="code">max</code>. |
| </p> |
| <p> |
| The inclusive scan operation takes a binary operator <code class="code">op</code> |
| with an identity <code class="code">I</code> and <code class="code">n</code> (where |
| <code class="code">n</code> is the size of the work-group) elements |
| <code class="code">[a0, a1, ... an-1]</code> and returns |
| <code class="code">[a0, (a0 <span class="emphasis"><em>op</em></span> a1), ... (a0 <span class="emphasis"><em>op</em></span> a1 |
| <span class="emphasis"><em>op</em></span> ... <span class="emphasis"><em>op</em></span> an-1)]</code>. |
| If <<code class="code">op</code>> = <code class="code">add</code>, the identity |
| <code class="code">I</code> is 0. If <<code class="code">op</code>> = <code class="code">min</code>, |
| the identity <code class="code">I</code> is <code class="constant">INT_MAX</code>, |
| <code class="constant">UINT_MAX</code>, <code class="constant">LONG_MAX</code>, |
| <code class="constant">ULONG_MAX</code>, for <span class="type">int</span>, |
| <span class="type">uint</span>, <span class="type">long</span>, <span class="type">ulong</span> types |
| and is <code class="code">+INF</code> for floating-point types. Similarly |
| if <<code class="code">op</code>> = max, the identity <code class="code">I</code> is |
| <code class="constant">INT_MIN</code>, 0, <code class="constant">LONG_MIN</code>, |
| 0 and <code class="code">-INF</code>. |
| </p> |
| <p> |
| Consider the following example: |
| </p> |
| <p> |
| </p> |
| <div class="literallayout"> |
| <p> |
| <code class="code"><br /> |
| void foo(int *p)<br /> |
| {<br /> |
| ... <br /> |
| int prefix_sum_val = work_group_scan_inclusive_add(<br /> |
| p[get_local_id(0)]);<br /> |
| }</code> |
| </p> |
| </div> |
| <p> |
| </p> |
| <p> |
| For the example above, let's assume that the work-group |
| size is 8 and p points to the following |
| elements [3 1 7 0 4 1 6 3]. Work-item 0 calls |
| <code class="function">work_group_scan_inclusive_add</code> |
| with 3 and returns 3. Work-item 1 calls |
| <code class="function">work_group_scan_inclusive_add</code> with 1 and |
| returns 4. The full set of values returned by |
| <code class="function">work_group_scan_inclusive_add</code> |
| for work-items 0 ... 7 are [3 4 11 11 14 16 22 25]. |
| </p> |
| <p> |
| The exclusive scan operation takes a binary |
| associative operator <code class="varname">op</code> with an |
| identity <code class="code">I</code> and <code class="code">n</code> |
| (where <code class="code">n</code> is the size of the work-group) |
| elements <code class="code">[a0, a1, ... an-1]</code> and returns <code class="code">[I, a0, |
| (a0 <span class="emphasis"><em>op</em></span> a1), ... (a0 <span class="emphasis"><em>op</em></span> a1 |
| <span class="emphasis"><em>op</em></span> ... <span class="emphasis"><em>op</em></span> an-2)]</code>. For the |
| example above, the exclusive scan |
| add operation on the ordered set [3 1 7 0 4 1 6 3] |
| would return [0 3 4 11 11 14 16 22]. |
| </p> |
| <p> |
| NOTE: The order of floating-point operations is not guaranteed for the |
| <code class="function">work_group_reduce_<span class="emphasis"><em><op></em></span></code>, |
| <code class="function">work_group_scan_inclusive_<span class="emphasis"><em><op></em></span></code> and |
| <code class="function">work_group_scan_exclusive_<span class="emphasis"><em><op></em></span></code> |
| built-in functions that operate on <span class="type">half</span>, <span class="type">float</span> and |
| <span class="type">double</span> data types. |
| The order of these floating-point operations is also non-deterministic |
| for a given workgroup. |
| </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#namedest=work_group_scan_exclusive" target="OpenCL Spec">OpenCL Specification</a> |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="seealso"></a> |
| <h2>Also see</h2> |
| <p> |
| <a class="citerefentry" href="work_group_scan_inclusive.html"><span class="citerefentry"><span class="refentrytitle">work_group_scan_inclusive</span></span></a>, |
| <a class="citerefentry" href="work_group_reduce.html"><span class="citerefentry"><span class="refentrytitle">work_group_reduce</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 © 2007-2015 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 |
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| in all copies or substantial portions of the Materials. |
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