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| <title>__local</title> |
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| <meta name="keywords" content="__local" /> |
| </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="__local"></a> |
| <h1>__local</h1> |
| <p> |
| Address Space Qualifier. |
| </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"> |
| __local |
| local |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="description"></a> |
| <h2>Description</h2> |
| <p> |
| OpenCL implements the following disjoint address spaces: <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a>, |
| <code class="function">__local</code>, |
| <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a> and <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</span></span></a>. |
| </p> |
| <p> |
| </p> |
| <p> |
| The address space qualifier may be used in variable declarations to specify the region of memory that is used to allocate the object. The C syntax for type qualifiers is extended in OpenCL to include an address space name as a valid type qualifier. If the type of an object is qualified by an address space name, the object is allocated in the specified address name; otherwise, the object is allocated in the generic address space. |
| </p> |
| <p> |
| The address space names without the __ prefix i.e. <code class="function">global</code>, <code class="function">local</code>, <code class="function">constant</code> and <code class="function">private</code> may be substituted for the corresponding address space names with the __ prefix. |
| </p> |
| <p> |
| The generic address space name for arguments to a function in a program, or local variables of a function is <code class="function">__private</code>. All function arguments shall be in the <code class="function">__private</code> address space. |
| </p> |
| <p> |
| <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> function arguments declared to be a pointer of a type can point to one of the following address spaces only: <code class="function">__global</code>, <code class="function">__local</code> or <code class="function">__constant</code>. A pointer to address space A can only be assigned to a pointer to the same address space A. Casting a pointer to address space A to a pointer to address space B is illegal. |
| </p> |
| <p> |
| The <code class="function">__kernel</code> function arguments declared to be of type <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a></span> or <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a></span> |
| always point to the <code class="function">__global</code> address space. |
| </p> |
| <p> |
| There is no generic address space name for program scope variables. All program scope variables must be declared in the <code class="function">__constant</code> address space. |
| </p> |
| <p> |
| The <code class="function">__constant</code> or <code class="function">constant</code> |
| address space name is used to describe variables allocated in |
| global memory and which are accessed inside a kernel(s) as read-only variables. These read- |
| only variables can be accessed by all (global) work-items of the kernel during its execution. Pointers to the <code class="function">__constant</code> address space are allowed arguments to functions (including <code class="function">__kernel</code> functions) and for variables declared inside functions. Variables allocated in the <code class="function">__constant</code> address space can only be defined as program scope variables and are required to be initialized. |
| </p> |
| <p> |
| Writes to variables declared with the <code class="function">__constant</code> address space qualifier in the OpenCL program source should be a compile-time error. |
| </p> |
| <p> |
| All string literal storage shall be in the <code class="function">__constant</code> address space. |
| </p> |
| <p> |
| NOTE: Any argument to a kernel that is declared with the <code class="function">__constant</code> address space qualifier counts as a separate constant argument. The relevant device capabilities CL_DEVICE_MAX_CONSTANT_ARGS and CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE are described in the table for <a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>. |
| </p> |
| <p> |
| Variables inside a function or in program scope can also be declared with the <code class="function">__constant</code> address qualifier. Implementations are not required to aggregate these declarations into the fewest number of constant arguments. This behavior is implementation defined. |
| </p> |
| <p> |
| Thus portable code must conservatively assume that each variable declared inside a function or in program scope with the <code class="function">__constant</code> qualifier counts as a separate constant argument. |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="description"></a> |
| <h2>Description</h2> |
| <p> |
| The <code class="function">__local</code> or <code class="function">local</code> address space name is |
| used to describe variables that need to be allocated in local memory and are shared by |
| all work-items of a work-group. Pointers to the <code class="function">__local</code> address |
| space are allowed as arguments to functions (including <code class="function">__kernel</code> |
| functions). Variables allocated in the <code class="function">__local</code> address space can |
| also be defined inside a <code class="function">__kernel</code> function only. |
| </p> |
| </div> |
| <div class="refsect2"> |
| <a id="example1"></a> |
| <h3> |
| Example |
| </h3> |
| <div class="informaltable"> |
| <table border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left"> |
| // Declares a pointer p in the __private address space that |
| // points to an int object in address space __global |
| |
| __global int *p; |
| |
| |
| // Declares an array of 4 floats in the __private address space. |
| |
| float x[4]; |
| |
| |
| // Examples of variables allocated in the __local address space |
| // inside a __kernel function |
| |
| __kernel void my_func(...) |
| { |
| __local float a; // A single float allocated |
| // in local address space |
| |
| __local float b[10]; // An array of 10 floats |
| // allocated in local address space. |
| } |
| |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <p> |
| Variables allocated in the <code class="function">__local</code> address space inside a <code class="function">__kernel</code> function cannot be initialized. |
| </p> |
| <div class="literallayout"> |
| <p><br /> |
| __kernel void my_func(...)<br /> |
| {<br /> |
| local float a = 1; // not allowed<br /> |
| __local float b;<br /> |
| b = 1; // allowed<br /> |
| }<br /> |
| </p> |
| </div> |
| <p>NOTE: Variables allocated in the <code class="function">__local</code> address space inside a <code class="function">__kernel</code> function are allocated for each work-group executing the kernel.</p> |
| </div> |
| <div class="refsect1"> |
| <a id="specification"></a> |
| <h2>Specification</h2> |
| <p> |
| <img src="pdficon_small1.gif" /> |
| |
| <a href="http://www.khronos.org/registry/cl/specs/opencl-1.1.pdf#page=182" target="OpenCL Spec">OpenCL Specification</a> |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="seealso"></a> |
| <h2>Also see</h2> |
| <p> |
| <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a>, |
| <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a>, |
| <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</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 © 2007-2010 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. |
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