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| <title>__global</title> |
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| <meta name="keywords" content=" __global " /> |
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| <div class="refentry"> |
| <a id="idm1"></a> |
| <div class="titlepage"></div> |
| <div xmlns="" class="refnamediv"> |
| <a xmlns="http://www.w3.org/1999/xhtml" id="__global"></a> |
| <h1>__global</h1> |
| <p> |
| Address space qualifier. |
| </p> |
| </div> |
| <div class="refsect2"> |
| <a id="synopsis"></a> |
| <h3> |
| </h3> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
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| <col align="left" class="col1" /> |
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| <td align="left"> |
| __global |
| global |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="description"></a> |
| <h2>Description</h2> |
| <p> |
| OpenCL implements the following disjoint address spaces: <code class="function">__global</code>, <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>, <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> |
| 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 arguments to a <code class="function">__kernel</code> function 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. All program scope variables must be declared in the <code class="function">__constant</code> address space. |
| </p> |
| <p> |
| The <code class="function">__global</code> or <code class="function">global</code> address space |
| name is used to refer to memory objects (buffer or |
| image objects) allocated from the global memory pool. |
| </p> |
| <p> |
| A buffer memory object can be declared as a pointer to a scalar, vector or user-defined struct. |
| This allows the kernel to read and/or write any location in the buffer. |
| </p> |
| <p> |
| The actual size of the array memory object is determined when the memory object is allocated |
| via appropriate API calls in the host code. |
| </p> |
| <p> |
| If an image memory object is attached to an argument declared with this qualifier, the argument must be declared as type <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a></span> for a 2D image memory object or as type <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a></span> |
| for a 3D image memory object. The elements of an image memory object cannot be directly accessed. Built-in functions to read from and write to an image memory object are provided. |
| </p> |
| <p> |
| The const qualifier can also be used with the <code class="constant">__global</code> qualifier to specify a read-only buffer memory object. |
| </p> |
| </div> |
| <div class="refsect2"> |
| <a id="example1"></a> |
| <h3> |
| Examples |
| </h3> |
| <div class="informaltable"> |
| <table class="informaltable" 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]; |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| <p> |
| |
| </p> |
| <div class="refsect2"> |
| <a id="example2"></a> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left"> |
| __global float4 *color; // An array of float4 elements |
| typedef struct { |
| float a[3]; |
| int b[2]; |
| } foo_t; |
| __global foo_t *my_info; // An array of foo_t elements. |
| __global image2d_t texture; // A 2D texture image |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </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-1.0.pdf#page=150" target="OpenCL Spec">OpenCL Specification</a> |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="seealso"></a> |
| <h2>Also see</h2> |
| <p> |
| <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</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 © 2007-2009 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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