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    <title>__global</title>
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        <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">
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__global
global
                        </td>
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        </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>
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// 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>
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      <p> 
	
	</p>
      <div class="refsect2">
        <a id="example2"></a>
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__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>
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      </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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