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| <refentry> |
| <refentryinfo> |
| <keywordset> |
| <keyword> |
| __global |
| </keyword> |
| </keywordset> |
| </refentryinfo> |
| |
| <refmeta> |
| <refentrytitle>__global</refentrytitle> |
| |
| <refmiscinfo> |
| <copyright> |
| <year>2007-2009</year> |
| <holder>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.</holder> |
| </copyright> |
| </refmiscinfo> |
| <manvolnum>2</manvolnum> |
| </refmeta> |
| |
| <!-- ================================ SYNOPSIS --> |
| |
| <refnamediv id="__global"> |
| <refname>__global</refname> |
| |
| <refpurpose> |
| Address space qualifier. |
| </refpurpose> |
| </refnamediv> |
| |
| |
| <!-- ALTERNATIVE SYNTAX SYNOPSIS (NON-FUNCTION) --> |
| <refsect2 id="synopsis"> |
| <title> |
| </title> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __global |
| global |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| </refsect2> |
| |
| |
| <!-- ================================ DESCRIPTION --> |
| |
| <refsect1 id="description"><title>Description</title> |
| <para> |
| OpenCL implements the following disjoint address spaces: <function>__global</function>, <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>, <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry> and <citerefentry href="private"><refentrytitle>__private</refentrytitle></citerefentry>. |
| </para> |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| The address space names without the __ prefix i.e. <function>global</function>, <function>local</function>, <function>constant</function> and <function>private</function> may be substituted for the corresponding address space names with the __ prefix. |
| </para> |
| |
| <para> |
| The generic address space name for arguments to a function in a program, or local variables of a function is <function>__private</function>. All arguments to a <function>__kernel</function> function shall be in the <function>__private</function> address space. |
| </para> |
| |
| <para> |
| <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> function arguments declared to be a pointer of a type can point to one of the following address spaces only: <function>__global</function>, <function>__local</function> or <function>__constant</function>. 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. |
| </para> |
| |
| <para> |
| The <function>__kernel</function> function arguments declared to be of type <type><citerefentry href="otherDataTypes"><refentrytitle>image2d_t</refentrytitle></citerefentry></type> or <type><citerefentry href="otherDataTypes"><refentrytitle>image3d_t</refentrytitle></citerefentry></type> |
| always point to the <function>__global</function> address space. All program scope variables must be declared in the <function>__constant</function> address space. |
| </para> |
| <para> |
| The <function>__global</function> or <function>global</function> address space |
| name is used to refer to memory objects (buffer or |
| image objects) allocated from the global memory pool. |
| </para> |
| |
| <para> |
| 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. |
| </para> |
| |
| <para> |
| The actual size of the array memory object is determined when the memory object is allocated |
| via appropriate API calls in the host code. |
| </para> |
| |
| <para> |
| If an image memory object is attached to an argument declared with this qualifier, the argument must be declared as type <type><citerefentry href="otherDataTypes"><refentrytitle>image2d_t</refentrytitle></citerefentry></type> for a 2D image memory object or as type <type><citerefentry href="otherDataTypes"><refentrytitle>image3d_t</refentrytitle></citerefentry></type> |
| 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. |
| </para> |
| |
| <para> |
| The const qualifier can also be used with the <constant>__global</constant> qualifier to specify a read-only buffer memory object. |
| </para> |
| |
| </refsect1> |
| |
| |
| <!-- ================================ EXAMPLE --> |
| |
| <refsect2 id="example1"> |
| <title> |
| Examples |
| </title> |
| |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| // 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]; |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| </refsect2> |
| <para> |
| |
| </para> |
| <refsect2 id="example2"> |
| <informaltable frame="none"> |
| <tgroup cols="1" align="left" colsep="0" rowsep="0"> |
| <colspec colname="col1" colnum="1" /> |
| <tbody> |
| <row> |
| <entry> |
| __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 |
| </entry> |
| </row> |
| </tbody> |
| </tgroup> |
| </informaltable> |
| </refsect2> |
| |
| |
| |
| <!-- ================================ SPECIFICATION --> |
| <!-- Set the "uri" attribute in the <olink /> element to the "named destination" for the PDF page |
| --> |
| <refsect1 id="specification"><title>Specification</title> |
| <para> |
| <imageobject> |
| <imagedata fileref="pdficon_small1.gif" format="gif" /> |
| </imageobject> |
| |
| <olink uri="addressSpaceQualifier">OpenCL Specification</olink> |
| </para> |
| </refsect1> |
| |
| |
| <!-- ================================ ALSO SEE --> |
| |
| <refsect1 id="seealso"><title>Also see</title> |
| <para> |
| <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>, |
| <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>, |
| <citerefentry href="private"><refentrytitle>__private</refentrytitle></citerefentry> |
| </para> |
| </refsect1> |
| |
| |
| |
| <!-- ============================== COPYRIGHT --> |
| <!-- Content included from copyright.inc.xsl --> |
| |
| <refsect3 id="Copyright"><title></title> |
| <imageobject> |
| <imagedata fileref="KhronosLogo.jpg" format="jpg" /> |
| </imageobject> |
| <para /> |
| </refsect3> |
| |
| </refentry> |
| |