/usr/share/doc/opencl-1.2-html-doc/global.html

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    <title>__global</title>
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      <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">
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__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>,
      <code class="function">__local</code>, <code class="function">__constant</code>, and
      <code class="function">__private</code> 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>
      Function arguments of type
      <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a></span>,
      <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a></span>,
      <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_array_t</span></span></a></span>,
      <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_t</span></span></a></span>,
      <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_buffer_t</span></span></a></span>, and
      <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_array_t</span></span></a></span>
      refer to image memory objects allocated in the <code class="function">__global</code> address space.
    </p>
      </div>
      <div class="refsect1">
        <a id="notes"></a>
        <h2>Notes</h2>
        <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 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 object, 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 object, as type
            <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_array_t</span></span></a></span>
            for a 2D image array object, as type
            <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_t</span></span></a></span>
            for a 1D image object, as type
            <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_buffer_t</span></span></a></span>
            for a 1D image buffer object, and as type
            <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image1d_array_t</span></span></a></span>
            for a 1D image array object. The elements of an image object cannot be directly accessed.
            Built-in functions to read from and write to an image object are provided.
        </p>
        <p>
            The const qualifier can also be used with the <code class="function">__global</code> qualifier to
            specify a read-only buffer memory object.
        </p>
      </div>
      <div class="refsect2">
        <a id="example1"></a>
        <h3>
            Examples
        </h3>
        <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. For example:
    </p>
        <div class="informaltable">
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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>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
      There is no address space for function return values. Using an address space qualifier in
      a function return type declaration will generate a compilation error, unless the return
      type is declared as a pointer type and the qualifier is used on the points-to address space.
    </p>
        <p>
      For example:
    </p>
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                <td align="left">
__private int f() { ... } // should generate an error
__local int *f() { ... } // allowed
__local int * __private f() { ... }; // should generate an error.
            </td>
              </tr>
            </tbody>
          </table>
        </div>
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                <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.
                        </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-1.2.pdf#page=222" 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 © 2007-2011 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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opencl-1.2-html-doc 1.0~svn33624-1 / usr / share / doc / opencl-1.2-html-doc / global.html
