sdk/1.1/docs/man/private.xml

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<refentry>
    <refentryinfo>
        <keywordset>
            <keyword>__private</keyword>
        </keywordset>
    </refentryinfo>

    <refmeta>                                    
        <refentrytitle>__private</refentrytitle>

        <refmiscinfo>
            <copyright>
                <year>2007-2010</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>3</manvolnum>
    </refmeta>

<!-- ================================ SYNOPSIS -->

    <refnamediv id="__private">             
        <refname>__private</refname>

        <refpurpose>
            Address Space Qualifier.
        </refpurpose>
    </refnamediv>


    <!-- ALTERNATIVE SYNTAX SYNOPSIS (NON-FUNCTION) -->
    <refsect2 id="synopsis">
        <title>
        </title>

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                        <entry>
__private
private
                        </entry>
                    </row>
                </tbody>
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        </informaltable>
    </refsect2>


<!-- ================================ DESCRIPTION  -->

    <refsect1 id="description"><title>Description</title>
        <para>
OpenCL implements the following disjoint address spaces: <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry>, <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>, 
<citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>
and <function>__private</function>.
        <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 function arguments 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. 
 </para>

        <para>
There is no generic address space name for program scope variables. All program scope variables must be declared in the <function>__constant</function> address space.
        </para>

        <para>
The <function>__constant</function> or <function>constant</function>
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 <function>__constant</function> address space are allowed arguments to functions (including <function>__kernel</function> functions) and for variables declared inside functions. Variables allocated in the <function>__constant</function> address space can only be defined as program scope variables and are required to be initialized.
        </para>
        <para>
Writes to variables declared with the <function>__constant</function> address space qualifier in the OpenCL program source should be a compile-time error.
        </para>
        <para>
All string literal storage shall be in the <function>__constant</function> address space.
        </para>
        <para>
        NOTE: Any argument to a kernel that is declared with the <function>__constant</function> 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 <citerefentry><refentrytitle>clGetDeviceInfo</refentrytitle></citerefentry>.
        </para>
        <para>
Variables inside a function or in program scope can also be declared with the <function>__constant</function> address qualifier. Implementations are not required to aggregate these declarations into the fewest number of constant arguments. This behavior is implementation defined.
        </para>
        <para>
Thus portable code must conservatively assume that each variable declared inside a function or in program scope with the <function>__constant</function> qualifier counts as a separate constant argument.
        </para>
    </refsect1>

    

<!-- ================================ NOTES  -->

    <refsect1 id="notes"><title>Notes</title>
        <para>
            Variables inside a <function>__kernel</function> function not declared with an address space qualifier, all variables inside non-kernel functions, and all function arguments are in the <function>__private</function> or <function>private</function> address space. Variables declared as pointers are considered to point to the <function>__private</function> address space if an address space qualifier is not specified except for arguments declared to be of type <citerefentry href="otherDataTypes"><refentrytitle>image2d_t</refentrytitle></citerefentry>, and <citerefentry href="otherDataTypes"><refentrytitle>image3d_t</refentrytitle></citerefentry> implicitly point to the <function>__global</function> address space.

The <function>__global</function>, <function>__constant</function>, <function>__local</function>, <function>__private</function>, <function>global</function>, <function>constant</function>, <function>local</function>, and <function>private</function> names are reserved for use as address space qualifiers and shall not be used otherwise.
        </para>
    </refsect1>
        
<!-- ================================ EXAMPLE  -->

    <refsect2 id="example1">
        <title>
            Example
        </title>

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                        <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>



<!-- ================================ SPECIFICATION  -->
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    <refsect1 id="specification"><title>Specification</title>
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            <olink uri="addressSpaceQualifier">OpenCL Specification</olink>
        </para>
    </refsect1>


<!-- ================================ ALSO SEE  -->

    <refsect1 id="seealso"><title>Also see</title>
        <para>
            <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry>, 
            <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>, 
            <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>
        </para>
    </refsect1>



<!-- ============================== COPYRIGHT -->
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