sdk/2.1/docs/man/as_typen.xml

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<refentry>
    <refentryinfo>
        <keywordset>
            <keyword>Reinterpreting Types, as_typen(), as_type()</keyword>
        </keywordset>
    </refentryinfo>

    <refmeta>
        <refentrytitle>Reinterpreting Types Using as_type() and as_typen()</refentrytitle>

        <refmiscinfo>
            <copyright>
                <year>2007-2013</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="ReinterpretingTypesUsingas_typen()">
        <refname>as_type(), as_type<emphasis>n</emphasis>()</refname>
        <refpurpose>
        </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>
as_type()
                        </entry>
                    </row>
                    <row>
                        <entry>
as_type<replaceable>n</replaceable>()
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect2>

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

    <refsect1 id="description"><title>Description</title>
        <para>
          All data types described in <citerefentry href="scalarDataTypes"><refentrytitle>Scalar
          Data Types</refentrytitle></citerefentry> and
          <citerefentry href="vectorDataTypes"><refentrytitle>Vector Data
          Types</refentrytitle></citerefentry> (except <type>bool</type>, <type>half</type>
          (unless  the <citerefentry><refentrytitle>cl_khr_fp16</refentrytitle></citerefentry>
          extension is supported), and <type>void</type>) may be also reinterpreted as another
          data type of the same size using the <function>as_type()</function> operator for scalar
          data types and the <function>as_type<replaceable>n</replaceable>()</function> operator
          for vector data types. When the operand and result type contain the same number of
          elements, the bits in the operand shall be returned directly without modification as
          the new type. The usual type promotion for function arguments shall not be performed.
        </para>

        <para>
          For example, <code>as_float(0x3f800000)</code> returns <code>1.0f</code>, which is
          the value that the bit pattern <code>0x3f800000</code> has if viewed as an IEEE-754
          single precision value.
        </para>

        <para>
          When the operand and result type contain a different number of elements, the result
          shall be implementation-defined except if the operand is a 4-component vector and the
          result is a 3-component vector.  In this case, the bits in the operand shall be returned
          directly without modification as the new type. That is, a conforming implementation shall
          explicitly define a behavior, but two conforming implementations need not have the same
          behavior when the number of elements in the result and operand types does not match. The
          implementation may define the result to contain all, some or none of the original bits
          in whatever order it chooses. It is an error to use the  <function>as_type()</function>
          or  <function>as_type<replaceable>n</replaceable>()</function> operators to reinterpret
          data to a type of a different number of bytes.
        </para>
    </refsect1>

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

    <refsect1 id="notes"><title>Notes</title>
        <para>
          While the union is intended to reflect the organization
          of data in memory, the <function>as_type()</function> and
          <function>as_type<replaceable>n</replaceable>()</function> constructs are intended
          to reflect the organization of data in register. The <function>as_type()</function>
          and <function>as_type<replaceable>n</replaceable>()</function> constructs are intended
          to compile to no instructions on devices that use a shared register file designed to
          operate on both the operand and result types.
        </para>

        <para>
          Note that while differences in memory organization are expected to largely be limited
          to those arising from endianness, the register based representation may also differ
          due to size of the element in register. (For example, an architecture may load a char
          into a 32-bit register, or a char vector into a SIMD vector register with fixed 32-bit
          element size.)
        </para>

        <para>
          If the element count does not match, then the implementation should pick a data
          representation that most closely matches what would happen if an appropriate result type
          operator was applied to a register containing data of the source type. If the number of
          elements matches, then the <function>as_type<replaceable>n</replaceable>()</function>
          should faithfully reproduce the behavior expected from a similar data type
          reinterpretation using memory/unions.  So, for example if an implementation stores
          all single precision data as double in register, it should implement as_int( float )
          by first downconverting the double to single precision and then (if necessary) moving
          the single precision bits to a register suitable for operating on integer data.
        </para>

        <para>
          If data stored in different address spaces do not have the same endianness, then the
          "dominant endianness" of the device should prevail.
        </para>
    </refsect1>

<!-- ================================ EXAMPLE  -->

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

        <informaltable frame="none">
            <tgroup cols="1" align="left" colsep="0" rowsep="0">
                <colspec colname="col1" colnum="1" />
                <tbody>
                    <row>
                        <entry>
float f = 1.0f;
uint u = as_uint(f);  // Legal. Contains:  0x3f800000

float4 f = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
// Legal. Contains: (int4)
// (0x3f800000, 0x40000000, 0x40400000, 0x40800000)
int4 i = as_int4(f);

float4 f, g;
int4 is_less = f &lt; g;

// Legal. f[i] = f[i] &lt; g[i] ? f[i] : 0.0f
f = as_float4(as_int4(f) &amp; is_less);

int i;
// Legal. Result is implementation-defined.
short2 j = as_short2(i);

int4 i;
// Legal. Result is implementation-defined.
short8 j = as_short8(i);

float4 f;
//Error. result and operand have different size
double4 g = as_double4(f);   // Only if double is supported.

float4 f;
// Legal. g.xyz will have same values as f.xyz. g.w is undefined
float3 g = as_float3(f);

                        </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="as_typen">OpenCL Specification</olink>
        </para>
    </refsect1>

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

    <refsect1 id="seealso"><title>Also see</title>
        <para>
            <citerefentry href="scalarDataTypes"><refentrytitle>Scalar Data Types</refentrytitle></citerefentry>,
            <citerefentry href="vectorDataTypes"><refentrytitle>Vector Data Types</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>

<!-- 3-Jun-2013 -->
</refentry>