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@ -67,27 +67,15 @@ xml:id="dbdoclet.50655244_pgfId-1095944">
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static, auto, and register storage.</para>
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<para>Pointers to vector types are defined like pointers of other C/C++
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types. Pointers to objects may be defined to have const and volatile
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properties. While the preferred alignment for vector data types is a
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multiple of 16 bytes, pointers may point to vector objects at an arbitrary
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alignment.</para>
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properties.</para>
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<para>The preferred way to access vectors at an application-defined address
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is by using vector pointers and the C/C++ dereference operator *. Similar
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to other C /C++ data types, the array reference operator [ ] may be used to
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access vector objects with a vector pointer with the usual definition to
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access the n-th vector element from a vector pointer. The use of vector
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built-in functions such as vec_xl and vec_xst is discouraged except for
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languages where no dereference operators are available.</para>
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<programlisting>vector char vca;
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vector char vcb;
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vector int via;
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int a[4];
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void *vp;
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via = *(vector int *) &a[0];
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vca = (vector char) via;
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vcb = vca;
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vca = *(vector char *)vp;
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*(vector char *)&a[0] = vca;</programlisting>
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access the n-th vector element from a vector pointer. The dereference
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operator * may <emphasis>not</emphasis> be used to access data that is
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not aligned at least to a quadword boundary. Built-in functions such as
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vec_xl and vec_xst are provided for unaligned data access.</para>
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<para>Compilers are expected to recognize and optimize multiple operations
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that can be optimized into a single hardware instruction. For example, a
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load and splat hardware instruction might be generated for the following
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@ -578,12 +566,6 @@ register vector double vd = vec_splats(*double_ptr);</programlisting>
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</tbody>
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</tgroup>
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</table>
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<note>
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<para><emphasis role="bold">Reminder</emphasis>: The assignment operator = is the
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preferred way to assign values from one vector data type to
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another vector data type in accordance with the C and C++
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programming languages.</para>
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</note>
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<para> </para>
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<bridgehead>Extended Data Movement Functions</bridgehead>
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<para>The built-in functions in
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@ -702,25 +684,20 @@ register vector double vd = vec_splats(*double_ptr);</programlisting>
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of these sequences in new code is discouraged and usually results in
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worse performance. It is recommended (but not required) that compilers
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issue a warning when these functions are used in little-endian
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environments. It is recommended that programmers use the assignment
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operator = or the vector vec_xl and vec_xst vector built-in functions to
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access unaligned data streams.</para>
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<para>The set of extended mnemonics in
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<xref linkend="dbdoclet.50655244_62451" /> may be provided by some
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compilers and are not required by the Power SIMD programming interfaces.
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In particular, the assignment operator = will have the same effect of
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copying values between vector data types and provides a preferable method
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to assign values while giving the compiler more freedom to optimize data
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allocation. The only use for these functions is to support some coding
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patterns enabling big-endian vector layout code sequences in both
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big-endian and little-endian environments. Memory access built-in
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environments. It is recommended that programmers use the vec_xl and
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vec_xst vector built-in functions to access unaligned data
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streams.</para>
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<para>The built-in functions in
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<xref linkend="dbdoclet.50655244_62451" /> provide unaligned access to
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data in memory that is to be copied to or from a variable having vector
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data type. Memory access built-in
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functions that specify a vector element format (that is, the w4 and d2
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forms) are deprecated. They will be phased out in future versions of this
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specification because vec_xl and vec_xst provide overloaded
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layout-specific memory access based on the specified vector data
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type.</para>
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<table frame="all" pgwide="1" xml:id="dbdoclet.50655244_62451">
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<title>Optional Built-In Memory Access Functions</title>
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<title>VSX Memory Access Built-In Functions</title>
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<tgroup cols="3">
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<colspec colname="c1" colwidth="15*" align="center" />
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<colspec colname="c2" colwidth="35*" align="center" />
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@ -1137,7 +1114,7 @@ register vector double vd = vec_splats(*double_ptr);</programlisting>
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<xref linkend="dbdoclet.50655244_21918" />.</para>
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<para> </para>
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<table frame="all" pgwide="1" xml:id="dbdoclet.50655244_21918">
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<title>Optional Built-In Memory Access Functions (BE Layout in LE
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<title>VSX Built-In Memory Access Functions (BE Layout in LE
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Mode)</title>
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<tgroup cols="3">
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<colspec colname="c1" colwidth="15*" align="center"/>
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Bill Schmidt
7 years ago