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Programming-Guides/Porting_Vector_Intrinsics/sec_simple_examples.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="sec_simple_examples">
<title>Some simple examples</title>
<para>For example; a vector double splat looks like this:
<programlisting><![CDATA[/* Create a vector with both elements equal to F. */
extern __inline __m128d __attribute__((__gnu_inline__, __always_inline__, __artificial__))
_mm_set1_pd (double __F)
{
return __extension__ (__m128d){ __F, __F };
}]]></programlisting></para>
<para>Another example:
<programlisting><![CDATA[extern __inline __m128d __attribute__((__gnu_inline__, __always_inline__, __artificial__))
_mm_add_pd (__m128d __A, __m128d __B)
{
return (__m128d) ((__v2df)__A + (__v2df)__B);
}]]></programlisting></para>
<para>Note in the example above the cast to __v2df for the operation. Both
__m128d and __v2df are vector double, but __v2df does no have the <literal>__may_alias__</literal>
attribute. And one more example:
<programlisting><![CDATA[extern __inline __m128i __attribute__((__gnu_inline__, __always_inline__, __artificial__))
_mm_mullo_epi16 (__m128i __A, __m128i __B)
{
return (__m128i) ((__v8hu)__A * (__v8hu)__B);
}]]></programlisting></para>
<para>Note this requires a cast for the compiler to generate the correct
code for the intended operation. The parameters and result are the generic
interface
type <literal>__m128i</literal>, which is a vector long long with the
<literal>__may_alias__</literal> attribute. But
operation is a vector multiply low on unsigned short elements.
So not only do we use the cast to drop the <literal>__may_alias__</literal>
attribute but we also need to cast to
the correct type (<literal>__v8hu</literal> or vector unsigned short)
for the specified operation.</para>
<para>I have successfully copied these (and similar) source snippets over
to the PPC64LE implementation unchanged. This of course assumes the associated
types are defined and with compatible attributes.</para>
</section>