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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Copyright (c) 2017 OpenPOWER Foundation
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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version="5.0"
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xml:id="sec_simple_examples">
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<title>Some simple examples</title>
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<para>For example; a vector double splat looks like this:
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<programlisting><![CDATA[/* Create a vector with both elements equal to F. */
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extern __inline __m128d __attribute__((__gnu_inline__, __always_inline__, __artificial__))
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_mm_set1_pd (double __F)
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{
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return __extension__ (__m128d){ __F, __F };
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}]]></programlisting></para>
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<para>Another example:
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<programlisting><![CDATA[extern __inline __m128d __attribute__((__gnu_inline__, __always_inline__, __artificial__))
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_mm_add_pd (__m128d __A, __m128d __B)
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{
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return (__m128d) ((__v2df)__A + (__v2df)__B);
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}]]></programlisting></para>
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<para>Note in the example above the cast to __v2df for the operation. Both
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__m128d and __v2df are vector double, but __v2df does no have the <literal>__may_alias__</literal>
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attribute. And one more example:
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<programlisting><![CDATA[extern __inline __m128i __attribute__((__gnu_inline__, __always_inline__, __artificial__))
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_mm_mullo_epi16 (__m128i __A, __m128i __B)
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{
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return (__m128i) ((__v8hu)__A * (__v8hu)__B);
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}]]></programlisting></para>
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<para>Note this requires a cast for the compiler to generate the correct
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code for the intended operation. The parameters and result are the generic
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interface
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type <literal>__m128i</literal>, which is a vector long long with the
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<literal>__may_alias__</literal> attribute. But
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operation is a vector multiply low on unsigned short elements.
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So not only do we use the cast to drop the <literal>__may_alias__</literal>
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attribute but we also need to cast to
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the correct type (<literal>__v8hu</literal> or vector unsigned short)
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for the specified operation.</para>
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<para>I have successfully copied these (and similar) source snippets over
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to the PPC64LE implementation unchanged. This of course assumes the associated
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types are defined and with compatible attributes.</para>
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</section>
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