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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_powerisa_vector_intrinsics">
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<title>PowerISA Vector Intrinsics</title>
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<para>The
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<emphasis role="bold">OpenPOWER ELF V2 application binary interface (ABI): Chapter 6.</emphasis>
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<emphasis><emphasis role="bold">Vector Programming Interfaces</emphasis></emphasis> and
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<emphasis><emphasis role="bold">Appendix A. Predefined Functions for Vector
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Programming</emphasis></emphasis> document the current and proposed vector built-ins we expect all
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C/C++ compilers implement. </para>
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<para>Some of these operations are endian sensitive and the compiler needs
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to make corresponding adjustments as it generates code for endian sensitive
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built-ins. There is a good overview for this in the
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<emphasis role="bold">OpenPOWER ABI Section</emphasis>
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<emphasis><emphasis role="bold">6.4.
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Vector Built-in Functions</emphasis></emphasis>.</para>
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<para>Appendix A is organized (sorted) by built-in name, output type, then
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parameter types. Most built-ins are overloaded
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as the named operation (vec_add,
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vec_sub, vec_mul, vec_cmpeq, ...) applies to multiple types. </para>
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<para>So the <literal>vec_add</literal> built-in applies to all the signed and unsigned
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integer types (char, short, in, and long) plus float and double floating-point
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types. The compiler looks at the parameter type to select the vector
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instruction (or instruction sequence) that implements the add operation on
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that type. The compiler infers the output result type from the operation and
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input parameters and will complain if the target variable type is not
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compatible. Some examples:
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<programlisting><![CDATA[vector signed char vec_add (vector signed char, vector signed char);
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vector unsigned char vec_add (vector unsigned char, vector unsigned char);
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vector signed short vec_add (vector signed short, vector signed short);
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vector unsigned short vec_add (vector unsigned short, vector unsigned short);
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vector signed int vec_add (vector signed int, vector signed int);
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vector unsigned int vec_add (vector unsigned int, vector unsigned int);
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vector signed int vec_add (vector signed long, vector signed long);
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vector unsigned int vec_add (vector unsigned long, vector unsigned long);
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vector float vec_add (vector float, vector float);
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vector double vec_add (vector double, vector double);]]></programlisting></para>
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<para>This is one key difference between PowerISA built-ins and Intel
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Intrinsics (Intel Intrinsics are not overloaded
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and include type information in
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the name). This is why it is so important to understand the vector element
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types and to add the appropriate type casts to get the correct results.</para>
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<para>The de facto standard implementation in GCC is defined in the include
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file <literal><altivec.h></literal> and documented in the GCC online documentation in
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<link xlink:href="https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/PowerPC-AltiVec_002fVSX-Built-in-Functions.html#PowerPC-AltiVec_002fVSX-Built-in-Functions">6.59.20 PowerPC
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AltiVec Built-in Functions</link>. The header file name and section title
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reflect the origin of the Vector Facility, but recent versions of GCC altivec.h
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include built-ins for newer PowerISA 2.06 and 2.07 VMX plus VSX extensions.
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This is a work in progress where your (older) distro GCC compiler may not
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include built-ins for the latest PowerISA 3.0 or ABI edition. So before you use
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a built-in you find in the ABI Appendix A, check the specific
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<link xlink:href="https://gcc.gnu.org/onlinedocs/">GCC online documentation</link> for the
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GCC version you are using.</para>
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</section>
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