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58 lines
2.2 KiB
XML
58 lines
2.2 KiB
XML
8 years ago
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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_prefered_methods">
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7 years ago
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<title>Preferred methods</title>
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8 years ago
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<para>As we will see there are multiple ways to implement the logic of
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these intrinsics. Some implementation methods are preferred because they allow
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the compiler to select instructions and provided the most flexibility for
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optimization across the whole sequence. Other methods may be required to
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deliver a specific semantic or to deliver better optimization than the current
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compiler is capable of. Some methods are more portable across multiple
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compilers (GCC, LLVM, ...). All of this should be taken into consideration for
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each intrinsic implementation. In general we should use the following list as a
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guide to these decisions:</para>
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7 years ago
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<orderedlist spacing="compact">
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8 years ago
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<listitem>
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<para>Use C vector arithmetic, logical, dereference, etc., operators in
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preference to intrinsics.</para>
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</listitem>
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<listitem>
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<para>Use the bi-endian interfaces from Appendix A of the ABI in
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preference to other intrinsics when available, as these are designed for
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portability among compilers.</para>
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</listitem>
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<listitem>
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<para>Use other, less well documented intrinsics (such as
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<literal>__builtin_vsx_*</literal>) when no better facility is available, in preference to
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assembly.</para>
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</listitem>
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<listitem>
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<para>If necessary, use inline assembly, but know what you're
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doing.</para>
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</listitem>
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</orderedlist>
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</section>
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