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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_performance_mmx">
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<title>Using MMX intrinsics</title>
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<para>MMX was the first and oldest SIMD extension and initially filled a
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need for wider (64-bit) integer and additional registers. This is back when
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processors were 32-bit and 8 x 32-bit registers was starting to cramp our
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programming style. Now 64-bit processors, larger register sets, and 128-bit (or
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larger) vector SIMD extensions are common. There is simply no good reason to
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write new code using the (now) very limited MMX capabilities. </para>
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<para>We recommend that existing MMX codes be rewritten to use the newer
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SSE and VMX/VSX intrinsics or using the more portable GCC builtin vector
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support or in the case of si64 operations use C scalar code. The MMX si64
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scalars are just (64-bit) operations on long long int types and any
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modern C compiler can handle this type. The char / short in SIMD operations
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should all be promoted to 128-bit SIMD operations on GCC builtin vectors. Both
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will improve cross platform portability and performance.</para>
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</section>
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