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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_sse"> |
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<title>Using SSE float and double scalars</title> |
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<para>For SSE scalar float / double intrinsics, “hand” optimization is no |
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longer necessary. This was important, when SSE was initially introduced, and |
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compiler support was limited or nonexistent. Also SSE scalar float / double |
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provided additional (16) registers and IEEE-754 compliance, not available from |
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the 8087 floating point architecture that preceded it. So application |
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developers where motivated to use SSE instructions versus what the compiler was |
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generating at the time.</para> |
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<para>Modern compilers can now generate and optimize these (SSE |
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scalar) instructions for Intel from C standard scalar code. Of course PowerISA |
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supported IEEE-754 float and double and had 32 dedicated floating point |
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registers from the start (and now 64 with VSX). So replacing Intel specific |
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scalar intrinsic implementation with the equivalent C language scalar |
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implementation is usually a win; it allows the compiler to apply the latest |
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optimization and tuning for the latest generation processor, and is portable to |
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other platforms where the compiler can also apply the latest optimization and |
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tuning for that processor's latest generation.</para> |
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</section> |
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