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Mark Knecht posted on Tue, 10 Mar 2015 17:40:33 -0700 as excerpted: |
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> On Tue, Mar 10, 2015 at 5:27 PM, Frank Peters <frank.peters@×××××××.net> |
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> wrote: |
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>> On Tue, 10 Mar 2015 17:17:11 -0700 Mark Knecht <markknecht@×××××.com> |
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>> wrote: |
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>> |
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>> |
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>>> I've had no problems, as best I can tell, with ffmpeg and these |
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>>> settings. |
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>>> |
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>>> |
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>> Well, if the use of the mmxext flag leads to instructions in the |
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>> compiled code which the cpu does not have, then CRASH. |
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>> |
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>> But the SSE instruction sets supersede MMX (and mmxext) and so the |
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>> mmxext flag is really unnecessary on Core i7 and many newer processors. |
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>> (Ffmpeg may have reasons for still using MMX but I don't know.) |
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>> |
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>> Frank Peters |
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> |
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> True, but I don't think it's likely as the old mmxext flags (AMD only |
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> possibly?) became a subset of SSE. That said, report the bug and copy us |
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> on the report. I'd be interested in hearing what the developers say. |
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AFAIK (and verified by wikipedia, see the links below), all amd64 aka |
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x86_64 CPUs ship with mmx/mmxext/sse/sse2. It was part of the base amd64 |
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spec, and as such, mmxext should be considered available on any amd64 |
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based machine. |
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|
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More specifically, according to wikipedia, AMD's second generation 3DNow |
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(called various things, there was apparently never an official name) was |
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introduced in the first-gen Athlon CPUs. The combined 24 new |
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instructions were segregated into 5 new 3DNow instructions and 19 new MMX |
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instructions in tech manuals, and some pre-amd64 CPUs actually shipped |
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with the 5 additional 3DNow instructions only, while customer-focused |
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literature tended to blur the lines and refer to the 24 instructions |
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combined as enhanced 3DNow technology. |
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|
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Meanwhile, the 19 new MMX instructions were a subset of Intel's SSE (v1) |
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instruction set. This SSE subset of 19 instructions is apparently what |
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mmxext actually refers to. Thus, anything with sse in the cpuflags by |
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definition has mmxext as well. |
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So you can actually verify your CPU mmxext safe using two different |
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methods. (1) It's in the amd64/x86_64 baseline definition, so if your |
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machine is amd64/X86_64, it's automatically mmxext. (2) SSE supersets |
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mmxext, so if sse appears in the cpuflags, it's automatically mmxext as |
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well. |
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|
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|
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https://en.wikipedia.org/wiki/3DNow!#3DNow_extensions |
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(In particular, see the 3DNow or MMX Extensions paragraph.) |
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https://en.wikipedia.org/wiki/X86-64#Architectural_features |
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(In particular, see the SSE Instructions paragraph.) |
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-- |
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Duncan - List replies preferred. No HTML msgs. |
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"Every nonfree program has a lord, a master -- |
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and if you use the program, he is your master." Richard Stallman |
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