[FFmpeg-devel] [PATCH] some SIMD write-combining for h264

Alexander Strange astrange
Mon Jan 18 02:09:16 CET 2010

On Sun, Jan 17, 2010 at 7:54 PM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> Alexander Strange <astrange <at> ithinksw.com> writes:
>> >>> also what sets __MMX__ ? we have our own defines for that
>> >>
>> >> It's a gcc builtin define, set based on ./configure --cpu=x adding
>> >> -march. ?HAVE_MMX is for the build and not the host cpu family, and
>> >> this is inlined asm, so it can't use it.
>> >
>> > Huh? ?Host... build???
>> Oh, that was supposed to be "target"...
>> Anyway, this is MMX being used like the cmov/clz inlines, so it depends on the
>> given --cpu and not on the build system's capabilities.
> Could you explain once more why this shouldn't be HAVE_MMX?
> If the user passes --disable-mmx to configure, he imo expects MMX to be disabled.
> Carl Eugen

HAVE_MMX isn't enough to enable it - './configure --cpu=i586' enables
HAVE_MMX, but i586 doesn't have it.
Technically I'd say --disable-mmx should pass -mno-mmx to gcc, but
that seems like a complicated change to configure, so I'll check
HAVE_MMX to disable it as well.

Also, the second patch is broken now, so I'll have to redo it.

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