[FFmpeg-devel] [FFmpeg-cvslog] avutil/mem: Optimize fill32() by unrolling and using 64bit

[Michael Niedermayer]

On Sun, Jan 20, 2019 at 10:33:26PM +0100, Carl Eugen Hoyos wrote:
> 2019-01-20 22:22 GMT+01:00, Michael Niedermayer <git at videolan.org>:
> > ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Thu
> > Jan 17 22:35:10 2019 +0100| [12b1338be376a3e5fb606d9fe41b58dc4a9e62c7] |
> > committer: Michael Niedermayer
> >
> > avutil/mem: Optimize fill32() by unrolling and using 64bit
> >
> > Reviewed-by: Marton Balint <cus at passwd.hu>
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> >
> >> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=12b1338be376a3e5fb606d9fe41b58dc4a9e62c7
> > ---
> >
> >  libavutil/mem.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/libavutil/mem.c b/libavutil/mem.c
> > index 6149755a6b..88fe09b179 100644
> > --- a/libavutil/mem.c
> > +++ b/libavutil/mem.c
> > @@ -399,6 +399,18 @@ static void fill32(uint8_t *dst, int len)
> >  {
> >      uint32_t v = AV_RN32(dst - 4);
> >
> > +#if HAVE_FAST_64BIT
> 
> I suspect this should be !X86_32

> 
> > +    uint64_t v2= v + ((uint64_t)v<<32);
> > +    while (len >= 32) {
> > +        AV_WN64(dst   , v2);
> > +        AV_WN64(dst+ 8, v2);
> > +        AV_WN64(dst+16, v2);
> > +        AV_WN64(dst+24, v2);
> > +        dst += 32;
> > +        len -= 32;
> > +    }
> 
> How can I test the performance of this function?

with the testcase from the fuzzer (it should be substantially
faster in this case with teh next commit)

it should also be possible to test it with some fate tests
as this is used by some.
You can add a abort() and run fate to see which tests use it




[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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