[FFmpeg-devel] [PATCH 1/3] avutil/imgutils: Optimize writing 4 bytes in memset_bytes()

[Michael Niedermayer]

On Wed, Dec 26, 2018 at 10:16:47PM +0100, Marton Balint wrote:
> 
> 
> On Wed, 26 Dec 2018, Paul B Mahol wrote:
> 
> >On 12/26/18, Michael Niedermayer <michael at niedermayer.cc> wrote:
> >>On Wed, Dec 26, 2018 at 04:32:17PM +0100, Paul B Mahol wrote:
> >>>On 12/25/18, Michael Niedermayer <michael at niedermayer.cc> wrote:
> >>>> Fixes: Timeout
> >>>> Fixes:
> >>>> 11502/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WCMV_fuzzer-5664893810769920
> >>>> Before: Executed
> >>>> clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WCMV_fuzzer-5664893810769920
> >>>> in 11294 ms
> >>>> After : Executed
> >>>> clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WCMV_fuzzer-5664893810769920
> >>>> in 4249 ms
> >>>>
> >>>> Found-by: continuous fuzzing process
> >>>> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> >>>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> >>>> ---
> >>>>  libavutil/imgutils.c | 6 ++++++
> >>>>  1 file changed, 6 insertions(+)
> >>>>
> >>>> diff --git a/libavutil/imgutils.c b/libavutil/imgutils.c
> >>>> index 4938a7ef67..cc38f1e878 100644
> >>>> --- a/libavutil/imgutils.c
> >>>> +++ b/libavutil/imgutils.c
> >>>> @@ -529,6 +529,12 @@ static void memset_bytes(uint8_t *dst, size_t
> >>>> dst_size,
> >>>> uint8_t *clear,
> >>>>          }
> >>>>      } else if (clear_size == 4) {
> >>>>          uint32_t val = AV_RN32(clear);
> >>>> +        uint64_t val8 = val * 0x100000001ULL;
> >>>> +        for (; dst_size >= 32; dst_size -= 32) {
> >>>> +            AV_WN64(dst   , val8); AV_WN64(dst+ 8, val8);
> >>>> +            AV_WN64(dst+16, val8); AV_WN64(dst+24, val8);
> >>>> +            dst += 32;
> >>>> +        }
> >>>>          for (; dst_size >= 4; dst_size -= 4) {
> >>>>              AV_WN32(dst, val);
> >>>>              dst += 4;
> >>>> --
> >>>> 2.20.1
> >>>>
> >>>
> >>>NAK, implement special memset function instead.
> >>
> >>I can move the added loop into a seperate function, if thats what you
> >>suggest ?
> >
> >No, don't do that.
> >
> >>All the code is already in a "special" memset though, this is
> >>memset_bytes()
> >>
> >
> >I guess function is less useful if its static. So any duplicate should
> >be avoided in codebase.
> 
> Isn't av_memcpy_backptr does almost exactly what is needed here? That can
> also be optimized further if needed.

av_memcpy_backptr() copies data with overlap, its more like a recursive
memmove(). 

thx
[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No snowflake in an avalanche ever feels responsible. -- Voltaire
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