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

[Marton Balint]

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.

Thanks,
Marton