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

[Paul B Mahol]

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.