On 7/28/2019 8:56 AM, Michael Niedermayer wrote: > On Sun, Jul 28, 2019 at 12:45:36AM +0200, Reimar Döffinger wrote: >> >> >> On 28.07.2019, at 00:31, Michael Niedermayer <mich...@niedermayer.cc> wrote: >> >>> This merges several byte operations and avoids some shifts inside the loop >>> >>> Improves: Timeout (330sec -> 134sec) >>> Improves: >>> 15599/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MSZH_fuzzer-5658127116009472 >>> >>> Found-by: continuous fuzzing process >>> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg >>> Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> >>> --- >>> libavcodec/lcldec.c | 10 +++++----- >>> 1 file changed, 5 insertions(+), 5 deletions(-) >>> >>> diff --git a/libavcodec/lcldec.c b/libavcodec/lcldec.c >>> index 104defa5f5..c3787b3cbe 100644 >>> --- a/libavcodec/lcldec.c >>> +++ b/libavcodec/lcldec.c >>> @@ -391,13 +391,13 @@ static int decode_frame(AVCodecContext *avctx, void >>> *data, int *got_frame, AVPac >>> break; >>> case IMGTYPE_YUV422: >>> for (row = 0; row < height; row++) { >>> - for (col = 0; col < width - 3; col += 4) { >>> + for (col = 0; col < (width - 2)>>1; col += 2) { >>> memcpy(y_out + col, encoded, 4); >>> encoded += 4; >>> - u_out[ col >> 1 ] = *encoded++ + 128; >>> - u_out[(col >> 1) + 1] = *encoded++ + 128; >>> - v_out[ col >> 1 ] = *encoded++ + 128; >>> - v_out[(col >> 1) + 1] = *encoded++ + 128; >>> + AV_WN16(u_out + col, AV_RN16(encoded) ^ 0x8080); >>> + encoded += 2; >>> + AV_WN16(v_out + col, AV_RN16(encoded) ^ 0x8080); >>> + encoded += 2; >> >> Huh? Surely the pixel stride used for y_out still needs to be double of the >> u/v one? > >> I suspect doing only the AV_RN16/xor optimization might be best, the one >> shift saved seems not worth the risk/complexity... > > if you want i can remove the shift change ? > with the fixed shift change its 155sec, if i remove the shift optimization > its 170sec > > patch for the 155 case below: > > commit 56998b7d57a2cd0ed7f53981c50e76fd419cd86f (HEAD) > Author: Michael Niedermayer <mich...@niedermayer.cc> > Date: Sat Jul 27 22:46:34 2019 +0200 > > avcodec/lcldec: Optimize YUV422 case > > This merges several byte operations and avoids some shifts inside the loop > > Improves: Timeout (330sec -> 155sec) > Improves: > 15599/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MSZH_fuzzer-5658127116009472 > > Found-by: continuous fuzzing process > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > diff --git a/libavcodec/lcldec.c b/libavcodec/lcldec.c > index 104defa5f5..9e018ff5a9 100644 > --- a/libavcodec/lcldec.c > +++ b/libavcodec/lcldec.c > @@ -391,13 +391,13 @@ static int decode_frame(AVCodecContext *avctx, void > *data, int *got_frame, AVPac > break; > case IMGTYPE_YUV422: > for (row = 0; row < height; row++) { > - for (col = 0; col < width - 3; col += 4) { > - memcpy(y_out + col, encoded, 4); > + for (col = 0; col < (width - 2)>>1; col += 2) { > + memcpy(y_out + 2 * col, encoded, 4); > encoded += 4; > - u_out[ col >> 1 ] = *encoded++ + 128; > - u_out[(col >> 1) + 1] = *encoded++ + 128; > - v_out[ col >> 1 ] = *encoded++ + 128; > - v_out[(col >> 1) + 1] = *encoded++ + 128; > + AV_WN16(u_out + col, AV_RN16(encoded) ^ 0x8080); > + encoded += 2; > + AV_WN16(v_out + col, AV_RN16(encoded) ^ 0x8080); > + encoded += 2; > } > y_out -= frame->linesize[0]; > u_out -= frame->linesize[1]; > [...]
As others pointed before, this kind of optimization is usually meant for the SIMD implementations and not the C boilerplate/reference. So prioritize readability above speed if possible when choosing which version to apply. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
