[FFmpeg-devel] [PATCH 1/2] avcodec/lcldec: Optimize YUV422 case

[Michael Niedermayer]

On Sun, Jul 28, 2019 at 12:45:36AM +0200, Reimar Döffinger wrote:
> 
> 
> On 28.07.2019, at 00:31, Michael Niedermayer <michael at 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 <michael at 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 <michael at 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 <michael at 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];
[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
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