On Sun, 9 Jul 2017 22:37:46 -0400
"Ronald S. Bultje" <rsbul...@gmail.com> wrote:
> Hi,
>
> On Sun, Jul 9, 2017 at 9:19 PM, Michael Niedermayer <mich...@niedermayer.cc>
> wrote:
>
> > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
> > ---
> > libavcodec/mpegvideo.c | 15 ++++++++++++++-
> > 1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> > index e29558b3a2..574b3854e0 100644
> > --- a/libavcodec/mpegvideo.c
> > +++ b/libavcodec/mpegvideo.c
> > @@ -495,7 +495,20 @@ int ff_mpeg_update_thread_context(AVCodecContext
> > *dst,
> > // in that case dst may need a reinit
> > if (!s->context_initialized) {
> > int err;
> > - memcpy(s, s1, sizeof(MpegEncContext));
> > +#define COPY(x) s->x = s1->x;
> >
>
> Unused?
>
>
> > +#define COPYR(a, b) memcpy(&s->a, &s1->a, ((uint8_t*)&s->b) -
> > ((uint8_t*)&s->a))
> > + COPYR(h263_aic, qscale);
> > + COPYR(lambda, mv_dir);
> > + COPYR(no_rounding, dest);
> > + COPYR(mb_index2xy, resync_mb_x);
> > + COPYR(next_p_frame_damaged, h263_aic_dir);
> > + COPYR(h263_slice_structured, mcsel);
> > + COPYR(quant_precision, first_slice_line);
> > + COPYR(flipflop_rounding, gb);
> > + COPYR(gop_picture_number, picture_structure);
> > + COPYR(picture_structure, pblocks);
> > + COPYR(decode_mb, er);
> > + COPYR(error_rate, noise_reduction);
>
>
> This is very obscure... The obscure part is what happens when fields get
> (through refactoring) reordered or new fields get inserted...
>
> I also appear to remember that we used to use this same pattern for h264
> also, but we don't anymore. Does anyone remember why?
Do you mean 0ba471d7d864c712f45d7ac6aca4829aba025adc?
h264: eliminate copy_fields
It is very fragile against fields being moved and hides what is actually
being copied. Copy all the fields explicitly instead.
Seems justification enough for me.
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