On Wed, Mar 1, 2023 at 3:22 PM Jeremy Dorfman <jdorf...@google.com> wrote:
>
> On Wed, Mar 1, 2023 at 2:07 PM James Almer <jamr...@gmail.com> wrote:
> >
> > On 3/1/2023 3:50 PM, Jeremy Dorfman wrote:
> > > null pointer arithmetic is undefined behavior in C.
> > > ---
> > > libavcodec/h264dec.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
> > > index 2d691731c5..ef698f2630 100644
> > > --- a/libavcodec/h264dec.c
> > > +++ b/libavcodec/h264dec.c
> > > @@ -912,8 +912,8 @@ static int finalize_frame(H264Context *h, AVFrame
> > > *dst, H264Picture *out, int *g
> > > av_log(h->avctx, AV_LOG_DEBUG, "Duplicating field %d to
> > > fill missing\n", field);
> > >
> > > for (p = 0; p<4; p++) {
> > > - dst_data[p] = f->data[p] + (field^1)*f->linesize[p];
> > > - src_data[p] = f->data[p] + field *f->linesize[p];
> > > + dst_data[p] = f->data[p] ? f->data[p] +
> > > (field^1)*f->linesize[p] : NULL;
> > > + src_data[p] = f->data[p] ? f->data[p] + field
> > > *f->linesize[p] : NULL;
> > > linesizes[p] = 2*f->linesize[p];
> > > }
> >
> > Probably cleaner and clearer to do it like this:
> >
> > dst_data[p] = FF_PTR_ADD(f->data[p], (field^1)*f->linesize[p]);
> > src_data[p] = FF_PTR_ADD(f->data[p], field *f->linesize[p]);
>
> Thank you for the feedback. That seems reasonable to me; I wasn't aware of
> FF_PTR_ADD.
>
> ---
> libavcodec/h264dec.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
> index 2d691731c5..0ac04baa4d 100644
> --- a/libavcodec/h264dec.c
> +++ b/libavcodec/h264dec.c
> @@ -31,6 +31,7 @@
>
> #include "libavutil/avassert.h"
> #include "libavutil/imgutils.h"
> +#include "libavutil/internal.h"
> #include "libavutil/opt.h"
> #include "libavutil/thread.h"
> #include "libavutil/video_enc_params.h"
> @@ -912,8 +913,8 @@ static int finalize_frame(H264Context *h, AVFrame *dst,
> H264Picture *out, int *g
> av_log(h->avctx, AV_LOG_DEBUG, "Duplicating field %d to fill
> missing\n", field);
>
> for (p = 0; p<4; p++) {
> - dst_data[p] = f->data[p] + (field^1)*f->linesize[p];
> - src_data[p] = f->data[p] + field *f->linesize[p];
> + dst_data[p] = FF_PTR_ADD(f->data[p],
> (field^1)*f->linesize[p]);
> + src_data[p] = FF_PTR_ADD(f->data[p], field
> *f->linesize[p]);
> linesizes[p] = 2*f->linesize[p];
> }
>
I apologize for the mangled patch and spam. Hopefully this comes
through as text/plain without the corrupted patch:
---
libavcodec/h264dec.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index 2d691731c5..0ac04baa4d 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -31,6 +31,7 @@
#include "libavutil/avassert.h"
#include "libavutil/imgutils.h"
+#include "libavutil/internal.h"
#include "libavutil/opt.h"
#include "libavutil/thread.h"
#include "libavutil/video_enc_params.h"
@@ -912,8 +913,8 @@ static int finalize_frame(H264Context *h, AVFrame
*dst, H264Picture *out, int *g
av_log(h->avctx, AV_LOG_DEBUG, "Duplicating field %d to
fill missing\n", field);
for (p = 0; p<4; p++) {
- dst_data[p] = f->data[p] + (field^1)*f->linesize[p];
- src_data[p] = f->data[p] + field *f->linesize[p];
+ dst_data[p] = FF_PTR_ADD(f->data[p], (field^1)*f->linesize[p]);
+ src_data[p] = FF_PTR_ADD(f->data[p], field *f->linesize[p]);
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