[FFmpeg-devel] [RFC] WC3 decoder without AVPaletteControl

[Reimar Döffinger]

On Wed, Apr 15, 2009 at 04:17:24PM +0200, Michael Niedermayer wrote:
> On Sun, Apr 12, 2009 at 01:26:33PM +0200, Reimar D?ffinger wrote:
> > +int av_grow_packet(AVPacket *pkt, int grow_by)
> > +{
> > +    void *new_ptr;
> 
> > +    if (!grow_by)
> > +        return 0;
> 
> for what is that good for?

Avoiding a pointless realloc in case someone does something stupid like
av_grow_packet(pkt, 0);

> > +    if (pkt->size + FF_INPUT_BUFFER_PADDING_SIZE > INT_MAX - grow_by)
> > +        return -1;
> 
> could you write this in a way that is free of overflows please ;)

Hm. Bad "documentation", I hadn't decided what grow_by < 0 is supposed to
mean or if I should just make it unsigned (the latter I admit would not
help here).
So
> if (grow_by < 0 || pkt->size + FF_INPUT_BUFFER_PADDING_SIZE > INT_MAX - grow_by)
good enough?
I also assumed that pkt->size + FF_INPUT_BUFFER_PADDING_SIZE would not
overflow since the allocated buffer must already be that big, if you
dislike that.

> > Index: libavformat/utils.c
> > ===================================================================
> > --- libavformat/utils.c	(revision 18467)
> > +++ libavformat/utils.c	(working copy)
> > @@ -277,6 +277,20 @@
> >      return ret;
> >  }
> >  
> > +int av_append_packet(ByteIOContext *s, AVPacket *pkt, int size)
> > +{
> > +    int ret;
> > +    int old_size;
> > +    if (!pkt->size)
> > +        return av_get_packet(s, pkt, size);
> > +    old_size = pkt->size;
> > +    ret = av_grow_packet(pkt, size);
> 
> isnt av_grow_packet already checking for pkt->size==0 ?

Yes, but it only allocates a new packet then. av_get_packet also sets
pkt->pos. Sure, maybe a bit overkill for a single assignment, just
thought it might be more future-proof.