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

[Michael Niedermayer]

On Wed, Apr 15, 2009 at 05:29:14PM +0200, Reimar D?ffinger wrote:
> 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);

people should not do such stupid things


> 
> > > +    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.

maybe

   (unsigned)grow_by > INT_MAX - FF_INPUT_BUFFER_PADDING_SIZE 
|| pkt->size > INT_MAX - FF_INPUT_BUFFER_PADDING_SIZE - grow_by 

?


> 
> > > 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.

well, fine leave that then

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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