[FFmpeg-devel] [PATCH] avcodec/get_bits: Document skip_bits_long()

Michael Niedermayer michael at niedermayer.cc
Sat Mar 24 02:37:40 EET 2018


On Fri, Mar 23, 2018 at 10:02:39PM +0100, Thilo Borgmann wrote:
> Am 23.03.18 um 20:20 schrieb Michael Niedermayer:
> > Found-by: Kieran
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavcodec/get_bits.h | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
> > index 0c7f5ff0c6..3ec45e7ab6 100644
> > --- a/libavcodec/get_bits.h
> > +++ b/libavcodec/get_bits.h
> > @@ -201,6 +201,13 @@ static inline int get_bits_count(const GetBitContext *s)
> >      return s->index;
> >  }
> >  
> > +/**
> > + * Skips the specified number of bits.
> > + * @param n the number of bits to skip,
> > + *          For the UNCHECKED_BITSTREAM_READER this must not cause the distance
> > + *          from the start to overflow int32_t. Staying within the bitstream + padding
> > + *          is sufficient too.
>                   ^^^^^^^^^^
> Shouldn't this be "required" or "necessary"?

The bitstream reader must be able to index the whole bitstream and the padding
otherwise it would have some issues, actually it possibly does have a bug there
i need to double check this

currently it uses int32, so if the input is bigger the reader will reject this
so just staying within that size should be fine
that is unless iam missing something

[...]


> And nit: "something, too."

will fix

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

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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