[FFmpeg-devel] [avformat] Prevent undefined shift with wrap_bits > 63.

[Michael Niedermayer]

On Mon, Nov 20, 2017 at 01:15:24PM -0800, Dale Curtis wrote:
> On Mon, Nov 20, 2017 at 12:40 PM, Michael Niedermayer <
> michael at niedermayer.cc> wrote:
> 
> > On Mon, Nov 20, 2017 at 12:05:05PM -0800, Dale Curtis wrote:
> > > On Sat, Nov 18, 2017 at 2:44 AM, Michael Niedermayer
> > <michael at niedermayer.cc
> > > > wrote:
> > > >
> > > > this would skip the code for wrap_bits >= 63, this does not look
> > > > correct
> > > >
> > >
> > > Why do you think that's incorrect? The max int64_t value is 1 << 63 and 2
> > > << 63 == 1 << 64 ?
> >
> > I think its incorrect because the change would completely skip the loop
> > but a wrap of "1<<64" would still need pts to be filled in.
> >
> 
> There's no way this code can work with a wrap_bits > 63.  2<<64 > uint64_t.

i dont dispute that, what i meant was more high level

that is, "what that code should be doing", i think is different from
skiping the code


> The best we can do over my change is to make wrap_bits == 63 work by
> changing the line from 2LL << (wrap_bits - 1) to 2ULL << (wrap_bits -
> 1). av_compare_mod takes a uint64_t in this position so that should be
> okay. How does that sound?

I think that could end with the correct result

thanks

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

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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