[FFmpeg-devel] [PATCH 4/4] avcodec/apedec: use ff_clz() instead of while loop

[Anton Khirnov]

Quoting Paul B Mahol (2020-10-06 10:19:13)
> On Tue, Oct 06, 2020 at 10:08:58AM +0200, Anton Khirnov wrote:
> > Quoting Paul B Mahol (2020-10-06 02:17:14)
> > > Signed-off-by: Paul B Mahol <onemda at gmail.com>
> > > ---
> > >  libavcodec/apedec.c | 10 +++-------
> > >  1 file changed, 3 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
> > > index 8fe7b5ee86..ea36247eb9 100644
> > > --- a/libavcodec/apedec.c
> > > +++ b/libavcodec/apedec.c
> > > @@ -575,14 +575,10 @@ static inline int ape_decode_value_3990(APEContext *ctx, APERice *rice)
> > >          base = range_decode_culfreq(ctx, pivot);
> > >          range_decode_update(ctx, 1, base);
> > >      } else {
> > > -        int base_hi = pivot, base_lo;
> > > -        int bbits = 0;
> > > +        int base_hi, base_lo;
> > > +        int bbits = 16 - ff_clz(pivot);
> > 
> > This assumes unsigned is always 32bit, no?
> 
> ksum is 32 bit, from which pivot is derived.
> 
> Should I use explicitly uint32_t type instead?
> Where is unsigned not 32bit?

I don't think uint32_t would help, as ff_clz() can expand to a compiler
builtin.

What I'm concerned about is the unstated assumption about
sizeof(int/unsigned) == 4 spreading through the codebase. It's already
present in plenty of places, so I certainly don't intend to block your
patch over this. But we should consider explitly documenting this, and
maybe testing in configure.

-- 
Anton Khirnov