[FFmpeg-devel] [PATCH 1/2] libavfilter/signature_lookup: fix possible division by zero

[Gerion Entrup]

Am Dienstag, 7. Mai 2024, 19:46:28 MESZ schrieb Michael Niedermayer:
> On Mon, May 06, 2024 at 12:30:39AM +0200, Gerion Entrup wrote:
> > ---
> >  libavfilter/signature_lookup.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavfilter/signature_lookup.c b/libavfilter/signature_lookup.c
> > index a0ca818a9b..b39a3e225b 100644
> > --- a/libavfilter/signature_lookup.c
> > +++ b/libavfilter/signature_lookup.c
> > @@ -128,7 +128,7 @@ static int get_jaccarddist(SignatureContext *sc, CoarseSignature *first, CoarseS
> >      int jaccarddist, i, composdist = 0, cwthcount = 0;
> >      for (i = 0; i < 5; i++) {
> >          if ((jaccarddist = intersection_word(first->data[i], second->data[i])) > 0) {
> > -            jaccarddist /= union_word(first->data[i], second->data[i]);
> > +            jaccarddist /= FFMAX(union_word(first->data[i], second->data[i]), 1);
> >          }
> 
> for which input data does this cause a division by 0 ?

Sorry for the late answer. I missed your mail somehow.
union_word counts the amount of one bits that are created when you are "or"ing
the course signatures. So, when the underlying videos are so different that all
bits of the created signatures are different, the "or"-operator will always
return 0 and so also its sum (I have not tested this).

Gerion

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