[FFmpeg-devel] [PATCH] dvbsubdec: fix division by zero in compute_default_clut

[Michael Niedermayer]

On Wed, Nov 09, 2016 at 08:52:54PM +0100, Andreas Cadhalpun wrote:
> On 09.11.2016 02:27, Michael Niedermayer wrote:
> > On Tue, Nov 08, 2016 at 10:36:01PM +0100, Andreas Cadhalpun wrote:
> >> Since the loop goes down to i = 0 the number of iterations (variable
> >> count) is the original i, not i - 1.
> >> In the case of i originally being 1, this miscalculation resulted in
> >> a division by zero.
> >>
> >> This problem was introduced in commit
> >> 4b90dcb8493552c17a811c8b1e6538dae4061f9d.
> >>
> >> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> >> ---
> >>  libavcodec/dvbsubdec.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
> >> index e9f4765..31898ea 100644
> >> --- a/libavcodec/dvbsubdec.c
> >> +++ b/libavcodec/dvbsubdec.c
> >> @@ -810,7 +810,7 @@ static void compute_default_clut(AVSubtitleRect *rect, int w, int h)
> >>          list_inv[     i ] = bestv;
> >>      }
> >>  
> >> -    count = i - 1;
> >> +    count = i;
> >>      for (i--; i>=0; i--) {
> >>          int v = i*255/count;
> >>          AV_WN32(rect->data[1] + 4*list_inv[i], RGBA(v/2,v,v/2,v));
> > 
> > with this a 2 color text would be 50% and 100% transparent
> > it should be transparent background and opaque text,
> > count = FFMAX(i - 1, 1);
> > seems better to me
> 
> OK, patch doing that is attached.
> 
> Best regards,
> Andreas
> 

>  dvbsubdec.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 10b117a15971daf75d61efe486b961d3cc59d480  0001-dvbsubdec-fix-division-by-zero-in-compute_default_cl.patch
> From 436318575abf482e1ea144f651c47bc2730e41a2 Mon Sep 17 00:00:00 2001
> From: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> Date: Tue, 8 Nov 2016 22:32:42 +0100
> Subject: [PATCH] dvbsubdec: fix division by zero in compute_default_clut
> 
> This problem was introduced in commit
> 4b90dcb8493552c17a811c8b1e6538dae4061f9d.
> 
> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> ---
>  libavcodec/dvbsubdec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

LGTM

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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