On Wed, Nov 11, 2015 at 09:31:18PM +0100, Andreas Cadhalpun wrote:
> On 11.11.2015 14:55, Michael Niedermayer wrote:
> > On Sun, Nov 08, 2015 at 10:02:56PM +0100, Andreas Cadhalpun wrote:
> >> This fixes a SIGFPE crash in the aac_fixed decoder.
> >>
> >> Signed-off-by: Andreas Cadhalpun <andreas.cadhal...@googlemail.com>
> >> ---
> >> libavcodec/aacsbr_fixed.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/libavcodec/aacsbr_fixed.c b/libavcodec/aacsbr_fixed.c
> >> index f942d74..efe40f2 100644
> >> --- a/libavcodec/aacsbr_fixed.c
> >> +++ b/libavcodec/aacsbr_fixed.c
> >> @@ -434,8 +434,8 @@ static void sbr_gain_calc(AACContext *ac,
> >> SpectralBandReplication *sbr,
> >> gain_max = FLOAT_100000;
> >> for (m = sbr->f_tablelim[k] - sbr->kx[1]; m <
> >> sbr->f_tablelim[k + 1] - sbr->kx[1]; m++) {
> >> SoftFloat q_m_max = av_div_sf(
> >> - av_mul_sf(sbr->q_m[e][m],
> >> gain_max),
> >> - sbr->gain[e][m]);
> >> + av_add_sf(FLOAT_EPSILON,
> >> av_mul_sf(sbr->q_m[e][m], gain_max)),
> >> + av_add_sf(FLOAT_EPSILON,
> >> sbr->gain[e][m]));
> >
> > is gain == 0 here ?
>
> Yes: sbr->gain[e][m] == {mant = 0, exp = -126}
>
> > isnt that invalid ?
>
> I'm not sure, but it can happen, when q_mapped is very small, which can be
> caused by noise_facs becoming tiny in sbr_dequant.
> That's kind of the opposite problem of 'envelope scalefactors overflowing'.sbr_dequant() does not look like it can set noise_facs to 0 except by underflow of the exponent range that "has" to be invalid as this depends on the implementation [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB What does censorship reveal? It reveals fear. -- Julian Assange
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