On Thu, Nov 24, 2016 at 01:15:54AM +0100, Andreas Cadhalpun wrote:
> On 23.11.2016 03:22, Michael Niedermayer wrote:
> > On Sun, Nov 13, 2016 at 09:29:11PM +0100, Andreas Cadhalpun wrote:
> >> It causes division by zero crashes.
> >>
> >> Signed-off-by: Andreas Cadhalpun <andreas.cadhal...@googlemail.com>
> >> ---
> >> libavcodec/aacsbr_fixed.c | 4 ++++
> >> 1 file changed, 4 insertions(+)
> >>
> >> diff --git a/libavcodec/aacsbr_fixed.c b/libavcodec/aacsbr_fixed.c
> >> index b26314a..d2a7027 100644
> >> --- a/libavcodec/aacsbr_fixed.c
> >> +++ b/libavcodec/aacsbr_fixed.c
> >> @@ -429,6 +429,10 @@ static void sbr_gain_calc(AACContext *ac,
> >> SpectralBandReplication *sbr,
> >> av_add_sf(FLOAT_1,
> >> sbr->e_curr[e][m]),
> >> av_add_sf(FLOAT_1,
> >> sbr->q_mapped[e][m]))));
> >> }
> >> + if (sbr->gain[e][m].mant == 0) {
> >> + sbr->gain[e][m] = FLOAT_1;
> >> + sbr->gain[e][m].exp = MIN_EXP;
> >> + }
> >
> > Why is this not not needed for the float code ?
>
> Because float can represent smaller absolute values than normalized SoftFloat.
>
> > is there a shortcomming in the SoftFloat code ?
>
> In a way, because the SoftFloat gets normalized, e.g.:
> * float: 2.16840434e-19 * 2.77555756e-17 / 10337.5293 = 5.82201677e-40
> * SoftFloat: av_div_sf(av_mul_sf({mant = 536870912, exp = -61}, {mant =
> 536870912, exp = -54}),
> {mant = 677439305, exp = 14}) = {mant = 850858499,
> exp = -130} = FLOAT_0hmm does increasing the limits for SoftFloats exponent solve this ? If that works and doesnt break anything it would be good to have SoftFloat cover the range float has [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB No human being will ever know the Truth, for even if they happen to say it by chance, they would not even known they had done so. -- Xenophanes
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