[FFmpeg-devel] [PATCH 1/3] aacsbr_fixed: avoid division by zero in sbr_gain_calc

[Andreas Cadhalpun]

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.Cadhalpun at 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'.

Best regards,
Andreas