[FFmpeg-devel] [PATCH 2/3] bink: get rid of double precission float use

[Michael Niedermayer]

On Tue, Feb 07, 2012 at 08:06:19PM +0100, Vitor Sessak wrote:
> On Mon, Feb 6, 2012 at 7:31 PM, Michael Niedermayer <michaelni at gmx.at>
> wrote:
> > Add a small table of integers and out commented code to generate it with
> > the double precision code.
> 
> Not against the idea, but note that this should not be needed for
> bit-exactness: I checked that all the double values are far enough from
> integers for this code to be bitexact across archs.

do you think its better to leave the double prec code ?
    

> 
> > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> > ---
> >  libavcodec/bink.c |   36 ++++++++++++++++++++++++------------
> >  1 files changed, 24 insertions(+), 12 deletions(-)
> >
> > diff --git a/libavcodec/bink.c b/libavcodec/bink.c
> > index ff8bc8a..c77c139 100644
> > --- a/libavcodec/bink.c
> > +++ b/libavcodec/bink.c
> > @@ -1222,40 +1222,52 @@ static int decode_frame(AVCodecContext *avctx,
> void *data, int *data_size, AVPac
> >  static av_cold void binkb_calc_quant(void)
> >  {
> >     uint8_t inv_bink_scan[64];
> > -    double s[64];
> > +    static const int s[64]={
> > +        1073741824,1489322693,1402911301,1262586814,1073741824,
> 843633538, 581104888, 296244703,
> > +
>  1489322693,2065749918,1945893874,1751258219,1489322693,1170153332,
> 806015634, 410903207,
> > +
>  1402911301,1945893874,1832991949,1649649171,1402911301,1102260336,
> 759250125, 387062357,
> > +        1262586814,1751258219,1649649171,1484645031,1262586814,
> 992008094, 683307060, 348346918,
> > +        1073741824,1489322693,1402911301,1262586814,1073741824,
> 843633538, 581104888, 296244703,
> > +         843633538,1170153332,1102260336, 992008094, 843633538,
> 662838617, 456571181, 232757969,
> > +         581104888, 806015634, 759250125, 683307060, 581104888,
> 456571181, 314491699, 160326478,
> > +         296244703, 410903207, 387062357, 348346918, 296244703,
> 232757969, 160326478,  81733730,
> > +    };
> >     int i, j;
> > -
> > +#define C (1LL<<30)
> > +#if 0
> >     for (j = 0; j < 8; j++) {
> >         for (i = 0; i < 8; i++) {
> >             if (j && j != 4)
> >                if (i && i != 4)
> 
> > -                   s[j*8 + i] = cos(j * M_PI/16.0) * cos(i * M_PI/16.0)
> * 2.0;
> > +                   s[j*8 + i] = llrint(cos(j * M_PI/16.0) * cos(i *
> M_PI/16.0) * 2.0 * C);
> 
> Are you sure about this change? This will make the table different from the
> reference decoder (and I bet also from the reference encoder), and thus
> should change the output in a negative way.

where does a table that is used outside the init function become
different ?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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