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

[Vitor Sessak]

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.

> 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.

-Vitor