[FFmpeg-devel] [PATCHv2] avcodec/dcaenc: avoid wasteful cos calls

[Paul B Mahol]

On 12/10/15, Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
> cos has symmetry; use this.
>
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavcodec/dcaenc.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/dcaenc.c b/libavcodec/dcaenc.c
> index 5a6bdac..6fcfb1a 100644
> --- a/libavcodec/dcaenc.c
> +++ b/libavcodec/dcaenc.c
> @@ -169,8 +169,16 @@ static int encode_init(AVCodecContext *avctx)
>      if (!cos_table[0]) {
>          int j, k;
>
> -        for (i = 0; i < 2048; i++) {
> +        cos_table[0] = 0x7fffffff;
> +        cos_table[512] = 0;
> +        cos_table[1024] = -cos_table[0];
> +        for (i = 1; i < 512; i++) {
>              cos_table[i]   = (int32_t)(0x7fffffff * cos(M_PI * i / 1024));
> +            cos_table[1024-i] = -cos_table[i];
> +            cos_table[1024+i] = -cos_table[i];
> +            cos_table[2048-i] = cos_table[i];
> +        }
> +        for (i = 0; i < 2048; i++) {
>              cb_to_level[i] = (int32_t)(0x7fffffff * pow(10, -0.005 * i));
>          }
>
> --
> 2.6.3

Ok, if produced table is same.

>
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