[FFmpeg-devel] [PATCH 6/9] sbrdsp: unroll sbr_autocorrelate_c

[Paul B Mahol]

On 4/4/13, Christophe Gisquet <christophe.gisquet at gmail.com> wrote:
> 1410 cycles to 1148 on Arrandale/Win64.
> ---
>  libavcodec/sbrdsp.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/libavcodec/sbrdsp.c b/libavcodec/sbrdsp.c
> index 6fede79..e2280cc 100644
> --- a/libavcodec/sbrdsp.c
> +++ b/libavcodec/sbrdsp.c
> @@ -122,9 +122,34 @@ static av_always_inline void autocorrelate(const float
> x[40][2],
>
>  static void sbr_autocorrelate_c(const float x[40][2], float phi[3][2][2])
>  {
> +#if 0
> +    // This code is slower because it multiplies memory accesses.
> +    // It is left as eucational purpose and because it may offer

nit++++++: typo: eucational

> +    // a better reference for writing arch-specific dsp functions.
>      autocorrelate(x, phi, 0);
>      autocorrelate(x, phi, 1);
>      autocorrelate(x, phi, 2);
> +#else
> +    float real_sum2 = x[ 0][0] * x[ 2][0] + x[ 0][1] * x[ 2][1];
> +    float imag_sum2 = x[ 0][0] * x[ 2][1] - x[ 0][1] * x[ 2][0];
> +    float real_sum1 = 0.f, imag_sum1 = 0.f, real_sum0 = 0.0f;
> +    int   i;
> +    for (i = 1; i < 38; i++) {
> +        real_sum0 += x[i][0] * x[i  ][0] + x[i][1] * x[i  ][1];
> +        real_sum1 += x[i][0] * x[i+1][0] + x[i][1] * x[i+1][1];
> +        imag_sum1 += x[i][0] * x[i+1][1] - x[i][1] * x[i+1][0];
> +        real_sum2 += x[i][0] * x[i+2][0] + x[i][1] * x[i+2][1];
> +        imag_sum2 += x[i][0] * x[i+2][1] - x[i][1] * x[i+2][0];
> +    }
> +    phi[2-2][1][0] = real_sum2;
> +    phi[2-2][1][1] = imag_sum2;
> +    phi[2  ][1][0] = real_sum0 + x[ 0][0] * x[ 0][0] + x[ 0][1] * x[
> 0][1];
> +    phi[1  ][0][0] = real_sum0 + x[38][0] * x[38][0] + x[38][1] *
> x[38][1];
> +    phi[2-1][1][0] = real_sum1 + x[ 0][0] * x[ 1][0] + x[ 0][1] * x[
> 1][1];
> +    phi[2-1][1][1] = imag_sum1 + x[ 0][0] * x[ 1][1] - x[ 0][1] * x[
> 1][0];
> +    phi[0  ][0][0] = real_sum1 + x[38][0] * x[39][0] + x[38][1] *
> x[39][1];
> +    phi[0  ][0][1] = imag_sum1 + x[38][0] * x[39][1] - x[38][1] *
> x[39][0];
> +#endif
>  }
>
>  static void sbr_hf_gen_c(float (*X_high)[2], const float (*X_low)[2],
> --
> 1.8.0.msysgit.0

It should be OK if it always produce same output.