[FFmpeg-devel] [PATCH 2/2] lavc/aacsbr: sbr_dequant optimization

[Ganesh Ajjanagadde]

On Tue, Dec 15, 2015 at 9:53 PM, Ganesh Ajjanagadde
<gajjanagadde at gmail.com> wrote:
> This uses ff_exp2fi to get a speedup (~ 6x).
>
> sample benchmark (Haswell, GNU/Linux):
> old:
>   19102 decicycles in sbr_dequant,    1023 runs,      1 skips
>   19002 decicycles in sbr_dequant,    2045 runs,      3 skips
>   17638 decicycles in sbr_dequant,    4093 runs,      3 skips
>   15825 decicycles in sbr_dequant,    8189 runs,      3 skips
>   16404 decicycles in sbr_dequant,   16379 runs,      5 skips
>
> new:
>    3063 decicycles in sbr_dequant,    1024 runs,      0 skips
>    3049 decicycles in sbr_dequant,    2048 runs,      0 skips
>    2968 decicycles in sbr_dequant,    4096 runs,      0 skips
>    2818 decicycles in sbr_dequant,    8191 runs,      1 skips
>    2853 decicycles in sbr_dequant,   16383 runs,      1 skips
>
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavcodec/aacsbr.c | 34 ++++++++++++++++++++++------------
>  1 file changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/libavcodec/aacsbr.c b/libavcodec/aacsbr.c
> index d1e3a91..15956e3 100644
> --- a/libavcodec/aacsbr.c
> +++ b/libavcodec/aacsbr.c
> @@ -33,6 +33,7 @@
>  #include "aacsbrdata.h"
>  #include "aacsbr_tablegen.h"
>  #include "fft.h"
> +#include "internal.h"
>  #include "aacps.h"
>  #include "sbrdsp.h"
>  #include "libavutil/internal.h"
> @@ -73,15 +74,22 @@ static void sbr_dequant(SpectralBandReplication *sbr, int id_aac)
>  {
>      int k, e;
>      int ch;
> -
> +    static const double exp2_tab[2] = {1, M_SQRT2};
>      if (id_aac == TYPE_CPE && sbr->bs_coupling) {
> -        float alpha      = sbr->data[0].bs_amp_res ?  1.0f :  0.5f;
> -        float pan_offset = sbr->data[0].bs_amp_res ? 12.0f : 24.0f;
> +        int pan_offset = sbr->data[0].bs_amp_res ? 12 : 24;
>          for (e = 1; e <= sbr->data[0].bs_num_env; e++) {
>              for (k = 0; k < sbr->n[sbr->data[0].bs_freq_res[e]]; k++) {
> -                float temp1 = exp2f(sbr->data[0].env_facs_q[e][k] * alpha + 7.0f);
> -                float temp2 = exp2f((pan_offset - sbr->data[1].env_facs_q[e][k]) * alpha);
> -                float fac;
> +                float temp1, temp2, fac;
> +                if (sbr->data[0].bs_amp_res) {
> +                    temp1 = ff_exp2fi(sbr->data[0].env_facs_q[e][k] + 7);
> +                    temp2 = ff_exp2fi(pan_offset - sbr->data[1].env_facs_q[e][k]);
> +                }
> +                else {
> +                    temp1 = ff_exp2fi((sbr->data[0].env_facs_q[e][k]>>1) + 7) *
> +                            exp2_tab[sbr->data[0].env_facs_q[e][k] & 1];
> +                    temp2 = ff_exp2fi((pan_offset - sbr->data[1].env_facs_q[e][k])>>1) *
> +                            exp2_tab[(pan_offset - sbr->data[1].env_facs_q[e][k]) & 1];
> +                }
>                  if (temp1 > 1E20) {
>                      av_log(NULL, AV_LOG_ERROR, "envelope scalefactor overflow in dequant\n");
>                      temp1 = 1;
> @@ -93,8 +101,8 @@ static void sbr_dequant(SpectralBandReplication *sbr, int id_aac)
>          }
>          for (e = 1; e <= sbr->data[0].bs_num_noise; e++) {
>              for (k = 0; k < sbr->n_q; k++) {
> -                float temp1 = exp2f(NOISE_FLOOR_OFFSET - sbr->data[0].noise_facs_q[e][k] + 1);
> -                float temp2 = exp2f(12 - sbr->data[1].noise_facs_q[e][k]);
> +                float temp1 = ff_exp2fi(NOISE_FLOOR_OFFSET - sbr->data[0].noise_facs_q[e][k] + 1);
> +                float temp2 = ff_exp2fi(12 - sbr->data[1].noise_facs_q[e][k]);
>                  float fac;
>                  av_assert0(temp1 <= 1E20);
>                  fac = temp1 / (1.0f + temp2);
> @@ -104,11 +112,13 @@ static void sbr_dequant(SpectralBandReplication *sbr, int id_aac)
>          }
>      } else { // SCE or one non-coupled CPE
>          for (ch = 0; ch < (id_aac == TYPE_CPE) + 1; ch++) {
> -            float alpha = sbr->data[ch].bs_amp_res ? 1.0f : 0.5f;
>              for (e = 1; e <= sbr->data[ch].bs_num_env; e++)
>                  for (k = 0; k < sbr->n[sbr->data[ch].bs_freq_res[e]]; k++){
> -                    sbr->data[ch].env_facs[e][k] =
> -                        exp2f(alpha * sbr->data[ch].env_facs_q[e][k] + 6.0f);
> +                    if (sbr->data[ch].bs_amp_res)
> +                        sbr->data[ch].env_facs[e][k] = ff_exp2fi(sbr->data[ch].env_facs_q[e][k] + 6);
> +                    else
> +                        sbr->data[ch].env_facs[e][k] = ff_exp2fi((sbr->data[ch].env_facs_q[e][k]>>1) + 6)
> +                                                       * exp2_tab[sbr->data[ch].env_facs_q[e][k] & 1];
>                      if (sbr->data[ch].env_facs[e][k] > 1E20) {
>                          av_log(NULL, AV_LOG_ERROR, "envelope scalefactor overflow in dequant\n");
>                          sbr->data[ch].env_facs[e][k] = 1;
> @@ -118,7 +128,7 @@ static void sbr_dequant(SpectralBandReplication *sbr, int id_aac)
>              for (e = 1; e <= sbr->data[ch].bs_num_noise; e++)
>                  for (k = 0; k < sbr->n_q; k++)
>                      sbr->data[ch].noise_facs[e][k] =
> -                        exp2f(NOISE_FLOOR_OFFSET - sbr->data[ch].noise_facs_q[e][k]);
> +                        ff_exp2fi(NOISE_FLOOR_OFFSET - sbr->data[ch].noise_facs_q[e][k]);
>          }
>      }
>  }
> --
> 2.6.4
>

ping for aac maintainers: Rostislav? thanks.