[FFmpeg-soc] [soc]: r5497 - aac-sbr/aacsbr.c

[Alex Converse]

On Sat, Dec 5, 2009 at 10:42 AM, alexc <subversion at mplayerhq.hu> wrote:
> Author: alexc
> Date: Sat Dec  5 16:42:06 2009
> New Revision: 5497
>
> Log:
> Use the derivation of f_tablelow to remove loops from sbr_env_noise_floors.
>
> Modified:
>   aac-sbr/aacsbr.c
>
> Modified: aac-sbr/aacsbr.c
> ==============================================================================
> --- aac-sbr/aacsbr.c    Sat Dec  5 16:42:04 2009        (r5496)
> +++ aac-sbr/aacsbr.c    Sat Dec  5 16:42:06 2009        (r5497)
> @@ -937,6 +937,7 @@ static void sbr_env_noise_floors(Spectra
>  {
>     int delta = (ch == 1 && sbr->bs_coupling == 1) ? 2 : 1;
>     int i, k, l;
> +    const int temp = sbr->n[1] & 1;
>     for (l = 0; l < ch_data->bs_num_env[1]; l++) {
>         if (ch_data->bs_df_env[l]) {
>             // bs_freq_res[0] == bs_freq_res[bs_num_env[1]] from prev frame
> @@ -944,22 +945,13 @@ static void sbr_env_noise_floors(Spectra
>                 for (k = 0; k < sbr->n[ch_data->bs_freq_res[l + 1]]; k++)
>                     sbr->env_facs[ch][l + 1][k] = sbr->env_facs[ch][l][k] + delta * ch_data->bs_data_env[l][k];
>             } else if (ch_data->bs_freq_res[l + 1]) {
> -                i = 0; // optimisation : f_* are ascending freq bands so start at last i for each search
>                 for (k = 0; k < sbr->n[ch_data->bs_freq_res[l + 1]]; k++) {
> -                    // find i such that f_tablelow[i] <= f_tablehigh[k] < f_tablelow[i + 1]
> -                    for (; i < sbr->n[0]; i++)
> -                        if (sbr->f_tablelow[i]     <= sbr->f_tablehigh[k] &&
> -                            sbr->f_tablelow[i + 1] >  sbr->f_tablehigh[k])
> -                            break;
> +                    i = (k + temp) >> 1; // find i such that f_tablelow[i] <= f_tablehigh[k] < f_tablelow[i + 1]
>                     sbr->env_facs[ch][l + 1][k] = sbr->env_facs[ch][l][i] + delta * ch_data->bs_data_env[l][k];
>                 }
>             } else {
> -                i = 0; // optimisation : f_* are ascending freq bands so start at last i for each search
>                 for (k = 0; k < sbr->n[ch_data->bs_freq_res[l + 1]]; k++) {
> -                    // find i such that f_tablehigh[i] == f_tablelow[k]
> -                    for (; i < sbr->n[1]; i++)
> -                        if (sbr->f_tablehigh[i] == sbr->f_tablelow[k])
> -                            break;
> +                    i = k ? 2*k - temp : 0; // find i such that f_tablehigh[i] == f_tablelow[k]
>                     sbr->env_facs[ch][l + 1][k] = sbr->env_facs[ch][l][i] + delta * ch_data->bs_data_env[l][k];
>                 }
>             }

Sometimes I think they write this so backwards in the spec just to see
if anyone is paying attention :)