[FFmpeg-devel] [PATCH] AAC decoder

[Michael Niedermayer]

On Mon, Jun 02, 2008 at 12:33:57PM +0100, Robert Swain wrote:
> 2008/4/2 Michael Niedermayer <michaelni at gmx.at>:
> > On Tue, Apr 01, 2008 at 04:56:48PM +0200, Andreas ?man wrote:
> >> +
> >> +/**
> >> + * Decode spectral data
> >> + * reference: Table 4.50
> >> + */
> >> +static int spectral_data(AACContext * ac, GetBitContext * gb, const ics_struct * ics, const int cb[][64], int * icoef) {
> >
> >> +    static const int unsigned_cb[] = { 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1 };
> >
> > unsigned_cb[x] == x&10
> >
> >
> >> +    int i, k, g;
> >> +    const uint16_t * offsets = ics->swb_offset;
> >> +
> >> +    for (g = 0; g < ics->num_window_groups; g++) {
> >> +        for (i = 0; i < ics->max_sfb; i++) {
> >> +            const int cur_cb = cb[g][i];
> >> +            const int dim = cur_cb >= FIRST_PAIR_HCB ? 2 : 4;
> >> +            int group;
> >> +            if (cur_cb == INTENSITY_HCB2 || cur_cb == INTENSITY_HCB) {
> >> +                continue;
> >> +            }
> >> +            if (cur_cb == NOISE_HCB) {
> >> +                for (group = 0; group < ics->group_len[g]; group++) {
> >> +                    for (k = offsets[i]; k < offsets[i+1]; k++)
> >> +                        icoef[group*128+k] = av_random(&ac->random_state) & 0x0000FFFF;
> >> +                }
> >> +                continue;
> >> +            }
> >> +            if (cur_cb == ZERO_HCB) {
> >> +                for (group = 0; group < ics->group_len[g]; group++) {
> >> +                    memset(icoef + group * 128 + offsets[i], 0, (offsets[i+1] - offsets[i])*sizeof(int));
> >> +                }
> >> +                continue;
> >> +            }
> > [...]
> >
> >> +                                while (get_bits1(gb)) n++;
> >> +                                ptr[j] = (1<<n) + get_bits(gb, n);
> >> +                            }
> >> +                        }
> >> +                    }
> >> +                    for (j = 0; j < dim; j++)
> >> +                        icoef[group*128+k+j] = sign[j] * ptr[j];
> >
> > This is really ugly, so much unneeded code, reading signs in a temporary array
> > copying values and then multplying and throwig the intermediate arrays away.
> 
> How about the attached patch? Any further suggestions?
> 
> Rob

> Index: aac.c
> ===================================================================
> --- aac.c	(revision 2326)
> +++ aac.c	(working copy)
> @@ -1214,23 +1214,20 @@
>              }else if (cur_cb != INTENSITY_HCB2 && cur_cb != INTENSITY_HCB) {
>                  for (group = 0; group < ics->group_len[g]; group++) {
>                      for (k = offsets[i]; k < offsets[i+1]; k += dim) {
> -                        int index = get_vlc2(gb, ac->books[cur_cb - 1].table, 6, 3);
> +                        const int index = get_vlc2(gb, ac->books[cur_cb - 1].table, 6, 3);
> +                        const int idx1 = index * dim, idx2 = (group << 7) + k;
>                          int j;
> -                        int sign[4] = {1,1,1,1};
> -                        int ptr[4];
>                          if (index == -1) {
>                              av_log(ac->avccontext, AV_LOG_ERROR, "Error in spectral data\n");
>                              return -1;
>                          }

> -                        memcpy(ptr, &ac->vq[cur_cb - 1][index * dim], dim*sizeof(int));

whatever *ptr= &ac->vq[cur_cb - 1][index * dim]
might be cleaner thabn n the repeated use of ac->vq[cur_cb - 1][index * dim]

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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