aac.c

                            cf = VMUL4(cf, vq, cb_idx, sf + idx);
                        } while (len -= 4);
                    }
                    break;

                case 1:
                    for (group = 0; group < g_len; group++, cfo+=128) {
                        float *cf = cfo;
                        int len = off_len;

                        do {
                            const int index = get_vlc2(gb, vlc_tab, 8, 2);
                            unsigned nnz;
                            unsigned cb_idx;
                            uint32_t bits;

                            if (index >= cb_size) {
                                err_idx = index;
                                goto err_cb_overflow;
                            }

                            cb_idx = cb_vector_idx[index];
                            nnz = cb_idx >> 8 & 15;
                            bits = get_bits(gb, nnz) << (32-nnz);
                            cf = VMUL4S(cf, vq, cb_idx, bits, sf + idx);
                        } while (len -= 4);
                    }
                    break;

                case 2:
                    for (group = 0; group < g_len; group++, cfo+=128) {
                        float *cf = cfo;
                        int len = off_len;

                        do {
                            const int index = get_vlc2(gb, vlc_tab, 8, 2);
                            unsigned cb_idx;

                            if (index >= cb_size) {
                                err_idx = index;
                                goto err_cb_overflow;
                            }

                            cb_idx = cb_vector_idx[index];
                            cf = VMUL2(cf, vq, cb_idx, sf + idx);
                        } while (len -= 2);
                    }
                    break;

                case 3:
                case 4:
                    for (group = 0; group < g_len; group++, cfo+=128) {
                        float *cf = cfo;
                        int len = off_len;

                        do {
                            const int index = get_vlc2(gb, vlc_tab, 8, 2);
                            unsigned nnz;
                            unsigned cb_idx;
                            unsigned sign;

                            if (index >= cb_size) {
                                err_idx = index;
                                goto err_cb_overflow;
                            }

                            cb_idx = cb_vector_idx[index];
                            nnz = cb_idx >> 8 & 15;
                            sign = get_bits(gb, nnz) << (cb_idx >> 12);
                            cf = VMUL2S(cf, vq, cb_idx, sign, sf + idx);
                        } while (len -= 2);
                    }
                    break;

                default:
                    for (group = 0; group < g_len; group++, cfo+=128) {
                        float *cf = cfo;
                        uint32_t *icf = (uint32_t *) cf;
                        int len = off_len;

                        do {
                            const int index = get_vlc2(gb, vlc_tab, 8, 2);
                            unsigned nzt, nnz;
                            unsigned cb_idx;
                            uint32_t bits;
                            int j;

                            if (!index) {
                                *icf++ = 0;
                                *icf++ = 0;
                                continue;
                            }

                            if (index >= cb_size) {
                                err_idx = index;
                                goto err_cb_overflow;
                            }

                            cb_idx = cb_vector_idx[index];
                            nnz = cb_idx >> 12;
                            nzt = cb_idx >> 8;
                            bits = get_bits(gb, nnz) << (32-nnz);

                            for (j = 0; j < 2; j++) {
                                if (nzt & 1<<j) {
                                    int n = 4;
                                    /* The total length of escape_sequence must be < 22 bits according
                                       to the specification (i.e. max is 111111110xxxxxxxxxxxx). */
                                    while (get_bits1(gb) && n < 13) n++;
                                    if (n == 13) {
                                        av_log(ac->avccontext, AV_LOG_ERROR, "error in spectral data, ESC overflow\n");
                                        return -1;
                                    }
                                    n = (1 << n) + get_bits(gb, n);
                                    *icf++ = cbrt_tab[n] | (bits & 1<<31);
                                    bits <<= 1;
                                } else {
                                    unsigned v = ((const uint32_t*)vq)[cb_idx & 15];
                                    *icf++ = (bits & 1<<31) | v;
                                    bits <<= !!v;
                                }
                                cb_idx >>= 4;
                            }
                        } while (len -= 2);

                        ac->dsp.vector_fmul_scalar(cfo, cfo, sf[idx], off_len);
                    }
                }
            }
        }
        coef += g_len << 7;
    }

    if (pulse_present) {
        idx = 0;
        for (i = 0; i < pulse->num_pulse; i++) {
            float co = coef_base[ pulse->pos[i] ];
            while (offsets[idx + 1] <= pulse->pos[i])
                idx++;
            if (band_type[idx] != NOISE_BT && sf[idx]) {
                float ico = -pulse->amp[i];
                if (co) {
                    co /= sf[idx];
                    ico = co / sqrtf(sqrtf(fabsf(co))) + (co > 0 ? -ico : ico);
                }
                coef_base[ pulse->pos[i] ] = cbrtf(fabsf(ico)) * ico * sf[idx];
            }
        }
    }
    return 0;

err_cb_overflow:
    av_log(ac->avccontext, AV_LOG_ERROR,
           "Read beyond end of ff_aac_codebook_vectors[%d][]. index %d >= %d\n",
           band_type[idx], err_idx, ff_aac_spectral_sizes[band_type[idx]]);
    return -1;
}

static av_always_inline float flt16_round(float pf)
{
    union float754 tmp;
    tmp.f = pf;
    tmp.i = (tmp.i + 0x00008000U) & 0xFFFF0000U;
    return tmp.f;
}

static av_always_inline float flt16_even(float pf)
{
    union float754 tmp;
    tmp.f = pf;
    tmp.i = (tmp.i + 0x00007FFFU + (tmp.i & 0x00010000U >> 16)) & 0xFFFF0000U;
    return tmp.f;
}

static av_always_inline float flt16_trunc(float pf)
{
    union float754 pun;
    pun.f = pf;
    pun.i &= 0xFFFF0000U;
    return pun.f;
}

static void predict(AACContext *ac, PredictorState *ps, float *coef,
                    int output_enable)
{
    const float a     = 0.953125; // 61.0 / 64
    const float alpha = 0.90625;  // 29.0 / 32
    float e0, e1;
    float pv;
    float k1, k2;

    k1 = ps->var0 > 1 ? ps->cor0 * flt16_even(a / ps->var0) : 0;
    k2 = ps->var1 > 1 ? ps->cor1 * flt16_even(a / ps->var1) : 0;

    pv = flt16_round(k1 * ps->r0 + k2 * ps->r1);
    if (output_enable)
        *coef += pv * ac->sf_scale;

    e0 = *coef / ac->sf_scale;
    e1 = e0 - k1 * ps->r0;

    ps->cor1 = flt16_trunc(alpha * ps->cor1 + ps->r1 * e1);
    ps->var1 = flt16_trunc(alpha * ps->var1 + 0.5 * (ps->r1 * ps->r1 + e1 * e1));
    ps->cor0 = flt16_trunc(alpha * ps->cor0 + ps->r0 * e0);
    ps->var0 = flt16_trunc(alpha * ps->var0 + 0.5 * (ps->r0 * ps->r0 + e0 * e0));

    ps->r1 = flt16_trunc(a * (ps->r0 - k1 * e0));
    ps->r0 = flt16_trunc(a * e0);
}

/**
 * Apply AAC-Main style frequency domain prediction.
 */
static void apply_prediction(AACContext *ac, SingleChannelElement *sce)
{
    int sfb, k;

    if (!sce->ics.predictor_initialized) {
        reset_all_predictors(sce->predictor_state);
        sce->ics.predictor_initialized = 1;
    }

    if (sce->ics.window_sequence[0] != EIGHT_SHORT_SEQUENCE) {
        for (sfb = 0; sfb < ff_aac_pred_sfb_max[ac->m4ac.sampling_index]; sfb++) {
            for (k = sce->ics.swb_offset[sfb]; k < sce->ics.swb_offset[sfb + 1]; k++) {
                predict(ac, &sce->predictor_state[k], &sce->coeffs[k],
                        sce->ics.predictor_present && sce->ics.prediction_used[sfb]);
            }
        }
        if (sce->ics.predictor_reset_group)
            reset_predictor_group(sce->predictor_state, sce->ics.predictor_reset_group);
    } else
        reset_all_predictors(sce->predictor_state);
}

/**
 * Decode an individual_channel_stream payload; reference: table 4.44.
 *
 * @param   common_window   Channels have independent [0], or shared [1], Individual Channel Stream information.
 * @param   scale_flag      scalable [1] or non-scalable [0] AAC (Unused until scalable AAC is implemented.)
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_ics(AACContext *ac, SingleChannelElement *sce,
                      GetBitContext *gb, int common_window, int scale_flag)
{
    Pulse pulse;
    TemporalNoiseShaping    *tns = &sce->tns;
    IndividualChannelStream *ics = &sce->ics;
    float *out = sce->coeffs;
    int global_gain, pulse_present = 0;

    /* This assignment is to silence a GCC warning about the variable being used
     * uninitialized when in fact it always is.
     */
    pulse.num_pulse = 0;

    global_gain = get_bits(gb, 8);

    if (!common_window && !scale_flag) {
        if (decode_ics_info(ac, ics, gb, 0) < 0)
            return -1;
    }

    if (decode_band_types(ac, sce->band_type, sce->band_type_run_end, gb, ics) < 0)
        return -1;
    if (decode_scalefactors(ac, sce->sf, gb, global_gain, ics, sce->band_type, sce->band_type_run_end) < 0)
        return -1;

    pulse_present = 0;
    if (!scale_flag) {
        if ((pulse_present = get_bits1(gb))) {
            if (ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE) {
                av_log(ac->avccontext, AV_LOG_ERROR, "Pulse tool not allowed in eight short sequence.\n");
                return -1;
            }
            if (decode_pulses(&pulse, gb, ics->swb_offset, ics->num_swb)) {
                av_log(ac->avccontext, AV_LOG_ERROR, "Pulse data corrupt or invalid.\n");
                return -1;
            }
        }
        if ((tns->present = get_bits1(gb)) && decode_tns(ac, tns, gb, ics))
            return -1;
        if (get_bits1(gb)) {
            av_log_missing_feature(ac->avccontext, "SSR", 1);
            return -1;
        }
    }

    if (decode_spectrum_and_dequant(ac, out, gb, sce->sf, pulse_present, &pulse, ics, sce->band_type) < 0)
        return -1;

    if (ac->m4ac.object_type == AOT_AAC_MAIN && !common_window)
        apply_prediction(ac, sce);

    return 0;
}

/**
 * Mid/Side stereo decoding; reference: 4.6.8.1.3.
 */
static void apply_mid_side_stereo(AACContext *ac, ChannelElement *cpe)
{
    const IndividualChannelStream *ics = &cpe->ch[0].ics;
    float *ch0 = cpe->ch[0].coeffs;
    float *ch1 = cpe->ch[1].coeffs;
    int g, i, group, idx = 0;
    const uint16_t *offsets = ics->swb_offset;
    for (g = 0; g < ics->num_window_groups; g++) {
        for (i = 0; i < ics->max_sfb; i++, idx++) {
            if (cpe->ms_mask[idx] &&
                    cpe->ch[0].band_type[idx] < NOISE_BT && cpe->ch[1].band_type[idx] < NOISE_BT) {
                for (group = 0; group < ics->group_len[g]; group++) {
                    ac->dsp.butterflies_float(ch0 + group * 128 + offsets[i],
                                              ch1 + group * 128 + offsets[i],
                                              offsets[i+1] - offsets[i]);
                }
            }
        }
        ch0 += ics->group_len[g] * 128;
        ch1 += ics->group_len[g] * 128;
    }
}

/**
 * intensity stereo decoding; reference: 4.6.8.2.3
 *
 * @param   ms_present  Indicates mid/side stereo presence. [0] mask is all 0s;
 *                      [1] mask is decoded from bitstream; [2] mask is all 1s;
 *                      [3] reserved for scalable AAC
 */
static void apply_intensity_stereo(ChannelElement *cpe, int ms_present)
{
    const IndividualChannelStream *ics = &cpe->ch[1].ics;
    SingleChannelElement         *sce1 = &cpe->ch[1];
    float *coef0 = cpe->ch[0].coeffs, *coef1 = cpe->ch[1].coeffs;
    const uint16_t *offsets = ics->swb_offset;
    int g, group, i, k, idx = 0;
    int c;
    float scale;
    for (g = 0; g < ics->num_window_groups; g++) {
        for (i = 0; i < ics->max_sfb;) {
            if (sce1->band_type[idx] == INTENSITY_BT || sce1->band_type[idx] == INTENSITY_BT2) {
                const int bt_run_end = sce1->band_type_run_end[idx];
                for (; i < bt_run_end; i++, idx++) {
                    c = -1 + 2 * (sce1->band_type[idx] - 14);
                    if (ms_present)
                        c *= 1 - 2 * cpe->ms_mask[idx];
                    scale = c * sce1->sf[idx];
                    for (group = 0; group < ics->group_len[g]; group++)
                        for (k = offsets[i]; k < offsets[i + 1]; k++)
                            coef1[group * 128 + k] = scale * coef0[group * 128 + k];
                }
            } else {
                int bt_run_end = sce1->band_type_run_end[idx];
                idx += bt_run_end - i;
                i    = bt_run_end;
            }
        }
        coef0 += ics->group_len[g] * 128;
        coef1 += ics->group_len[g] * 128;
    }
}

/**
 * Decode a channel_pair_element; reference: table 4.4.
 *
 * @param   elem_id Identifies the instance of a syntax element.
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_cpe(AACContext *ac, GetBitContext *gb, ChannelElement *cpe)
{
    int i, ret, common_window, ms_present = 0;

    common_window = get_bits1(gb);
    if (common_window) {
        if (decode_ics_info(ac, &cpe->ch[0].ics, gb, 1))
            return -1;
        i = cpe->ch[1].ics.use_kb_window[0];
        cpe->ch[1].ics = cpe->ch[0].ics;
        cpe->ch[1].ics.use_kb_window[1] = i;
        ms_present = get_bits(gb, 2);
        if (ms_present == 3) {
            av_log(ac->avccontext, AV_LOG_ERROR, "ms_present = 3 is reserved.\n");
            return -1;
        } else if (ms_present)
            decode_mid_side_stereo(cpe, gb, ms_present);
    }
    if ((ret = decode_ics(ac, &cpe->ch[0], gb, common_window, 0)))
        return ret;
    if ((ret = decode_ics(ac, &cpe->ch[1], gb, common_window, 0)))
        return ret;

    if (common_window) {
        if (ms_present)
            apply_mid_side_stereo(ac, cpe);
        if (ac->m4ac.object_type == AOT_AAC_MAIN) {
            apply_prediction(ac, &cpe->ch[0]);
            apply_prediction(ac, &cpe->ch[1]);
        }
    }

    apply_intensity_stereo(cpe, ms_present);
    return 0;
}

/**
 * Decode coupling_channel_element; reference: table 4.8.
 *
 * @param   elem_id Identifies the instance of a syntax element.
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_cce(AACContext *ac, GetBitContext *gb, ChannelElement *che)
{
    int num_gain = 0;
    int c, g, sfb, ret;
    int sign;
    float scale;
    SingleChannelElement *sce = &che->ch[0];
    ChannelCoupling     *coup = &che->coup;

    coup->coupling_point = 2 * get_bits1(gb);
    coup->num_coupled = get_bits(gb, 3);
    for (c = 0; c <= coup->num_coupled; c++) {
        num_gain++;
        coup->type[c] = get_bits1(gb) ? TYPE_CPE : TYPE_SCE;
        coup->id_select[c] = get_bits(gb, 4);
        if (coup->type[c] == TYPE_CPE) {
            coup->ch_select[c] = get_bits(gb, 2);
            if (coup->ch_select[c] == 3)
                num_gain++;
        } else
            coup->ch_select[c] = 2;
    }
    coup->coupling_point += get_bits1(gb) || (coup->coupling_point >> 1);

    sign  = get_bits(gb, 1);
    scale = pow(2., pow(2., (int)get_bits(gb, 2) - 3));

    if ((ret = decode_ics(ac, sce, gb, 0, 0)))
        return ret;

    for (c = 0; c < num_gain; c++) {
        int idx  = 0;
        int cge  = 1;
        int gain = 0;
        float gain_cache = 1.;
        if (c) {
            cge = coup->coupling_point == AFTER_IMDCT ? 1 : get_bits1(gb);
            gain = cge ? get_vlc2(gb, vlc_scalefactors.table, 7, 3) - 60: 0;
            gain_cache = pow(scale, -gain);
        }
        if (coup->coupling_point == AFTER_IMDCT) {
            coup->gain[c][0] = gain_cache;
        } else {
            for (g = 0; g < sce->ics.num_window_groups; g++) {
                for (sfb = 0; sfb < sce->ics.max_sfb; sfb++, idx++) {
                    if (sce->band_type[idx] != ZERO_BT) {
                        if (!cge) {
                            int t = get_vlc2(gb, vlc_scalefactors.table, 7, 3) - 60;
                            if (t) {
                                int s = 1;
                                t = gain += t;
                                if (sign) {
                                    s  -= 2 * (t & 0x1);
                                    t >>= 1;
                                }
                                gain_cache = pow(scale, -t) * s;
                            }
                        }
                        coup->gain[c][idx] = gain_cache;
                    }
                }
            }
        }
    }
    return 0;
}

/**
 * Decode Spectral Band Replication extension data; reference: table 4.55.
 *
 * @param   crc flag indicating the presence of CRC checksum
 * @param   cnt length of TYPE_FIL syntactic element in bytes
 *
 * @return  Returns number of bytes consumed from the TYPE_FIL element.
 */
static int decode_sbr_extension(AACContext *ac, GetBitContext *gb,
                                int crc, int cnt)
{
    // TODO : sbr_extension implementation
    av_log_missing_feature(ac->avccontext, "SBR", 0);
    skip_bits_long(gb, 8 * cnt - 4); // -4 due to reading extension type
    return cnt;
}

/**
 * Parse whether channels are to be excluded from Dynamic Range Compression; reference: table 4.53.
 *
 * @return  Returns number of bytes consumed.
 */
static int decode_drc_channel_exclusions(DynamicRangeControl *che_drc,
                                         GetBitContext *gb)
{
    int i;
    int num_excl_chan = 0;

    do {
        for (i = 0; i < 7; i++)
            che_drc->exclude_mask[num_excl_chan++] = get_bits1(gb);
    } while (num_excl_chan < MAX_CHANNELS - 7 && get_bits1(gb));

    return num_excl_chan / 7;
}

/**
 * Decode dynamic range information; reference: table 4.52.
 *
 * @param   cnt length of TYPE_FIL syntactic element in bytes
 *
 * @return  Returns number of bytes consumed.
 */
static int decode_dynamic_range(DynamicRangeControl *che_drc,
                                GetBitContext *gb, int cnt)
{
    int n             = 1;
    int drc_num_bands = 1;
    int i;

    /* pce_tag_present? */
    if (get_bits1(gb)) {
        che_drc->pce_instance_tag  = get_bits(gb, 4);
        skip_bits(gb, 4); // tag_reserved_bits
        n++;
    }

    /* excluded_chns_present? */
    if (get_bits1(gb)) {
        n += decode_drc_channel_exclusions(che_drc, gb);
    }

    /* drc_bands_present? */
    if (get_bits1(gb)) {
        che_drc->band_incr            = get_bits(gb, 4);
        che_drc->interpolation_scheme = get_bits(gb, 4);
        n++;
        drc_num_bands += che_drc->band_incr;
        for (i = 0; i < drc_num_bands; i++) {
            che_drc->band_top[i] = get_bits(gb, 8);
            n++;
        }
    }

    /* prog_ref_level_present? */
    if (get_bits1(gb)) {
        che_drc->prog_ref_level = get_bits(gb, 7);
        skip_bits1(gb); // prog_ref_level_reserved_bits
        n++;
    }

    for (i = 0; i < drc_num_bands; i++) {
        che_drc->dyn_rng_sgn[i] = get_bits1(gb);
        che_drc->dyn_rng_ctl[i] = get_bits(gb, 7);
        n++;
    }

    return n;
}

/**
 * Decode extension data (incomplete); reference: table 4.51.
 *
 * @param   cnt length of TYPE_FIL syntactic element in bytes
 *
 * @return Returns number of bytes consumed
 */
static int decode_extension_payload(AACContext *ac, GetBitContext *gb, int cnt)
{
    int crc_flag = 0;
    int res = cnt;
    switch (get_bits(gb, 4)) { // extension type
    case EXT_SBR_DATA_CRC:
        crc_flag++;
    case EXT_SBR_DATA:
        res = decode_sbr_extension(ac, gb, crc_flag, cnt);
        break;
    case EXT_DYNAMIC_RANGE:
        res = decode_dynamic_range(&ac->che_drc, gb, cnt);
        break;
    case EXT_FILL:
    case EXT_FILL_DATA:
    case EXT_DATA_ELEMENT:
    default:
        skip_bits_long(gb, 8 * cnt - 4);
        break;
    };
    return res;
}

/**
 * Decode Temporal Noise Shaping filter coefficients and apply all-pole filters; reference: 4.6.9.3.
 *
 * @param   decode  1 if tool is used normally, 0 if tool is used in LTP.
 * @param   coef    spectral coefficients
 */
static void apply_tns(float coef[1024], TemporalNoiseShaping *tns,
                      IndividualChannelStream *ics, int decode)
{
    const int mmm = FFMIN(ics->tns_max_bands, ics->max_sfb);
    int w, filt, m, i;
    int bottom, top, order, start, end, size, inc;
    float lpc[TNS_MAX_ORDER];

    for (w = 0; w < ics->num_windows; w++) {
        bottom = ics->num_swb;
        for (filt = 0; filt < tns->n_filt[w]; filt++) {
            top    = bottom;
            bottom = FFMAX(0, top - tns->length[w][filt]);
            order  = tns->order[w][filt];
            if (order == 0)
                continue;

            // tns_decode_coef
            compute_lpc_coefs(tns->coef[w][filt], order, lpc, 0, 0, 0);

            start = ics->swb_offset[FFMIN(bottom, mmm)];
            end   = ics->swb_offset[FFMIN(   top, mmm)];
            if ((size = end - start) <= 0)
                continue;
            if (tns->direction[w][filt]) {
                inc = -1;
                start = end - 1;
            } else {
                inc = 1;
            }
            start += w * 128;

            // ar filter
            for (m = 0; m < size; m++, start += inc)
                for (i = 1; i <= FFMIN(m, order); i++)
                    coef[start] -= coef[start - i * inc] * lpc[i - 1];
        }
    }
}

/**
 * Conduct IMDCT and windowing.
 */
static void imdct_and_windowing(AACContext *ac, SingleChannelElement *sce)
{
    IndividualChannelStream *ics = &sce->ics;
    float *in    = sce->coeffs;
    float *out   = sce->ret;
    float *saved = sce->saved;
    const float *swindow      = ics->use_kb_window[0] ? ff_aac_kbd_short_128 : ff_sine_128;
    const float *lwindow_prev = ics->use_kb_window[1] ? ff_aac_kbd_long_1024 : ff_sine_1024;
    const float *swindow_prev = ics->use_kb_window[1] ? ff_aac_kbd_short_128 : ff_sine_128;
    float *buf  = ac->buf_mdct;
    float *temp = ac->temp;
    int i;

    // imdct
    if (ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE) {
        if (ics->window_sequence[1] == ONLY_LONG_SEQUENCE || ics->window_sequence[1] == LONG_STOP_SEQUENCE)
            av_log(ac->avccontext, AV_LOG_WARNING,
                   "Transition from an ONLY_LONG or LONG_STOP to an EIGHT_SHORT sequence detected. "
                   "If you heard an audible artifact, please submit the sample to the FFmpeg developers.\n");
        for (i = 0; i < 1024; i += 128)
            ff_imdct_half(&ac->mdct_small, buf + i, in + i);
    } else
        ff_imdct_half(&ac->mdct, buf, in);

    /* window overlapping
     * NOTE: To simplify the overlapping code, all 'meaningless' short to long
     * and long to short transitions are considered to be short to short
     * transitions. This leaves just two cases (long to long and short to short)
     * with a little special sauce for EIGHT_SHORT_SEQUENCE.
     */
    if ((ics->window_sequence[1] == ONLY_LONG_SEQUENCE || ics->window_sequence[1] == LONG_STOP_SEQUENCE) &&
            (ics->window_sequence[0] == ONLY_LONG_SEQUENCE || ics->window_sequence[0] == LONG_START_SEQUENCE)) {
        ac->dsp.vector_fmul_window(    out,               saved,            buf,         lwindow_prev, ac->add_bias, 512);
    } else {
        for (i = 0; i < 448; i++)
            out[i] = saved[i] + ac->add_bias;

        if (ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE) {
            ac->dsp.vector_fmul_window(out + 448 + 0*128, saved + 448,      buf + 0*128, swindow_prev, ac->add_bias, 64);
            ac->dsp.vector_fmul_window(out + 448 + 1*128, buf + 0*128 + 64, buf + 1*128, swindow,      ac->add_bias, 64);
            ac->dsp.vector_fmul_window(out + 448 + 2*128, buf + 1*128 + 64, buf + 2*128, swindow,      ac->add_bias, 64);
            ac->dsp.vector_fmul_window(out + 448 + 3*128, buf + 2*128 + 64, buf + 3*128, swindow,      ac->add_bias, 64);
            ac->dsp.vector_fmul_window(temp,              buf + 3*128 + 64, buf + 4*128, swindow,      ac->add_bias, 64);
            memcpy(                    out + 448 + 4*128, temp, 64 * sizeof(float));
        } else {
            ac->dsp.vector_fmul_window(out + 448,         saved + 448,      buf,         swindow_prev, ac->add_bias, 64);
            for (i = 576; i < 1024; i++)
                out[i] = buf[i-512] + ac->add_bias;
        }
    }

    // buffer update
    if (ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE) {
        for (i = 0; i < 64; i++)
            saved[i] = temp[64 + i] - ac->add_bias;
        ac->dsp.vector_fmul_window(saved + 64,  buf + 4*128 + 64, buf + 5*128, swindow, 0, 64);
        ac->dsp.vector_fmul_window(saved + 192, buf + 5*128 + 64, buf + 6*128, swindow, 0, 64);
        ac->dsp.vector_fmul_window(saved + 320, buf + 6*128 + 64, buf + 7*128, swindow, 0, 64);
        memcpy(                    saved + 448, buf + 7*128 + 64,  64 * sizeof(float));
    } else if (ics->window_sequence[0] == LONG_START_SEQUENCE) {
        memcpy(                    saved,       buf + 512,        448 * sizeof(float));
        memcpy(                    saved + 448, buf + 7*128 + 64,  64 * sizeof(float));
    } else { // LONG_STOP or ONLY_LONG
        memcpy(                    saved,       buf + 512,        512 * sizeof(float));
    }
}

/**
 * Apply dependent channel coupling (applied before IMDCT).
 *
 * @param   index   index into coupling gain array
 */
static void apply_dependent_coupling(AACContext *ac,
                                     SingleChannelElement *target,
                                     ChannelElement *cce, int index)
{
    IndividualChannelStream *ics = &cce->ch[0].ics;
    const uint16_t *offsets = ics->swb_offset;
    float *dest = target->coeffs;
    const float *src = cce->ch[0].coeffs;
    int g, i, group, k, idx = 0;
    if (ac->m4ac.object_type == AOT_AAC_LTP) {
        av_log(ac->avccontext, AV_LOG_ERROR,
               "Dependent coupling is not supported together with LTP\n");
        return;
    }
    for (g = 0; g < ics->num_window_groups; g++) {
        for (i = 0; i < ics->max_sfb; i++, idx++) {
            if (cce->ch[0].band_type[idx] != ZERO_BT) {
                const float gain = cce->coup.gain[index][idx];
                for (group = 0; group < ics->group_len[g]; group++) {
                    for (k = offsets[i]; k < offsets[i + 1]; k++) {
                        // XXX dsputil-ize
                        dest[group * 128 + k] += gain * src[group * 128 + k];
                    }
                }
            }
        }
        dest += ics->group_len[g] * 128;
        src  += ics->group_len[g] * 128;
    }
}

/**
 * Apply independent channel coupling (applied after IMDCT).
 *
 * @param   index   index into coupling gain array
 */
static void apply_independent_coupling(AACContext *ac,
                                       SingleChannelElement *target,
                                       ChannelElement *cce, int index)
{
    int i;
    const float gain = cce->coup.gain[index][0];
    const float bias = ac->add_bias;
    const float *src = cce->ch[0].ret;
    float *dest = target->ret;

    for (i = 0; i < 1024; i++)
        dest[i] += gain * (src[i] - bias);
}

/**
 * channel coupling transformation interface
 *
 * @param   index   index into coupling gain array
 * @param   apply_coupling_method   pointer to (in)dependent coupling function
 */
static void apply_channel_coupling(AACContext *ac, ChannelElement *cc,
                                   enum RawDataBlockType type, int elem_id,
                                   enum CouplingPoint coupling_point,
                                   void (*apply_coupling_method)(AACContext *ac, SingleChannelElement *target, ChannelElement *cce, int index))
{
    int i, c;

    for (i = 0; i < MAX_ELEM_ID; i++) {
        ChannelElement *cce = ac->che[TYPE_CCE][i];
        int index = 0;

        if (cce && cce->coup.coupling_point == coupling_point) {
            ChannelCoupling *coup = &cce->coup;

            for (c = 0; c <= coup->num_coupled; c++) {
                if (coup->type[c] == type && coup->id_select[c] == elem_id) {
                    if (coup->ch_select[c] != 1) {
                        apply_coupling_method(ac, &cc->ch[0], cce, index);
                        if (coup->ch_select[c] != 0)
                            index++;
                    }
                    if (coup->ch_select[c] != 2)
                        apply_coupling_method(ac, &cc->ch[1], cce, index++);
                } else
                    index += 1 + (coup->ch_select[c] == 3);
            }
        }
    }
}

/**
 * Convert spectral data to float samples, applying all supported tools as appropriate.
 */
static void spectral_to_sample(AACContext *ac)
{
    int i, type;
    for (type = 3; type >= 0; type--) {
        for (i = 0; i < MAX_ELEM_ID; i++) {
            ChannelElement *che = ac->che[type][i];
            if (che) {
                if (type <= TYPE_CPE)
                    apply_channel_coupling(ac, che, type, i, BEFORE_TNS, apply_dependent_coupling);
                if (che->ch[0].tns.present)
                    apply_tns(che->ch[0].coeffs, &che->ch[0].tns, &che->ch[0].ics, 1);
                if (che->ch[1].tns.present)
                    apply_tns(che->ch[1].coeffs, &che->ch[1].tns, &che->ch[1].ics, 1);
                if (type <= TYPE_CPE)
                    apply_channel_coupling(ac, che, type, i, BETWEEN_TNS_AND_IMDCT, apply_dependent_coupling);
                if (type != TYPE_CCE || che->coup.coupling_point == AFTER_IMDCT)
                    imdct_and_windowing(ac, &che->ch[0]);
                if (type == TYPE_CPE)
                    imdct_and_windowing(ac, &che->ch[1]);
                if (type <= TYPE_CCE)
                    apply_channel_coupling(ac, che, type, i, AFTER_IMDCT, apply_independent_coupling);
            }
        }
    }
}

static int parse_adts_frame_header(AACContext *ac, GetBitContext *gb)
{
    int size;
    AACADTSHeaderInfo hdr_info;

    size = ff_aac_parse_header(gb, &hdr_info);
    if (size > 0) {
        if (ac->output_configured != OC_LOCKED && hdr_info.chan_config) {
            enum ChannelPosition new_che_pos[4][MAX_ELEM_ID];
            memset(new_che_pos, 0, 4 * MAX_ELEM_ID * sizeof(new_che_pos[0][0]));
            ac->m4ac.chan_config = hdr_info.chan_config;
            if (set_default_channel_config(ac, new_che_pos, hdr_info.chan_config))
                return -7;
            if (output_configure(ac, ac->che_pos, new_che_pos, hdr_info.chan_config, OC_TRIAL_FRAME))
                return -7;
        } else if (ac->output_configured != OC_LOCKED) {
            ac->output_configured = OC_NONE;
        }
        if (ac->output_configured != OC_LOCKED)
            ac->m4ac.sbr = -1;
        ac->m4ac.sample_rate     = hdr_info.sample_rate;
        ac->m4ac.sampling_index  = hdr_info.sampling_index;
        ac->m4ac.object_type     = hdr_info.object_type;
        if (!ac->avccontext->sample_rate)
            ac->avccontext->sample_rate = hdr_info.sample_rate;
        if (hdr_info.num_aac_frames == 1) {
            if (!hdr_info.crc_absent)
                skip_bits(gb, 16);
        } else {
            av_log_missing_feature(ac->avccontext, "More than one AAC RDB per ADTS frame is", 0);
            return -1;
        }
    }
    return size;
}

static int aac_decode_frame(AVCodecContext *avccontext, void *data,
                            int *data_size, AVPacket *avpkt)
{
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    AACContext *ac = avccontext->priv_data;
    ChannelElement *che = NULL;
    GetBitContext gb;
    enum RawDataBlockType elem_type;
    int err, elem_id, data_size_tmp;

    init_get_bits(&gb, buf, buf_size * 8);

    if (show_bits(&gb, 12) == 0xfff) {
        if (parse_adts_frame_header(ac, &gb) < 0) {
            av_log(avccontext, AV_LOG_ERROR, "Error decoding AAC frame header.\n");
            return -1;
        }
        if (ac->m4ac.sampling_index > 12) {
            av_log(ac->avccontext, AV_LOG_ERROR, "invalid sampling rate index %d\n", ac->m4ac.sampling_index);
            return -1;
        }
    }

    // parse
    while ((elem_type = get_bits(&gb, 3)) != TYPE_END) {
        elem_id = get_bits(&gb, 4);

        if (elem_type < TYPE_DSE && !(che=get_che(ac, elem_type, elem_id))) {
            av_log(ac->avccontext, AV_LOG_ERROR, "channel element %d.%d is not allocated\n", elem_type, elem_id);
            return -1;
        }

        switch (elem_type) {

        case TYPE_SCE:
            err = decode_ics(ac, &che->ch[0], &gb, 0, 0);
            break;

        case TYPE_CPE:
            err = decode_cpe(ac, &gb, che);
            break;

        case TYPE_CCE:
            err = decode_cce(ac, &gb, che);
            break;

        case TYPE_LFE:
            err = decode_ics(ac, &che->ch[0], &gb, 0, 0);
            break;

        case TYPE_DSE:
            skip_data_stream_element(&gb);
            err = 0;
            break;

        case TYPE_PCE: {
            enum ChannelPosition new_che_pos[4][MAX_ELEM_ID];
            memset(new_che_pos, 0, 4 * MAX_ELEM_ID * sizeof(new_che_pos[0][0]));
            if ((err = decode_pce(ac, new_che_pos, &gb)))
                break;
            if (ac->output_configured > OC_TRIAL_PCE)
                av_log(avccontext, AV_LOG_ERROR,
                       "Not evaluating a further program_config_element as this construct is dubious at best.\n");
            else
                err = output_configure(ac, ac->che_pos, new_che_pos, 0, OC_TRIAL_PCE);
            break;
        }

        case TYPE_FIL:
            if (elem_id == 15)
                elem_id += get_bits(&gb, 8) - 1;
            while (elem_id > 0)
                elem_id -= decode_extension_payload(ac, &gb, elem_id);
            err = 0; /* FIXME */
            break;

        default:
            err = -1; /* should not happen, but keeps compiler happy */
            break;
        }

        if (err)
            return err;
    }

    spectral_to_sample(ac);

    if (!ac->is_saved) {
        ac->is_saved = 1;
        *data_size = 0;
        return buf_size;
    }

    data_size_tmp = 1024 * avccontext->channels * sizeof(int16_t);
    if (*data_size < data_size_tmp) {
        av_log(avccontext, AV_LOG_ERROR,
               "Output buffer too small (%d) or trying to output too many samples (%d) for this frame.\n",
               *data_size, data_size_tmp);
        return -1;
    }
    *data_size = data_size_tmp;

    ac->dsp.float_to_int16_interleave(data, (const float **)ac->output_data, 1024, avccontext->channels);

    if (ac->output_configured)
        ac->output_configured = OC_LOCKED;

    return buf_size;
}

static av_cold int aac_decode_close(AVCodecContext *avccontext)
{
    AACContext *ac = avccontext->priv_data;
    int i, type;

    for (i = 0; i < MAX_ELEM_ID; i++) {
        for (type = 0; type < 4; type++)
            av_freep(&ac->che[type][i]);
    }

    ff_mdct_end(&ac->mdct);
    ff_mdct_end(&ac->mdct_small);
    return 0;
}

AVCodec aac_decoder = {