aacdec.c

                       GetBitContext *gb, uint8_t max_sfb)
{
    int sfb;

    ltp->lag  = get_bits(gb, 11);
    ltp->coef = ltp_coef[get_bits(gb, 3)];
    for (sfb = 0; sfb < FFMIN(max_sfb, MAX_LTP_LONG_SFB); sfb++)
        ltp->used[sfb] = get_bits1(gb);
}

/**
 * Decode Individual Channel Stream info; reference: table 4.6.
 */
static int decode_ics_info(AACContext *ac, IndividualChannelStream *ics,
                           GetBitContext *gb)
{
    if (get_bits1(gb)) {
        av_log(ac->avctx, AV_LOG_ERROR, "Reserved bit set.\n");
        return AVERROR_INVALIDDATA;
    }
    ics->window_sequence[1] = ics->window_sequence[0];
    ics->window_sequence[0] = get_bits(gb, 2);
    ics->use_kb_window[1]   = ics->use_kb_window[0];
    ics->use_kb_window[0]   = get_bits1(gb);
    ics->num_window_groups  = 1;
    ics->group_len[0]       = 1;
    if (ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE) {
        int i;
        ics->max_sfb = get_bits(gb, 4);
        for (i = 0; i < 7; i++) {
            if (get_bits1(gb)) {
                ics->group_len[ics->num_window_groups - 1]++;
            } else {
                ics->num_window_groups++;
                ics->group_len[ics->num_window_groups - 1] = 1;
            }
        }
        ics->num_windows       = 8;
        ics->swb_offset        =    ff_swb_offset_128[ac->oc[1].m4ac.sampling_index];
        ics->num_swb           =   ff_aac_num_swb_128[ac->oc[1].m4ac.sampling_index];
        ics->tns_max_bands     = ff_tns_max_bands_128[ac->oc[1].m4ac.sampling_index];
        ics->predictor_present = 0;
    } else {
        ics->max_sfb               = get_bits(gb, 6);
        ics->num_windows           = 1;
        ics->swb_offset            =    ff_swb_offset_1024[ac->oc[1].m4ac.sampling_index];
        ics->num_swb               =   ff_aac_num_swb_1024[ac->oc[1].m4ac.sampling_index];
        ics->tns_max_bands         = ff_tns_max_bands_1024[ac->oc[1].m4ac.sampling_index];
        ics->predictor_present     = get_bits1(gb);
        ics->predictor_reset_group = 0;
        if (ics->predictor_present) {
            if (ac->oc[1].m4ac.object_type == AOT_AAC_MAIN) {
                if (decode_prediction(ac, ics, gb)) {
                    goto fail;
                }
            } else if (ac->oc[1].m4ac.object_type == AOT_AAC_LC) {
                av_log(ac->avctx, AV_LOG_ERROR, "Prediction is not allowed in AAC-LC.\n");
                goto fail;
            } else {
                if ((ics->ltp.present = get_bits(gb, 1)))
                    decode_ltp(&ics->ltp, gb, ics->max_sfb);
            }
        }
    }

    if (ics->max_sfb > ics->num_swb) {
        av_log(ac->avctx, AV_LOG_ERROR,
               "Number of scalefactor bands in group (%d) exceeds limit (%d).\n",
               ics->max_sfb, ics->num_swb);
        goto fail;
    }

    return 0;
fail:
    ics->max_sfb = 0;
    return AVERROR_INVALIDDATA;
}

/**
 * Decode band types (section_data payload); reference: table 4.46.
 *
 * @param   band_type           array of the used band type
 * @param   band_type_run_end   array of the last scalefactor band of a band type run
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_band_types(AACContext *ac, enum BandType band_type[120],
                             int band_type_run_end[120], GetBitContext *gb,
                             IndividualChannelStream *ics)
{
    int g, idx = 0;
    const int bits = (ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE) ? 3 : 5;
    for (g = 0; g < ics->num_window_groups; g++) {
        int k = 0;
        while (k < ics->max_sfb) {
            uint8_t sect_end = k;
            int sect_len_incr;
            int sect_band_type = get_bits(gb, 4);
            if (sect_band_type == 12) {
                av_log(ac->avctx, AV_LOG_ERROR, "invalid band type\n");
                return -1;
            }
            do {
                sect_len_incr = get_bits(gb, bits);
                sect_end += sect_len_incr;
                if (get_bits_left(gb) < 0) {
                    av_log(ac->avctx, AV_LOG_ERROR, "decode_band_types: "overread_err);
                    return -1;
                }
                if (sect_end > ics->max_sfb) {
                    av_log(ac->avctx, AV_LOG_ERROR,
                           "Number of bands (%d) exceeds limit (%d).\n",
                           sect_end, ics->max_sfb);
                    return -1;
                }
            } while (sect_len_incr == (1 << bits) - 1);
            for (; k < sect_end; k++) {
                band_type        [idx]   = sect_band_type;
                band_type_run_end[idx++] = sect_end;
            }
        }
    }
    return 0;
}

/**
 * Decode scalefactors; reference: table 4.47.
 *
 * @param   global_gain         first scalefactor value as scalefactors are differentially coded
 * @param   band_type           array of the used band type
 * @param   band_type_run_end   array of the last scalefactor band of a band type run
 * @param   sf                  array of scalefactors or intensity stereo positions
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_scalefactors(AACContext *ac, float sf[120], GetBitContext *gb,
                               unsigned int global_gain,
                               IndividualChannelStream *ics,
                               enum BandType band_type[120],
                               int band_type_run_end[120])
{
    int g, i, idx = 0;
    int offset[3] = { global_gain, global_gain - 90, 0 };
    int clipped_offset;
    int noise_flag = 1;
    for (g = 0; g < ics->num_window_groups; g++) {
        for (i = 0; i < ics->max_sfb;) {
            int run_end = band_type_run_end[idx];
            if (band_type[idx] == ZERO_BT) {
                for (; i < run_end; i++, idx++)
                    sf[idx] = 0.;
            } else if ((band_type[idx] == INTENSITY_BT) || (band_type[idx] == INTENSITY_BT2)) {
                for (; i < run_end; i++, idx++) {
                    offset[2] += get_vlc2(gb, vlc_scalefactors.table, 7, 3) - 60;
                    clipped_offset = av_clip(offset[2], -155, 100);
                    if (offset[2] != clipped_offset) {
                        av_log_ask_for_sample(ac->avctx, "Intensity stereo "
                                "position clipped (%d -> %d).\nIf you heard an "
                                "audible artifact, there may be a bug in the "
                                "decoder. ", offset[2], clipped_offset);
                    }
                    sf[idx] = ff_aac_pow2sf_tab[-clipped_offset + POW_SF2_ZERO];
                }
            } else if (band_type[idx] == NOISE_BT) {
                for (; i < run_end; i++, idx++) {
                    if (noise_flag-- > 0)
                        offset[1] += get_bits(gb, 9) - 256;
                    else
                        offset[1] += get_vlc2(gb, vlc_scalefactors.table, 7, 3) - 60;
                    clipped_offset = av_clip(offset[1], -100, 155);
                    if (offset[1] != clipped_offset) {
                        av_log_ask_for_sample(ac->avctx, "Noise gain clipped "
                                "(%d -> %d).\nIf you heard an audible "
                                "artifact, there may be a bug in the decoder. ",
                                offset[1], clipped_offset);
                    }
                    sf[idx] = -ff_aac_pow2sf_tab[clipped_offset + POW_SF2_ZERO];
                }
            } else {
                for (; i < run_end; i++, idx++) {
                    offset[0] += get_vlc2(gb, vlc_scalefactors.table, 7, 3) - 60;
                    if (offset[0] > 255U) {
                        av_log(ac->avctx, AV_LOG_ERROR,
                               "Scalefactor (%d) out of range.\n", offset[0]);
                        return -1;
                    }
                    sf[idx] = -ff_aac_pow2sf_tab[offset[0] - 100 + POW_SF2_ZERO];
                }
            }
        }
    }
    return 0;
}

/**
 * Decode pulse data; reference: table 4.7.
 */
static int decode_pulses(Pulse *pulse, GetBitContext *gb,
                         const uint16_t *swb_offset, int num_swb)
{
    int i, pulse_swb;
    pulse->num_pulse = get_bits(gb, 2) + 1;
    pulse_swb        = get_bits(gb, 6);
    if (pulse_swb >= num_swb)
        return -1;
    pulse->pos[0]    = swb_offset[pulse_swb];
    pulse->pos[0]   += get_bits(gb, 5);
    if (pulse->pos[0] > 1023)
        return -1;
    pulse->amp[0]    = get_bits(gb, 4);
    for (i = 1; i < pulse->num_pulse; i++) {
        pulse->pos[i] = get_bits(gb, 5) + pulse->pos[i - 1];
        if (pulse->pos[i] > 1023)
            return -1;
        pulse->amp[i] = get_bits(gb, 4);
    }
    return 0;
}

/**
 * Decode Temporal Noise Shaping data; reference: table 4.48.
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_tns(AACContext *ac, TemporalNoiseShaping *tns,
                      GetBitContext *gb, const IndividualChannelStream *ics)
{
    int w, filt, i, coef_len, coef_res, coef_compress;
    const int is8 = ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE;
    const int tns_max_order = is8 ? 7 : ac->oc[1].m4ac.object_type == AOT_AAC_MAIN ? 20 : 12;
    for (w = 0; w < ics->num_windows; w++) {
        if ((tns->n_filt[w] = get_bits(gb, 2 - is8))) {
            coef_res = get_bits1(gb);

            for (filt = 0; filt < tns->n_filt[w]; filt++) {
                int tmp2_idx;
                tns->length[w][filt] = get_bits(gb, 6 - 2 * is8);

                if ((tns->order[w][filt] = get_bits(gb, 5 - 2 * is8)) > tns_max_order) {
                    av_log(ac->avctx, AV_LOG_ERROR, "TNS filter order %d is greater than maximum %d.\n",
                           tns->order[w][filt], tns_max_order);
                    tns->order[w][filt] = 0;
                    return -1;
                }
                if (tns->order[w][filt]) {
                    tns->direction[w][filt] = get_bits1(gb);
                    coef_compress = get_bits1(gb);
                    coef_len = coef_res + 3 - coef_compress;
                    tmp2_idx = 2 * coef_compress + coef_res;

                    for (i = 0; i < tns->order[w][filt]; i++)
                        tns->coef[w][filt][i] = tns_tmp2_map[tmp2_idx][get_bits(gb, coef_len)];
                }
            }
        }
    }
    return 0;
}

/**
 * Decode Mid/Side data; reference: table 4.54.
 *
 * @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 decode_mid_side_stereo(ChannelElement *cpe, GetBitContext *gb,
                                   int ms_present)
{
    int idx;
    if (ms_present == 1) {
        for (idx = 0; idx < cpe->ch[0].ics.num_window_groups * cpe->ch[0].ics.max_sfb; idx++)
            cpe->ms_mask[idx] = get_bits1(gb);
    } else if (ms_present == 2) {
        memset(cpe->ms_mask, 1,  sizeof(cpe->ms_mask[0]) * cpe->ch[0].ics.num_window_groups * cpe->ch[0].ics.max_sfb);
    }
}

#ifndef VMUL2
static inline float *VMUL2(float *dst, const float *v, unsigned idx,
                           const float *scale)
{
    float s = *scale;
    *dst++ = v[idx    & 15] * s;
    *dst++ = v[idx>>4 & 15] * s;
    return dst;
}
#endif

#ifndef VMUL4
static inline float *VMUL4(float *dst, const float *v, unsigned idx,
                           const float *scale)
{
    float s = *scale;
    *dst++ = v[idx    & 3] * s;
    *dst++ = v[idx>>2 & 3] * s;
    *dst++ = v[idx>>4 & 3] * s;
    *dst++ = v[idx>>6 & 3] * s;
    return dst;
}
#endif

#ifndef VMUL2S
static inline float *VMUL2S(float *dst, const float *v, unsigned idx,
                            unsigned sign, const float *scale)
{
    union av_intfloat32 s0, s1;

    s0.f = s1.f = *scale;
    s0.i ^= sign >> 1 << 31;
    s1.i ^= sign      << 31;

    *dst++ = v[idx    & 15] * s0.f;
    *dst++ = v[idx>>4 & 15] * s1.f;

    return dst;
}
#endif

#ifndef VMUL4S
static inline float *VMUL4S(float *dst, const float *v, unsigned idx,
                            unsigned sign, const float *scale)
{
    unsigned nz = idx >> 12;
    union av_intfloat32 s = { .f = *scale };
    union av_intfloat32 t;

    t.i = s.i ^ (sign & 1U<<31);
    *dst++ = v[idx    & 3] * t.f;

    sign <<= nz & 1; nz >>= 1;
    t.i = s.i ^ (sign & 1U<<31);
    *dst++ = v[idx>>2 & 3] * t.f;

    sign <<= nz & 1; nz >>= 1;
    t.i = s.i ^ (sign & 1U<<31);
    *dst++ = v[idx>>4 & 3] * t.f;

    sign <<= nz & 1;
    t.i = s.i ^ (sign & 1U<<31);
    *dst++ = v[idx>>6 & 3] * t.f;

    return dst;
}
#endif

/**
 * Decode spectral data; reference: table 4.50.
 * Dequantize and scale spectral data; reference: 4.6.3.3.
 *
 * @param   coef            array of dequantized, scaled spectral data
 * @param   sf              array of scalefactors or intensity stereo positions
 * @param   pulse_present   set if pulses are present
 * @param   pulse           pointer to pulse data struct
 * @param   band_type       array of the used band type
 *
 * @return  Returns error status. 0 - OK, !0 - error
 */
static int decode_spectrum_and_dequant(AACContext *ac, float coef[1024],
                                       GetBitContext *gb, const float sf[120],
                                       int pulse_present, const Pulse *pulse,
                                       const IndividualChannelStream *ics,
                                       enum BandType band_type[120])
{
    int i, k, g, idx = 0;
    const int c = 1024 / ics->num_windows;
    const uint16_t *offsets = ics->swb_offset;
    float *coef_base = coef;

    for (g = 0; g < ics->num_windows; g++)
        memset(coef + g * 128 + offsets[ics->max_sfb], 0, sizeof(float) * (c - offsets[ics->max_sfb]));

    for (g = 0; g < ics->num_window_groups; g++) {
        unsigned g_len = ics->group_len[g];

        for (i = 0; i < ics->max_sfb; i++, idx++) {
            const unsigned cbt_m1 = band_type[idx] - 1;
            float *cfo = coef + offsets[i];
            int off_len = offsets[i + 1] - offsets[i];
            int group;

            if (cbt_m1 >= INTENSITY_BT2 - 1) {
                for (group = 0; group < g_len; group++, cfo+=128) {
                    memset(cfo, 0, off_len * sizeof(float));
                }
            } else if (cbt_m1 == NOISE_BT - 1) {
                for (group = 0; group < g_len; group++, cfo+=128) {
                    float scale;
                    float band_energy;

                    for (k = 0; k < off_len; k++) {
                        ac->random_state  = lcg_random(ac->random_state);
                        cfo[k] = ac->random_state;
                    }

                    band_energy = ac->dsp.scalarproduct_float(cfo, cfo, off_len);
                    scale = sf[idx] / sqrtf(band_energy);
                    ac->fdsp.vector_fmul_scalar(cfo, cfo, scale, off_len);
                }
            } else {
                const float *vq = ff_aac_codebook_vector_vals[cbt_m1];
                const uint16_t *cb_vector_idx = ff_aac_codebook_vector_idx[cbt_m1];
                VLC_TYPE (*vlc_tab)[2] = vlc_spectral[cbt_m1].table;
                OPEN_READER(re, gb);

                switch (cbt_m1 >> 1) {
                case 0:
                    for (group = 0; group < g_len; group++, cfo+=128) {
                        float *cf = cfo;
                        int len = off_len;

                        do {
                            int code;
                            unsigned cb_idx;

                            UPDATE_CACHE(re, gb);
                            GET_VLC(code, re, gb, vlc_tab, 8, 2);
                            cb_idx = cb_vector_idx[code];
                            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 {
                            int code;
                            unsigned nnz;
                            unsigned cb_idx;
                            uint32_t bits;

                            UPDATE_CACHE(re, gb);
                            GET_VLC(code, re, gb, vlc_tab, 8, 2);
                            cb_idx = cb_vector_idx[code];
                            nnz = cb_idx >> 8 & 15;
                            bits = nnz ? GET_CACHE(re, gb) : 0;
                            LAST_SKIP_BITS(re, gb, 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 {
                            int code;
                            unsigned cb_idx;

                            UPDATE_CACHE(re, gb);
                            GET_VLC(code, re, gb, vlc_tab, 8, 2);
                            cb_idx = cb_vector_idx[code];
                            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 {
                            int code;
                            unsigned nnz;
                            unsigned cb_idx;
                            unsigned sign;

                            UPDATE_CACHE(re, gb);
                            GET_VLC(code, re, gb, vlc_tab, 8, 2);
                            cb_idx = cb_vector_idx[code];
                            nnz = cb_idx >> 8 & 15;
                            sign = nnz ? SHOW_UBITS(re, gb, nnz) << (cb_idx >> 12) : 0;
                            LAST_SKIP_BITS(re, gb, nnz);
                            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 {
                            int code;
                            unsigned nzt, nnz;
                            unsigned cb_idx;
                            uint32_t bits;
                            int j;

                            UPDATE_CACHE(re, gb);
                            GET_VLC(code, re, gb, vlc_tab, 8, 2);

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

                            cb_idx = cb_vector_idx[code];
                            nnz = cb_idx >> 12;
                            nzt = cb_idx >> 8;
                            bits = SHOW_UBITS(re, gb, nnz) << (32-nnz);
                            LAST_SKIP_BITS(re, gb, nnz);

                            for (j = 0; j < 2; j++) {
                                if (nzt & 1<<j) {
                                    uint32_t b;
                                    int n;
                                    /* The total length of escape_sequence must be < 22 bits according
                                       to the specification (i.e. max is 111111110xxxxxxxxxxxx). */
                                    UPDATE_CACHE(re, gb);
                                    b = GET_CACHE(re, gb);
                                    b = 31 - av_log2(~b);

                                    if (b > 8) {
                                        av_log(ac->avctx, AV_LOG_ERROR, "error in spectral data, ESC overflow\n");
                                        return -1;
                                    }

                                    SKIP_BITS(re, gb, b + 1);
                                    b += 4;
                                    n = (1 << b) + SHOW_UBITS(re, gb, b);
                                    LAST_SKIP_BITS(re, gb, b);
                                    *icf++ = cbrt_tab[n] | (bits & 1U<<31);
                                    bits <<= 1;
                                } else {
                                    unsigned v = ((const uint32_t*)vq)[cb_idx & 15];
                                    *icf++ = (bits & 1U<<31) | v;
                                    bits <<= !!v;
                                }
                                cb_idx >>= 4;
                            }
                        } while (len -= 2);

                        ac->fdsp.vector_fmul_scalar(cfo, cfo, sf[idx], off_len);
                    }
                }

                CLOSE_READER(re, gb);
            }
        }
        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;
}

static av_always_inline float flt16_round(float pf)
{
    union av_intfloat32 tmp;
    tmp.f = pf;
    tmp.i = (tmp.i + 0x00008000U) & 0xFFFF0000U;
    return tmp.f;
}

static av_always_inline float flt16_even(float pf)
{
    union av_intfloat32 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 av_intfloat32 pun;
    pun.f = pf;
    pun.i &= 0xFFFF0000U;
    return pun.f;
}

static av_always_inline void predict(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;
    float   r0 = ps->r0,     r1 = ps->r1;
    float cor0 = ps->cor0, cor1 = ps->cor1;
    float var0 = ps->var0, var1 = ps->var1;

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

    pv = flt16_round(k1 * r0 + k2 * r1);
    if (output_enable)
        *coef += pv;

    e0 = *coef;
    e1 = e0 - k1 * r0;

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

    ps->r1 = flt16_trunc(a * (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->oc[1].m4ac.sampling_index]; sfb++) {
            for (k = sce->ics.swb_offset[sfb]; k < sce->ics.swb_offset[sfb + 1]; k++) {
                predict(&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)
            return AVERROR_INVALIDDATA;
    }

    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->avctx, 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->avctx, 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->avctx, "SSR", 1);
            return AVERROR_PATCHWELCOME;
        }
    }

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

    if (ac->oc[1].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(AACContext *ac, 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, 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++)
                        ac->fdsp.vector_fmul_scalar(coef1 + group * 128 + offsets[i],
                                                    coef0 + group * 128 + offsets[i],
                                                    scale,
                                                    offsets[i + 1] - offsets[i]);
                }
            } 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.
 *
 * @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))
            return AVERROR_INVALIDDATA;
        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;
        if (cpe->ch[1].ics.predictor_present && (ac->oc[1].m4ac.object_type != AOT_AAC_MAIN))
            if ((cpe->ch[1].ics.ltp.present = get_bits(gb, 1)))
                decode_ltp(&cpe->ch[1].ics.ltp, gb, cpe->ch[1].ics.max_sfb);
        ms_present = get_bits(gb, 2);
        if (ms_present == 3) {
            av_log(ac->avctx, 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->oc[1].m4ac.object_type == AOT_AAC_MAIN) {
            apply_prediction(ac, &cpe->ch[0]);
            apply_prediction(ac, &cpe->ch[1]);
        }
    }

    apply_intensity_stereo(ac, cpe, ms_present);
    return 0;
}

static const float cce_scale[] = {
    1.09050773266525765921, //2^(1/8)
    1.18920711500272106672, //2^(1/4)
    M_SQRT2,
    2,
};

/**
 * Decode coupling_channel_element; reference: table 4.8.
 *
 * @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 = cce_scale[get_bits(gb, 2)];

    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 = powf(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 = powf(scale, -t) * s;
                            }
                        }
                        coup->gain[c][idx] = gain_cache;
                    }
                }
            }
        }
    }
    return 0;
}

/**
 * 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.
 *
 * @return  Returns number of bytes consumed.
 */
static int decode_dynamic_range(DynamicRangeControl *che_drc,
                                GetBitContext *gb)
{
    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;
}

static int decode_fill(AACContext *ac, GetBitContext *gb, int len) {
    uint8_t buf[256];
    int i, major, minor;

    if (len < 13+7*8)
        goto unknown;

    get_bits(gb, 13); len -= 13;

    for(i=0; i+1<sizeof(buf) && len>=8; i++, len-=8)
        buf[i] = get_bits(gb, 8);

    buf[i] = 0;
    if (ac->avctx->debug & FF_DEBUG_PICT_INFO)
        av_log(ac->avctx, AV_LOG_DEBUG, "FILL:%s\n", buf);

    if (sscanf(buf, "libfaac %d.%d", &major, &minor) == 2){
        ac->avctx->internal->skip_samples = 1024;
    }

unknown:
    skip_bits_long(gb, len);