/*
  * AC-3 Audio Decoder

  * This code was developed as part of Google Summer of Code 2006.
  * E-AC-3 support was added as part of Google Summer of Code 2007.

  *

  * Copyright (c) 2006 Kartikey Mahendra BHATT (bhattkm at gmail dot com)

  * Copyright (c) 2007-2008 Bartlomiej Wolowiec <bartek.wolowiec@gmail.com>

  * Copyright (c) 2007 Justin Ruggles <justin.ruggles@gmail.com>

  *

  * This file is part of FFmpeg.

  *

  * FFmpeg is free software; you can redistribute it and/or

  * modify it under the terms of the GNU Lesser General Public

  * License as published by the Free Software Foundation; either

  * version 2.1 of the License, or (at your option) any later version.

  *

  * FFmpeg is distributed in the hope that it will be useful,

  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

  * Lesser General Public License for more details.

  *

  * You should have received a copy of the GNU Lesser General Public

  * License along with FFmpeg; if not, write to the Free Software

  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include <stdio.h>
 #include <stddef.h>
 #include <math.h>
 #include <string.h>
 

 #include "libavutil/channel_layout.h"

 #include "libavutil/crc.h"

 #include "libavutil/downmix_info.h"

 #include "libavutil/opt.h"

 #include "bswapdsp.h"

 #include "internal.h"

 #include "aac_ac3_parser.h"

 #include "ac3_parser.h"

 #include "ac3dec.h"

 #include "ac3dec_data.h"

 #include "kbdwin.h"

 /**
  * table for ungrouping 3 values in 7 bits.
  * used for exponents and bap=2 mantissas
  */
 static uint8_t ungroup_3_in_7_bits_tab[128][3];

 /** tables for ungrouping mantissas */

 static int b1_mantissas[32][3];
 static int b2_mantissas[128][3];
 static int b3_mantissas[8];
 static int b4_mantissas[128][2];
 static int b5_mantissas[16];

 /**
  * Quantization table: levels for symmetric. bits for asymmetric.
  * reference: Table 7.18 Mapping of bap to Quantizer
  */

 static const uint8_t quantization_tab[16] = {

     0, 3, 5, 7, 11, 15,
     5, 6, 7, 8, 9, 10, 11, 12, 14, 16
 };

 /** dynamic range table. converts codes to scale factors. */

 static float dynamic_range_tab[256];

 static float heavy_dynamic_range_tab[256];

 /** Adjustments in dB gain */

 static const float gain_levels[9] = {
     LEVEL_PLUS_3DB,
     LEVEL_PLUS_1POINT5DB,

     LEVEL_ONE,

     LEVEL_MINUS_1POINT5DB,

     LEVEL_MINUS_3DB,
     LEVEL_MINUS_4POINT5DB,
     LEVEL_MINUS_6DB,

     LEVEL_ZERO,

     LEVEL_MINUS_9DB
 };

 /** Adjustments in dB gain (LFE, +10 to -21 dB) */
 static const float gain_levels_lfe[32] = {
     3.162275, 2.818382, 2.511886, 2.238719, 1.995261, 1.778278, 1.584893,
     1.412536, 1.258924, 1.122018, 1.000000, 0.891251, 0.794328, 0.707946,
     0.630957, 0.562341, 0.501187, 0.446683, 0.398107, 0.354813, 0.316227,
     0.281838, 0.251188, 0.223872, 0.199526, 0.177828, 0.158489, 0.141253,
     0.125892, 0.112201, 0.100000, 0.089125
 };
 

 /**
  * Table for default stereo downmixing coefficients
  * reference: Section 7.8.2 Downmixing Into Two Channels
  */
 static const uint8_t ac3_default_coeffs[8][5][2] = {

     { { 2, 7 }, { 7, 2 },                               },
     { { 4, 4 },                                         },
     { { 2, 7 }, { 7, 2 },                               },
     { { 2, 7 }, { 5, 5 }, { 7, 2 },                     },
     { { 2, 7 }, { 7, 2 }, { 6, 6 },                     },
     { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 8, 8 },           },
     { { 2, 7 }, { 7, 2 }, { 6, 7 }, { 7, 6 },           },
     { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },

 };

 /**

  * Symmetrical Dequantization
  * reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
  *            Tables 7.19 to 7.23
  */

 static inline int

 symmetric_dequant(int code, int levels)

 {

     return ((code - (levels >> 1)) << 24) / levels;

 }
 

 /*
  * Initialize tables at runtime.
  */

 static av_cold void ac3_tables_init(void)

 {

     int i;

     /* generate table for ungrouping 3 values in 7 bits
        reference: Section 7.1.3 Exponent Decoding */

     for (i = 0; i < 128; i++) {

         ungroup_3_in_7_bits_tab[i][0] =  i / 25;
         ungroup_3_in_7_bits_tab[i][1] = (i % 25) / 5;
         ungroup_3_in_7_bits_tab[i][2] = (i % 25) % 5;
     }
 

     /* generate grouped mantissa tables
        reference: Section 7.3.5 Ungrouping of Mantissas */

     for (i = 0; i < 32; i++) {

         /* bap=1 mantissas */

         b1_mantissas[i][0] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][0], 3);
         b1_mantissas[i][1] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][1], 3);
         b1_mantissas[i][2] = symmetric_dequant(ff_ac3_ungroup_3_in_5_bits_tab[i][2], 3);

     }

     for (i = 0; i < 128; i++) {

         /* bap=2 mantissas */

         b2_mantissas[i][0] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][0], 5);
         b2_mantissas[i][1] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][1], 5);
         b2_mantissas[i][2] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][2], 5);

 
         /* bap=4 mantissas */
         b4_mantissas[i][0] = symmetric_dequant(i / 11, 11);
         b4_mantissas[i][1] = symmetric_dequant(i % 11, 11);
     }
     /* generate ungrouped mantissa tables
        reference: Tables 7.21 and 7.23 */

     for (i = 0; i < 7; i++) {

         /* bap=3 mantissas */
         b3_mantissas[i] = symmetric_dequant(i, 7);
     }

     for (i = 0; i < 15; i++) {

         /* bap=5 mantissas */
         b5_mantissas[i] = symmetric_dequant(i, 15);
     }

     /* generate dynamic range table
        reference: Section 7.7.1 Dynamic Range Control */

     for (i = 0; i < 256; i++) {

         int v = (i >> 5) - ((i >> 7) << 3) - 5;

         dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);

     }

 
     /* generate compr dynamic range table
        reference: Section 7.7.2 Heavy Compression */
     for (i = 0; i < 256; i++) {
         int v = (i >> 4) - ((i >> 7) << 4) - 4;
         heavy_dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0xF) | 0x10);
     }
 

 }
 

 /**
  * AVCodec initialization
  */

 static av_cold int ac3_decode_init(AVCodecContext *avctx)

 {

     AC3DecodeContext *s = avctx->priv_data;

     int i;
 

     s->avctx = avctx;

     ff_ac3_common_init();

     ac3_tables_init();

     ff_mdct_init(&s->imdct_256, 8, 1, 1.0);
     ff_mdct_init(&s->imdct_512, 9, 1, 1.0);

     AC3_RENAME(ff_kbd_window_init)(s->window, 5.0, 256);

     ff_bswapdsp_init(&s->bdsp);

 #if (USE_FIXED)

     s->fdsp = avpriv_alloc_fixed_dsp(avctx->flags & CODEC_FLAG_BITEXACT);
 #else

     s->fdsp = avpriv_float_dsp_alloc(avctx->flags & CODEC_FLAG_BITEXACT);

 #endif
 

     ff_ac3dsp_init(&s->ac3dsp, avctx->flags & CODEC_FLAG_BITEXACT);

     ff_fmt_convert_init(&s->fmt_conv, avctx);

     av_lfg_init(&s->dith_state, 0);

     if (USE_FIXED)

         avctx->sample_fmt = AV_SAMPLE_FMT_S16P;
     else
         avctx->sample_fmt = AV_SAMPLE_FMT_FLTP;

     /* allow downmixing to stereo or mono */

 #if FF_API_REQUEST_CHANNELS
 FF_DISABLE_DEPRECATION_WARNINGS
     if (avctx->request_channels == 1)
         avctx->request_channel_layout = AV_CH_LAYOUT_MONO;
     else if (avctx->request_channels == 2)
         avctx->request_channel_layout = AV_CH_LAYOUT_STEREO;
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
     if (avctx->channels > 1 &&
         avctx->request_channel_layout == AV_CH_LAYOUT_MONO)
         avctx->channels = 1;
     else if (avctx->channels > 2 &&
              avctx->request_channel_layout == AV_CH_LAYOUT_STEREO)
         avctx->channels = 2;

     s->downmixed = 1;

     for (i = 0; i < AC3_MAX_CHANNELS; i++) {
         s->xcfptr[i] = s->transform_coeffs[i];
         s->dlyptr[i] = s->delay[i];
     }
 

     return 0;

 }
 

 /**

  * Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.

  * GetBitContext within AC3DecodeContext must point to

  * the start of the synchronized AC-3 bitstream.

  */

 static int ac3_parse_header(AC3DecodeContext *s)

 {

     GetBitContext *gbc = &s->gbc;
     int i;
 
     /* read the rest of the bsi. read twice for dual mono mode. */

     i = !s->channel_mode;

     do {

         s->dialog_normalization[(!s->channel_mode)-i] = -get_bits(gbc, 5);
         if (s->dialog_normalization[(!s->channel_mode)-i] == 0) {
             s->dialog_normalization[(!s->channel_mode)-i] = -31;
         }
         if (s->target_level != 0) {
             s->level_gain[(!s->channel_mode)-i] = powf(2.0f,
                 (float)(s->target_level -
                 s->dialog_normalization[(!s->channel_mode)-i])/6.0f);
         }
         if (s->compression_exists[(!s->channel_mode)-i] = get_bits1(gbc)) {
             s->heavy_dynamic_range[(!s->channel_mode)-i] =
                 AC3_HEAVY_RANGE(get_bits(gbc, 8));
         }

         if (get_bits1(gbc))
             skip_bits(gbc, 8); //skip language code
         if (get_bits1(gbc))
             skip_bits(gbc, 7); //skip audio production information
     } while (i--);
 
     skip_bits(gbc, 2); //skip copyright bit and original bitstream bit
 

     /* skip the timecodes or parse the Alternate Bit Stream Syntax */

     if (s->bitstream_id != 6) {
         if (get_bits1(gbc))
             skip_bits(gbc, 14); //skip timecode1
         if (get_bits1(gbc))
             skip_bits(gbc, 14); //skip timecode2
     } else {

         if (get_bits1(gbc)) {
             s->preferred_downmix       = get_bits(gbc, 2);
             s->center_mix_level_ltrt   = get_bits(gbc, 3);

             s->surround_mix_level_ltrt = av_clip(get_bits(gbc, 3), 3, 7);

             s->center_mix_level        = get_bits(gbc, 3);

             s->surround_mix_level      = av_clip(get_bits(gbc, 3), 3, 7);

         }

         if (get_bits1(gbc)) {
             s->dolby_surround_ex_mode = get_bits(gbc, 2);
             s->dolby_headphone_mode   = get_bits(gbc, 2);
             skip_bits(gbc, 10); // skip adconvtyp (1), xbsi2 (8), encinfo (1)
         }
     }

 
     /* skip additional bitstream info */
     if (get_bits1(gbc)) {
         i = get_bits(gbc, 6);
         do {
             skip_bits(gbc, 8);

         } while (i--);

     }
 
     return 0;
 }
 
 /**

  * Common function to parse AC-3 or E-AC-3 frame header

  */
 static int parse_frame_header(AC3DecodeContext *s)
 {

     AC3HeaderInfo hdr, *phdr=&hdr;

     int err;

     err = avpriv_ac3_parse_header2(&s->gbc, &phdr);

     if (err)

         return err;
 
     /* get decoding parameters from header info */

     s->bit_alloc_params.sr_code     = hdr.sr_code;

     s->bitstream_id                 = hdr.bitstream_id;

     s->bitstream_mode               = hdr.bitstream_mode;

     s->channel_mode                 = hdr.channel_mode;

     s->lfe_on                       = hdr.lfe_on;

     s->bit_alloc_params.sr_shift    = hdr.sr_shift;

     s->sample_rate                  = hdr.sample_rate;

     s->bit_rate                     = hdr.bit_rate;
     s->channels                     = hdr.channels;
     s->fbw_channels                 = s->channels - s->lfe_on;
     s->lfe_ch                       = s->fbw_channels + 1;
     s->frame_size                   = hdr.frame_size;

     s->preferred_downmix            = AC3_DMIXMOD_NOTINDICATED;

     s->center_mix_level             = hdr.center_mix_level;

     s->center_mix_level_ltrt        = 4; // -3.0dB

     s->surround_mix_level           = hdr.surround_mix_level;

     s->surround_mix_level_ltrt      = 4; // -3.0dB
     s->lfe_mix_level_exists         = 0;

     s->num_blocks                   = hdr.num_blocks;

     s->frame_type                   = hdr.frame_type;

     s->substreamid                  = hdr.substreamid;

     s->dolby_surround_mode          = hdr.dolby_surround_mode;

     s->dolby_surround_ex_mode       = AC3_DSUREXMOD_NOTINDICATED;
     s->dolby_headphone_mode         = AC3_DHEADPHONMOD_NOTINDICATED;

     if (s->lfe_on) {
         s->start_freq[s->lfe_ch]     = 0;
         s->end_freq[s->lfe_ch]       = 7;

         s->num_exp_groups[s->lfe_ch] = 2;
         s->channel_in_cpl[s->lfe_ch] = 0;
     }
 

     if (s->bitstream_id <= 10) {

         s->eac3                  = 0;
         s->snr_offset_strategy   = 2;
         s->block_switch_syntax   = 1;
         s->dither_flag_syntax    = 1;
         s->bit_allocation_syntax = 1;
         s->fast_gain_syntax      = 0;
         s->first_cpl_leak        = 0;
         s->dba_syntax            = 1;
         s->skip_syntax           = 1;
         memset(s->channel_uses_aht, 0, sizeof(s->channel_uses_aht));

         return ac3_parse_header(s);

     } else if (CONFIG_EAC3_DECODER) {

         s->eac3 = 1;
         return ff_eac3_parse_header(s);

     } else {
         av_log(s->avctx, AV_LOG_ERROR, "E-AC-3 support not compiled in\n");

         return AVERROR(ENOSYS);

     }

 }
 
 /**
  * Set stereo downmixing coefficients based on frame header info.
  * reference: Section 7.8.2 Downmixing Into Two Channels
  */
 static void set_downmix_coeffs(AC3DecodeContext *s)
 {
     int i;

     float cmix = gain_levels[s->  center_mix_level];
     float smix = gain_levels[s->surround_mix_level];

     float norm0, norm1;

     float downmix_coeffs[AC3_MAX_CHANNELS][2];

     for (i = 0; i < s->fbw_channels; i++) {

         downmix_coeffs[i][0] = gain_levels[ac3_default_coeffs[s->channel_mode][i][0]];
         downmix_coeffs[i][1] = gain_levels[ac3_default_coeffs[s->channel_mode][i][1]];

     }

     if (s->channel_mode > 1 && s->channel_mode & 1) {

         downmix_coeffs[1][0] = downmix_coeffs[1][1] = cmix;

     }

     if (s->channel_mode == AC3_CHMODE_2F1R || s->channel_mode == AC3_CHMODE_3F1R) {

         int nf = s->channel_mode - 2;

         downmix_coeffs[nf][0] = downmix_coeffs[nf][1] = smix * LEVEL_MINUS_3DB;

     }

     if (s->channel_mode == AC3_CHMODE_2F2R || s->channel_mode == AC3_CHMODE_3F2R) {

         int nf = s->channel_mode - 4;

         downmix_coeffs[nf][0] = downmix_coeffs[nf+1][1] = smix;

     }

     /* renormalize */
     norm0 = norm1 = 0.0;

     for (i = 0; i < s->fbw_channels; i++) {

         norm0 += downmix_coeffs[i][0];
         norm1 += downmix_coeffs[i][1];

     }
     norm0 = 1.0f / norm0;
     norm1 = 1.0f / norm1;

     for (i = 0; i < s->fbw_channels; i++) {

         downmix_coeffs[i][0] *= norm0;
         downmix_coeffs[i][1] *= norm1;

     }
 

     if (s->output_mode == AC3_CHMODE_MONO) {
         for (i = 0; i < s->fbw_channels; i++)

             downmix_coeffs[i][0] = (downmix_coeffs[i][0] +
                                     downmix_coeffs[i][1]) * LEVEL_MINUS_3DB;
     }
     for (i = 0; i < s->fbw_channels; i++) {
         s->downmix_coeffs[i][0] = FIXR12(downmix_coeffs[i][0]);
         s->downmix_coeffs[i][1] = FIXR12(downmix_coeffs[i][1]);

     }

 }
 

 /**

  * Decode the grouped exponents according to exponent strategy.
  * reference: Section 7.1.3 Exponent Decoding

  */

 static int decode_exponents(GetBitContext *gbc, int exp_strategy, int ngrps,

                             uint8_t absexp, int8_t *dexps)

 {

     int i, j, grp, group_size;

     int dexp[256];
     int expacc, prevexp;
 
     /* unpack groups */

     group_size = exp_strategy + (exp_strategy == EXP_D45);

     for (grp = 0, i = 0; grp < ngrps; grp++) {

         expacc = get_bits(gbc, 7);

         dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0];
         dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1];
         dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2];

     }

     /* convert to absolute exps and expand groups */
     prevexp = absexp;

     for (i = 0, j = 0; i < ngrps * 3; i++) {

         prevexp += dexp[i] - 2;

         if (prevexp > 24U)

             return -1;

         switch (group_size) {

         case 4: dexps[j++] = prevexp;
                 dexps[j++] = prevexp;
         case 2: dexps[j++] = prevexp;
         case 1: dexps[j++] = prevexp;

         }

     }

     return 0;

 }
 

 /**

  * Generate transform coefficients for each coupled channel in the coupling

  * range using the coupling coefficients and coupling coordinates.
  * reference: Section 7.4.3 Coupling Coordinate Format
  */

 static void calc_transform_coeffs_cpl(AC3DecodeContext *s)

 {

     int bin, band, ch;

 
     bin = s->start_freq[CPL_CH];
     for (band = 0; band < s->num_cpl_bands; band++) {

         int band_start = bin;

         int band_end = bin + s->cpl_band_sizes[band];

         for (ch = 1; ch <= s->fbw_channels; ch++) {
             if (s->channel_in_cpl[ch]) {

                 int cpl_coord = s->cpl_coords[ch][band] << 5;

                 for (bin = band_start; bin < band_end; bin++) {

                     s->fixed_coeffs[ch][bin] =
                         MULH(s->fixed_coeffs[CPL_CH][bin] << 4, cpl_coord);

                 }
                 if (ch == 2 && s->phase_flags[band]) {
                     for (bin = band_start; bin < band_end; bin++)
                         s->fixed_coeffs[2][bin] = -s->fixed_coeffs[2][bin];

                 }

             }

         }

         bin = band_end;

     }
 }
 

 /**
  * Grouped mantissas for 3-level 5-level and 11-level quantization
  */
 typedef struct {

     int b1_mant[2];
     int b2_mant[2];
     int b4_mant;
     int b1;
     int b2;
     int b4;

 } mant_groups;
 

 /**

  * Decode the transform coefficients for a particular channel

  * reference: Section 7.3 Quantization and Decoding of Mantissas
  */

 static void ac3_decode_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_groups *m)

 {

     int start_freq = s->start_freq[ch_index];

     int end_freq   = s->end_freq[ch_index];
     uint8_t *baps  = s->bap[ch_index];
     int8_t *exps   = s->dexps[ch_index];

     int32_t *coeffs = s->fixed_coeffs[ch_index];

     int dither     = (ch_index == CPL_CH) || s->dither_flag[ch_index];

     GetBitContext *gbc = &s->gbc;

     int freq;

     for (freq = start_freq; freq < end_freq; freq++) {

         int bap = baps[freq];
         int mantissa;

         switch (bap) {
         case 0:

             /* random noise with approximate range of -0.707 to 0.707 */

             if (dither)

                 mantissa = (((av_lfg_get(&s->dith_state)>>8)*181)>>8) - 5931008;

             else
                 mantissa = 0;
             break;
         case 1:
             if (m->b1) {
                 m->b1--;
                 mantissa = m->b1_mant[m->b1];
             } else {
                 int bits      = get_bits(gbc, 5);
                 mantissa      = b1_mantissas[bits][0];
                 m->b1_mant[1] = b1_mantissas[bits][1];
                 m->b1_mant[0] = b1_mantissas[bits][2];
                 m->b1         = 2;
             }
             break;
         case 2:
             if (m->b2) {
                 m->b2--;
                 mantissa = m->b2_mant[m->b2];
             } else {
                 int bits      = get_bits(gbc, 7);
                 mantissa      = b2_mantissas[bits][0];
                 m->b2_mant[1] = b2_mantissas[bits][1];
                 m->b2_mant[0] = b2_mantissas[bits][2];
                 m->b2         = 2;
             }
             break;
         case 3:
             mantissa = b3_mantissas[get_bits(gbc, 3)];
             break;
         case 4:
             if (m->b4) {
                 m->b4 = 0;
                 mantissa = m->b4_mant;
             } else {
                 int bits   = get_bits(gbc, 7);
                 mantissa   = b4_mantissas[bits][0];
                 m->b4_mant = b4_mantissas[bits][1];
                 m->b4      = 1;
             }
             break;
         case 5:
             mantissa = b5_mantissas[get_bits(gbc, 4)];
             break;
         default: /* 6 to 15 */
             /* Shift mantissa and sign-extend it. */

             if (bap > 15) {
                 av_log(s->avctx, AV_LOG_ERROR, "bap %d is invalid in plain AC-3\n", bap);
                 bap = 15;
             }

             mantissa = get_sbits(gbc, quantization_tab[bap]);
             mantissa <<= 24 - quantization_tab[bap];
             break;

         }

         coeffs[freq] = mantissa >> exps[freq];

     }
 }
 

 /**

  * Remove random dithering from coupling range coefficients with zero-bit
  * mantissas for coupled channels which do not use dithering.

  * reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)
  */

 static void remove_dithering(AC3DecodeContext *s) {

     int ch, i;
 

     for (ch = 1; ch <= s->fbw_channels; ch++) {
         if (!s->dither_flag[ch] && s->channel_in_cpl[ch]) {
             for (i = s->start_freq[CPL_CH]; i < s->end_freq[CPL_CH]; i++) {
                 if (!s->bap[CPL_CH][i])

                     s->fixed_coeffs[ch][i] = 0;

             }
         }
     }
 }
 

 static void decode_transform_coeffs_ch(AC3DecodeContext *s, int blk, int ch,

                                        mant_groups *m)

 {
     if (!s->channel_uses_aht[ch]) {

         ac3_decode_transform_coeffs_ch(s, ch, m);

     } else {
         /* if AHT is used, mantissas for all blocks are encoded in the first
            block of the frame. */
         int bin;

         if (!blk && CONFIG_EAC3_DECODER)

             ff_eac3_decode_transform_coeffs_aht_ch(s, ch);

         for (bin = s->start_freq[ch]; bin < s->end_freq[ch]; bin++) {

             s->fixed_coeffs[ch][bin] = s->pre_mantissa[ch][bin][blk] >> s->dexps[ch][bin];

         }
     }
 }
 

 /**

  * Decode the transform coefficients.

  */

 static void decode_transform_coeffs(AC3DecodeContext *s, int blk)

 {

     int ch, end;

     int got_cplchan = 0;

     mant_groups m;
 

     m.b1 = m.b2 = m.b4 = 0;

     for (ch = 1; ch <= s->channels; ch++) {

         /* transform coefficients for full-bandwidth channel */

         decode_transform_coeffs_ch(s, blk, ch, &m);

         /* transform coefficients for coupling channel come right after the

            coefficients for the first coupled channel*/

         if (s->channel_in_cpl[ch])  {

             if (!got_cplchan) {

                 decode_transform_coeffs_ch(s, blk, CPL_CH, &m);

                 calc_transform_coeffs_cpl(s);

                 got_cplchan = 1;
             }

             end = s->end_freq[CPL_CH];

         } else {

             end = s->end_freq[ch];

         }

         do

             s->fixed_coeffs[ch][end] = 0;

         while (++end < 256);

     }

     /* zero the dithered coefficients for appropriate channels */

     remove_dithering(s);

 }
 

 /**

  * Stereo rematrixing.

  * reference: Section 7.5.4 Rematrixing : Decoding Technique
  */

 static void do_rematrixing(AC3DecodeContext *s)

 {

     int bnd, i;

     int end, bndend;
 

     end = FFMIN(s->end_freq[1], s->end_freq[2]);

     for (bnd = 0; bnd < s->num_rematrixing_bands; bnd++) {
         if (s->rematrixing_flags[bnd]) {
             bndend = FFMIN(end, ff_ac3_rematrix_band_tab[bnd + 1]);
             for (i = ff_ac3_rematrix_band_tab[bnd]; i < bndend; i++) {

                 int tmp0 = s->fixed_coeffs[1][i];

                 s->fixed_coeffs[1][i] += s->fixed_coeffs[2][i];

                 s->fixed_coeffs[2][i]  = tmp0 - s->fixed_coeffs[2][i];

             }
         }

     }
 }

 /**
  * Inverse MDCT Transform.
  * Convert frequency domain coefficients to time-domain audio samples.
  * reference: Section 7.9.4 Transformation Equations
  */

 static inline void do_imdct(AC3DecodeContext *s, int channels)

 {

     int ch;

     for (ch = 1; ch <= channels; ch++) {

         if (s->block_switch[ch]) {

             int i;

             FFTSample *x = s->tmp_output + 128;

             for (i = 0; i < 128; i++)
                 x[i] = s->transform_coeffs[ch][2 * i];

             s->imdct_256.imdct_half(&s->imdct_256, s->tmp_output, x);

 #if USE_FIXED

             s->fdsp->vector_fmul_window_scaled(s->outptr[ch - 1], s->delay[ch - 1],
                                        s->tmp_output, s->window, 128, 8);
 #else

             s->fdsp->vector_fmul_window(s->outptr[ch - 1], s->delay[ch - 1],

                                        s->tmp_output, s->window, 128);

 #endif

             for (i = 0; i < 128; i++)
                 x[i] = s->transform_coeffs[ch][2 * i + 1];
             s->imdct_256.imdct_half(&s->imdct_256, s->delay[ch - 1], x);

         } else {

             s->imdct_512.imdct_half(&s->imdct_512, s->tmp_output, s->transform_coeffs[ch]);

 #if USE_FIXED

             s->fdsp->vector_fmul_window_scaled(s->outptr[ch - 1], s->delay[ch - 1],
                                        s->tmp_output, s->window, 128, 8);
 #else

             s->fdsp->vector_fmul_window(s->outptr[ch - 1], s->delay[ch - 1],

                                        s->tmp_output, s->window, 128);

 #endif
             memcpy(s->delay[ch - 1], s->tmp_output + 128, 128 * sizeof(FFTSample));

         }

     }
 }
 

 /**

  * Upmix delay samples from stereo to original channel layout.
  */
 static void ac3_upmix_delay(AC3DecodeContext *s)
 {

     int channel_data_size = sizeof(s->delay[0]);

     switch (s->channel_mode) {
     case AC3_CHMODE_DUALMONO:
     case AC3_CHMODE_STEREO:
         /* upmix mono to stereo */
         memcpy(s->delay[1], s->delay[0], channel_data_size);
         break;
     case AC3_CHMODE_2F2R:
         memset(s->delay[3], 0, channel_data_size);
     case AC3_CHMODE_2F1R:
         memset(s->delay[2], 0, channel_data_size);
         break;
     case AC3_CHMODE_3F2R:
         memset(s->delay[4], 0, channel_data_size);
     case AC3_CHMODE_3F1R:
         memset(s->delay[3], 0, channel_data_size);
     case AC3_CHMODE_3F:
         memcpy(s->delay[2], s->delay[1], channel_data_size);
         memset(s->delay[1], 0, channel_data_size);
         break;

     }
 }
 
 /**

  * Decode band structure for coupling, spectral extension, or enhanced coupling.

  * The band structure defines how many subbands are in each band.  For each
  * subband in the range, 1 means it is combined with the previous band, and 0
  * means that it starts a new band.
  *

  * @param[in] gbc bit reader context
  * @param[in] blk block number
  * @param[in] eac3 flag to indicate E-AC-3
  * @param[in] ecpl flag to indicate enhanced coupling
  * @param[in] start_subband subband number for start of range
  * @param[in] end_subband subband number for end of range
  * @param[in] default_band_struct default band structure table
  * @param[out] num_bands number of bands (optionally NULL)
  * @param[out] band_sizes array containing the number of bins in each band (optionally NULL)
  */
 static void decode_band_structure(GetBitContext *gbc, int blk, int eac3,
                                   int ecpl, int start_subband, int end_subband,
                                   const uint8_t *default_band_struct,

                                   int *num_bands, uint8_t *band_sizes)

 {

     int subbnd, bnd, n_subbands, n_bands=0;

     uint8_t bnd_sz[22];

     uint8_t coded_band_struct[22];
     const uint8_t *band_struct;

 
     n_subbands = end_subband - start_subband;
 
     /* decode band structure from bitstream or use default */
     if (!eac3 || get_bits1(gbc)) {
         for (subbnd = 0; subbnd < n_subbands - 1; subbnd++) {

             coded_band_struct[subbnd] = get_bits1(gbc);

         }

         band_struct = coded_band_struct;

     } else if (!blk) {

         band_struct = &default_band_struct[start_subband+1];
     } else {
         /* no change in band structure */
         return;

     }
 
     /* calculate number of bands and band sizes based on band structure.
        note that the first 4 subbands in enhanced coupling span only 6 bins
        instead of 12. */
     if (num_bands || band_sizes ) {

         n_bands = n_subbands;

         bnd_sz[0] = ecpl ? 6 : 12;
         for (bnd = 0, subbnd = 1; subbnd < n_subbands; subbnd++) {
             int subbnd_size = (ecpl && subbnd < 4) ? 6 : 12;

             if (band_struct[subbnd - 1]) {

                 n_bands--;
                 bnd_sz[bnd] += subbnd_size;
             } else {
                 bnd_sz[++bnd] = subbnd_size;
             }
         }
     }
 
     /* set optional output params */
     if (num_bands)
         *num_bands = n_bands;
     if (band_sizes)

         memcpy(band_sizes, bnd_sz, n_bands);

 }
 
 /**

  * Decode a single audio block from the AC-3 bitstream.

  */

 static int decode_audio_block(AC3DecodeContext *s, int blk)

 {

     int fbw_channels = s->fbw_channels;
     int channel_mode = s->channel_mode;

     int i, bnd, seg, ch;

     int different_transforms;
     int downmix_output;

     int cpl_in_use;

     GetBitContext *gbc = &s->gbc;

     uint8_t bit_alloc_stages[AC3_MAX_CHANNELS] = { 0 };

     /* block switch flags */

     different_transforms = 0;

     if (s->block_switch_syntax) {

         for (ch = 1; ch <= fbw_channels; ch++) {
             s->block_switch[ch] = get_bits1(gbc);

             if (ch > 1 && s->block_switch[ch] != s->block_switch[1])

                 different_transforms = 1;
         }

     }

     /* dithering flags */

     if (s->dither_flag_syntax) {

         for (ch = 1; ch <= fbw_channels; ch++) {
             s->dither_flag[ch] = get_bits1(gbc);
         }

     }

     /* dynamic range */

     i = !s->channel_mode;

     do {

         if (get_bits1(gbc)) {

             /* Allow asymmetric application of DRC when drc_scale > 1.
                Amplification of quiet sounds is enhanced */

             int range_bits = get_bits(gbc, 8);
             INTFLOAT range = AC3_RANGE(range_bits);
             if (range_bits <= 127 || s->drc_scale <= 1.0)

                 s->dynamic_range[i] = AC3_DYNAMIC_RANGE(range);

             else
                 s->dynamic_range[i] = range;

         } else if (blk == 0) {

             s->dynamic_range[i] = AC3_DYNAMIC_RANGE1;

         }

     } while (i--);

     /* spectral extension strategy */
     if (s->eac3 && (!blk || get_bits1(gbc))) {

         s->spx_in_use = get_bits1(gbc);
         if (s->spx_in_use) {
             int dst_start_freq, dst_end_freq, src_start_freq,
                 start_subband, end_subband;
 
             /* determine which channels use spx */
             if (s->channel_mode == AC3_CHMODE_MONO) {
                 s->channel_uses_spx[1] = 1;
             } else {
                 for (ch = 1; ch <= fbw_channels; ch++)
                     s->channel_uses_spx[ch] = get_bits1(gbc);
             }
 
             /* get the frequency bins of the spx copy region and the spx start
                and end subbands */
             dst_start_freq = get_bits(gbc, 2);
             start_subband  = get_bits(gbc, 3) + 2;
             if (start_subband > 7)
                 start_subband += start_subband - 7;
             end_subband    = get_bits(gbc, 3) + 5;

 #if USE_FIXED

             s->spx_dst_end_freq = end_freq_inv_tab[end_subband-5];

 #endif

             if (end_subband   > 7)
                 end_subband   += end_subband   - 7;
             dst_start_freq = dst_start_freq * 12 + 25;
             src_start_freq = start_subband  * 12 + 25;
             dst_end_freq   = end_subband    * 12 + 25;
 
             /* check validity of spx ranges */
             if (start_subband >= end_subband) {
                 av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
                        "range (%d >= %d)\n", start_subband, end_subband);

                 return AVERROR_INVALIDDATA;

             }
             if (dst_start_freq >= src_start_freq) {
                 av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
                        "copy start bin (%d >= %d)\n", dst_start_freq, src_start_freq);

                 return AVERROR_INVALIDDATA;

             }
 
             s->spx_dst_start_freq = dst_start_freq;
             s->spx_src_start_freq = src_start_freq;

             if (!USE_FIXED)
                 s->spx_dst_end_freq   = dst_end_freq;

 
             decode_band_structure(gbc, blk, s->eac3, 0,
                                   start_subband, end_subband,
                                   ff_eac3_default_spx_band_struct,
                                   &s->num_spx_bands,
                                   s->spx_band_sizes);
         } else {
             for (ch = 1; ch <= fbw_channels; ch++) {
                 s->channel_uses_spx[ch] = 0;
                 s->first_spx_coords[ch] = 1;
             }

         }
     }
 

     /* spectral extension coordinates */
     if (s->spx_in_use) {
         for (ch = 1; ch <= fbw_channels; ch++) {
             if (s->channel_uses_spx[ch]) {
                 if (s->first_spx_coords[ch] || get_bits1(gbc)) {

                     INTFLOAT spx_blend;

                     int bin, master_spx_coord;
 
                     s->first_spx_coords[ch] = 0;

                     spx_blend = AC3_SPX_BLEND(get_bits(gbc, 5));

                     master_spx_coord = get_bits(gbc, 2) * 3;
 
                     bin = s->spx_src_start_freq;
                     for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
                         int bandsize;
                         int spx_coord_exp, spx_coord_mant;

                         INTFLOAT nratio, sblend, nblend;

 #if USE_FIXED

                         int64_t accu;
                         /* calculate blending factors */
                         bandsize = s->spx_band_sizes[bnd];
                         accu = (int64_t)((bin << 23) + (bandsize << 22)) * s->spx_dst_end_freq;
                         nratio = (int)(accu >> 32);
                         nratio -= spx_blend << 18;
 
                         if (nratio < 0) {
                             nblend = 0;
                             sblend = 0x800000;
                         } else if (nratio > 0x7fffff) {

                             nblend = 14529495; // sqrt(3) in FP.23

                             sblend = 0;
                         } else {
                             nblend = fixed_sqrt(nratio, 23);
                             accu = (int64_t)nblend * 1859775393;
                             nblend = (int)((accu + (1<<29)) >> 30);
                             sblend = fixed_sqrt(0x800000 - nratio, 23);
                         }
 #else
                         float spx_coord;

 
                         /* calculate blending factors */
                         bandsize = s->spx_band_sizes[bnd];
                         nratio = ((float)((bin + (bandsize >> 1))) / s->spx_dst_end_freq) - spx_blend;
                         nratio = av_clipf(nratio, 0.0f, 1.0f);

                         nblend = sqrtf(3.0f * nratio); // noise is scaled by sqrt(3)
                                                        // to give unity variance

                         sblend = sqrtf(1.0f - nratio);

 #endif

                         bin += bandsize;
 
                         /* decode spx coordinates */
                         spx_coord_exp  = get_bits(gbc, 4);
                         spx_coord_mant = get_bits(gbc, 2);
                         if (spx_coord_exp == 15) spx_coord_mant <<= 1;
                         else                     spx_coord_mant += 4;
                         spx_coord_mant <<= (25 - spx_coord_exp - master_spx_coord);
 
                         /* multiply noise and signal blending factors by spx coordinate */

 #if USE_FIXED

                         accu = (int64_t)nblend * spx_coord_mant;
                         s->spx_noise_blend[ch][bnd]  = (int)((accu + (1<<22)) >> 23);
                         accu = (int64_t)sblend * spx_coord_mant;
                         s->spx_signal_blend[ch][bnd] = (int)((accu + (1<<22)) >> 23);
 #else
                         spx_coord = spx_coord_mant * (1.0f / (1 << 23));

                         s->spx_noise_blend [ch][bnd] = nblend * spx_coord;
                         s->spx_signal_blend[ch][bnd] = sblend * spx_coord;

 #endif

                     }
                 }
             } else {
                 s->first_spx_coords[ch] = 1;
             }
         }
     }

     /* coupling strategy */

     if (s->eac3 ? s->cpl_strategy_exists[blk] : get_bits1(gbc)) {

         memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);

         if (!s->eac3)

             s->cpl_in_use[blk] = get_bits1(gbc);

         if (s->cpl_in_use[blk]) {

             /* coupling in use */

             int cpl_start_subband, cpl_end_subband;

             if (channel_mode < AC3_CHMODE_STEREO) {
                 av_log(s->avctx, AV_LOG_ERROR, "coupling not allowed in mono or dual-mono\n");

                 return AVERROR_INVALIDDATA;

             }
 

             /* check for enhanced coupling */
             if (s->eac3 && get_bits1(gbc)) {
                 /* TODO: parse enhanced coupling strategy info */

                 avpriv_request_sample(s->avctx, "Enhanced coupling");

                 return AVERROR_PATCHWELCOME;

             }
 

             /* determine which channels are coupled */

             if (s->eac3 && s->channel_mode == AC3_CHMODE_STEREO) {
                 s->channel_in_cpl[1] = 1;
                 s->channel_in_cpl[2] = 1;
             } else {

                 for (ch = 1; ch <= fbw_channels; ch++)
                     s->channel_in_cpl[ch] = get_bits1(gbc);

             }

             /* phase flags in use */

             if (channel_mode == AC3_CHMODE_STEREO)

                 s->phase_flags_in_use = get_bits1(gbc);

             /* coupling frequency range */

             cpl_start_subband = get_bits(gbc, 4);

             cpl_end_subband = s->spx_in_use ? (s->spx_src_start_freq - 37) / 12 :
                                               get_bits(gbc, 4) + 3;

             if (cpl_start_subband >= cpl_end_subband) {
                 av_log(s->avctx, AV_LOG_ERROR, "invalid coupling range (%d >= %d)\n",

                        cpl_start_subband, cpl_end_subband);

                 return AVERROR_INVALIDDATA;

             }

             s->start_freq[CPL_CH] = cpl_start_subband * 12 + 37;

             s->end_freq[CPL_CH]   = cpl_end_subband   * 12 + 37;

             decode_band_structure(gbc, blk, s->eac3, 0, cpl_start_subband,
                                   cpl_end_subband,
                                   ff_eac3_default_cpl_band_struct,

                                   &s->num_cpl_bands, s->cpl_band_sizes);

         } else {

             /* coupling not in use */

             for (ch = 1; ch <= fbw_channels; ch++) {

                 s->channel_in_cpl[ch] = 0;

                 s->first_cpl_coords[ch] = 1;
             }

             s->first_cpl_leak = s->eac3;

             s->phase_flags_in_use = 0;

         }

     } else if (!s->eac3) {

         if (!blk) {
             av_log(s->avctx, AV_LOG_ERROR, "new coupling strategy must "
                    "be present in block 0\n");

             return AVERROR_INVALIDDATA;

         } else {
             s->cpl_in_use[blk] = s->cpl_in_use[blk-1];
         }

     }

     cpl_in_use = s->cpl_in_use[blk];

     /* coupling coordinates */

     if (cpl_in_use) {

         int cpl_coords_exist = 0;

         for (ch = 1; ch <= fbw_channels; ch++) {

             if (s->channel_in_cpl[ch]) {

                 if ((s->eac3 && s->first_cpl_coords[ch]) || get_bits1(gbc)) {

                     int master_cpl_coord, cpl_coord_exp, cpl_coord_mant;

                     s->first_cpl_coords[ch] = 0;

                     cpl_coords_exist = 1;

                     master_cpl_coord = 3 * get_bits(gbc, 2);

                     for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {

                         cpl_coord_exp = get_bits(gbc, 4);
                         cpl_coord_mant = get_bits(gbc, 4);

                         if (cpl_coord_exp == 15)

                             s->cpl_coords[ch][bnd] = cpl_coord_mant << 22;

                         else

                             s->cpl_coords[ch][bnd] = (cpl_coord_mant + 16) << 21;
                         s->cpl_coords[ch][bnd] >>= (cpl_coord_exp + master_cpl_coord);

                     }

                 } else if (!blk) {

                     av_log(s->avctx, AV_LOG_ERROR, "new coupling coordinates must "
                            "be present in block 0\n");

                     return AVERROR_INVALIDDATA;

                 }

             } else {
                 /* channel not in coupling */
                 s->first_cpl_coords[ch] = 1;

             }
         }

         /* phase flags */

         if (channel_mode == AC3_CHMODE_STEREO && cpl_coords_exist) {

             for (bnd = 0; bnd < s->num_cpl_bands; bnd++) {

                 s->phase_flags[bnd] = s->phase_flags_in_use? get_bits1(gbc) : 0;

             }
         }

     }

     /* stereo rematrixing strategy and band structure */

     if (channel_mode == AC3_CHMODE_STEREO) {

         if ((s->eac3 && !blk) || get_bits1(gbc)) {

             s->num_rematrixing_bands = 4;

             if (cpl_in_use && s->start_freq[CPL_CH] <= 61) {

                 s->num_rematrixing_bands -= 1 + (s->start_freq[CPL_CH] == 37);

             } else if (s->spx_in_use && s->spx_src_start_freq <= 61) {
                 s->num_rematrixing_bands--;
             }

             for (bnd = 0; bnd < s->num_rematrixing_bands; bnd++)

                 s->rematrixing_flags[bnd] = get_bits1(gbc);

         } else if (!blk) {

             av_log(s->avctx, AV_LOG_WARNING, "Warning: "
                    "new rematrixing strategy not present in block 0\n");

             s->num_rematrixing_bands = 0;

         }

     }
 

     /* exponent strategies for each channel */

     for (ch = !cpl_in_use; ch <= s->channels; ch++) {

         if (!s->eac3)

             s->exp_strategy[blk][ch] = get_bits(gbc, 2 - (ch == s->lfe_ch));

         if (s->exp_strategy[blk][ch] != EXP_REUSE)

             bit_alloc_stages[ch] = 3;
     }
 

     /* channel bandwidth */

     for (ch = 1; ch <= fbw_channels; ch++) {

         s->start_freq[ch] = 0;

         if (s->exp_strategy[blk][ch] != EXP_REUSE) {

             int group_size;

             int prev = s->end_freq[ch];
             if (s->channel_in_cpl[ch])
                 s->end_freq[ch] = s->start_freq[CPL_CH];

             else if (s->channel_uses_spx[ch])
                 s->end_freq[ch] = s->spx_src_start_freq;

             else {

                 int bandwidth_code = get_bits(gbc, 6);

                 if (bandwidth_code > 60) {

                     av_log(s->avctx, AV_LOG_ERROR, "bandwidth code = %d > 60\n", bandwidth_code);

                     return AVERROR_INVALIDDATA;

                 }

                 s->end_freq[ch] = bandwidth_code * 3 + 73;

             }

             group_size = 3 << (s->exp_strategy[blk][ch] - 1);

             s->num_exp_groups[ch] = (s->end_freq[ch] + group_size-4) / group_size;
             if (blk > 0 && s->end_freq[ch] != prev)

                 memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);

         }

     }

     if (cpl_in_use && s->exp_strategy[blk][CPL_CH] != EXP_REUSE) {

         s->num_exp_groups[CPL_CH] = (s->end_freq[CPL_CH] - s->start_freq[CPL_CH]) /

                                     (3 << (s->exp_strategy[blk][CPL_CH] - 1));

     }

     /* decode exponents for each channel */

     for (ch = !cpl_in_use; ch <= s->channels; ch++) {

         if (s->exp_strategy[blk][ch] != EXP_REUSE) {

             s->dexps[ch][0] = get_bits(gbc, 4) << !ch;

             if (decode_exponents(gbc, s->exp_strategy[blk][ch],

                                  s->num_exp_groups[ch], s->dexps[ch][0],
                                  &s->dexps[ch][s->start_freq[ch]+!!ch])) {

                 av_log(s->avctx, AV_LOG_ERROR, "exponent out-of-range\n");

                 return AVERROR_INVALIDDATA;

             }

             if (ch != CPL_CH && ch != s->lfe_ch)

                 skip_bits(gbc, 2); /* skip gainrng */

         }

     }

     /* bit allocation information */

     if (s->bit_allocation_syntax) {

         if (get_bits1(gbc)) {
             s->bit_alloc_params.slow_decay = ff_ac3_slow_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
             s->bit_alloc_params.fast_decay = ff_ac3_fast_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
             s->bit_alloc_params.slow_gain  = ff_ac3_slow_gain_tab[get_bits(gbc, 2)];
             s->bit_alloc_params.db_per_bit = ff_ac3_db_per_bit_tab[get_bits(gbc, 2)];

             s->bit_alloc_params.floor  = ff_ac3_floor_tab[get_bits(gbc, 3)];

             for (ch = !cpl_in_use; ch <= s->channels; ch++)

                 bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
         } else if (!blk) {

             av_log(s->avctx, AV_LOG_ERROR, "new bit allocation info must "
                    "be present in block 0\n");

             return AVERROR_INVALIDDATA;

         }

     }

     /* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */

     if (!s->eac3 || !blk) {
         if (s->snr_offset_strategy && get_bits1(gbc)) {

             int snr = 0;
             int csnr;
             csnr = (get_bits(gbc, 6) - 15) << 4;
             for (i = ch = !cpl_in_use; ch <= s->channels; ch++) {
                 /* snr offset */
                 if (ch == i || s->snr_offset_strategy == 2)
                     snr = (csnr + get_bits(gbc, 4)) << 2;
                 /* run at least last bit allocation stage if snr offset changes */

                 if (blk && s->snr_offset[ch] != snr) {

                     bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 1);
                 }
                 s->snr_offset[ch] = snr;

 
                 /* fast gain (normal AC-3 only) */
                 if (!s->eac3) {
                     int prev = s->fast_gain[ch];

                     s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];

                     /* run last 2 bit allocation stages if fast gain changes */

                     if (blk && prev != s->fast_gain[ch])

                         bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
                 }

             }

         } else if (!s->eac3 && !blk) {

             av_log(s->avctx, AV_LOG_ERROR, "new snr offsets must be present in block 0\n");

             return AVERROR_INVALIDDATA;

         }

     }

     /* fast gain (E-AC-3 only) */
     if (s->fast_gain_syntax && get_bits1(gbc)) {
         for (ch = !cpl_in_use; ch <= s->channels; ch++) {
             int prev = s->fast_gain[ch];
             s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];
             /* run last 2 bit allocation stages if fast gain changes */

             if (blk && prev != s->fast_gain[ch])

                 bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
         }
     } else if (s->eac3 && !blk) {
         for (ch = !cpl_in_use; ch <= s->channels; ch++)
             s->fast_gain[ch] = ff_ac3_fast_gain_tab[4];
     }
 
     /* E-AC-3 to AC-3 converter SNR offset */
     if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT && get_bits1(gbc)) {
         skip_bits(gbc, 10); // skip converter snr offset
     }
 

     /* coupling leak information */

     if (cpl_in_use) {

         if (s->first_cpl_leak || get_bits1(gbc)) {
             int fl = get_bits(gbc, 3);
             int sl = get_bits(gbc, 3);
             /* run last 2 bit allocation stages for coupling channel if
                coupling leak changes */

             if (blk && (fl != s->bit_alloc_params.cpl_fast_leak ||
                 sl != s->bit_alloc_params.cpl_slow_leak)) {

                 bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);

             }
             s->bit_alloc_params.cpl_fast_leak = fl;
             s->bit_alloc_params.cpl_slow_leak = sl;
         } else if (!s->eac3 && !blk) {

             av_log(s->avctx, AV_LOG_ERROR, "new coupling leak info must "
                    "be present in block 0\n");

             return AVERROR_INVALIDDATA;

         }

         s->first_cpl_leak = 0;

     }

     /* delta bit allocation information */

     if (s->dba_syntax && get_bits1(gbc)) {

         /* delta bit allocation exists (strategy) */

         for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {

             s->dba_mode[ch] = get_bits(gbc, 2);
             if (s->dba_mode[ch] == DBA_RESERVED) {
                 av_log(s->avctx, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");

                 return AVERROR_INVALIDDATA;

             }

             bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);

         }

         /* channel delta offset, len and bit allocation */

         for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {

             if (s->dba_mode[ch] == DBA_NEW) {

                 s->dba_nsegs[ch] = get_bits(gbc, 3) + 1;
                 for (seg = 0; seg < s->dba_nsegs[ch]; seg++) {

                     s->dba_offsets[ch][seg] = get_bits(gbc, 5);
                     s->dba_lengths[ch][seg] = get_bits(gbc, 4);

                     s->dba_values[ch][seg]  = get_bits(gbc, 3);

                 }

                 /* run last 2 bit allocation stages if new dba values */
                 bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);

             }

         }

     } else if (blk == 0) {
         for (ch = 0; ch <= s->channels; ch++) {

             s->dba_mode[ch] = DBA_NONE;

         }

     }

     /* Bit allocation */

     for (ch = !cpl_in_use; ch <= s->channels; ch++) {
         if (bit_alloc_stages[ch] > 2) {

             /* Exponent mapping into PSD and PSD integration */

             ff_ac3_bit_alloc_calc_psd(s->dexps[ch],
                                       s->start_freq[ch], s->end_freq[ch],
                                       s->psd[ch], s->band_psd[ch]);

         }

         if (bit_alloc_stages[ch] > 1) {

             /* Compute excitation function, Compute masking curve, and
                Apply delta bit allocation */

             if (ff_ac3_bit_alloc_calc_mask(&s->bit_alloc_params, s->band_psd[ch],

                                            s->start_freq[ch],  s->end_freq[ch],
                                            s->fast_gain[ch],   (ch == s->lfe_ch),
                                            s->dba_mode[ch],    s->dba_nsegs[ch],

                                            s->dba_offsets[ch], s->dba_lengths[ch],

                                            s->dba_values[ch],  s->mask[ch])) {

                 av_log(s->avctx, AV_LOG_ERROR, "error in bit allocation\n");

                 return AVERROR_INVALIDDATA;

             }

         }

         if (bit_alloc_stages[ch] > 0) {

             /* Compute bit allocation */

             const uint8_t *bap_tab = s->channel_uses_aht[ch] ?
                                      ff_eac3_hebap_tab : ff_ac3_bap_tab;

             s->ac3dsp.bit_alloc_calc_bap(s->mask[ch], s->psd[ch],

                                       s->start_freq[ch], s->end_freq[ch],
                                       s->snr_offset[ch],
                                       s->bit_alloc_params.floor,

                                       bap_tab, s->bap[ch]);

         }

     }

     /* unused dummy data */

     if (s->skip_syntax && get_bits1(gbc)) {

         int skipl = get_bits(gbc, 9);

         while (skipl--)

             skip_bits(gbc, 8);

     }

     /* unpack the transform coefficients

        this also uncouples channels if coupling is in use. */

     decode_transform_coeffs(s, blk);

     /* TODO: generate enhanced coupling coordinates and uncouple */
 

     /* recover coefficients if rematrixing is in use */

     if (s->channel_mode == AC3_CHMODE_STEREO)

         do_rematrixing(s);

     /* apply scaling to coefficients (headroom, dynrng) */

     for (ch = 1; ch <= s->channels; ch++) {

         int audio_channel = 0;

         INTFLOAT gain;

         if (s->channel_mode == AC3_CHMODE_DUALMONO)
             audio_channel = 2-ch;
         if (s->heavy_compression && s->compression_exists[audio_channel])
             gain = s->heavy_dynamic_range[audio_channel];
         else
             gain = s->dynamic_range[audio_channel];
 

 #if USE_FIXED

         scale_coefs(s->transform_coeffs[ch], s->fixed_coeffs[ch], gain, 256);
 #else

         if (s->target_level != 0)
           gain = gain * s->level_gain[audio_channel];

         gain *= 1.0 / 4194304.0f;

         s->fmt_conv.int32_to_float_fmul_scalar(s->transform_coeffs[ch],
                                                s->fixed_coeffs[ch], gain, 256);

 #endif

     }

     /* apply spectral extension to high frequency bins */

     if (s->spx_in_use && CONFIG_EAC3_DECODER) {

         ff_eac3_apply_spectral_extension(s);
     }
 

     /* downmix and MDCT. order depends on whether block switching is used for
        any channel in this block. this is because coefficients for the long
        and short transforms cannot be mixed. */
     downmix_output = s->channels != s->out_channels &&
                      !((s->output_mode & AC3_OUTPUT_LFEON) &&
                      s->fbw_channels == s->out_channels);

     if (different_transforms) {

         /* the delay samples have already been downmixed, so we upmix the delay
            samples in order to reconstruct all channels before downmixing. */

         if (s->downmixed) {

             s->downmixed = 0;
             ac3_upmix_delay(s);
         }
 
         do_imdct(s, s->channels);
 

         if (downmix_output) {

 #if USE_FIXED

             ac3_downmix_c_fixed16(s->outptr, s->downmix_coeffs,
                               s->out_channels, s->fbw_channels, 256);
 #else

             s->ac3dsp.downmix(s->outptr, s->downmix_coeffs,

                               s->out_channels, s->fbw_channels, 256);

 #endif

         }
     } else {

         if (downmix_output) {

             s->ac3dsp.AC3_RENAME(downmix)(s->xcfptr + 1, s->downmix_coeffs,
                                           s->out_channels, s->fbw_channels, 256);

         }
 

         if (downmix_output && !s->downmixed) {

             s->downmixed = 1;

             s->ac3dsp.AC3_RENAME(downmix)(s->dlyptr, s->downmix_coeffs,
                                           s->out_channels, s->fbw_channels, 128);

         }

         do_imdct(s, s->out_channels);

     }
 

     return 0;

 }
 

 /**
  * Decode a single AC-3 frame.

  */

 static int ac3_decode_frame(AVCodecContext * avctx, void *data,
                             int *got_frame_ptr, AVPacket *avpkt)

 {

     AVFrame *frame     = data;

     const uint8_t *buf = avpkt->data;
     int buf_size = avpkt->size;

     AC3DecodeContext *s = avctx->priv_data;

     int blk, ch, err, ret;

     const uint8_t *channel_map;

     const SHORTFLOAT *output[AC3_MAX_CHANNELS];

     enum AVMatrixEncoding matrix_encoding;

     AVDownmixInfo *downmix_info;

     /* copy input buffer to decoder context to avoid reading past the end
        of the buffer, which can be caused by a damaged input stream. */

     if (buf_size >= 2 && AV_RB16(buf) == 0x770B) {
         // seems to be byte-swapped AC-3
         int cnt = FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE) >> 1;

         s->bdsp.bswap16_buf((uint16_t *) s->input_buffer,
                             (const uint16_t *) buf, cnt);

     } else

         memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE));

     buf = s->input_buffer;
     /* initialize the GetBitContext with the start of valid AC-3 Frame */

     init_get_bits(&s->gbc, buf, buf_size * 8);

     /* parse the syncinfo */

     err = parse_frame_header(s);

     if (err) {

         switch (err) {
         case AAC_AC3_PARSE_ERROR_SYNC:
             av_log(avctx, AV_LOG_ERROR, "frame sync error\n");

             return AVERROR_INVALIDDATA;

         case AAC_AC3_PARSE_ERROR_BSID:
             av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n");
             break;
         case AAC_AC3_PARSE_ERROR_SAMPLE_RATE:
             av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
             break;
         case AAC_AC3_PARSE_ERROR_FRAME_SIZE:
             av_log(avctx, AV_LOG_ERROR, "invalid frame size\n");
             break;
         case AAC_AC3_PARSE_ERROR_FRAME_TYPE:
             /* skip frame if CRC is ok. otherwise use error concealment. */
             /* TODO: add support for substreams and dependent frames */
             if (s->frame_type == EAC3_FRAME_TYPE_DEPENDENT || s->substreamid) {

                 av_log(avctx, AV_LOG_WARNING, "unsupported frame type : "

                        "skipping frame\n");
                 *got_frame_ptr = 0;

                 return buf_size;

             } else {
                 av_log(avctx, AV_LOG_ERROR, "invalid frame type\n");
             }
             break;

         case AAC_AC3_PARSE_ERROR_CRC:
         case AAC_AC3_PARSE_ERROR_CHANNEL_CFG:

             break;

         default: // Normal AVERROR do not try to recover.
             *got_frame_ptr = 0;
             return err;

         }

     } else {
         /* check that reported frame size fits in input buffer */
         if (s->frame_size > buf_size) {
             av_log(avctx, AV_LOG_ERROR, "incomplete frame\n");
             err = AAC_AC3_PARSE_ERROR_FRAME_SIZE;

         } else if (avctx->err_recognition & (AV_EF_CRCCHECK|AV_EF_CAREFUL)) {

             /* check for crc mismatch */

             if (av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, &buf[2],
                        s->frame_size - 2)) {

                 av_log(avctx, AV_LOG_ERROR, "frame CRC mismatch\n");

                 if (avctx->err_recognition & AV_EF_EXPLODE)
                     return AVERROR_INVALIDDATA;

                 err = AAC_AC3_PARSE_ERROR_CRC;
             }
         }

     }

     /* if frame is ok, set audio parameters */
     if (!err) {

         avctx->sample_rate = s->sample_rate;

         avctx->bit_rate    = s->bit_rate;

     }

     /* channel config */
     if (!err || (s->channels && s->out_channels != s->channels)) {

         s->out_channels = s->channels;

         s->output_mode  = s->channel_mode;
         if (s->lfe_on)

             s->output_mode |= AC3_OUTPUT_LFEON;

         if (s->channels > 1 &&
             avctx->request_channel_layout == AV_CH_LAYOUT_MONO) {
             s->out_channels = 1;
             s->output_mode  = AC3_CHMODE_MONO;
         } else if (s->channels > 2 &&
                    avctx->request_channel_layout == AV_CH_LAYOUT_STEREO) {
             s->out_channels = 2;
             s->output_mode  = AC3_CHMODE_STEREO;

         }

         s->loro_center_mix_level   = gain_levels[s->  center_mix_level];
         s->loro_surround_mix_level = gain_levels[s->surround_mix_level];

         s->ltrt_center_mix_level   = LEVEL_MINUS_3DB;
         s->ltrt_surround_mix_level = LEVEL_MINUS_3DB;

         /* set downmixing coefficients if needed */

         if (s->channels != s->out_channels && !((s->output_mode & AC3_OUTPUT_LFEON) &&

                 s->fbw_channels == s->out_channels)) {
             set_downmix_coeffs(s);
         }

     } else if (!s->channels) {
         av_log(avctx, AV_LOG_ERROR, "unable to determine channel mode\n");

         return AVERROR_INVALIDDATA;
     }

     avctx->channels = s->out_channels;

     avctx->channel_layout = avpriv_ac3_channel_layout_tab[s->output_mode & ~AC3_OUTPUT_LFEON];
     if (s->output_mode & AC3_OUTPUT_LFEON)
         avctx->channel_layout |= AV_CH_LOW_FREQUENCY;

     /* set audio service type based on bitstream mode for AC-3 */
     avctx->audio_service_type = s->bitstream_mode;
     if (s->bitstream_mode == 0x7 && s->channels > 1)
         avctx->audio_service_type = AV_AUDIO_SERVICE_TYPE_KARAOKE;

     /* get output buffer */

     frame->nb_samples = s->num_blocks * AC3_BLOCK_SIZE;

     if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)

         return ret;
 

     /* decode the audio blocks */

     channel_map = ff_ac3_dec_channel_map[s->output_mode & ~AC3_OUTPUT_LFEON][s->lfe_on];

     for (ch = 0; ch < AC3_MAX_CHANNELS; ch++) {
         output[ch] = s->output[ch];

         s->outptr[ch] = s->output[ch];

     }

     for (ch = 0; ch < s->channels; ch++) {
         if (ch < s->out_channels)

             s->outptr[channel_map[ch]] = (SHORTFLOAT *)frame->data[ch];

     }

     for (blk = 0; blk < s->num_blocks; blk++) {

         if (!err && decode_audio_block(s, blk)) {
             av_log(avctx, AV_LOG_ERROR, "error decoding the audio block\n");

             err = 1;

         }

         if (err)
             for (ch = 0; ch < s->out_channels; ch++)

                 memcpy(((SHORTFLOAT*)frame->data[ch]) + AC3_BLOCK_SIZE*blk, output[ch], AC3_BLOCK_SIZE*sizeof(SHORTFLOAT));

         for (ch = 0; ch < s->out_channels; ch++)

             output[ch] = s->outptr[channel_map[ch]];

         for (ch = 0; ch < s->out_channels; ch++) {

             if (!ch || channel_map[ch])
                 s->outptr[channel_map[ch]] += AC3_BLOCK_SIZE;

         }

     }

     av_frame_set_decode_error_flags(frame, err ? FF_DECODE_ERROR_INVALID_BITSTREAM : 0);

     /* keep last block for error concealment in next frame */
     for (ch = 0; ch < s->out_channels; ch++)

         memcpy(s->output[ch], output[ch], AC3_BLOCK_SIZE*sizeof(SHORTFLOAT));

     /*
      * AVMatrixEncoding
      *
      * Check whether the input layout is compatible, and make sure we're not
      * downmixing (else the matrix encoding is no longer applicable).
      */
     matrix_encoding = AV_MATRIX_ENCODING_NONE;
     if (s->channel_mode == AC3_CHMODE_STEREO &&
         s->channel_mode == (s->output_mode & ~AC3_OUTPUT_LFEON)) {
         if (s->dolby_surround_mode == AC3_DSURMOD_ON)
             matrix_encoding = AV_MATRIX_ENCODING_DOLBY;
         else if (s->dolby_headphone_mode == AC3_DHEADPHONMOD_ON)
             matrix_encoding = AV_MATRIX_ENCODING_DOLBYHEADPHONE;
     } else if (s->channel_mode >= AC3_CHMODE_2F2R &&
                s->channel_mode == (s->output_mode & ~AC3_OUTPUT_LFEON)) {
         switch (s->dolby_surround_ex_mode) {
         case AC3_DSUREXMOD_ON: // EX or PLIIx
             matrix_encoding = AV_MATRIX_ENCODING_DOLBYEX;
             break;
         case AC3_DSUREXMOD_PLIIZ:
             matrix_encoding = AV_MATRIX_ENCODING_DPLIIZ;
             break;
         default: // not indicated or off
             break;
         }
     }
     if ((ret = ff_side_data_update_matrix_encoding(frame, matrix_encoding)) < 0)
         return ret;
 

     /* AVDownmixInfo */
     if ((downmix_info = av_downmix_info_update_side_data(frame))) {
         switch (s->preferred_downmix) {
         case AC3_DMIXMOD_LTRT:
             downmix_info->preferred_downmix_type = AV_DOWNMIX_TYPE_LTRT;
             break;
         case AC3_DMIXMOD_LORO:
             downmix_info->preferred_downmix_type = AV_DOWNMIX_TYPE_LORO;
             break;
         case AC3_DMIXMOD_DPLII:
             downmix_info->preferred_downmix_type = AV_DOWNMIX_TYPE_DPLII;
             break;
         default:
             downmix_info->preferred_downmix_type = AV_DOWNMIX_TYPE_UNKNOWN;
             break;
         }
         downmix_info->center_mix_level        = gain_levels[s->       center_mix_level];
         downmix_info->center_mix_level_ltrt   = gain_levels[s->  center_mix_level_ltrt];
         downmix_info->surround_mix_level      = gain_levels[s->     surround_mix_level];
         downmix_info->surround_mix_level_ltrt = gain_levels[s->surround_mix_level_ltrt];
         if (s->lfe_mix_level_exists)
             downmix_info->lfe_mix_level       = gain_levels_lfe[s->lfe_mix_level];
         else
             downmix_info->lfe_mix_level       = 0.0; // -inf dB
     } else
         return AVERROR(ENOMEM);
 

     *got_frame_ptr = 1;

     return FFMIN(buf_size, s->frame_size);

 }

 /**
  * Uninitialize the AC-3 decoder.

  */

 static av_cold int ac3_decode_end(AVCodecContext *avctx)

 {

     AC3DecodeContext *s = avctx->priv_data;

     ff_mdct_end(&s->imdct_512);
     ff_mdct_end(&s->imdct_256);

     av_freep(&s->fdsp);

     return 0;
 }
 

 #define OFFSET(x) offsetof(AC3DecodeContext, x)
 #define PAR (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)