third_party_ffmpeg/libavcodec/ac3dec.c

/*
 * AC-3 Audio Decoder
 * This code is developed as part of Google Summer of Code 2006 Program.
 *
 * Copyright (c) 2006 Kartikey Mahendra BHATT (bhattkm at gmail dot com).
 *
 * For exponent decoding the code is inspired by the code in liba52 by
 * Michel Lespinasse and Aaron Holtzman.
 * http://liba52.sourceforge.net
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 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
 * General Public License for more details.
 *
 * You should have received a copy of the GNU 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>

#define ALT_BITSTREAM_READER

#include "avcodec.h"
#include "ac3.h"
#include "ac3tab.h"
#include "bitstream.h"
#include "dsputil.h"
#include "random.h"

static const int nfchans_tbl[8] = { 2, 1, 2, 3, 3, 4, 4, 5 };

/* table for exponent to scale_factor mapping
 * scale_factor[i] = 2 ^ -(i + 15)
 */
static float scale_factors[25];

/** table for grouping exponents */
static uint8_t exp_ungroup_tbl[128][3];

static int16_t l3_quantizers_1[32];
static int16_t l3_quantizers_2[32];
static int16_t l3_quantizers_3[32];

static int16_t l5_quantizers_1[128];
static int16_t l5_quantizers_2[128];
static int16_t l5_quantizers_3[128];

static int16_t l7_quantizers[7];

static int16_t l11_quantizers_1[128];
static int16_t l11_quantizers_2[128];

static int16_t l15_quantizers[15];

static const uint8_t qntztab[16] = { 0, 5, 7, 3, 7, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16 };

/* Adjustmens in dB gain */
#define LEVEL_MINUS_3DB         0.7071067811865476
#define LEVEL_MINUS_4POINT5DB   0.5946035575013605
#define LEVEL_MINUS_6DB         0.5000000000000000
#define LEVEL_PLUS_3DB          1.4142135623730951
#define LEVEL_PLUS_6DB          2.0000000000000000
#define LEVEL_ZERO              0.0000000000000000

static const float clevs[4] = { LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB,
    LEVEL_MINUS_6DB, LEVEL_MINUS_4POINT5DB };

static const float slevs[4] = { LEVEL_MINUS_3DB, LEVEL_MINUS_6DB, LEVEL_ZERO, LEVEL_MINUS_6DB };

#define BLOCK_SIZE    256

/* Output and input configurations. */
#define AC3_OUTPUT_UNMODIFIED   0x01
#define AC3_OUTPUT_MONO         0x02
#define AC3_OUTPUT_STEREO       0x04
#define AC3_OUTPUT_DOLBY        0x08
#define AC3_OUTPUT_LFEON        0x10

typedef struct {
    uint16_t crc1;
    uint8_t  fscod;

    uint8_t  acmod;
    uint8_t  cmixlev;
    uint8_t  surmixlev;
    uint8_t  dsurmod;

    uint8_t  blksw;
    uint8_t  dithflag;
    uint8_t  cplinu;
    uint8_t  chincpl;
    uint8_t  phsflginu;
    uint8_t  cplbegf;
    uint8_t  cplendf;
    uint8_t  cplcoe;
    uint32_t cplbndstrc;
    uint8_t  rematstr;
    uint8_t  rematflg;
    uint8_t  cplexpstr;
    uint8_t  lfeexpstr;
    uint8_t  chexpstr[5];
    uint8_t  sdcycod;
    uint8_t  fdcycod;
    uint8_t  sgaincod;
    uint8_t  dbpbcod;
    uint8_t  floorcod;
    uint8_t  csnroffst;
    uint8_t  cplfsnroffst;
    uint8_t  cplfgaincod;
    uint8_t  fsnroffst[5];
    uint8_t  fgaincod[5];
    uint8_t  lfefsnroffst;
    uint8_t  lfefgaincod;
    uint8_t  cplfleak;
    uint8_t  cplsleak;
    uint8_t  cpldeltbae;
    uint8_t  deltbae[5];
    uint8_t  cpldeltnseg;
    uint8_t  cpldeltoffst[8];
    uint8_t  cpldeltlen[8];
    uint8_t  cpldeltba[8];
    uint8_t  deltnseg[5];
    uint8_t  deltoffst[5][8];
    uint8_t  deltlen[5][8];
    uint8_t  deltba[5][8];

    /* Derived Attributes. */
    int      sampling_rate;
    int      bit_rate;
    int      frame_size;

    int      nfchans;           //number of channels
    int      lfeon;             //lfe channel in use

    float    dynrng;            //dynamic range gain
    float    dynrng2;           //dynamic range gain for 1+1 mode
    float    chcoeffs[6];       //normalized channel coefficients
    float    cplco[5][18];      //coupling coordinates
    int      ncplbnd;           //number of coupling bands
    int      ncplsubnd;         //number of coupling sub bands
    int      cplstrtmant;       //coupling start mantissa
    int      cplendmant;        //coupling end mantissa
    int      endmant[5];        //channel end mantissas
    AC3BitAllocParameters bit_alloc_params; ///< bit allocation parameters

    uint8_t  dcplexps[256];     //decoded coupling exponents
    uint8_t  dexps[5][256];     //decoded fbw channel exponents
    uint8_t  dlfeexps[256];     //decoded lfe channel exponents
    uint8_t  cplbap[256];       //coupling bit allocation pointers
    uint8_t  bap[5][256];       //fbw channel bit allocation pointers
    uint8_t  lfebap[256];       //lfe channel bit allocation pointers

    int      blkoutput;         //output configuration for block

    DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][BLOCK_SIZE]);  //transform coefficients

    /* For IMDCT. */
    MDCTContext imdct_512;  //for 512 sample imdct transform
    MDCTContext imdct_256;  //for 256 sample imdct transform
    DSPContext  dsp;        //for optimization

    DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS][BLOCK_SIZE]);    //output after imdct transform and windowing
    DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS][BLOCK_SIZE]);     //delay - added to the next block
    DECLARE_ALIGNED_16(float, tmp_imdct[BLOCK_SIZE]);               //temporary storage for imdct transform
    DECLARE_ALIGNED_16(float, tmp_output[BLOCK_SIZE * 2]);          //temporary storage for output before windowing
    DECLARE_ALIGNED_16(float, window[BLOCK_SIZE]);                  //window coefficients

    /* Miscellaneous. */
    GetBitContext gb;
    AVRandomState dith_state;   //for dither generation
} AC3DecodeContext;

/*********** BEGIN INIT HELPER FUNCTIONS ***********/
/**
 * Generate a Kaiser-Bessel Derived Window.
 */
static void ac3_window_init(float *window)
{
   int i, j;
   double sum = 0.0, bessel, tmp;
   double local_window[256];
   double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);

   for (i = 0; i < 256; i++) {
       tmp = i * (256 - i) * alpha2;
       bessel = 1.0;
       for (j = 100; j > 0; j--) /* defaul to 100 iterations */
           bessel = bessel * tmp / (j * j) + 1;
       sum += bessel;
       local_window[i] = sum;
   }

   sum++;
   for (i = 0; i < 256; i++)
       window[i] = sqrt(local_window[i] / sum);
}

/*
 * Generate quantizer tables.
 */
static void generate_quantizers_table(int16_t quantizers[], int level, int length)
{
    int i;

    for (i = 0; i < length; i++)
        quantizers[i] = ((2 * i - level + 1) << 15) / level;
}

static void generate_quantizers_table_1(int16_t quantizers[], int level, int length1, int length2, int size)
{
    int i, j;
    int16_t v;

    for (i = 0; i < length1; i++) {
        v = ((2 * i - level + 1) << 15) / level;
        for (j = 0; j < length2; j++)
            quantizers[i * length2 + j] = v;
    }

    for (i = length1 * length2; i < size; i++)
        quantizers[i] = 0;
}

static void generate_quantizers_table_2(int16_t quantizers[], int level, int length1, int length2, int size)
{
    int i, j;
    int16_t v;

    for (i = 0; i < length1; i++) {
        v = ((2 * (i % level) - level + 1) << 15) / level;
        for (j = 0; j < length2; j++)
            quantizers[i * length2 + j] = v;
    }

    for (i = length1 * length2; i < size; i++)
        quantizers[i] = 0;

}

static void generate_quantizers_table_3(int16_t quantizers[], int level, int length1, int length2, int size)
{
    int i, j;

    for (i = 0; i < length1; i++)
        for (j = 0; j < length2; j++)
            quantizers[i * length2 + j] = ((2 * (j % level) - level + 1) << 15) / level;

    for (i = length1 * length2; i < size; i++)
        quantizers[i] = 0;
}

/*
 * Initialize tables at runtime.
 */
static void ac3_tables_init(void)
{
    int i;

    /* Quantizer ungrouping tables. */
    // for level-3 quantizers
    generate_quantizers_table_1(l3_quantizers_1, 3, 3, 9, 32);
    generate_quantizers_table_2(l3_quantizers_2, 3, 9, 3, 32);
    generate_quantizers_table_3(l3_quantizers_3, 3, 9, 3, 32);

    //for level-5 quantizers
    generate_quantizers_table_1(l5_quantizers_1, 5, 5, 25, 128);
    generate_quantizers_table_2(l5_quantizers_2, 5, 25, 5, 128);
    generate_quantizers_table_3(l5_quantizers_3, 5, 25, 5, 128);

    //for level-7 quantizers
    generate_quantizers_table(l7_quantizers, 7, 7);

    //for level-4 quantizers
    generate_quantizers_table_2(l11_quantizers_1, 11, 11, 11, 128);
    generate_quantizers_table_3(l11_quantizers_2, 11, 11, 11, 128);

    //for level-15 quantizers
    generate_quantizers_table(l15_quantizers, 15, 15);
    /* End Quantizer ungrouping tables. */

    //generate scale factors
    for (i = 0; i < 25; i++)
        scale_factors[i] = pow(2.0, -(i + 15));

    /* generate exponent tables
       reference: Section 7.1.3 Exponent Decoding */
    for(i=0; i<128; i++) {
        exp_ungroup_tbl[i][0] =  i / 25;
        exp_ungroup_tbl[i][1] = (i % 25) / 5;
        exp_ungroup_tbl[i][2] = (i % 25) % 5;
    }
}


static int ac3_decode_init(AVCodecContext *avctx)
{
    AC3DecodeContext *ctx = avctx->priv_data;

    ac3_common_init();
    ac3_tables_init();
    ff_mdct_init(&ctx->imdct_256, 8, 1);
    ff_mdct_init(&ctx->imdct_512, 9, 1);
    ac3_window_init(ctx->window);
    dsputil_init(&ctx->dsp, avctx);
    av_init_random(0, &ctx->dith_state);

    return 0;
}
/*********** END INIT FUNCTIONS ***********/

/* Synchronize to ac3 bitstream.
 * This function searches for the syncword '0xb77'.
 *
 * @param buf Pointer to "probable" ac3 bitstream buffer
 * @param buf_size Size of buffer
 * @return Returns the position where syncword is found, -1 if no syncword is found
 */
static int ac3_synchronize(uint8_t *buf, int buf_size)
{
    int i;

    for (i = 0; i < buf_size - 1; i++)
        if (buf[i] == 0x0b && buf[i + 1] == 0x77)
            return i;

    return -1;
}

/* Parse the 'sync_info' from the ac3 bitstream.
 * This function extracts the sync_info from ac3 bitstream.
 * GetBitContext within AC3DecodeContext must point to
 * start of the synchronized ac3 bitstream.
 *
 * @param ctx  AC3DecodeContext
 * @return Returns framesize, returns 0 if fscod, frmsizecod or bsid is not valid
 */
static int ac3_parse_sync_info(AC3DecodeContext *ctx)
{
    GetBitContext *gb = &ctx->gb;
    int frmsizecod, bsid;

    skip_bits(gb, 16); //skip the sync_word, sync_info->sync_word = get_bits(gb, 16);
    ctx->crc1 = get_bits(gb, 16);
    ctx->fscod = get_bits(gb, 2);
    if (ctx->fscod == 0x03)
        return 0;
    frmsizecod = get_bits(gb, 6);
    if (frmsizecod >= 38)
        return 0;
    ctx->sampling_rate = ff_ac3_freqs[ctx->fscod];
    ctx->bit_rate = ff_ac3_bitratetab[frmsizecod >> 1];

    /* we include it here in order to determine validity of ac3 frame */
    bsid = get_bits(gb, 5);
    if (bsid > 0x08)
        return 0;
    skip_bits(gb, 3); //skip the bsmod, bsi->bsmod = get_bits(gb, 3);

    switch (ctx->fscod) {
        case 0x00:
            ctx->frame_size = 4 * ctx->bit_rate;
            return ctx->frame_size;
        case 0x01:
            ctx->frame_size = 2 * (320 * ctx->bit_rate / 147 + (frmsizecod & 1));
            return ctx->frame_size;
        case 0x02:
            ctx->frame_size =  6 * ctx->bit_rate;
            return ctx->frame_size;
    }

    /* never reached */
    return 0;
}

/* Parse bsi from ac3 bitstream.
 * This function extracts the bitstream information (bsi) from ac3 bitstream.
 *
 * @param ctx AC3DecodeContext after processed by ac3_parse_sync_info
 */
static void ac3_parse_bsi(AC3DecodeContext *ctx)
{
    GetBitContext *gb = &ctx->gb;
    int i;

    ctx->cmixlev = 0;
    ctx->surmixlev = 0;
    ctx->dsurmod = 0;
    ctx->nfchans = 0;
    ctx->cpldeltbae = DBA_NONE;
    ctx->cpldeltnseg = 0;
    for (i = 0; i < 5; i++) {
        ctx->deltbae[i] = DBA_NONE;
        ctx->deltnseg[i] = 0;
    }
    ctx->dynrng = 1.0;
    ctx->dynrng2 = 1.0;

    ctx->acmod = get_bits(gb, 3);
    ctx->nfchans = nfchans_tbl[ctx->acmod];

    if (ctx->acmod & 0x01 && ctx->acmod != 0x01)
        ctx->cmixlev = get_bits(gb, 2);
    if (ctx->acmod & 0x04)
        ctx->surmixlev = get_bits(gb, 2);
    if (ctx->acmod == 0x02)
        ctx->dsurmod = get_bits(gb, 2);

    ctx->lfeon = get_bits1(gb);

    i = !(ctx->acmod);
    do {
        skip_bits(gb, 5); //skip dialog normalization
        if (get_bits1(gb))
            skip_bits(gb, 8); //skip compression
        if (get_bits1(gb))
            skip_bits(gb, 8); //skip language code
        if (get_bits1(gb))
            skip_bits(gb, 7); //skip audio production information
    } while (i--);

    skip_bits(gb, 2); //skip copyright bit and original bitstream bit

    if (get_bits1(gb))
        skip_bits(gb, 14); //skip timecode1
    if (get_bits1(gb))
        skip_bits(gb, 14); //skip timecode2

    if (get_bits1(gb)) {
        i = get_bits(gb, 6); //additional bsi length
        do {
            skip_bits(gb, 8);
        } while(i--);
    }
}

/**
 * Decodes the grouped exponents.
 * This function decodes the coded exponents according to exponent strategy
 * and stores them in the decoded exponents buffer.
 *
 * @param[in]  gb      GetBitContext which points to start of coded exponents
 * @param[in]  expstr  Exponent coding strategy
 * @param[in]  ngrps   Number of grouped exponents
 * @param[in]  absexp  Absolute exponent or DC exponent
 * @param[out] dexps   Decoded exponents are stored in dexps
 */
static void decode_exponents(GetBitContext *gb, int expstr, int ngrps,
                             uint8_t absexp, uint8_t *dexps)
{
    int i, j, grp, grpsize;
    int dexp[256];
    int expacc, prevexp;

    /* unpack groups */
    grpsize = expstr + (expstr == EXP_D45);
    for(grp=0,i=0; grp<ngrps; grp++) {
        expacc = get_bits(gb, 7);
        dexp[i++] = exp_ungroup_tbl[expacc][0];
        dexp[i++] = exp_ungroup_tbl[expacc][1];
        dexp[i++] = exp_ungroup_tbl[expacc][2];
    }

    /* convert to absolute exps and expand groups */
    prevexp = absexp;
    for(i=0; i<ngrps*3; i++) {
        prevexp = av_clip(prevexp + dexp[i]-2, 0, 24);
        for(j=0; j<grpsize; j++) {
            dexps[(i*grpsize)+j] = prevexp;
        }
    }
}

/* Performs bit allocation.
 * This function performs bit allocation for the requested chanenl.
 */
static void do_bit_allocation(AC3DecodeContext *ctx, int chnl)
{
    int fgain, snroffset;

    if (chnl == 5) {
        fgain = ff_fgaintab[ctx->cplfgaincod];
        snroffset = (((ctx->csnroffst - 15) << 4) + ctx->cplfsnroffst) << 2;
        ac3_parametric_bit_allocation(&ctx->bit_alloc_params, ctx->cplbap,
                                      ctx->dcplexps, ctx->cplstrtmant,
                                      ctx->cplendmant, snroffset, fgain, 0,
                                      ctx->cpldeltbae, ctx->cpldeltnseg,
                                      ctx->cpldeltoffst, ctx->cpldeltlen,
                                      ctx->cpldeltba);
    }
    else if (chnl == 6) {
        fgain = ff_fgaintab[ctx->lfefgaincod];
        snroffset = (((ctx->csnroffst - 15) << 4) + ctx->lfefsnroffst) << 2;
        ac3_parametric_bit_allocation(&ctx->bit_alloc_params, ctx->lfebap,
                                      ctx->dlfeexps, 0, 7, snroffset, fgain, 1,
                                      DBA_NONE, 0, NULL, NULL, NULL);
    }
    else {
        fgain = ff_fgaintab[ctx->fgaincod[chnl]];
        snroffset = (((ctx->csnroffst - 15) << 4) + ctx->fsnroffst[chnl]) << 2;
        ac3_parametric_bit_allocation(&ctx->bit_alloc_params, ctx->bap[chnl],
                                      ctx->dexps[chnl], 0, ctx->endmant[chnl],
                                      snroffset, fgain, 0, ctx->deltbae[chnl],
                                      ctx->deltnseg[chnl], ctx->deltoffst[chnl],
                                      ctx->deltlen[chnl], ctx->deltba[chnl]);
    }
}

typedef struct { /* grouped mantissas for 3-level 5-leve and 11-level quantization */
    int16_t l3_quantizers[3];
    int16_t l5_quantizers[3];
    int16_t l11_quantizers[2];
    int l3ptr;
    int l5ptr;
    int l11ptr;
} mant_groups;

#define TRANSFORM_COEFF(tc, m, e, f) (tc) = (m) * (f)[(e)]

/* Get the transform coefficients for coupling channel and uncouple channels.
 * The coupling transform coefficients starts at the the cplstrtmant, which is
 * equal to endmant[ch] for fbw channels. Hence we can uncouple channels before
 * getting transform coefficients for the channel.
 */
static int get_transform_coeffs_cpling(AC3DecodeContext *ctx, mant_groups *m)
{
    GetBitContext *gb = &ctx->gb;
    int ch, start, end, cplbndstrc, bnd, gcode, tbap;
    float cplcos[5], cplcoeff;
    uint8_t *exps = ctx->dcplexps;
    uint8_t *bap = ctx->cplbap;

    cplbndstrc = ctx->cplbndstrc;
    start = ctx->cplstrtmant;
    bnd = 0;

    while (start < ctx->cplendmant) {
        end = start + 12;
        while (cplbndstrc & 1) {
            end += 12;
            cplbndstrc >>= 1;
        }
        cplbndstrc >>= 1;
        for (ch = 0; ch < ctx->nfchans; ch++)
            cplcos[ch] = ctx->chcoeffs[ch] * ctx->cplco[ch][bnd];
        bnd++;

        while (start < end) {
            tbap = bap[start];
            switch(tbap) {
                case 0:
                    for (ch = 0; ch < ctx->nfchans; ch++)
                        if (((ctx->chincpl) >> ch) & 1) {
                            if ((ctx->dithflag >> ch) & 1) {
                                TRANSFORM_COEFF(cplcoeff, av_random(&ctx->dith_state) & 0xFFFF, exps[start], scale_factors);
                                ctx->transform_coeffs[ch + 1][start] = cplcoeff * cplcos[ch] * LEVEL_MINUS_3DB;
                            } else
                                ctx->transform_coeffs[ch + 1][start] = 0;
                        }
                    start++;
                    continue;
                case 1:
                    if (m->l3ptr > 2) {
                        gcode = get_bits(gb, 5);
                        m->l3_quantizers[0] = l3_quantizers_1[gcode];
                        m->l3_quantizers[1] = l3_quantizers_2[gcode];
                        m->l3_quantizers[2] = l3_quantizers_3[gcode];
                        m->l3ptr = 0;
                    }
                    TRANSFORM_COEFF(cplcoeff, m->l3_quantizers[m->l3ptr++], exps[start], scale_factors);
                    break;

                case 2:
                    if (m->l5ptr > 2) {
                        gcode = get_bits(gb, 7);
                        m->l5_quantizers[0] = l5_quantizers_1[gcode];
                        m->l5_quantizers[1] = l5_quantizers_2[gcode];
                        m->l5_quantizers[2] = l5_quantizers_3[gcode];
                        m->l5ptr = 0;
                    }
                    TRANSFORM_COEFF(cplcoeff, m->l5_quantizers[m->l5ptr++], exps[start], scale_factors);
                    break;

                case 3:
                    TRANSFORM_COEFF(cplcoeff, l7_quantizers[get_bits(gb, 3)], exps[start], scale_factors);
                    break;

                case 4:
                    if (m->l11ptr > 1) {
                        gcode = get_bits(gb, 7);
                        m->l11_quantizers[0] = l11_quantizers_1[gcode];
                        m->l11_quantizers[1] = l11_quantizers_2[gcode];
                        m->l11ptr = 0;
                    }
                    TRANSFORM_COEFF(cplcoeff, m->l11_quantizers[m->l11ptr++], exps[start], scale_factors);
                    break;

                case 5:
                    TRANSFORM_COEFF(cplcoeff, l15_quantizers[get_bits(gb, 4)], exps[start], scale_factors);
                    break;

                default:
                    TRANSFORM_COEFF(cplcoeff, get_sbits(gb, qntztab[tbap]) << (16 - qntztab[tbap]),
                            exps[start], scale_factors);
            }
            for (ch = 0; ch < ctx->nfchans; ch++)
                if ((ctx->chincpl >> ch) & 1)
                    ctx->transform_coeffs[ch + 1][start] = cplcoeff * cplcos[ch];
            start++;
        }
    }

    return 0;
}

/* Get the transform coefficients for particular channel */
static int get_transform_coeffs_ch(AC3DecodeContext *ctx, int ch_index, mant_groups *m)
{
    GetBitContext *gb = &ctx->gb;
    int i, gcode, tbap, dithflag, end;
    uint8_t *exps;
    uint8_t *bap;
    float *coeffs;
    float factors[25];

    for (i = 0; i < 25; i++)
        factors[i] = scale_factors[i] * ctx->chcoeffs[ch_index];

    if (ch_index != -1) { /* fbw channels */
        dithflag = (ctx->dithflag >> ch_index) & 1;
        exps = ctx->dexps[ch_index];
        bap = ctx->bap[ch_index];
        coeffs = ctx->transform_coeffs[ch_index + 1];
        end = ctx->endmant[ch_index];
    } else if (ch_index == -1) {
        dithflag = 0;
        exps = ctx->dlfeexps;
        bap = ctx->lfebap;
        coeffs = ctx->transform_coeffs[0];
        end = 7;
    }


    for (i = 0; i < end; i++) {
        tbap = bap[i];
        switch (tbap) {
            case 0:
                if (!dithflag) {
                    coeffs[i] = 0;
                    continue;
                }
                else {
                    TRANSFORM_COEFF(coeffs[i], av_random(&ctx->dith_state) & 0xFFFF, exps[i], factors);
                    coeffs[i] *= LEVEL_MINUS_3DB;
                    continue;
                }

            case 1:
                if (m->l3ptr > 2) {
                    gcode = get_bits(gb, 5);
                    m->l3_quantizers[0] = l3_quantizers_1[gcode];
                    m->l3_quantizers[1] = l3_quantizers_2[gcode];
                    m->l3_quantizers[2] = l3_quantizers_3[gcode];
                    m->l3ptr = 0;
                }
                TRANSFORM_COEFF(coeffs[i], m->l3_quantizers[m->l3ptr++], exps[i], factors);
                continue;

            case 2:
                if (m->l5ptr > 2) {
                    gcode = get_bits(gb, 7);
                    m->l5_quantizers[0] = l5_quantizers_1[gcode];
                    m->l5_quantizers[1] = l5_quantizers_2[gcode];
                    m->l5_quantizers[2] = l5_quantizers_3[gcode];
                    m->l5ptr = 0;
                }
                TRANSFORM_COEFF(coeffs[i], m->l5_quantizers[m->l5ptr++], exps[i], factors);
                continue;

            case 3:
                TRANSFORM_COEFF(coeffs[i], l7_quantizers[get_bits(gb, 3)], exps[i], factors);
                continue;

            case 4:
                if (m->l11ptr > 1) {
                    gcode = get_bits(gb, 7);
                    m->l11_quantizers[0] = l11_quantizers_1[gcode];
                    m->l11_quantizers[1] = l11_quantizers_2[gcode];
                    m->l11ptr = 0;
                }
                TRANSFORM_COEFF(coeffs[i], m->l11_quantizers[m->l11ptr++], exps[i], factors);
                continue;

            case 5:
                TRANSFORM_COEFF(coeffs[i], l15_quantizers[get_bits(gb, 4)], exps[i], factors);
                continue;

            default:
                TRANSFORM_COEFF(coeffs[i], get_sbits(gb, qntztab[tbap]) << (16 - qntztab[tbap]), exps[i], factors);
                continue;
        }
    }

    return 0;
}

/* Get the transform coefficients.
 * This function extracts the tranform coefficients form the ac3 bitstream.
 * This function is called after bit allocation is performed.
 */
static int get_transform_coeffs(AC3DecodeContext * ctx)
{
    int i, end;
    int got_cplchan = 0;
    mant_groups m;

    m.l3ptr = m.l5ptr = m.l11ptr = 3;

    for (i = 0; i < ctx->nfchans; i++) {
        /* transform coefficients for individual channel */
        if (get_transform_coeffs_ch(ctx, i, &m))
            return -1;
        /* tranform coefficients for coupling channels */
        if ((ctx->chincpl >> i) & 1)  {
            if (!got_cplchan) {
                if (get_transform_coeffs_cpling(ctx, &m)) {
                    av_log(NULL, AV_LOG_ERROR, "error in decoupling channels\n");
                    return -1;
                }
                got_cplchan = 1;
            }
            end = ctx->cplendmant;
        } else
            end = ctx->endmant[i];
        do
            ctx->transform_coeffs[i + 1][end] = 0;
        while(++end < 256);
    }
    if (ctx->lfeon) {
        if (get_transform_coeffs_ch(ctx, -1, &m))
                return -1;
        for (i = 7; i < 256; i++) {
            ctx->transform_coeffs[0][i] = 0;
        }
    }

    return 0;
}

/* Rematrixing routines. */
static void do_rematrixing1(AC3DecodeContext *ctx, int start, int end)
{
    float tmp0, tmp1;

    while (start < end) {
        tmp0 = ctx->transform_coeffs[1][start];
        tmp1 = ctx->transform_coeffs[2][start];
        ctx->transform_coeffs[1][start] = tmp0 + tmp1;
        ctx->transform_coeffs[2][start] = tmp0 - tmp1;
        start++;
    }
}

static void do_rematrixing(AC3DecodeContext *ctx)
{
    int bnd1 = 13, bnd2 = 25, bnd3 = 37, bnd4 = 61;
    int end, bndend;

    end = FFMIN(ctx->endmant[0], ctx->endmant[1]);

    if (ctx->rematflg & 1)
        do_rematrixing1(ctx, bnd1, bnd2);

    if (ctx->rematflg & 2)
        do_rematrixing1(ctx, bnd2, bnd3);

    bndend = bnd4;
    if (bndend > end) {
        bndend = end;
        if (ctx->rematflg & 4)
            do_rematrixing1(ctx, bnd3, bndend);
    } else {
        if (ctx->rematflg & 4)
            do_rematrixing1(ctx, bnd3, bnd4);
        if (ctx->rematflg & 8)
            do_rematrixing1(ctx, bnd4, end);
    }
}

/* This function sets the normalized channel coefficients.
 * Transform coefficients are multipllied by the channel
 * coefficients to get normalized transform coefficients.
 */
static void get_downmix_coeffs(AC3DecodeContext *ctx)
{
    int from = ctx->acmod;
    int to = ctx->blkoutput;
    float clev = clevs[ctx->cmixlev];
    float slev = slevs[ctx->surmixlev];
    float nf = 1.0; //normalization factor for downmix coeffs
    int i;

    if (!ctx->acmod) {
        ctx->chcoeffs[0] = 2 * ctx->dynrng;
        ctx->chcoeffs[1] = 2 * ctx->dynrng2;
    } else {
        for (i = 0; i < ctx->nfchans; i++)
            ctx->chcoeffs[i] = 2 * ctx->dynrng;
    }

    if (to == AC3_OUTPUT_UNMODIFIED)
        return;

    switch (from) {
        case AC3_ACMOD_DUALMONO:
            switch (to) {
                case AC3_OUTPUT_MONO:
                case AC3_OUTPUT_STEREO: /* We Assume that sum of both mono channels is requested */
                    nf = 0.5;
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    break;
            }
            break;
        case AC3_ACMOD_MONO:
            switch (to) {
                case AC3_OUTPUT_STEREO:
                    nf = LEVEL_MINUS_3DB;
                    ctx->chcoeffs[0] *= nf;
                    break;
            }
            break;
        case AC3_ACMOD_STEREO:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    nf = LEVEL_MINUS_3DB;
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    break;
            }
            break;
        case AC3_ACMOD_3F:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    nf = LEVEL_MINUS_3DB / (1.0 + clev);
                    ctx->chcoeffs[0] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[2] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[1] *= ((nf * clev * LEVEL_MINUS_3DB) / 2.0);
                    break;
                case AC3_OUTPUT_STEREO:
                    nf = 1.0 / (1.0 + clev);
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[2] *= nf;
                    ctx->chcoeffs[1] *= (nf * clev);
                    break;
            }
            break;
        case AC3_ACMOD_2F1R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    nf = 2.0 * LEVEL_MINUS_3DB / (2.0 + slev);
                    ctx->chcoeffs[0] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[1] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[2] *= (nf * slev * LEVEL_MINUS_3DB);
                    break;
                case AC3_OUTPUT_STEREO:
                    nf = 1.0 / (1.0 + (slev * LEVEL_MINUS_3DB));
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    ctx->chcoeffs[2] *= (nf * slev * LEVEL_MINUS_3DB);
                    break;
                case AC3_OUTPUT_DOLBY:
                    nf = 1.0 / (1.0 + LEVEL_MINUS_3DB);
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    ctx->chcoeffs[2] *= (nf * LEVEL_MINUS_3DB);
                    break;
            }
            break;
        case AC3_ACMOD_3F1R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    nf = LEVEL_MINUS_3DB / (1.0 + clev + (slev / 2.0));
                    ctx->chcoeffs[0] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[2] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[1] *= (nf * clev * LEVEL_PLUS_3DB);
                    ctx->chcoeffs[3] *= (nf * slev * LEVEL_MINUS_3DB);
                    break;
                case AC3_OUTPUT_STEREO:
                    nf = 1.0 / (1.0 + clev + (slev * LEVEL_MINUS_3DB));
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[2] *= nf;
                    ctx->chcoeffs[1] *= (nf * clev);
                    ctx->chcoeffs[3] *= (nf * slev * LEVEL_MINUS_3DB);
                    break;
                case AC3_OUTPUT_DOLBY:
                    nf = 1.0 / (1.0 + (2.0 * LEVEL_MINUS_3DB));
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    ctx->chcoeffs[1] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[3] *= (nf * LEVEL_MINUS_3DB);
                    break;
            }
            break;
        case AC3_ACMOD_2F2R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    nf = LEVEL_MINUS_3DB / (1.0 + slev);
                    ctx->chcoeffs[0] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[1] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[2] *= (nf * slev * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[3] *= (nf * slev * LEVEL_MINUS_3DB);
                    break;
                case AC3_OUTPUT_STEREO:
                    nf = 1.0 / (1.0 + slev);
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    ctx->chcoeffs[2] *= (nf * slev);
                    ctx->chcoeffs[3] *= (nf * slev);
                    break;
                case AC3_OUTPUT_DOLBY:
                    nf = 1.0 / (1.0 + (2.0 * LEVEL_MINUS_3DB));
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    ctx->chcoeffs[2] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[3] *= (nf * LEVEL_MINUS_3DB);
                    break;
            }
            break;
        case AC3_ACMOD_3F2R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    nf = LEVEL_MINUS_3DB / (1.0 + clev + slev);
                    ctx->chcoeffs[0] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[2] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[1] *= (nf * clev * LEVEL_PLUS_3DB);
                    ctx->chcoeffs[3] *= (nf * slev * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[4] *= (nf * slev * LEVEL_MINUS_3DB);
                    break;
                case AC3_OUTPUT_STEREO:
                    nf = 1.0 / (1.0 + clev + slev);
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[2] *= nf;
                    ctx->chcoeffs[1] *= (nf * clev);
                    ctx->chcoeffs[3] *= (nf * slev);
                    ctx->chcoeffs[4] *= (nf * slev);
                    break;
                case AC3_OUTPUT_DOLBY:
                    nf = 1.0 / (1.0 + (3.0 * LEVEL_MINUS_3DB));
                    ctx->chcoeffs[0] *= nf;
                    ctx->chcoeffs[1] *= nf;
                    ctx->chcoeffs[1] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[3] *= (nf * LEVEL_MINUS_3DB);
                    ctx->chcoeffs[4] *= (nf * LEVEL_MINUS_3DB);
                    break;
            }
            break;
    }
}

/*********** BEGIN DOWNMIX FUNCTIONS ***********/
static inline void mix_dualmono_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] += output[2][i];
    memset(output[2], 0, sizeof(output[2]));
}

static inline void mix_dualmono_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float tmp;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        tmp = output[1][i] + output[2][i];
        output[1][i] = output[2][i] = tmp;
    }
}

static inline void upmix_mono_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[2][i] = output[1][i];
}

static inline void mix_stereo_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] += output[2][i];
    memset(output[2], 0, sizeof(output[2]));
}

static inline void mix_3f_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] += (output[2][i] + output[3][i]);
    memset(output[2], 0, sizeof(output[2]));
    memset(output[3], 0, sizeof(output[3]));
}

static inline void mix_3f_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += output[2][i];
        output[2][i] += output[3][i];
    }
    memset(output[3], 0, sizeof(output[3]));
}

static inline void mix_2f_1r_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] += (output[2][i] + output[3][i]);
    memset(output[2], 0, sizeof(output[2]));
    memset(output[3], 0, sizeof(output[3]));

}

static inline void mix_2f_1r_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += output[2][i];
        output[2][i] += output[3][i];
    }
    memset(output[3], 0, sizeof(output[3]));
}

static inline void mix_2f_1r_to_dolby(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] -= output[3][i];
        output[2][i] += output[3][i];
    }
    memset(output[3], 0, sizeof(output[3]));
}

static inline void mix_3f_1r_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] = (output[2][i] + output[3][i] + output[4][i]);
    memset(output[2], 0, sizeof(output[2]));
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
}

static inline void mix_3f_1r_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += (output[2][i] + output[4][i]);
        output[2][i] += (output[3][i] + output[4][i]);
    }
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
}

static inline void mix_3f_1r_to_dolby(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += (output[2][i] - output[4][i]);
        output[2][i] += (output[3][i] + output[4][i]);
    }
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
}

static inline void mix_2f_2r_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] = (output[2][i] + output[3][i] + output[4][i]);
    memset(output[2], 0, sizeof(output[2]));
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
}

static inline void mix_2f_2r_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += output[3][i];
        output[2][i] += output[4][i];
    }
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
}

static inline void mix_2f_2r_to_dolby(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] -= output[3][i];
        output[2][i] += output[4][i];
    }
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
}

static inline void mix_3f_2r_to_mono(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++)
        output[1][i] += (output[2][i] + output[3][i] + output[4][i] + output[5][i]);
    memset(output[2], 0, sizeof(output[2]));
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
    memset(output[5], 0, sizeof(output[5]));
}

static inline void mix_3f_2r_to_stereo(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += (output[2][i] + output[4][i]);
        output[2][i] += (output[3][i] + output[5][i]);
    }
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
    memset(output[5], 0, sizeof(output[5]));
}

static inline void mix_3f_2r_to_dolby(AC3DecodeContext *ctx)
{
    int i;
    float (*output)[BLOCK_SIZE] = ctx->output;

    for (i = 0; i < 256; i++) {
        output[1][i] += (output[2][i] - output[4][i] - output[5][i]);
        output[2][i] += (output[3][i] + output[4][i] + output[5][i]);
    }
    memset(output[3], 0, sizeof(output[3]));
    memset(output[4], 0, sizeof(output[4]));
    memset(output[5], 0, sizeof(output[5]));
}
/*********** END DOWNMIX FUNCTIONS ***********/

/* Downmix the output.
 * This function downmixes the output when the number of input
 * channels is not equal to the number of output channels requested.
 */
static void do_downmix(AC3DecodeContext *ctx)
{
    int from = ctx->acmod;
    int to = ctx->blkoutput;

    if (to == AC3_OUTPUT_UNMODIFIED)
        return;

    switch (from) {
        case AC3_ACMOD_DUALMONO:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_dualmono_to_mono(ctx);
                    break;
                case AC3_OUTPUT_STEREO: /* We assume that sum of both mono channels is requested */
                    mix_dualmono_to_stereo(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_MONO:
            switch (to) {
                case AC3_OUTPUT_STEREO:
                    upmix_mono_to_stereo(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_STEREO:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_stereo_to_mono(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_3F:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_3f_to_mono(ctx);
                    break;
                case AC3_OUTPUT_STEREO:
                    mix_3f_to_stereo(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_2F1R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_2f_1r_to_mono(ctx);
                    break;
                case AC3_OUTPUT_STEREO:
                    mix_2f_1r_to_stereo(ctx);
                    break;
                case AC3_OUTPUT_DOLBY:
                    mix_2f_1r_to_dolby(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_3F1R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_3f_1r_to_mono(ctx);
                    break;
                case AC3_OUTPUT_STEREO:
                    mix_3f_1r_to_stereo(ctx);
                    break;
                case AC3_OUTPUT_DOLBY:
                    mix_3f_1r_to_dolby(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_2F2R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_2f_2r_to_mono(ctx);
                    break;
                case AC3_OUTPUT_STEREO:
                    mix_2f_2r_to_stereo(ctx);
                    break;
                case AC3_OUTPUT_DOLBY:
                    mix_2f_2r_to_dolby(ctx);
                    break;
            }
            break;
        case AC3_ACMOD_3F2R:
            switch (to) {
                case AC3_OUTPUT_MONO:
                    mix_3f_2r_to_mono(ctx);
                    break;
                case AC3_OUTPUT_STEREO:
                    mix_3f_2r_to_stereo(ctx);
                    break;
                case AC3_OUTPUT_DOLBY:
                    mix_3f_2r_to_dolby(ctx);
                    break;
            }
            break;
    }
}

/* This function performs the imdct on 256 sample transform
 * coefficients.
 */
static void do_imdct_256(AC3DecodeContext *ctx, int chindex)
{
    int i, k;
    float x[128];
    FFTComplex z[2][64];
    float *o_ptr = ctx->tmp_output;

    for(i=0; i<2; i++) {
        /* de-interleave coefficients */
        for(k=0; k<128; k++) {
            x[k] = ctx->transform_coeffs[chindex][2*k+i];
        }

        /* run standard IMDCT */
        ctx->imdct_256.fft.imdct_calc(&ctx->imdct_256, o_ptr, x, ctx->tmp_imdct);

        /* reverse the post-rotation & reordering from standard IMDCT */
        for(k=0; k<32; k++) {
            z[i][32+k].re = -o_ptr[128+2*k];
            z[i][32+k].im = -o_ptr[2*k];
            z[i][31-k].re =  o_ptr[2*k+1];
            z[i][31-k].im =  o_ptr[128+2*k+1];
        }
    }

    /* apply AC-3 post-rotation & reordering */
    for(k=0; k<64; k++) {
        o_ptr[    2*k  ] = -z[0][   k].im;
        o_ptr[    2*k+1] =  z[0][63-k].re;
        o_ptr[128+2*k  ] = -z[0][   k].re;
        o_ptr[128+2*k+1] =  z[0][63-k].im;
        o_ptr[256+2*k  ] = -z[1][   k].re;
        o_ptr[256+2*k+1] =  z[1][63-k].im;
        o_ptr[384+2*k  ] =  z[1][   k].im;
        o_ptr[384+2*k+1] = -z[1][63-k].re;
    }
}

/* IMDCT Transform. */
static inline void do_imdct(AC3DecodeContext *ctx)
{
    int ch;

    if (ctx->blkoutput & AC3_OUTPUT_LFEON) {
        ctx->imdct_512.fft.imdct_calc(&ctx->imdct_512, ctx->tmp_output,
                                      ctx->transform_coeffs[0], ctx->tmp_imdct);
    }
    for (ch=1; ch<=ctx->nfchans; ch++) {
        if ((ctx->blksw >> (ch-1)) & 1)
            do_imdct_256(ctx, ch);
        else
            ctx->imdct_512.fft.imdct_calc(&ctx->imdct_512, ctx->tmp_output,
                                          ctx->transform_coeffs[ch],
                                          ctx->tmp_imdct);

        ctx->dsp.vector_fmul_add_add(ctx->output[ch], ctx->tmp_output,
                                     ctx->window, ctx->delay[ch], 384, 256, 1);
        ctx->dsp.vector_fmul_reverse(ctx->delay[ch], ctx->tmp_output+256,
                                     ctx->window, 256);
    }
}

/* Parse the audio block from ac3 bitstream.
 * This function extract the audio block from the ac3 bitstream
 * and produces the output for the block. This function must
 * be called for each of the six audio block in the ac3 bitstream.
 */
static int ac3_parse_audio_block(AC3DecodeContext * ctx)
{
    int nfchans = ctx->nfchans;
    int acmod = ctx->acmod;
    int i, bnd, rbnd, seg, grpsize;
    GetBitContext *gb = &ctx->gb;
    int bit_alloc_flags = 0;
    uint8_t *dexps;
    int mstrcplco, cplcoexp, cplcomant;
    int dynrng, chbwcod, ngrps, cplabsexp, skipl;

    ctx->blksw = 0;
    for (i = 0; i < nfchans; i++) /*block switch flag */
        ctx->blksw |= get_bits1(gb) << i;

    ctx->dithflag = 0;
    for (i = 0; i < nfchans; i++) /* dithering flag */
        ctx->dithflag |= get_bits1(gb) << i;

    if (get_bits1(gb)) { /* dynamic range */
        dynrng = get_sbits(gb, 8);
        ctx->dynrng = ((((dynrng & 0x1f) | 0x20) << 13) * scale_factors[3 - (dynrng >> 5)]);
    }

    if (acmod == 0x00 && get_bits1(gb)) { /* dynamic range 1+1 mode */
        dynrng = get_sbits(gb, 8);
        ctx->dynrng2 = ((((dynrng & 0x1f) | 0x20) << 13) * scale_factors[3 - (dynrng >> 5)]);
    }

    get_downmix_coeffs(ctx);

    if (get_bits1(gb)) { /* coupling strategy */
        ctx->cplinu = get_bits1(gb);
        ctx->cplbndstrc = 0;
        ctx->chincpl = 0;
        if (ctx->cplinu) { /* coupling in use */
            for (i = 0; i < nfchans; i++)
                ctx->chincpl |= get_bits1(gb) << i;

            if (acmod == 0x02)
                ctx->phsflginu = get_bits1(gb); //phase flag in use

            ctx->cplbegf = get_bits(gb, 4);
            ctx->cplendf = get_bits(gb, 4);

            if (3 + ctx->cplendf - ctx->cplbegf < 0) {
                av_log(NULL, AV_LOG_ERROR, "cplendf = %d < cplbegf = %d\n", ctx->cplendf, ctx->cplbegf);
                return -1;
            }

            ctx->ncplbnd = ctx->ncplsubnd = 3 + ctx->cplendf - ctx->cplbegf;
            ctx->cplstrtmant = ctx->cplbegf * 12 + 37;
            ctx->cplendmant = ctx->cplendf * 12 + 73;
            for (i = 0; i < ctx->ncplsubnd - 1; i++) /* coupling band structure */
                if (get_bits1(gb)) {
                    ctx->cplbndstrc |= 1 << i;
                    ctx->ncplbnd--;
                }
        }
    }

    if (ctx->cplinu) {
        ctx->cplcoe = 0;

        for (i = 0; i < nfchans; i++)
            if ((ctx->chincpl) >> i & 1)
                if (get_bits1(gb)) { /* coupling co-ordinates */
                    ctx->cplcoe |= 1 << i;
                    mstrcplco = 3 * get_bits(gb, 2);
                    for (bnd = 0; bnd < ctx->ncplbnd; bnd++) {
                        cplcoexp = get_bits(gb, 4);
                        cplcomant = get_bits(gb, 4);
                        if (cplcoexp == 15)
                            cplcomant <<= 14;
                        else
                            cplcomant = (cplcomant | 0x10) << 13;
                        ctx->cplco[i][bnd] = cplcomant * scale_factors[cplcoexp + mstrcplco];
                    }
                }

        if (acmod == 0x02 && ctx->phsflginu && (ctx->cplcoe & 1 || ctx->cplcoe & 2))
            for (bnd = 0; bnd < ctx->ncplbnd; bnd++)
                if (get_bits1(gb))
                    ctx->cplco[1][bnd] = -ctx->cplco[1][bnd];
    }

    if (acmod == 0x02) {/* rematrixing */
        ctx->rematstr = get_bits1(gb);
        if (ctx->rematstr) {
            ctx->rematflg = 0;

            if (!(ctx->cplinu) || ctx->cplbegf > 2)
                for (rbnd = 0; rbnd < 4; rbnd++)
                    ctx->rematflg |= get_bits1(gb) << rbnd;
            if (ctx->cplbegf > 0 && ctx->cplbegf <= 2 && ctx->cplinu)
                for (rbnd = 0; rbnd < 3; rbnd++)
                    ctx->rematflg |= get_bits1(gb) << rbnd;
            if (ctx->cplbegf == 0 && ctx->cplinu)
                for (rbnd = 0; rbnd < 2; rbnd++)
                    ctx->rematflg |= get_bits1(gb) << rbnd;
        }
    }

    ctx->cplexpstr = EXP_REUSE;
    ctx->lfeexpstr = EXP_REUSE;
    if (ctx->cplinu) /* coupling exponent strategy */
        ctx->cplexpstr = get_bits(gb, 2);
    for (i = 0; i < nfchans; i++)  /* channel exponent strategy */
        ctx->chexpstr[i] = get_bits(gb, 2);
    if (ctx->lfeon)  /* lfe exponent strategy */
        ctx->lfeexpstr = get_bits1(gb);

    for (i = 0; i < nfchans; i++) /* channel bandwidth code */
        if (ctx->chexpstr[i] != EXP_REUSE) {
            if ((ctx->chincpl >> i) & 1)
                ctx->endmant[i] = ctx->cplstrtmant;
            else {
                chbwcod = get_bits(gb, 6);
                if (chbwcod > 60) {
                    av_log(NULL, AV_LOG_ERROR, "chbwcod = %d > 60", chbwcod);
                    return -1;
                }
                ctx->endmant[i] = chbwcod * 3 + 73;
            }
        }

    if (ctx->cplexpstr != EXP_REUSE) {/* coupling exponents */
        bit_alloc_flags = 64;
        cplabsexp = get_bits(gb, 4) << 1;
        ngrps = (ctx->cplendmant - ctx->cplstrtmant) / (3 << (ctx->cplexpstr - 1));
        decode_exponents(gb, ctx->cplexpstr, ngrps, cplabsexp, ctx->dcplexps + ctx->cplstrtmant);
    }

    for (i = 0; i < nfchans; i++) /* fbw channel exponents */
        if (ctx->chexpstr[i] != EXP_REUSE) {
            bit_alloc_flags |= 1 << i;
            grpsize = 3 << (ctx->chexpstr[i] - 1);
            ngrps = (ctx->endmant[i] + grpsize - 4) / grpsize;
            dexps = ctx->dexps[i];
            dexps[0] = get_bits(gb, 4);
            decode_exponents(gb, ctx->chexpstr[i], ngrps, dexps[0], dexps + 1);
            skip_bits(gb, 2); /* skip gainrng */
        }

    if (ctx->lfeexpstr != EXP_REUSE) { /* lfe exponents */
        bit_alloc_flags |= 32;
        ctx->dlfeexps[0] = get_bits(gb, 4);
        decode_exponents(gb, ctx->lfeexpstr, 2, ctx->dlfeexps[0], ctx->dlfeexps + 1);
    }

    if (get_bits1(gb)) { /* bit allocation information */
        bit_alloc_flags = 127;
        ctx->sdcycod = get_bits(gb, 2);
        ctx->fdcycod = get_bits(gb, 2);
        ctx->sgaincod = get_bits(gb, 2);
        ctx->dbpbcod = get_bits(gb, 2);
        ctx->floorcod = get_bits(gb, 3);
    }

    if (get_bits1(gb)) { /* snroffset */
        bit_alloc_flags = 127;
        ctx->csnroffst = get_bits(gb, 6);
        if (ctx->cplinu) { /* coupling fine snr offset and fast gain code */
            ctx->cplfsnroffst = get_bits(gb, 4);
            ctx->cplfgaincod = get_bits(gb, 3);
        }
        for (i = 0; i < nfchans; i++) { /* channel fine snr offset and fast gain code */
            ctx->fsnroffst[i] = get_bits(gb, 4);
            ctx->fgaincod[i] = get_bits(gb, 3);
        }
        if (ctx->lfeon) { /* lfe fine snr offset and fast gain code */
            ctx->lfefsnroffst = get_bits(gb, 4);
            ctx->lfefgaincod = get_bits(gb, 3);
        }
    }

    if (ctx->cplinu && get_bits1(gb)) { /* coupling leak information */
        bit_alloc_flags |= 64;
        ctx->cplfleak = get_bits(gb, 3);
        ctx->cplsleak = get_bits(gb, 3);
    }

    if (get_bits1(gb)) { /* delta bit allocation information */
        bit_alloc_flags = 127;

        if (ctx->cplinu) {
            ctx->cpldeltbae = get_bits(gb, 2);
            if (ctx->cpldeltbae == DBA_RESERVED) {
                av_log(NULL, AV_LOG_ERROR, "coupling delta bit allocation strategy reserved\n");
                return -1;
            }
        }

        for (i = 0; i < nfchans; i++) {
            ctx->deltbae[i] = get_bits(gb, 2);
            if (ctx->deltbae[i] == DBA_RESERVED) {
                av_log(NULL, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");
                return -1;
            }
        }

        if (ctx->cplinu)
            if (ctx->cpldeltbae == DBA_NEW) { /*coupling delta offset, len and bit allocation */
                ctx->cpldeltnseg = get_bits(gb, 3);
                for (seg = 0; seg <= ctx->cpldeltnseg; seg++) {
                    ctx->cpldeltoffst[seg] = get_bits(gb, 5);
                    ctx->cpldeltlen[seg] = get_bits(gb, 4);
                    ctx->cpldeltba[seg] = get_bits(gb, 3);
                }
            }

        for (i = 0; i < nfchans; i++)
            if (ctx->deltbae[i] == DBA_NEW) {/*channel delta offset, len and bit allocation */
                ctx->deltnseg[i] = get_bits(gb, 3);
                for (seg = 0; seg <= ctx->deltnseg[i]; seg++) {
                    ctx->deltoffst[i][seg] = get_bits(gb, 5);
                    ctx->deltlen[i][seg] = get_bits(gb, 4);
                    ctx->deltba[i][seg] = get_bits(gb, 3);
                }
            }
    }

    if (bit_alloc_flags) {
        /* set bit allocation parameters */
        ctx->bit_alloc_params.fscod = ctx->fscod;
        ctx->bit_alloc_params.halfratecod = 0;
        ctx->bit_alloc_params.sdecay = ff_sdecaytab[ctx->sdcycod];
        ctx->bit_alloc_params.fdecay = ff_fdecaytab[ctx->fdcycod];
        ctx->bit_alloc_params.sgain = ff_sgaintab[ctx->sgaincod];
        ctx->bit_alloc_params.dbknee = ff_dbkneetab[ctx->dbpbcod];
        ctx->bit_alloc_params.floor = ff_floortab[ctx->floorcod];
        ctx->bit_alloc_params.cplfleak = ctx->cplfleak;
        ctx->bit_alloc_params.cplsleak = ctx->cplsleak;

        if (ctx->chincpl && (bit_alloc_flags & 64))
            do_bit_allocation(ctx, 5);
        for (i = 0; i < nfchans; i++)
            if ((bit_alloc_flags >> i) & 1)
                do_bit_allocation(ctx, i);
        if (ctx->lfeon && (bit_alloc_flags & 32))
            do_bit_allocation(ctx, 6);
    }

    if (get_bits1(gb)) { /* unused dummy data */
        skipl = get_bits(gb, 9);
        while(skipl--)
            skip_bits(gb, 8);
    }
    /* unpack the transform coefficients
     * * this also uncouples channels if coupling is in use.
     */
    if (get_transform_coeffs(ctx)) {
        av_log(NULL, AV_LOG_ERROR, "Error in routine get_transform_coeffs\n");
        return -1;
    }

    /* recover coefficients if rematrixing is in use */
    if (ctx->rematflg)
        do_rematrixing(ctx);

    do_downmix(ctx);

    do_imdct(ctx);

    return 0;
}

static inline int16_t convert(int32_t i)
{
    if (i > 0x43c07fff)
        return 32767;
    else if (i <= 0x43bf8000)
        return -32768;
    else
        return (i - 0x43c00000);
}

/* Decode ac3 frame.
 *
 * @param avctx Pointer to AVCodecContext
 * @param data Pointer to pcm smaples
 * @param data_size Set to number of pcm samples produced by decoding
 * @param buf Data to be decoded
 * @param buf_size Size of the buffer
 */
static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size, uint8_t *buf, int buf_size)
{
    AC3DecodeContext *ctx = (AC3DecodeContext *)avctx->priv_data;
    int frame_start;
    int16_t *out_samples = (int16_t *)data;
    int i, j, k, start;
    int32_t *int_ptr[6];

    for (i = 0; i < 6; i++)
        int_ptr[i] = (int32_t *)(&ctx->output[i]);

    //Synchronize the frame.
    frame_start = ac3_synchronize(buf, buf_size);
    if (frame_start == -1) {
        av_log(avctx, AV_LOG_ERROR, "frame is not synchronized\n");
        *data_size = 0;
        return buf_size;
    }

    //Initialize the GetBitContext with the start of valid AC3 Frame.
    init_get_bits(&(ctx->gb), buf + frame_start, (buf_size - frame_start) * 8);

    //Parse the syncinfo.
    //If 'fscod' or 'bsid' is not valid the decoder shall mute as per the standard.
    if (!ac3_parse_sync_info(ctx)) {
        av_log(avctx, AV_LOG_ERROR, "\n");
        *data_size = 0;
        return buf_size;
    }

    //Parse the BSI.
    //If 'bsid' is not valid decoder shall not decode the audio as per the standard.
    ac3_parse_bsi(ctx);

    avctx->sample_rate = ctx->sampling_rate;
    avctx->bit_rate = ctx->bit_rate;

    if (avctx->channels == 0) {
        ctx->blkoutput |= AC3_OUTPUT_UNMODIFIED;
        if (ctx->lfeon)
            ctx->blkoutput |= AC3_OUTPUT_LFEON;
        avctx->channels = ctx->nfchans + ctx->lfeon;
    }
    else if (avctx->channels == 1)
        ctx->blkoutput |= AC3_OUTPUT_MONO;
    else if (avctx->channels == 2) {
        if (ctx->dsurmod == 0x02)
            ctx->blkoutput |= AC3_OUTPUT_DOLBY;
        else
            ctx->blkoutput |= AC3_OUTPUT_STEREO;
    }
    else {
        if (avctx->channels < (ctx->nfchans + ctx->lfeon))
            av_log(avctx, AV_LOG_INFO, "ac3_decoder: AC3 Source Channels Are Less Then Specified %d: Output to %d Channels\n",avctx->channels, ctx->nfchans + ctx->lfeon);
        ctx->blkoutput |= AC3_OUTPUT_UNMODIFIED;
        if (ctx->lfeon)
            ctx->blkoutput |= AC3_OUTPUT_LFEON;
        avctx->channels = ctx->nfchans + ctx->lfeon;
    }

    //av_log(avctx, AV_LOG_INFO, "channels = %d \t bit rate = %d \t sampling rate = %d \n", avctx->channels, avctx->bit_rate * 1000, avctx->sample_rate);

    //Parse the Audio Blocks.
    for (i = 0; i < NB_BLOCKS; i++) {
        if (ac3_parse_audio_block(ctx)) {
            av_log(avctx, AV_LOG_ERROR, "error parsing the audio block\n");
            *data_size = 0;
            return ctx->frame_size;
        }
        start = (ctx->blkoutput & AC3_OUTPUT_LFEON) ? 0 : 1;
        for (k = 0; k < BLOCK_SIZE; k++)
            for (j = start; j <= avctx->channels; j++)
                *(out_samples++) = convert(int_ptr[j][k]);
    }
    *data_size = NB_BLOCKS * BLOCK_SIZE * avctx->channels * sizeof (int16_t);
    return ctx->frame_size;
}

/* Uninitialize ac3 decoder.
 */
static int ac3_decode_end(AVCodecContext *avctx)
{
    AC3DecodeContext *ctx = (AC3DecodeContext *)avctx->priv_data;
    ff_mdct_end(&ctx->imdct_512);
    ff_mdct_end(&ctx->imdct_256);

    return 0;
}

AVCodec ac3_decoder = {
    .name = "ac3",
    .type = CODEC_TYPE_AUDIO,
    .id = CODEC_ID_AC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init = ac3_decode_init,
    .close = ac3_decode_end,
    .decode = ac3_decode_frame,
};