PeerStreamer

/*

 * The simplest AC3 encoder

 * Copyright (c) 2000 Fabrice Bellard.

 *

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

 *

 * This library 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 this library; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file ac3enc.c

 * The simplest AC3 encoder.

 */

//#define DEBUG

//#define DEBUG_BITALLOC

#include "avcodec.h"

#include "bitstream.h"

#include "ac3.h"

typedef struct AC3EncodeContext {

    PutBitContext pb;

    int nb_channels;

    int nb_all_channels;

    int lfe_channel;

    int bit_rate;

    unsigned int sample_rate;

    unsigned int bsid;

    unsigned int frame_size_min; /* minimum frame size in case rounding is necessary */

    unsigned int frame_size; /* current frame size in words */

    int halfratecod;

    unsigned int frmsizecod;

    unsigned int fscod; /* frequency */

    unsigned int acmod;

    int lfe;

    unsigned int bsmod;

    short last_samples[AC3_MAX_CHANNELS][256];

    unsigned int chbwcod[AC3_MAX_CHANNELS];

    int nb_coefs[AC3_MAX_CHANNELS];

    /* bitrate allocation control */

    int sgaincod, sdecaycod, fdecaycod, dbkneecod, floorcod;

    AC3BitAllocParameters bit_alloc;

    int csnroffst;

    int fgaincod[AC3_MAX_CHANNELS];

    int fsnroffst[AC3_MAX_CHANNELS];

    /* mantissa encoding */

    int mant1_cnt, mant2_cnt, mant4_cnt;

} AC3EncodeContext;

#include "ac3tab.h"

#define MDCT_NBITS 9

#define N         (1 << MDCT_NBITS)

/* new exponents are sent if their Norm 1 exceed this number */

#define EXP_DIFF_THRESHOLD 1000

static void fft_init(int ln);

static void ac3_crc_init(void);

static inline int16_t fix15(float a)

{

    int v;

    v = (int)(a * (float)(1 << 15));

    if (v < -32767)

        v = -32767;

    else if (v > 32767)

        v = 32767;

    return v;

}

static inline int calc_lowcomp1(int a, int b0, int b1)

{

    if ((b0 + 256) == b1) {

        a = 384 ;

    } else if (b0 > b1) {

        a = a - 64;

        if (a < 0) a=0;

    }

    return a;

}

static inline int calc_lowcomp(int a, int b0, int b1, int bin)

{

    if (bin < 7) {

        if ((b0 + 256) == b1) {

            a = 384 ;

        } else if (b0 > b1) {

            a = a - 64;

            if (a < 0) a=0;

        }

    } else if (bin < 20) {

        if ((b0 + 256) == b1) {

            a = 320 ;

        } else if (b0 > b1) {

            a= a - 64;

            if (a < 0) a=0;

        }

    } else {

        a = a - 128;

        if (a < 0) a=0;

    }

    return a;

}

/* AC3 bit allocation. The algorithm is the one described in the AC3

   spec. */

void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,

                                   int8_t *exp, int start, int end,

                                   int snroffset, int fgain, int is_lfe,

                                   int deltbae,int deltnseg,

                                   uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba)

{

    int bin,i,j,k,end1,v,v1,bndstrt,bndend,lowcomp,begin;

    int fastleak,slowleak,address,tmp;

    int16_t psd[256]; /* scaled exponents */

    int16_t bndpsd[50]; /* interpolated exponents */

    int16_t excite[50]; /* excitation */

    int16_t mask[50];   /* masking value */

    /* exponent mapping to PSD */

    for(bin=start;bin<end;bin++) {

        psd[bin]=(3072 - (exp[bin] << 7));

    }

    /* PSD integration */

    j=start;

    k=masktab[start];

    do {

        v=psd[j];

        j++;

        end1=bndtab[k+1];

        if (end1 > end) end1=end;

        for(i=j;i<end1;i++) {

            int c,adr;

            /* logadd */

            v1=psd[j];

            c=v-v1;

            if (c >= 0) {

                adr=c >> 1;

                if (adr > 255) adr=255;

                v=v + latab[adr];

            } else {

                adr=(-c) >> 1;

                if (adr > 255) adr=255;

                v=v1 + latab[adr];

            }

            j++;

        }

        bndpsd[k]=v;

        k++;

    } while (end > bndtab[k]);

    /* excitation function */

    bndstrt = masktab[start];

    bndend = masktab[end-1] + 1;

    if (bndstrt == 0) {

        lowcomp = 0;

        lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1]) ;

        excite[0] = bndpsd[0] - fgain - lowcomp ;

        lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2]) ;

        excite[1] = bndpsd[1] - fgain - lowcomp ;

        begin = 7 ;

        for (bin = 2; bin < 7; bin++) {

            if (!(is_lfe && bin == 6))

                lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1]) ;

            fastleak = bndpsd[bin] - fgain ;

            slowleak = bndpsd[bin] - s->sgain ;

            excite[bin] = fastleak - lowcomp ;

            if (!(is_lfe && bin == 6)) {

                if (bndpsd[bin] <= bndpsd[bin+1]) {

                    begin = bin + 1 ;

                    break ;

                }

            }

        }

        end1=bndend;

        if (end1 > 22) end1=22;

        for (bin = begin; bin < end1; bin++) {

            if (!(is_lfe && bin == 6))

                lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin) ;

            fastleak -= s->fdecay ;

            v = bndpsd[bin] - fgain;

            if (fastleak < v) fastleak = v;

            slowleak -= s->sdecay ;

            v = bndpsd[bin] - s->sgain;

            if (slowleak < v) slowleak = v;

            v=fastleak - lowcomp;

            if (slowleak > v) v=slowleak;

            excite[bin] = v;

        }

        begin = 22;

    } else {

        /* coupling channel */

        begin = bndstrt;

        fastleak = (s->cplfleak << 8) + 768;

        slowleak = (s->cplsleak << 8) + 768;

    }

    for (bin = begin; bin < bndend; bin++) {

        fastleak -= s->fdecay ;

        v = bndpsd[bin] - fgain;

        if (fastleak < v) fastleak = v;

        slowleak -= s->sdecay ;

        v = bndpsd[bin] - s->sgain;

        if (slowleak < v) slowleak = v;

        v=fastleak;

        if (slowleak > v) v = slowleak;

        excite[bin] = v;

    }

    /* compute masking curve */

    for (bin = bndstrt; bin < bndend; bin++) {

        v1 = excite[bin];

        tmp = s->dbknee - bndpsd[bin];

        if (tmp > 0) {

            v1 += tmp >> 2;

        }

        v=hth[bin >> s->halfratecod][s->fscod];

        if (v1 > v) v=v1;

        mask[bin] = v;

    }

    /* delta bit allocation */

    if (deltbae == 0 || deltbae == 1) {

        int band, seg, delta;

        band = 0 ;

        for (seg = 0; seg < deltnseg; seg++) {

            band += deltoffst[seg] ;

            if (deltba[seg] >= 4) {

                delta = (deltba[seg] - 3) << 7;

            } else {

                delta = (deltba[seg] - 4) << 7;

            }

            for (k = 0; k < deltlen[seg]; k++) {

                mask[band] += delta ;

                band++ ;

            }

        }

    }

    /* compute bit allocation */

    i = start ;

    j = masktab[start] ;

    do {

        v=mask[j];

        v -= snroffset ;

        v -= s->floor ;

        if (v < 0) v = 0;

        v &= 0x1fe0 ;

        v += s->floor ;

        end1=bndtab[j] + bndsz[j];

        if (end1 > end) end1=end;

        for (k = i; k < end1; k++) {

            address = (psd[i] - v) >> 5 ;

            if (address < 0) address=0;

            else if (address > 63) address=63;

            bap[i] = baptab[address];

            i++;

        }

    } while (end > bndtab[j++]) ;

}

typedef struct IComplex {

    short re,im;

} IComplex;

static void fft_init(int ln)

{

    int i, j, m, n;

    float alpha;

    n = 1 << ln;

    for(i=0;i<(n/2);i++) {

        alpha = 2 * M_PI * (float)i / (float)n;

        costab[i] = fix15(cos(alpha));

        sintab[i] = fix15(sin(alpha));

    }

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

        m=0;

        for(j=0;j<ln;j++) {

            m |= ((i >> j) & 1) << (ln-j-1);

        }

        fft_rev[i]=m;

    }

}

/* butter fly op */

#define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1) \

{\

  int ax, ay, bx, by;\

  bx=pre1;\

  by=pim1;\

  ax=qre1;\

  ay=qim1;\

  pre = (bx + ax) >> 1;\

  pim = (by + ay) >> 1;\

  qre = (bx - ax) >> 1;\

  qim = (by - ay) >> 1;\

}

#define MUL16(a,b) ((a) * (b))

#define CMUL(pre, pim, are, aim, bre, bim) \

{\

   pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15;\

   pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15;\

}

/* do a 2^n point complex fft on 2^ln points. */

static void fft(IComplex *z, int ln)

{

    int        j, l, np, np2;

    int        nblocks, nloops;

    register IComplex *p,*q;

    int tmp_re, tmp_im;

    np = 1 << ln;

    /* reverse */

    for(j=0;j<np;j++) {

        int k;

        IComplex tmp;

        k = fft_rev[j];

        if (k < j) {

            tmp = z[k];

            z[k] = z[j];

            z[j] = tmp;

        }

    }

    /* pass 0 */

    p=&z[0];

    j=(np >> 1);

    do {

        BF(p[0].re, p[0].im, p[1].re, p[1].im,

           p[0].re, p[0].im, p[1].re, p[1].im);

        p+=2;

    } while (--j != 0);

    /* pass 1 */

    p=&z[0];

    j=np >> 2;

    do {

        BF(p[0].re, p[0].im, p[2].re, p[2].im,

           p[0].re, p[0].im, p[2].re, p[2].im);

        BF(p[1].re, p[1].im, p[3].re, p[3].im,

           p[1].re, p[1].im, p[3].im, -p[3].re);

        p+=4;

    } while (--j != 0);

    /* pass 2 .. ln-1 */

    nblocks = np >> 3;

    nloops = 1 << 2;

    np2 = np >> 1;

    do {

        p = z;

        q = z + nloops;

        for (j = 0; j < nblocks; ++j) {

            BF(p->re, p->im, q->re, q->im,

               p->re, p->im, q->re, q->im);

            p++;

            q++;

            for(l = nblocks; l < np2; l += nblocks) {

                CMUL(tmp_re, tmp_im, costab[l], -sintab[l], q->re, q->im);

                BF(p->re, p->im, q->re, q->im,

                   p->re, p->im, tmp_re, tmp_im);

                p++;

                q++;

            }

            p += nloops;

            q += nloops;

        }

        nblocks = nblocks >> 1;

        nloops = nloops << 1;

    } while (nblocks != 0);

}

/* do a 512 point mdct */

static void mdct512(int32_t *out, int16_t *in)

{

    int i, re, im, re1, im1;

    int16_t rot[N];

    IComplex x[N/4];

    /* shift to simplify computations */

    for(i=0;i<N/4;i++)

        rot[i] = -in[i + 3*N/4];

    for(i=N/4;i<N;i++)

        rot[i] = in[i - N/4];

    /* pre rotation */

    for(i=0;i<N/4;i++) {

        re = ((int)rot[2*i] - (int)rot[N-1-2*i]) >> 1;

        im = -((int)rot[N/2+2*i] - (int)rot[N/2-1-2*i]) >> 1;

        CMUL(x[i].re, x[i].im, re, im, -xcos1[i], xsin1[i]);

    }

    fft(x, MDCT_NBITS - 2);

    /* post rotation */

    for(i=0;i<N/4;i++) {

        re = x[i].re;

        im = x[i].im;

        CMUL(re1, im1, re, im, xsin1[i], xcos1[i]);

        out[2*i] = im1;

        out[N/2-1-2*i] = re1;

    }

}

/* XXX: use another norm ? */

static int calc_exp_diff(uint8_t *exp1, uint8_t *exp2, int n)

{

    int sum, i;

    sum = 0;

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

        sum += abs(exp1[i] - exp2[i]);

    }

    return sum;

}

static void compute_exp_strategy(uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

                                 uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                                 int ch, int is_lfe)

{

    int i, j;

    int exp_diff;

    /* estimate if the exponent variation & decide if they should be

       reused in the next frame */

    exp_strategy[0][ch] = EXP_NEW;

    for(i=1;i<NB_BLOCKS;i++) {

        exp_diff = calc_exp_diff(exp[i][ch], exp[i-1][ch], N/2);

#ifdef DEBUG

        av_log(NULL, AV_LOG_DEBUG, "exp_diff=%d\n", exp_diff);

#endif

        if (exp_diff > EXP_DIFF_THRESHOLD)

            exp_strategy[i][ch] = EXP_NEW;

        else

            exp_strategy[i][ch] = EXP_REUSE;

    }

    if (is_lfe)

        return;

    /* now select the encoding strategy type : if exponents are often

       recoded, we use a coarse encoding */

    i = 0;

    while (i < NB_BLOCKS) {

        j = i + 1;

        while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE)

            j++;

        switch(j - i) {

        case 1:

            exp_strategy[i][ch] = EXP_D45;

            break;

        case 2:

        case 3:

            exp_strategy[i][ch] = EXP_D25;

            break;

        default:

            exp_strategy[i][ch] = EXP_D15;

            break;

        }

        i = j;

    }

}

/* set exp[i] to min(exp[i], exp1[i]) */

static void exponent_min(uint8_t exp[N/2], uint8_t exp1[N/2], int n)

{

    int i;

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

        if (exp1[i] < exp[i])

            exp[i] = exp1[i];

    }

}

/* update the exponents so that they are the ones the decoder will

   decode. Return the number of bits used to code the exponents */

static int encode_exp(uint8_t encoded_exp[N/2],

                      uint8_t exp[N/2],

                      int nb_exps,

                      int exp_strategy)

{

    int group_size, nb_groups, i, j, k, exp_min;

    uint8_t exp1[N/2];

    switch(exp_strategy) {

    case EXP_D15:

        group_size = 1;

        break;

    case EXP_D25:

        group_size = 2;

        break;

    default:

    case EXP_D45:

        group_size = 4;

        break;

    }

    nb_groups = ((nb_exps + (group_size * 3) - 4) / (3 * group_size)) * 3;

    /* for each group, compute the minimum exponent */

    exp1[0] = exp[0]; /* DC exponent is handled separately */

    k = 1;

    for(i=1;i<=nb_groups;i++) {

        exp_min = exp[k];

        assert(exp_min >= 0 && exp_min <= 24);

        for(j=1;j<group_size;j++) {

            if (exp[k+j] < exp_min)

                exp_min = exp[k+j];

        }

        exp1[i] = exp_min;

        k += group_size;

    }

    /* constraint for DC exponent */

    if (exp1[0] > 15)

        exp1[0] = 15;

    /* Decrease the delta between each groups to within 2

     * so that they can be differentially encoded */

    for (i=1;i<=nb_groups;i++)

        exp1[i] = FFMIN(exp1[i], exp1[i-1] + 2);

    for (i=nb_groups-1;i>=0;i--)

        exp1[i] = FFMIN(exp1[i], exp1[i+1] + 2);

    /* now we have the exponent values the decoder will see */

    encoded_exp[0] = exp1[0];

    k = 1;

    for(i=1;i<=nb_groups;i++) {

        for(j=0;j<group_size;j++) {

            encoded_exp[k+j] = exp1[i];

        }

        k += group_size;

    }

#if defined(DEBUG)

    av_log(NULL, AV_LOG_DEBUG, "exponents: strategy=%d\n", exp_strategy);

    for(i=0;i<=nb_groups * group_size;i++) {

        av_log(NULL, AV_LOG_DEBUG, "%d ", encoded_exp[i]);

    }

    av_log(NULL, AV_LOG_DEBUG, "\n");

#endif

    return 4 + (nb_groups / 3) * 7;

}

/* return the size in bits taken by the mantissa */

static int compute_mantissa_size(AC3EncodeContext *s, uint8_t *m, int nb_coefs)

{

    int bits, mant, i;

    bits = 0;

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

        mant = m[i];

        switch(mant) {

        case 0:

            /* nothing */

            break;

        case 1:

            /* 3 mantissa in 5 bits */

            if (s->mant1_cnt == 0)

                bits += 5;

            if (++s->mant1_cnt == 3)

                s->mant1_cnt = 0;

            break;

        case 2:

            /* 3 mantissa in 7 bits */

            if (s->mant2_cnt == 0)

                bits += 7;

            if (++s->mant2_cnt == 3)

                s->mant2_cnt = 0;

            break;

        case 3:

            bits += 3;

            break;

        case 4:

            /* 2 mantissa in 7 bits */

            if (s->mant4_cnt == 0)

                bits += 7;

            if (++s->mant4_cnt == 2)

                s->mant4_cnt = 0;

            break;

        case 14:

            bits += 14;

            break;

        case 15:

            bits += 16;

            break;

        default:

            bits += mant - 1;

            break;

        }

    }

    return bits;

}

static int bit_alloc(AC3EncodeContext *s,

                     uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                     uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                     uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

                     int frame_bits, int csnroffst, int fsnroffst)

{

    int i, ch;

    /* compute size */

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

        s->mant1_cnt = 0;

        s->mant2_cnt = 0;

        s->mant4_cnt = 0;

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

            ac3_parametric_bit_allocation(&s->bit_alloc,

                                          bap[i][ch], (int8_t *)encoded_exp[i][ch],

                                          0, s->nb_coefs[ch],

                                          (((csnroffst-15) << 4) +

                                           fsnroffst) << 2,

                                          fgaintab[s->fgaincod[ch]],

                                          ch == s->lfe_channel,

                                          2, 0, NULL, NULL, NULL);

            frame_bits += compute_mantissa_size(s, bap[i][ch],

                                                 s->nb_coefs[ch]);

        }

    }

#if 0

    printf("csnr=%d fsnr=%d frame_bits=%d diff=%d\n",

           csnroffst, fsnroffst, frame_bits,

           16 * s->frame_size - ((frame_bits + 7) & ~7));

#endif

    return 16 * s->frame_size - frame_bits;

}

#define SNR_INC1 4

static int compute_bit_allocation(AC3EncodeContext *s,

                                  uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                                  uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],

                                  uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],

                                  int frame_bits)

{

    int i, ch;

    int csnroffst, fsnroffst;

    uint8_t bap1[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];

    static int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };

    /* init default parameters */

    s->sdecaycod = 2;

    s->fdecaycod = 1;

    s->sgaincod = 1;

    s->dbkneecod = 2;

    s->floorcod = 4;

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

        s->fgaincod[ch] = 4;

    /* compute real values */

    s->bit_alloc.fscod = s->fscod;

    s->bit_alloc.halfratecod = s->halfratecod;

    s->bit_alloc.sdecay = sdecaytab[s->sdecaycod] >> s->halfratecod;

    s->bit_alloc.fdecay = fdecaytab[s->fdecaycod] >> s->halfratecod;

    s->bit_alloc.sgain = sgaintab[s->sgaincod];

    s->bit_alloc.dbknee = dbkneetab[s->dbkneecod];

    s->bit_alloc.floor = floortab[s->floorcod];

    /* header size */

    frame_bits += 65;

    // if (s->acmod == 2)

    //    frame_bits += 2;

    frame_bits += frame_bits_inc[s->acmod];

    /* audio blocks */

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

        frame_bits += s->nb_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */

        if (s->acmod == 2) {

            frame_bits++; /* rematstr */

            if(i==0) frame_bits += 4;

        }

        frame_bits += 2 * s->nb_channels; /* chexpstr[2] * c */

        if (s->lfe)

            frame_bits++; /* lfeexpstr */

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

            if (exp_strategy[i][ch] != EXP_REUSE)

                frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */

        }

        frame_bits++; /* baie */

        frame_bits++; /* snr */

        frame_bits += 2; /* delta / skip */

    }

    frame_bits++; /* cplinu for block 0 */

    /* bit alloc info */

    /* sdcycod[2], fdcycod[2], sgaincod[2], dbpbcod[2], floorcod[3] */

    /* csnroffset[6] */

    /* (fsnoffset[4] + fgaincod[4]) * c */

    frame_bits += 2*4 + 3 + 6 + s->nb_all_channels * (4 + 3);

    /* auxdatae, crcrsv */

    frame_bits += 2;

    /* CRC */

    frame_bits += 16;

    /* now the big work begins : do the bit allocation. Modify the snr

       offset until we can pack everything in the requested frame size */

    csnroffst = s->csnroffst;

    while (csnroffst >= 0 &&

           bit_alloc(s, bap, encoded_exp, exp_strategy, frame_bits, csnroffst, 0) < 0)

        csnroffst -= SNR_INC1;

    if (csnroffst < 0) {

        av_log(NULL, AV_LOG_ERROR, "Yack, Error !!!\n");

        return -1;

    }

    while ((csnroffst + SNR_INC1) <= 63 &&

           bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits,

                     csnroffst + SNR_INC1, 0) >= 0) {

        csnroffst += SNR_INC1;

        memcpy(bap, bap1, sizeof(bap1));

    }

    while ((csnroffst + 1) <= 63 &&

           bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits, csnroffst + 1, 0) >= 0) {

        csnroffst++;

        memcpy(bap, bap1, sizeof(bap1));

    }

    fsnroffst = 0;

    while ((fsnroffst + SNR_INC1) <= 15 &&

           bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits,

                     csnroffst, fsnroffst + SNR_INC1) >= 0) {

        fsnroffst += SNR_INC1;

        memcpy(bap, bap1, sizeof(bap1));

    }

    while ((fsnroffst + 1) <= 15 &&

           bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits,

                     csnroffst, fsnroffst + 1) >= 0) {

        fsnroffst++;

        memcpy(bap, bap1, sizeof(bap1));

    }

    s->csnroffst = csnroffst;

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

        s->fsnroffst[ch] = fsnroffst;

#if defined(DEBUG_BITALLOC)

    {

        int j;

        for(i=0;i<6;i++) {

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

                printf("Block #%d Ch%d:\n", i, ch);

                printf("bap=");

                for(j=0;j<s->nb_coefs[ch];j++) {

                    printf("%d ",bap[i][ch][j]);

                }

                printf("\n");

            }

        }

    }

#endif

    return 0;

}

void ac3_common_init(void)

{

    int i, j, k, l, v;

    /* compute bndtab and masktab from bandsz */

    k = 0;

    l = 0;

    for(i=0;i<50;i++) {

        bndtab[i] = l;

        v = bndsz[i];

        for(j=0;j<v;j++) masktab[k++]=i;

        l += v;

    }

    bndtab[50] = 0;

}

static int AC3_encode_init(AVCodecContext *avctx)

{

    int freq = avctx->sample_rate;

    int bitrate = avctx->bit_rate;

    int channels = avctx->channels;

    AC3EncodeContext *s = avctx->priv_data;

    int i, j, ch;

    float alpha;

    static const uint8_t acmod_defs[6] = {

        0x01, /* C */

        0x02, /* L R */

        0x03, /* L C R */

        0x06, /* L R SL SR */

        0x07, /* L C R SL SR */

        0x07, /* L C R SL SR (+LFE) */

    };

    avctx->frame_size = AC3_FRAME_SIZE;

    /* number of channels */

    if (channels < 1 || channels > 6)

        return -1;

    s->acmod = acmod_defs[channels - 1];

    s->lfe = (channels == 6) ? 1 : 0;

    s->nb_all_channels = channels;

    s->nb_channels = channels > 5 ? 5 : channels;

    s->lfe_channel = s->lfe ? 5 : -1;

    /* frequency */

    for(i=0;i<3;i++) {

        for(j=0;j<3;j++)

            if ((ac3_freqs[j] >> i) == freq)

                goto found;

    }

    return -1;

 found:

    s->sample_rate = freq;

    s->halfratecod = i;

    s->fscod = j;

    s->bsid = 8 + s->halfratecod;

    s->bsmod = 0; /* complete main audio service */

    /* bitrate & frame size */

    bitrate /= 1000;

    for(i=0;i<19;i++) {

        if ((ac3_bitratetab[i] >> s->halfratecod) == bitrate)

            break;

    }

    if (i == 19)

        return -1;

    s->bit_rate = bitrate;

    s->frmsizecod = i << 1;

    s->frame_size_min = (bitrate * 1000 * AC3_FRAME_SIZE) / (freq * 16);

    /* for now we do not handle fractional sizes */

    s->frame_size = s->frame_size_min;

    /* bit allocation init */

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

        /* bandwidth for each channel */

        /* XXX: should compute the bandwidth according to the frame

           size, so that we avoid anoying high freq artefacts */

        s->chbwcod[ch] = 50; /* sample bandwidth as mpeg audio layer 2 table 0 */

        s->nb_coefs[ch] = ((s->chbwcod[ch] + 12) * 3) + 37;

    }

    if (s->lfe) {

        s->nb_coefs[s->lfe_channel] = 7; /* fixed */

    }

    /* initial snr offset */

    s->csnroffst = 40;

    ac3_common_init();

    /* mdct init */

    fft_init(MDCT_NBITS - 2);

    for(i=0;i<N/4;i++) {

        alpha = 2 * M_PI * (i + 1.0 / 8.0) / (float)N;

        xcos1[i] = fix15(-cos(alpha));

        xsin1[i] = fix15(-sin(alpha));

    }

    ac3_crc_init();

    avctx->coded_frame= avcodec_alloc_frame();

    avctx->coded_frame->key_frame= 1;

    return 0;

}

/* output the AC3 frame header */

static void output_frame_header(AC3EncodeContext *s, unsigned char *frame)

{

    init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE);

    put_bits(&s->pb, 16, 0x0b77); /* frame header */

    put_bits(&s->pb, 16, 0); /* crc1: will be filled later */

    put_bits(&s->pb, 2, s->fscod);

    put_bits(&s->pb, 6, s->frmsizecod + (s->frame_size - s->frame_size_min));

    put_bits(&s->pb, 5, s->bsid);

    put_bits(&s->pb, 3, s->bsmod);

    put_bits(&s->pb, 3, s->acmod);

    if ((s->acmod & 0x01) && s->acmod != 0x01)

        put_bits(&s->pb, 2, 1); /* XXX -4.5 dB */

    if (s->acmod & 0x04)

        put_bits(&s->pb, 2, 1); /* XXX -6 dB */

    if (s->acmod == 0x02)

        put_bits(&s->pb, 2, 0); /* surround not indicated */

    put_bits(&s->pb, 1, s->lfe); /* LFE */

    put_bits(&s->pb, 5, 31); /* dialog norm: -31 db */

    put_bits(&s->pb, 1, 0); /* no compression control word */

    put_bits(&s->pb, 1, 0); /* no lang code */

    put_bits(&s->pb, 1, 0); /* no audio production info */

    put_bits(&s->pb, 1, 0); /* no copyright */

    put_bits(&s->pb, 1, 1); /* original bitstream */

    put_bits(&s->pb, 1, 0); /* no time code 1 */

    put_bits(&s->pb, 1, 0); /* no time code 2 */

    put_bits(&s->pb, 1, 0); /* no addtional bit stream info */

}

/* symetric quantization on 'levels' levels */

static inline int sym_quant(int c, int e, int levels)

{

    int v;

    if (c >= 0) {

        v = (levels * (c << e)) >> 24;

        v = (v + 1) >> 1;

        v = (levels >> 1) + v;

    } else {

        v = (levels * ((-c) << e)) >> 24;

        v = (v + 1) >> 1;

        v = (levels >> 1) - v;

    }

    assert (v >= 0 && v < levels);

    return v;

}

/* asymetric quantization on 2^qbits levels */

static inline int asym_quant(int c, int e, int qbits)

{

    int lshift, m, v;

    lshift = e + qbits - 24;

    if (lshift >= 0)

        v = c << lshift;

    else

        v = c >> (-lshift);

    /* rounding */

    v = (v + 1) >> 1;

    m = (1 << (qbits-1));

    if (v >= m)

        v = m - 1;

    assert(v >= -m);

    return v & ((1 << qbits)-1);

}

/* Output one audio block. There are NB_BLOCKS audio blocks in one AC3

   frame */

static void output_audio_block(AC3EncodeContext *s,

                               uint8_t exp_strategy[AC3_MAX_CHANNELS],

                               uint8_t encoded_exp[AC3_MAX_CHANNELS][N/2],

                               uint8_t bap[AC3_MAX_CHANNELS][N/2],

                               int32_t mdct_coefs[AC3_MAX_CHANNELS][N/2],

                               int8_t global_exp[AC3_MAX_CHANNELS],

                               int block_num)

{

    int ch, nb_groups, group_size, i, baie, rbnd;

    uint8_t *p;

    uint16_t qmant[AC3_MAX_CHANNELS][N/2];

    int exp0, exp1;

    int mant1_cnt, mant2_cnt, mant4_cnt;

    uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr;

    int delta0, delta1, delta2;

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

        put_bits(&s->pb, 1, 0); /* 512 point MDCT */

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

        put_bits(&s->pb, 1, 1); /* no dither */

    put_bits(&s->pb, 1, 0); /* no dynamic range */

    if (block_num == 0) {

        /* for block 0, even if no coupling, we must say it. This is a

           waste of bit :-) */

        put_bits(&s->pb, 1, 1); /* coupling strategy present */

        put_bits(&s->pb, 1, 0); /* no coupling strategy */

    } else {

        put_bits(&s->pb, 1, 0); /* no new coupling strategy */

    }

    if (s->acmod == 2)

      {

        if(block_num==0)

          {

            /* first block must define rematrixing (rematstr)  */

            put_bits(&s->pb, 1, 1);

            /* dummy rematrixing rematflg(1:4)=0 */

            for (rbnd=0;rbnd<4;rbnd++)

              put_bits(&s->pb, 1, 0);

          }

        else

          {

            /* no matrixing (but should be used in the future) */

            put_bits(&s->pb, 1, 0);

          }

      }

#if defined(DEBUG)

    {

      static int count = 0;

      av_log(NULL, AV_LOG_DEBUG, "Block #%d (%d)\n", block_num, count++);

    }

#endif

    /* exponent strategy */

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

        put_bits(&s->pb, 2, exp_strategy[ch]);

    }

    if (s->lfe) {

        put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);

    }

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

        if (exp_strategy[ch] != EXP_REUSE)

            put_bits(&s->pb, 6, s->chbwcod[ch]);

    }

    /* exponents */

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

        switch(exp_strategy[ch]) {

        case EXP_REUSE:

            continue;

        case EXP_D15:

            group_size = 1;

            break;

        case EXP_D25:

            group_size = 2;

            break;

        default:

        case EXP_D45:

            group_size = 4;

            break;

        }

        nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);

        p = encoded_exp[ch];

        /* first exponent */

        exp1 = *p++;

        put_bits(&s->pb, 4, exp1);

        /* next ones are delta encoded */

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

            /* merge three delta in one code */

            exp0 = exp1;

            exp1 = p[0];

            p += group_size;

            delta0 = exp1 - exp0 + 2;

            exp0 = exp1;

            exp1 = p[0];

            p += group_size;

            delta1 = exp1 - exp0 + 2;

            exp0 = exp1;

            exp1 = p[0];

            p += group_size;

            delta2 = exp1 - exp0 + 2;

            put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);

        }

        if (ch != s->lfe_channel)

            put_bits(&s->pb, 2, 0); /* no gain range info */

    }

    /* bit allocation info */

    baie = (block_num == 0);

    put_bits(&s->pb, 1, baie);

    if (baie) {

        put_bits(&s->pb, 2, s->sdecaycod);

        put_bits(&s->pb, 2, s->fdecaycod);

        put_bits(&s->pb, 2, s->sgaincod);

        put_bits(&s->pb, 2, s->dbkneecod);

        put_bits(&s->pb, 3, s->floorcod);

    }

    /* snr offset */

    put_bits(&s->pb, 1, baie); /* always present with bai */

    if (baie) {

        put_bits(&s->pb, 6, s->csnroffst);

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

            put_bits(&s->pb, 4, s->fsnroffst[ch]);

            put_bits(&s->pb, 3, s->fgaincod[ch]);

        }

    }

    put_bits(&s->pb, 1, 0); /* no delta bit allocation */

    put_bits(&s->pb, 1, 0); /* no data to skip */

    /* mantissa encoding : we use two passes to handle the grouping. A

       one pass method may be faster, but it would necessitate to

       modify the output stream. */

    /* first pass: quantize */

    mant1_cnt = mant2_cnt = mant4_cnt = 0;

    qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

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

        int b, c, e, v;

        for(i=0;i<s->nb_coefs[ch];i++) {

            c = mdct_coefs[ch][i];

            e = encoded_exp[ch][i] - global_exp[ch];

            b = bap[ch][i];

            switch(b) {

            case 0:

                v = 0;

                break;

            case 1:

                v = sym_quant(c, e, 3);

                switch(mant1_cnt) {

                case 0:

                    qmant1_ptr = &qmant[ch][i];

                    v = 9 * v;

                    mant1_cnt = 1;

                    break;

                case 1:

                    *qmant1_ptr += 3 * v;

                    mant1_cnt = 2;

                    v = 128;

                    break;

                default:

                    *qmant1_ptr += v;

                    mant1_cnt = 0;

                    v = 128;

                    break;

                }

                break;

            case 2:

                v = sym_quant(c, e, 5);

                switch(mant2_cnt) {

                case 0:

                    qmant2_ptr = &qmant[ch][i];

                    v = 25 * v;

                    mant2_cnt = 1;

                    break;

                case 1:

                    *qmant2_ptr += 5 * v;

                    mant2_cnt = 2;

                    v = 128;

                    break;

                default:

                    *qmant2_ptr += v;

                    mant2_cnt = 0;

                    v = 128;

                    break;

                }

                break;

            case 3:

                v = sym_quant(c, e, 7);

                break;

            case 4:

                v = sym_quant(c, e, 11);

                switch(mant4_cnt) {

                case 0:

                    qmant4_ptr = &qmant[ch][i];

                    v = 11 * v;

                    mant4_cnt = 1;

                    break;

                default:

                    *qmant4_ptr += v;

                    mant4_cnt = 0;

                    v = 128;

                    break;

                }

                break;

            case 5:

                v = sym_quant(c, e, 15);

                break;

            case 14:

                v = asym_quant(c, e, 14);

                break;

            case 15:

                v = asym_quant(c, e, 16);

                break;

            default:

                v = asym_quant(c, e, b - 1);

                break;

            }

            qmant[ch][i] = v;

        }

    }

    /* second pass : output the values */

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

        int b, q;

        for(i=0;i<s->nb_coefs[ch];i++) {

            q = qmant[ch][i];

            b = bap[ch][i];

            switch(b) {

            case 0:

                break;

            case 1:

                if (q != 128)

                    put_bits(&s->pb, 5, q);

                break;

            case 2:

                if (q != 128)

                    put_bits(&s->pb, 7, q);

                break;

            case 3:

                put_bits(&s->pb, 3, q);

                break;

            case 4:

                if (q != 128)

                    put_bits(&s->pb, 7, q);

                break;

            case 14:

                put_bits(&s->pb, 14, q);

                break;

            case 15:

                put_bits(&s->pb, 16, q);

                break;

            default:

                put_bits(&s->pb, b - 1, q);

                break;

            }

        }

    }

}

/* compute the ac3 crc */

#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

static void ac3_crc_init(void)

{

    unsigned int c, n, k;

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

        c = n << 8;

        for (k = 0; k < 8; k++) {

            if (c & (1 << 15))

                c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);

            else

                c = c << 1;

        }

        crc_table[n] = c;

    }

}

static unsigned int ac3_crc(uint8_t *data, int n, unsigned int crc)

{

    int i;

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

        crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;

    }

    return crc;

}

static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)

{

    unsigned int c;

    c = 0;

    while (a) {

        if (a & 1)

            c ^= b;

        a = a >> 1;

        b = b << 1;

        if (b & (1 << 16))

            b ^= poly;

    }

    return c;

}

static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)

{

    unsigned int r;

    r = 1;

    while (n) {

        if (n & 1)

            r = mul_poly(r, a, poly);

        a = mul_poly(a, a, poly);

        n >>= 1;

    }

    return r;

}

/* compute log2(max(abs(tab[]))) */

static int log2_tab(int16_t *tab, int n)

{

    int i, v;

    v = 0;

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

        v |= abs(tab[i]);

    }

    return av_log2(v);

}