layer3.c

音频编码

         gr_infos->pow2gain += 2;
       gr_infos->scalefac_compress = getbits(mp,9);
/* window-switching flag == 1 for block_Type != 0 .. and block-type == 0 -> win-sw-flag = 0 */
       if(get1bit(mp)) 
       {
         int i;
         gr_infos->block_type = getbits_fast(mp,2);
         gr_infos->mixed_block_flag = get1bit(mp);
         gr_infos->table_select[0] = getbits_fast(mp,5);
         gr_infos->table_select[1] = getbits_fast(mp,5);
         /*
          * table_select[2] not needed, because there is no region2,
          * but to satisfy some verifications tools we set it either.
          */
         gr_infos->table_select[2] = 0;
         for(i=0;i<3;i++) {
	   unsigned int sbg = (getbits_fast(mp,3)<<3);
           gr_infos->full_gain[i] = gr_infos->pow2gain + sbg;
#ifndef NOANALYSIS
	   if (mpg123_pinfo!=NULL)
	     mpg123_pinfo->sub_gain[0][ch][i]=sbg/8;
#endif

	 }

         if(gr_infos->block_type == 0) {
           fprintf(stderr,"Blocktype == 0 and window-switching == 1 not allowed.\n");
		   /* error seems to be very good recoverable, so don't exit */
           /* exit(1); */
         }
         /* region_count/start parameters are implicit in this case. */       
/* check this again! */
         if(gr_infos->block_type == 2) {
            if (sfreq == 8)
                gr_infos->region1start = 36;
            else
                gr_infos->region1start = 36>>1;
         }
         else if(sfreq == 8)
/* check this for 2.5 and sfreq=8 */
           gr_infos->region1start = 108>>1;
         else
           gr_infos->region1start = 54>>1;
         gr_infos->region2start = 576>>1;
       }
       else 
       {
         int i,r0c,r1c;
         for (i=0; i<3; i++)
           gr_infos->table_select[i] = getbits_fast(mp,5);
         r0c = getbits_fast(mp,4);
         r1c = getbits_fast(mp,3);
         gr_infos->region1start = bandInfo[sfreq].longIdx[r0c+1] >> 1 ;
         gr_infos->region2start = bandInfo[sfreq].longIdx[r0c+1+r1c+1] >> 1;
         gr_infos->block_type = 0;
         gr_infos->mixed_block_flag = 0;
       }
       gr_infos->scalefac_scale = get1bit(mp);
       gr_infos->count1table_select = get1bit(mp);
   }
}

/*
 * read scalefactors
 */

static int
III_get_scale_factors_1(PMPSTR mp, int *scf,struct gr_info_s *gr_infos)
{
   static const unsigned char slen[2][16] = {
     {0, 0, 0, 0, 3, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4},
     {0, 1, 2, 3, 0, 1, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3}
   };
   int numbits;
   int num0 = slen[0][gr_infos->scalefac_compress];
   int num1 = slen[1][gr_infos->scalefac_compress];

    if (gr_infos->block_type == 2) 
    {
      int i=18;
      numbits = (num0 + num1) * 18;

      if (gr_infos->mixed_block_flag) {
         for (i=8;i;i--)
           *scf++ = getbits_fast(mp,num0);
         i = 9;
         numbits -= num0; /* num0 * 17 + num1 * 18 */
      }

      for (;i;i--)
        *scf++ = getbits_fast(mp,num0);
      for (i = 18; i; i--)
        *scf++ = getbits_fast(mp,num1);
      *scf++ = 0; *scf++ = 0; *scf++ = 0; /* short[13][0..2] = 0 */
    }
    else 
    {
      int i;
      int scfsi = gr_infos->scfsi;

      if(scfsi < 0) { /* scfsi < 0 => granule == 0 */
         for(i=11;i;i--)
           *scf++ = getbits_fast(mp,num0);
         for(i=10;i;i--)
           *scf++ = getbits_fast(mp,num1);
         numbits = (num0 + num1) * 10 + num0;
      }
      else {
        numbits = 0;
        if(!(scfsi & 0x8)) {
          for (i=6;i;i--)
            *scf++ = getbits_fast(mp,num0);
          numbits += num0 * 6;
        }
        else {
          scf += 6;
        }

        if(!(scfsi & 0x4)) {
          for (i=5;i;i--)
            *scf++ = getbits_fast(mp,num0);
          numbits += num0 * 5;
        }
        else {
          scf += 5;
        }

        if(!(scfsi & 0x2)) {
          for(i=5;i;i--)
            *scf++ = getbits_fast(mp,num1);
          numbits += num1 * 5;
        }
        else {
          scf += 5;
        }

        if(!(scfsi & 0x1)) {
          for (i=5;i;i--)
            *scf++ = getbits_fast(mp,num1);
          numbits += num1 * 5;
        }
        else {
          scf += 5;
        }
      }

      *scf++ = 0;  /* no l[21] in original sources */
    }
    return numbits;
}


static int
III_get_scale_factors_2(PMPSTR mp, int *scf,struct gr_info_s *gr_infos,int i_stereo)
{
  unsigned char *pnt;
  int i,j;
  unsigned int slen;
  int n = 0;
  int numbits = 0;

  static const unsigned char stab[3][6][4] = {
   { { 6, 5, 5,5 } , { 6, 5, 7,3 } , { 11,10,0,0} ,
     { 7, 7, 7,0 } , { 6, 6, 6,3 } , {  8, 8,5,0} } ,
   { { 9, 9, 9,9 } , { 9, 9,12,6 } , { 18,18,0,0} ,
     {12,12,12,0 } , {12, 9, 9,6 } , { 15,12,9,0} } ,
   { { 6, 9, 9,9 } , { 6, 9,12,6 } , { 15,18,0,0} ,
     { 6,15,12,0 } , { 6,12, 9,6 } , {  6,18,9,0} } }; 

  if(i_stereo) /* i_stereo AND second channel -> do_layer3() checks this */
    slen = i_slen2[gr_infos->scalefac_compress>>1];
  else
    slen = n_slen2[gr_infos->scalefac_compress];

  gr_infos->preflag = (slen>>15) & 0x1;

  n = 0;  
  if( gr_infos->block_type == 2 ) {
    n++;
    if(gr_infos->mixed_block_flag)
      n++;
  }

  pnt = (unsigned char *)stab[n][(slen>>12)&0x7];

  for(i=0;i<4;i++) {
    int num = slen & 0x7;
    slen >>= 3;
    if(num) {
      for(j=0;j<(int)(pnt[i]);j++)
        *scf++ = getbits_fast(mp,num);
      numbits += pnt[i] * num;
    }
    else {
      for(j=0;j<(int)(pnt[i]);j++)
        *scf++ = 0;
    }
  }
  
  n = (n << 1) + 1;
  for(i=0;i<n;i++)
    *scf++ = 0;

  return numbits;
}

static const int pretab1 [22] = {0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,2,2,3,3,3,2,0}; /* char enough ? */
static const int pretab2 [22] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

/*
 * don't forget to apply the same changes to III_dequantize_sample_ms() !!! 
 */
static int III_dequantize_sample(PMPSTR mp, real xr[SBLIMIT][SSLIMIT],int *scf,
   struct gr_info_s *gr_infos,int sfreq,int part2bits)
{
  int shift = 1 + gr_infos->scalefac_scale;
  real *xrpnt = (real *) xr;
  int l[3],l3;
  int part2remain = gr_infos->part2_3_length - part2bits;
  int *me;

  {
    int i;
    
    for(i=(&xr[SBLIMIT][0]-xrpnt)>>1;i>0;i--) {
      *xrpnt++ = 0.0;
      *xrpnt++ = 0.0;
    }

    xrpnt = (real *) xr;
  }

  {
    int bv       = gr_infos->big_values;
    int region1  = gr_infos->region1start;
    int region2  = gr_infos->region2start;

    l3 = ((576>>1)-bv)>>1;   
/*
 * we may lose the 'odd' bit here !! 
 * check this later again 
 */
    if(bv <= region1) {
      l[0] = bv; l[1] = 0; l[2] = 0;
    }
    else {
      l[0] = region1;
      if(bv <= region2) {
        l[1] = bv - l[0];  l[2] = 0;
      }
      else {
        l[1] = region2 - l[0]; l[2] = bv - region2;
      }
    }
  }
  /* MDH crash fix */
  {
      int i;
      for (i = 0; i < 3; i++) {
	  if (l[i] < 0) {
	      fprintf(stderr, "mpg123: Bogus region length (%d)\n", l[i]);
	      l[i] = 0;
	  }
      }
  }
  /* end MDH crash fix */

  if(gr_infos->block_type == 2) {
    /*
     * decoding with short or mixed mode BandIndex table 
     */
    int i,max[4];
    int step=0,lwin=0,cb=0;
    real v = 0.0;
    int *m,mc;

    if(gr_infos->mixed_block_flag) {
      max[3] = -1;
      max[0] = max[1] = max[2] = 2;
      m = map[sfreq][0];
      me = mapend[sfreq][0];
    }
    else {
      max[0] = max[1] = max[2] = max[3] = -1;
      /* max[3] not really needed in this case */
      m = map[sfreq][1];
      me = mapend[sfreq][1];
    }

    mc = 0;
    for(i=0;i<2;i++) {
      int lp = l[i];
      struct newhuff *h = (struct newhuff *)(ht+gr_infos->table_select[i]);
      for(;lp;lp--,mc--) {
        int x,y;
        if( (!mc) ) {
          mc = *m++;
          xrpnt = ((real *) xr) + (*m++);
          lwin = *m++;
          cb = *m++;
          if(lwin == 3) {
            v = gr_infos->pow2gain[(*scf++) << shift];
            step = 1;
          }
          else {
            v = gr_infos->full_gain[lwin][(*scf++) << shift];
            step = 3;
          }
        }
        {
          short *val = (short *)h->table;
          while((y=*val++)<0) {
            if (get1bit(mp))
              val -= y;
            part2remain--;
          }
          x = y >> 4;
          y &= 0xf;
        }
        if(x == 15) {
          max[lwin] = cb;
          part2remain -= h->linbits+1;
          x += getbits(mp,(int)h->linbits);
          if(get1bit(mp))
            *xrpnt = -ispow[x] * v;
          else
            *xrpnt =  ispow[x] * v;
        }
        else if(x) {
          max[lwin] = cb;
          if(get1bit(mp))
            *xrpnt = -ispow[x] * v;
          else
            *xrpnt =  ispow[x] * v;
          part2remain--;
        }
        else
          *xrpnt = 0.0;
        xrpnt += step;
        if(y == 15) {
          max[lwin] = cb;
          part2remain -= h->linbits+1;
          y += getbits(mp,(int)h->linbits);
          if(get1bit(mp))
            *xrpnt = -ispow[y] * v;
          else
            *xrpnt =  ispow[y] * v;
        }
        else if(y) {
          max[lwin] = cb;
          if(get1bit(mp))
            *xrpnt = -ispow[y] * v;
          else
            *xrpnt =  ispow[y] * v;
          part2remain--;
        }
        else
          *xrpnt = 0.0;
        xrpnt += step;
      }
    }
    for(;l3 && (part2remain > 0);l3--) {
      struct newhuff *h = (struct newhuff *)(htc+gr_infos->count1table_select);
      short *val = (short *)h->table,a;

      while((a=*val++)<0) {
        part2remain--;
        if(part2remain < 0) {
          part2remain++;
          a = 0;
          break;
        }
        if (get1bit(mp))
          val -= a;
      }
      for(i=0;i<4;i++) {
        if(!(i & 1)) {
          if(!mc) {
            mc = *m++;
            xrpnt = ((real *) xr) + (*m++);
            lwin = *m++;
            cb = *m++;
            if(lwin == 3) {
              v = gr_infos->pow2gain[(*scf++) << shift];
              step = 1;
            }
            else {
              v = gr_infos->full_gain[lwin][(*scf++) << shift];
              step = 3;
            }
          }
          mc--;
        }
        if( (a & (0x8>>i)) ) {
          max[lwin] = cb;
          part2remain--;
          if(part2remain < 0) {
            part2remain++;
            break;
          }
          if(get1bit(mp)) 
            *xrpnt = -v;
          else
            *xrpnt = v;
        }
        else
          *xrpnt = 0.0;
        xrpnt += step;
      }
    }
 
    while( m < me ) {
      if(!mc) {
        mc = *m++;
        xrpnt = ((real *) xr) + *m++;
        if( (*m++) == 3)
          step = 1;
        else
          step = 3;
        m++; /* cb */
      }
      mc--;
      *xrpnt = 0.0;
      xrpnt += step;
      *xrpnt = 0.0;
      xrpnt += step;
/* we could add a little opt. here:
 * if we finished a band for window 3 or a long band
 * further bands could copied in a simple loop without a
 * special 'map' decoding
 */
    }

    gr_infos->maxband[0] = max[0]+1;
    gr_infos->maxband[1] = max[1]+1;
    gr_infos->maxband[2] = max[2]+1;
    gr_infos->maxbandl = max[3]+1;

    {
      int rmax = max[0] > max[1] ? max[0] : max[1];
      rmax = (rmax > max[2] ? rmax : max[2]) + 1;
      gr_infos->maxb = rmax ? shortLimit[sfreq][rmax] : longLimit[sfreq][max[3]+1];
    }

  }
  else {
	/*
     * decoding with 'long' BandIndex table (block_type != 2)
     */
    int *pretab = (int *)(gr_infos->preflag ? pretab1 : pretab2);