cupl3.c

FreeAMP(MP3播放)程序源代码-用来研究MP3解码

   bitget(m, 2);			/* skip layer */
   prot = bitget(m, 1);		/* bitget prot bit */
   br_index = bitget(m, 4);
   m->cupl.sr_index = bitget(m, 2);
   m->cupl.pad = bitget(m, 1);
   bitget(m, 1);			/* skip to mode */
   m->cupl.side_info.mode = bitget(m, 2);	/* mode */
   m->cupl.side_info.mode_ext = bitget(m, 2);	/* mode ext */

   if (m->cupl.side_info.mode != 1)
      m->cupl.side_info.mode_ext = 0;

/* adjust global gain in ms mode to avoid having to mult by 1/sqrt(2) */
   m->cupl.ms_mode = m->cupl.side_info.mode_ext >> 1;
   m->cupl.is_mode = m->cupl.side_info.mode_ext & 1;

   m->cupl.crcbytes = 0;
   if (prot)
      bitget(m, 4);		/* skip to data */
   else
   {
      bitget(m, 20);		/* skip crc */
      m->cupl.crcbytes = 2;
   }

   if (br_index > 0)
   {				/* framebytes fixed for free format */
      if (m->cupl.mpeg25_flag == 0)
      {
	 m->cupl.framebytes =
	    1440 * mp_br_tableL3[m->cupl.id][br_index] / mp_sr20_table[m->cupl.id][m->cupl.sr_index];
      }
      else
      {
	 m->cupl.framebytes =
	    2880 * mp_br_tableL3[m->cupl.id][br_index] / mp_sr20_table[m->cupl.id][m->cupl.sr_index];
       //if( sr_index == 2 ) return 0;  // fail mpeg25 8khz
      }
   }
   m->cupl.side_info.main_data_begin = bitget(m, 8);
   if (m->cupl.side_info.mode == 3)
   {
      m->cupl.side_info.private_bits = bitget(m, 1);
      m->cupl.nchan = 1;
      m->cupl.stereo_flag = 0;
      side_bytes = (4 + 9);
/*-- with header --*/
   }
   else
   {
      m->cupl.side_info.private_bits = bitget(m, 2);
      m->cupl.nchan = 2;
      m->cupl.stereo_flag = 1;
      side_bytes = (4 + 17);
/*-- with header --*/
   }
   m->cupl.side_info.scfsi[1] = m->cupl.side_info.scfsi[0] = 0;


   for (ch = 0; ch < m->cupl.nchan; ch++)
   {
      m->cupl.side_info.gr[igr][ch].part2_3_length = bitget(m, 12);
      m->cupl.side_info.gr[igr][ch].big_values = bitget(m, 9);
	  
      if (m->cupl.side_info.gr[igr][ch].big_values > 288)
	  return -1; // to catch corrupt sideband data
      
      m->cupl.side_info.gr[igr][ch].global_gain = bitget(m, 8) + m->cupl.gain_adjust;
      if (m->cupl.ms_mode)
	 m->cupl.side_info.gr[igr][ch].global_gain -= 2;
      m->cupl.side_info.gr[igr][ch].scalefac_compress = bitget(m, 9);
      m->cupl.side_info.gr[igr][ch].window_switching_flag = bitget(m, 1);
      if (m->cupl.side_info.gr[igr][ch].window_switching_flag)
      {
	 m->cupl.side_info.gr[igr][ch].block_type = bitget(m, 2);
	 m->cupl.side_info.gr[igr][ch].mixed_block_flag = bitget(m, 1);
	 m->cupl.side_info.gr[igr][ch].table_select[0] = bitget(m, 5);
	 m->cupl.side_info.gr[igr][ch].table_select[1] = bitget(m, 5);
	 m->cupl.side_info.gr[igr][ch].subblock_gain[0] = bitget(m, 3);
	 m->cupl.side_info.gr[igr][ch].subblock_gain[1] = bitget(m, 3);
	 m->cupl.side_info.gr[igr][ch].subblock_gain[2] = bitget(m, 3);
       /* region count set in terms of long block cb's/bands  */
       /* r1 set so r0+r1+1 = 21 (lookup produces 576 bands ) */
       /* bt=1 or 3       54 samples */
       /* bt=2 mixed=0    36 samples */
       /* bt=2 mixed=1    54 (8 long sf) samples? or maybe 36 */
       /* region0 discussion says 54 but this would mix long */
       /* and short in region0 if scale factors switch */
       /* at band 36 (6 long scale factors) */
	 if ((m->cupl.side_info.gr[igr][ch].block_type == 2))
	 {
	    m->cupl.side_info.gr[igr][ch].region0_count = (6 - 1);	/* 36 samples */
	    m->cupl.side_info.gr[igr][ch].region1_count = 20 - (6 - 1);
	 }
	 else
	 {			/* long block type 1 or 3 */
	    m->cupl.side_info.gr[igr][ch].region0_count = (8 - 1);	/* 54 samples */
	    m->cupl.side_info.gr[igr][ch].region1_count = 20 - (8 - 1);
	 }
      }
      else
      {
	 m->cupl.side_info.gr[igr][ch].mixed_block_flag = 0;
	 m->cupl.side_info.gr[igr][ch].block_type = 0;
	 m->cupl.side_info.gr[igr][ch].table_select[0] = bitget(m, 5);
	 m->cupl.side_info.gr[igr][ch].table_select[1] = bitget(m, 5);
	 m->cupl.side_info.gr[igr][ch].table_select[2] = bitget(m, 5);
	 m->cupl.side_info.gr[igr][ch].region0_count = bitget(m, 4);
	 m->cupl.side_info.gr[igr][ch].region1_count = bitget(m, 3);
      }
      m->cupl.side_info.gr[igr][ch].preflag = 0;
      m->cupl.side_info.gr[igr][ch].scalefac_scale = bitget(m, 1);
      m->cupl.side_info.gr[igr][ch].count1table_select = bitget(m, 1);
   }

/* return  bytes in header + side info */
   return side_bytes;
}

/*-----------------------------------------------------------------*/
static void unpack_main(MPEG *m, unsigned char *pcm, int igr)
{
   int ch;
   int bit0;
   int n1, n2, n3, n4, nn2, nn3;
   int nn4;
   int qbits;
   int m0;


   for (ch = 0; ch < m->cupl.nchan; ch++)
   {
      bitget_init(m, m->cupl.buf + (m->cupl.main_pos_bit >> 3));
      bit0 = (m->cupl.main_pos_bit & 7);
      if (bit0)
	 bitget(m, bit0);
      m->cupl.main_pos_bit += m->cupl.side_info.gr[igr][ch].part2_3_length;
      bitget_init_end(m, m->cupl.buf + ((m->cupl.main_pos_bit + 39) >> 3));
/*-- scale factors --*/
      if (m->cupl.id)
	 unpack_sf_sub_MPEG1(m, &m->cupl.sf[igr][ch],
			  &m->cupl.side_info.gr[igr][ch], m->cupl.side_info.scfsi[ch], igr);
      else

         unpack_sf_sub_MPEG2(m, &m->cupl.sf[igr][ch],
			 &m->cupl.side_info.gr[igr][ch], m->cupl.is_mode & ch, &m->cupl.is_sf_info);

      if (m->eq->enableEQ)
      {
	      m->cupl.side_info.gr[igr][ch].global_gain += m->eq->EQ_gain_adjust;
      }

/*--- huff data ---*/
      n1 = m->cupl.sfBandIndex[0][m->cupl.side_info.gr[igr][ch].region0_count];
      n2 = m->cupl.sfBandIndex[0][m->cupl.side_info.gr[igr][ch].region0_count
			  + m->cupl.side_info.gr[igr][ch].region1_count + 1];
      n3 = m->cupl.side_info.gr[igr][ch].big_values;
      n3 = n3 + n3;


      if (n3 > m->cupl.band_limit)
	 n3 = m->cupl.band_limit;
      if (n2 > n3)
	 n2 = n3;
      if (n1 > n3)
	 n1 = n3;
      nn3 = n3 - n2;
      nn2 = n2 - n1;
      unpack_huff(m, m->cupl.sample[ch][igr], n1, 
                  m->cupl.side_info.gr[igr][ch].table_select[0]);
      unpack_huff(m, m->cupl.sample[ch][igr] + n1, nn2, 
                  m->cupl.side_info.gr[igr][ch].table_select[1]);
      unpack_huff(m, m->cupl.sample[ch][igr] + n2, nn3, 
                  m->cupl.side_info.gr[igr][ch].table_select[2]);
      qbits = m->cupl.side_info.gr[igr][ch].part2_3_length - (bitget_bits_used(m) - bit0);
      nn4 = unpack_huff_quad(m, m->cupl.sample[ch][igr] + n3, 
                             m->cupl.band_limit - n3, qbits,
			     m->cupl.side_info.gr[igr][ch].count1table_select);
      n4 = n3 + nn4;
      m->cupl.nsamp[igr][ch] = n4;
    //limit n4 or allow deqaunt to sf band 22
      if (m->cupl.side_info.gr[igr][ch].block_type == 2)
	 n4 = min(n4, m->cupl.band_limit12);
      else
	 n4 = min(n4, m->cupl.band_limit21);
      if (n4 < 576)
	 memset(m->cupl.sample[ch][igr] + n4, 0, sizeof(SAMPLE) * (576 - n4));
      if (m->cupl.bitdat.bs_ptr > m->cupl.bitdat.bs_ptr_end)
      {				// bad data overrun

	 memset(m->cupl.sample[ch][igr], 0, sizeof(SAMPLE) * (576));
      }
   }



/*--- dequant ---*/
   for (ch = 0; ch < m->cupl.nchan; ch++)
   {
      dequant(m,m->cupl.sample[ch][igr],
	      &m->cupl.nsamp[igr][ch],	/* nsamp updated for shorts */
	      &m->cupl.sf[igr][ch], &m->cupl.side_info.gr[igr][ch],
	      &m->cupl.cb_info[igr][ch], m->cupl.ncbl_mixed);
   }

/*--- ms stereo processing  ---*/
   if (m->cupl.ms_mode)
   {
      if (m->cupl.is_mode == 0)
      {
	 m0 = m->cupl.nsamp[igr][0];	/* process to longer of left/right */
	 if (m0 < m->cupl.nsamp[igr][1])
	    m0 = m->cupl.nsamp[igr][1];
      }
      else
      {				/* process to last cb in right */
	 m0 = m->cupl.sfBandIndex[m->cupl.cb_info[igr][1].cbtype][m->cupl.cb_info[igr][1].cbmax];
      }
      ms_process(m->cupl.sample[0][igr], m0);
   }

/*--- is stereo processing  ---*/
   if (m->cupl.is_mode)
   {
      if (m->cupl.id)
	 is_process_MPEG1(m, m->cupl.sample[0][igr], &m->cupl.sf[igr][1],
			  m->cupl.cb_info[igr], m->cupl.nsamp[igr][0], m->cupl.ms_mode);
      else
	 is_process_MPEG2(m,m->cupl.sample[0][igr], &m->cupl.sf[igr][1],
			  m->cupl.cb_info[igr], &m->cupl.is_sf_info,
			  m->cupl.nsamp[igr][0], m->cupl.ms_mode);
   }

/*-- adjust ms and is modes to max of left/right */
   if (m->cupl.side_info.mode_ext)
   {
      if (m->cupl.nsamp[igr][0] < m->cupl.nsamp[igr][1])
	 m->cupl.nsamp[igr][0] = m->cupl.nsamp[igr][1];
      else
	 m->cupl.nsamp[igr][1] = m->cupl.nsamp[igr][0];
   }

/*--- antialias ---*/
   for (ch = 0; ch < m->cupl.nchan; ch++)
   {
      if (m->cupl.cb_info[igr][ch].ncbl == 0)
	 continue;		/* have no long blocks */
      if (m->cupl.side_info.gr[igr][ch].mixed_block_flag)
	 n1 = 1;		/* 1 -> 36 samples */
      else
	 n1 = (m->cupl.nsamp[igr][ch] + 7) / 18;
      if (n1 > 31)
	 n1 = 31;
      antialias(m, m->cupl.sample[ch][igr], n1);
      n1 = 18 * n1 + 8;		/* update number of samples */
      if (n1 > m->cupl.nsamp[igr][ch])
	 m->cupl.nsamp[igr][ch] = n1;
   }



/*--- hybrid + sbt ---*/
   m->cupl.Xform(m, pcm, igr);


/*-- done --*/
}
/*--------------------------------------------------------------------*/
/*-----------------------------------------------------------------*/
IN_OUT L3audio_decode(void *mv, unsigned char *bs, unsigned char *pcm)
{
   MPEG *m = mv;
   return m->cupl.decode_function((MPEG *)mv, bs, pcm);
}

/*--------------------------------------------------------------------*/
IN_OUT L3audio_decode_MPEG1(void *mv, unsigned char *bs, unsigned char *pcm)
{
   MPEG *m = mv;
   int sync;
   IN_OUT in_out;
   int side_bytes;
   int nbytes;
   
   m->cupl.iframe++;

   bitget_init(m, bs);		/* initialize bit getter */
/* test sync */
   in_out.in_bytes = 0;		/* assume fail */
   in_out.out_bytes = 0;
   sync = bitget(m, 12);

   if (sync != 0xFFF)
      return in_out;		/* sync fail */
/*-----------*/

/*-- unpack side info --*/
   side_bytes = unpack_side_MPEG1(m);
   if (side_bytes < 0)
   {
       in_out.in_bytes = 0;
       return in_out;
   }
   m->cupl.padframebytes = m->cupl.framebytes + m->cupl.pad;
   in_out.in_bytes = m->cupl.padframebytes;

/*-- load main data and update buf pointer --*/
/*------------------------------------------- 
   if start point < 0, must just cycle decoder 
   if jumping into middle of stream, 
w---------------------------------------------*/
   m->cupl.buf_ptr0 = m->cupl.buf_ptr1 - m->cupl.side_info.main_data_begin;	/* decode start point */
   if (m->cupl.buf_ptr1 > BUF_TRIGGER)
   {				/* shift buffer */
      memmove(m->cupl.buf, m->cupl.buf + m->cupl.buf_ptr0, m->cupl.side_info.main_data_begin);
      m->cupl.buf_ptr0 = 0;
      m->cupl.buf_ptr1 = m->cupl.side_info.main_data_begin;
   }
   nbytes = m->cupl.padframebytes - side_bytes - m->cupl.crcbytes;

   // RAK: This is no bueno. :-(
	if (nbytes < 0 || nbytes > NBUF)
	{
	    in_out.in_bytes = 0;
		 return in_out;
   }

   memmove(m->cupl.buf + m->cupl.buf_ptr1, bs + side_bytes + m->cupl.crcbytes, nbytes);
   m->cupl.buf_ptr1 += nbytes;
/*-----------------------*/

   if (m->cupl.buf_ptr0 >= 0)
   {
// dump_frame(buf+buf_ptr0, 64);
      m->cupl.main_pos_bit = m->cupl.buf_ptr0 << 3;
      unpack_main(m,pcm, 0);
      unpack_main(m,pcm + m->cupl.half_outbytes, 1);
      in_out.out_bytes = m->cupl.outbytes;
   }
   else
   {
      memset(pcm, m->cupl.zero_level_pcm, m->cupl.outbytes);	/* fill out skipped frames */
      in_out.out_bytes = m->cupl.outbytes;
/* iframe--;  in_out.out_bytes = 0;  // test test */
   }

   return in_out;
}
/*--------------------------------------------------------------------*/
/*--------------------------------------------------------------------*/
IN_OUT L3audio_decode_MPEG2(void *mv, unsigned char *bs, unsigned char *pcm)
{
   MPEG *m = mv;
   int sync;
   IN_OUT in_out;
   int side_bytes;
   int nbytes;
   static int igr = 0;

   m->cupl.iframe++;


   bitget_init(m, bs);		/* initialize bit getter */
/* test sync */
   in_out.in_bytes = 0;		/* assume fail */
   in_out.out_bytes = 0;
   sync = bitget(m, 12);

// if( sync != 0xFFF ) return in_out;       /* sync fail */

   m->cupl.mpeg25_flag = 0;
   if (sync != 0xFFF)
   {
      m->cupl.mpeg25_flag = 1;		/* mpeg 2.5 sync */
      if (sync != 0xFFE)
	 return in_out;		/* sync fail */
   }
/*-----------*/


/*-- unpack side info --*/
   side_bytes = unpack_side_MPEG2(m,igr);
   if (side_bytes < 0)
   {
       in_out.in_bytes = 0;
       return in_out;
   }
   m->cupl.padframebytes = m->cupl.framebytes + m->cupl.pad;
   in_out.in_bytes = m->cupl.padframebytes;

   m->cupl.buf_ptr0 = m->cupl.buf_ptr1 - m->cupl.side_info.main_data_begin;	/* decode start point */
   if (m->cupl.buf_ptr1 > BUF_TRIGGER)
   {				/* shift buffer */
      memmove(m->cupl.buf, m->cupl.buf + m->cupl.buf_ptr0, m->cupl.side_info.main_data_begin);
      m->cupl.buf_ptr0 = 0;
      m->cupl.buf_ptr1 = m->cupl.side_info.main_data_begin;
   }