cupl3.c

这是一个mp3的源代码

   }

   if (br_index > 0)		/* framebytes fixed for free format */
	{
      framebytes =
	 2880 * mp_br_tableL3[id][br_index] / mp_sr20_table[id][sr_index];
   }

   side_info.main_data_begin = bitget(9);
   if (side_info.mode == 3)
   {
      side_info.private_bits = bitget(5);
      nchan = 1;
      stereo_flag = 0;
      side_bytes = (4 + 17);
/*-- with header --*/
   }
   else
   {
      side_info.private_bits = bitget(3);
      nchan = 2;
      stereo_flag = 1;
      side_bytes = (4 + 32);
/*-- with header --*/
   }
   for (ch = 0; ch < nchan; ch++)
      side_info.scfsi[ch] = bitget(4);
/* this always 0 (both igr) for short blocks */

   for (igr = 0; igr < 2; igr++)
   {
      for (ch = 0; ch < nchan; ch++)
      {
	 side_info.gr[igr][ch].part2_3_length = bitget(12);
	 side_info.gr[igr][ch].big_values = bitget(9);
	 side_info.gr[igr][ch].global_gain = bitget(8) + gain_adjust;
	 if (ms_mode)
	    side_info.gr[igr][ch].global_gain -= 2;
	 side_info.gr[igr][ch].scalefac_compress = bitget(4);
	 side_info.gr[igr][ch].window_switching_flag = bitget(1);
	 if (side_info.gr[igr][ch].window_switching_flag)
	 {
	    side_info.gr[igr][ch].block_type = bitget(2);
	    side_info.gr[igr][ch].mixed_block_flag = bitget(1);
	    side_info.gr[igr][ch].table_select[0] = bitget(5);
	    side_info.gr[igr][ch].table_select[1] = bitget(5);
	    side_info.gr[igr][ch].subblock_gain[0] = bitget(3);
	    side_info.gr[igr][ch].subblock_gain[1] = bitget(3);
	    side_info.gr[igr][ch].subblock_gain[2] = bitget(3);
	  /* region count set in terms of long block cb's/bands */
	  /* r1 set so r0+r1+1 = 21 (lookup produces 576 bands ) */
	  /* if(window_switching_flag) always 36 samples in region0 */
	    side_info.gr[igr][ch].region0_count = (8 - 1);	/* 36 samples */
	    side_info.gr[igr][ch].region1_count = 20 - (8 - 1);
	 }
	 else
	 {
	    side_info.gr[igr][ch].mixed_block_flag = 0;
	    side_info.gr[igr][ch].block_type = 0;
	    side_info.gr[igr][ch].table_select[0] = bitget(5);
	    side_info.gr[igr][ch].table_select[1] = bitget(5);
	    side_info.gr[igr][ch].table_select[2] = bitget(5);
	    side_info.gr[igr][ch].region0_count = bitget(4);
	    side_info.gr[igr][ch].region1_count = bitget(3);
	 }
	 side_info.gr[igr][ch].preflag = bitget(1);
	 side_info.gr[igr][ch].scalefac_scale = bitget(1);
	 side_info.gr[igr][ch].count1table_select = bitget(1);
      }
   }



/* return  bytes in header + side info */
   return side_bytes;
}
/*====================================================================*/
static int unpack_side_MPEG2(int igr)
{
   int prot;
   int br_index;
   int ch;
   int side_bytes;

/* decode partial header plus initial side info */
/* at entry bit getter points at id, sync skipped by caller */

   id = bitget(1);		/* id */
   bitget(2);			/* skip layer */
   prot = bitget(1);		/* bitget prot bit */
   br_index = bitget(4);
   sr_index = bitget(2);
   pad = bitget(1);
   bitget(1);			/* skip to mode */
   side_info.mode = bitget(2);	/* mode */
   side_info.mode_ext = bitget(2);	/* mode ext */

   if (side_info.mode != 1)
      side_info.mode_ext = 0;

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

   crcbytes = 0;
   if (prot)
      bitget(4);		/* skip to data */
   else
   {
      bitget(20);		/* skip crc */
      crcbytes = 2;
   }

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


   for (ch = 0; ch < nchan; ch++)
   {
      side_info.gr[igr][ch].part2_3_length = bitget(12);
      side_info.gr[igr][ch].big_values = bitget(9);
      side_info.gr[igr][ch].global_gain = bitget(8) + gain_adjust;
      if (ms_mode)
	 side_info.gr[igr][ch].global_gain -= 2;
      side_info.gr[igr][ch].scalefac_compress = bitget(9);
      side_info.gr[igr][ch].window_switching_flag = bitget(1);
      if (side_info.gr[igr][ch].window_switching_flag)
      {
	 side_info.gr[igr][ch].block_type = bitget(2);
	 side_info.gr[igr][ch].mixed_block_flag = bitget(1);
	 side_info.gr[igr][ch].table_select[0] = bitget(5);
	 side_info.gr[igr][ch].table_select[1] = bitget(5);
	 side_info.gr[igr][ch].subblock_gain[0] = bitget(3);
	 side_info.gr[igr][ch].subblock_gain[1] = bitget(3);
	 side_info.gr[igr][ch].subblock_gain[2] = bitget(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 ((side_info.gr[igr][ch].block_type == 2))
	 {
	    side_info.gr[igr][ch].region0_count = (6 - 1);	/* 36 samples */
	    side_info.gr[igr][ch].region1_count = 20 - (6 - 1);
	 }
	 else
	 {			/* long block type 1 or 3 */
	    side_info.gr[igr][ch].region0_count = (8 - 1);	/* 54 samples */
	    side_info.gr[igr][ch].region1_count = 20 - (8 - 1);
	 }
      }
      else
      {
	 side_info.gr[igr][ch].mixed_block_flag = 0;
	 side_info.gr[igr][ch].block_type = 0;
	 side_info.gr[igr][ch].table_select[0] = bitget(5);
	 side_info.gr[igr][ch].table_select[1] = bitget(5);
	 side_info.gr[igr][ch].table_select[2] = bitget(5);
	 side_info.gr[igr][ch].region0_count = bitget(4);
	 side_info.gr[igr][ch].region1_count = bitget(3);
      }
      side_info.gr[igr][ch].preflag = 0;
      side_info.gr[igr][ch].scalefac_scale = bitget(1);
      side_info.gr[igr][ch].count1table_select = bitget(1);
   }

/* return  bytes in header + side info */
   return side_bytes;
}
/*-----------------------------------------------------------------*/
static void unpack_main(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 < nchan; ch++)
   {
      bitget_init(buf + (main_pos_bit >> 3));
      bit0 = (main_pos_bit & 7);
      if (bit0)
	 bitget(bit0);
      main_pos_bit += side_info.gr[igr][ch].part2_3_length;
      bitget_init_end(buf + ((main_pos_bit + 39) >> 3));
/*-- scale factors --*/
      if (id)
	 unpack_sf_sub_MPEG1(&sf[igr][ch],
			  &side_info.gr[igr][ch], side_info.scfsi[ch], igr);
      else
	 unpack_sf_sub_MPEG2(&sf[igr][ch],
			 &side_info.gr[igr][ch], is_mode & ch, &is_sf_info);
/*--- huff data ---*/
      n1 = sfBandIndex[0][side_info.gr[igr][ch].region0_count];
      n2 = sfBandIndex[0][side_info.gr[igr][ch].region0_count
			  + side_info.gr[igr][ch].region1_count + 1];
      n3 = side_info.gr[igr][ch].big_values;
      n3 = n3 + n3;


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

	 memset(sample[ch][igr], 0, sizeof(SAMPLE) * (576));
      }
   }



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

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

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

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

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



/*--- hybrid + sbt ---*/
   Xform(pcm, igr);


/*-- done --*/
}
/*--------------------------------------------------------------------*/
/*-----------------------------------------------------------------*/
IN_OUT L3audio_decode(unsigned char *bs, unsigned char *pcm)
{
   return decode_function(bs, pcm);
}

/*--------------------------------------------------------------------*/
IN_OUT L3audio_decode_MPEG1(unsigned char *bs, unsigned char *pcm)
{
   int sync;
   IN_OUT in_out;
   int side_bytes;
   int nbytes;
   
   iframe++;

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

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

/*-- unpack side info --*/
   side_bytes = unpack_side_MPEG1();
   padframebytes = framebytes + pad;
   in_out.in_bytes = padframebytes;

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

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

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

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

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