sublay2.cpp

MP3解压程序源代码

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};


// data taken from ISO/IEC DIS 11172, Annexes 3-B.2[abcd] and 3-B.4:

// subbands 0-2 in tables 3-B.2a and 2b: (index is allocation)
static const uint32 table_ab1_codelength[16] =
  // bits per codeword
{ 0, 5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 };

static const real *table_ab1_groupingtables[16] =
  // pointer to sample grouping table, or NULL-pointer if ungrouped
{ 0, grouping_5bits, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

static const real table_ab1_factor[16] =
  // factor for requantization: (real)sample * factor - 1.0 gives requantized sample
{ 0.0, 1.0/2.0, 1.0/4.0, 1.0/8.0, 1.0/16.0, 1.0/32.0, 1.0/64.0,
  1.0/128.0, 1.0/256.0, 1.0/512.0, 1.0/1024.0, 1.0/2048.0,
  1.0/4096.0, 1.0/8192.0, 1.0/16384.0, 1.0/32768.0 };

static const real table_ab1_c[16] =
  // factor c for requantization from table 3-B.4
{ 0.0,           1.33333333333, 1.14285714286, 1.06666666666, 1.03225806452,
  1.01587301587, 1.00787401575, 1.00392156863, 1.00195694716, 1.00097751711,
  1.00048851979, 1.00024420024, 1.00012208522, 1.00006103888, 1.00003051851,
  1.00001525902 };
static const real table_ab1_d[16] =
  // addend d for requantization from table 3-B.4
{ 0.0,           0.50000000000, 0.25000000000, 0.12500000000, 0.06250000000,
  0.03125000000, 0.01562500000, 0.00781250000, 0.00390625000, 0.00195312500,
  0.00097656250, 0.00048828125, 0.00024414063, 0.00012207031, 0.00006103516,
  0.00003051758 };

// subbands 3-... tables 3-B.2a and 2b:
static const real *table_ab234_groupingtables[16] =
{ 0, grouping_5bits, grouping_7bits, 0, grouping_10bits, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

// subbands 3-10 in tables 3-B.2a and 2b:
static const uint32 table_ab2_codelength[16] =
{ 0, 5, 7, 3, 10, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16 };
static const real table_ab2_factor[16] =
{ 0.0, 1.0/2.0, 1.0/4.0, 1.0/4.0, 1.0/8.0, 1.0/8.0, 1.0/16.0,
  1.0/32.0, 1.0/64.0, 1.0/128.0, 1.0/256.0, 1.0/512.0,
  1.0/1024.0, 1.0/2048.0, 1.0/4096.0, 1.0/32768.0 };
static const real table_ab2_c[16] =
{ 0.0,           1.33333333333, 1.60000000000, 1.14285714286, 1.77777777777,
  1.06666666666, 1.03225806452, 1.01587301587, 1.00787401575, 1.00392156863,
  1.00195694716, 1.00097751711, 1.00048851979, 1.00024420024, 1.00012208522,
  1.00001525902 };
static const real table_ab2_d[16] =
{ 0.0,           0.50000000000, 0.50000000000, 0.25000000000, 0.50000000000,
  0.12500000000, 0.06250000000, 0.03125000000, 0.01562500000, 0.00781250000,
  0.00390625000, 0.00195312500, 0.00097656250, 0.00048828125, 0.00024414063,
  0.00003051758 };

// subbands 11-22 in tables 3-B.2a and 2b:
static const uint32 table_ab3_codelength[8] = { 0, 5, 7, 3, 10, 4, 5, 16 };
static const real table_ab3_factor[8] =
{ 0.0, 1.0/2.0, 1.0/4.0, 1.0/4.0, 1.0/8.0, 1.0/8.0, 1.0/16.0, 1.0/32768.0 };
static const real table_ab3_c[8] =
{ 0.0,           1.33333333333, 1.60000000000, 1.14285714286, 1.77777777777,
  1.06666666666, 1.03225806452, 1.00001525902 };
static const real table_ab3_d[8] =
{ 0.0,           0.50000000000, 0.50000000000, 0.25000000000, 0.50000000000,
  0.12500000000, 0.06250000000, 0.00003051758 };

// subbands 23-... in tables 3-B.2a and 2b:
static const uint32 table_ab4_codelength[4] = { 0, 5, 7, 16 };
static const real table_ab4_factor[8] = { 0.0, 1.0/2.0, 1.0/4.0, 1.0/32768.0 };
static const real table_ab4_c[4] = { 0.0, 1.33333333333, 1.60000000000, 1.00001525902 };
static const real table_ab4_d[4] = { 0.0, 0.50000000000, 0.50000000000, 0.00003051758 };

// subbands in tables 3-B.2c and 2d:
static const uint32 table_cd_codelength[16] =
{ 0, 5, 7, 10, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
static const real *table_cd_groupingtables[16] =
{ 0, grouping_5bits, grouping_7bits, grouping_10bits, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
static const real table_cd_factor[16] =
{ 0.0, 1.0/2.0, 1.0/4.0, 1.0/8.0, 1.0/8.0, 1.0/16.0, 1.0/32.0, 1.0/64.0,
  1.0/128.0, 1.0/256.0, 1.0/512.0, 1.0/1024.0, 1.0/2048.0, 1.0/4096.0,
  1.0/8192.0, 1.0/16384.0 };
static const real table_cd_c[16] =
{ 0.0,           1.33333333333, 1.60000000000, 1.77777777777, 1.06666666666,
  1.03225806452, 1.01587301587, 1.00787401575, 1.00392156863, 1.00195694716,
  1.00097751711, 1.00048851979, 1.00024420024, 1.00012208522, 1.00006103888,
  1.00003051851 };
static const real table_cd_d[16] =
{ 0.0,           0.50000000000, 0.50000000000, 0.50000000000, 0.12500000000,
  0.06250000000, 0.03125000000, 0.01562500000, 0.00781250000, 0.00390625000,
  0.00195312500, 0.00097656250, 0.00048828125, 0.00024414063, 0.00012207031,
  0.00006103516 };



/**********************/	// used for single channel mode
/*** Standard Class ***/	// and in derived class for intensity
/**********************/	// stereo mode

SubbandLayer2::SubbandLayer2(uint32 subbandnumber)
{
  this->subbandnumber = subbandnumber;
  groupnumber = samplenumber = 0;
}


uint32 SubbandLayer2::get_allocationlength(Header *header)
{

  if (header->version() == MPEG1) {

	  uint32 channel_bitrate = header->bitrate_index();

	  // calculate bitrate per channel:
	  if (header->mode() != single_channel)
		 if (channel_bitrate == 4)
			channel_bitrate = 1;
		 else
			channel_bitrate -= 4;

	  if (channel_bitrate == 1 || channel_bitrate == 2)
		 // table 3-B.2c or 3-B.2d
		 if (subbandnumber <= 1)
			return 4;
		 else
			return 3;
	  else
		 // tables 3-B.2a or 3-B.2b
		 if (subbandnumber <= 10)
			return 4;
		 else if (subbandnumber <= 22)
			return 3;
		 else
			return 2;

  } else { // MPEG-2 LSF -- Jeff

	  // table B.1 of ISO/IEC 13818-3
     if (subbandnumber <= 3)
     		return 4;
     else if (subbandnumber <= 10)
     		return 3;
     else
     		return 2;
  }

}

void SubbandLayer2::prepare_sample_reading(Header *header, uint32 allocation,
													 	 const real **groupingtable,
                                           real *factor, uint32 *codelength,
                                           real *c, real *d)
{
  uint32 channel_bitrate = header->bitrate_index();

  // calculate bitrate per channel:
  if (header->mode() != single_channel)
	 if (channel_bitrate == 4)
		channel_bitrate = 1;
	 else
		channel_bitrate -= 4;

  if (channel_bitrate == 1 || channel_bitrate == 2)
  {
	 // table 3-B.2c or 3-B.2d
	 *groupingtable = table_cd_groupingtables[allocation];
	 *factor = table_cd_factor[allocation];
	 *codelength = table_cd_codelength[allocation];
	 *c = table_cd_c[allocation];
	 *d = table_cd_d[allocation];
  }
  else
  {
	 // tables 3-B.2a or 3-B.2b
	 if (subbandnumber <= 2)
	 {
		*groupingtable = table_ab1_groupingtables[allocation];
		*factor = table_ab1_factor[allocation];
		*codelength = table_ab1_codelength[allocation];
      *c = table_ab1_c[allocation];
      *d = table_ab1_d[allocation];
    }
	 else
	 {
      *groupingtable = table_ab234_groupingtables[allocation];
		if (subbandnumber <= 10)
		{
			*factor = table_ab2_factor[allocation];
			*codelength = table_ab2_codelength[allocation];
			*c = table_ab2_c[allocation];
			*d = table_ab2_d[allocation];
      }
      else if (subbandnumber <= 22)
      {
			*factor = table_ab3_factor[allocation];
			*codelength = table_ab3_codelength[allocation];
			*c = table_ab3_c[allocation];
			*d = table_ab3_d[allocation];
      }
		else
      {
			*factor = table_ab4_factor[allocation];
			*codelength = table_ab4_codelength[allocation];
			*c = table_ab4_c[allocation];
			*d = table_ab4_d[allocation];
      }
    }
  }
}


void SubbandLayer2::read_allocation(Ibitstream *stream, Header *header, Crc16 *crc)
{
  register uint32 length = get_allocationlength(header);
  allocation = stream->get_bits(length);
  if (crc)
    crc->add_bits(allocation, length);
}


void SubbandLayer2::read_scalefactor_selection(Ibitstream *stream, Crc16 *crc)
{
  if (allocation)
  {
    scfsi = stream->get_bits(2);
    if (crc)
		crc->add_bits(scfsi, 2);
  }
}


void SubbandLayer2::read_scalefactor(Ibitstream *stream, Header *header)
{
  if (allocation)
  {
    switch (scfsi)
    {
      case 0:
  	   scalefactor1 = scalefactors[stream->get_bits(6)];
	   scalefactor2 = scalefactors[stream->get_bits(6)];
	   scalefactor3 = scalefactors[stream->get_bits(6)];
	   break;

		case 1:
	   scalefactor1 = scalefactor2 = scalefactors[stream->get_bits(6)];
	   scalefactor3 = scalefactors[stream->get_bits(6)];
	   break;
      case 2:
	   scalefactor1 = scalefactor2 = scalefactor3 =
      			    scalefactors[stream->get_bits(6)];
		break;

		case 3:
	   scalefactor1 = scalefactors[stream->get_bits(6)];
	   scalefactor2 = scalefactor3 = scalefactors[stream->get_bits(6)];
	   break;
    }
    prepare_sample_reading(header, allocation, &groupingtable,
			    &factor, &codelength, &c, &d);
  }
}