*/
static
enum mad_error III_sideinfo(struct mad_bitptr *ptr, unsigned int nch,
			    int lsf, struct sideinfo *si,
			    unsigned int *data_bitlen,
			    unsigned int *priv_bitlen)
{
  unsigned int ngr, gr, ch, i;
  enum mad_error result = MAD_ERROR_NONE;

  *data_bitlen = 0;
  *priv_bitlen = lsf ? ((nch == 1) ? 1 : 2) : ((nch == 1) ? 5 : 3);

  si->main_data_begin = mad_bit_read(ptr, lsf ? 8 : 9);
  si->private_bits    = mad_bit_read(ptr, *priv_bitlen);

  ngr = 1;
  if (!lsf) {
    ngr = 2;

    for (ch = 0; ch < nch; ++ch)
      si->scfsi[ch] = mad_bit_read(ptr, 4);
  }

  for (gr = 0; gr < ngr; ++gr) {
    struct granule *granule = &si->gr[gr];

    for (ch = 0; ch < nch; ++ch) {
      struct channel *channel = &granule->ch[ch];

      channel->part2_3_length    = mad_bit_read(ptr, 12);
      channel->big_values        = mad_bit_read(ptr, 9);
      channel->global_gain       = mad_bit_read(ptr, 8);
      channel->scalefac_compress = mad_bit_read(ptr, lsf ? 9 : 4);

      *data_bitlen += channel->part2_3_length;

      if (channel->big_values > 288 && result == 0)
	result = MAD_ERROR_BADBIGVALUES;

      channel->flags = 0;

      /* window_switching_flag */
      if (mad_bit_read(ptr, 1)) {
	channel->block_type = mad_bit_read(ptr, 2);

	if (channel->block_type == 0 && result == 0)
	  result = MAD_ERROR_BADBLOCKTYPE;

	if (!lsf && channel->block_type == 2 && si->scfsi[ch] && result == 0)
	  result = MAD_ERROR_BADSCFSI;

	channel->region0_count = 7;
	channel->region1_count = 36;

	if (mad_bit_read(ptr, 1))
	  channel->flags |= mixed_block_flag;
	else if (channel->block_type == 2)
	  channel->region0_count = 8;

	for (i = 0; i < 2; ++i)
	  channel->table_select[i] = mad_bit_read(ptr, 5);

# if defined(DEBUG)
	channel->table_select[2] = 4;  /* not used */
# endif

	for (i = 0; i < 3; ++i)
	  channel->subblock_gain[i] = mad_bit_read(ptr, 3);
      }
      else {
	channel->block_type = 0;

	for (i = 0; i < 3; ++i)
	  channel->table_select[i] = mad_bit_read(ptr, 5);

	channel->region0_count = mad_bit_read(ptr, 4);
	channel->region1_count = mad_bit_read(ptr, 3);
      }

      /* [preflag,] scalefac_scale, count1table_select */
      channel->flags |= mad_bit_read(ptr, lsf ? 2 : 3);
    }
  }

  return result;
}

/*
 * NAME:	III_scalefactors_lsf()
 * DESCRIPTION:	decode channel scalefactors for LSF from a bitstream
 */
static
unsigned int III_scalefactors_lsf(struct mad_bitptr *ptr,
				  struct channel *channel,
				  struct channel *gr1ch, int mode_extension)
{
  struct mad_bitptr start;
  unsigned int scalefac_compress, index, slen[4], part, n, i;
  unsigned char const *nsfb;

  start = *ptr;

  scalefac_compress = channel->scalefac_compress;
  index = (channel->block_type == 2) ?
    ((channel->flags & mixed_block_flag) ? 2 : 1) : 0;

  if (!((mode_extension & I_STEREO) && gr1ch)) {
    if (scalefac_compress < 400) {
      slen[0] = (scalefac_compress >> 4) / 5;
      slen[1] = (scalefac_compress >> 4) % 5;
      slen[2] = (scalefac_compress % 16) >> 2;
      slen[3] =  scalefac_compress %  4;

      nsfb = nsfb_table[0][index];
    }
    else if (scalefac_compress < 500) {
      scalefac_compress -= 400;

      slen[0] = (scalefac_compress >> 2) / 5;
      slen[1] = (scalefac_compress >> 2) % 5;
      slen[2] =  scalefac_compress %  4;
      slen[3] = 0;

      nsfb = nsfb_table[1][index];
    }
    else {
      scalefac_compress -= 500;

      slen[0] = scalefac_compress / 3;
      slen[1] = scalefac_compress % 3;
      slen[2] = 0;
      slen[3] = 0;

      channel->flags |= preflag;

      nsfb = nsfb_table[2][index];
    }

    n = 0;
    for (part = 0; part < 4; ++part) {
      for (i = 0; i < nsfb[part]; ++i)
	channel->scalefac[n++] = mad_bit_read(ptr, slen[part]);
    }

    while (n < 39)
      channel->scalefac[n++] = 0;
  }
  else {  /* (mode_extension & I_STEREO) && gr1ch (i.e. ch == 1) */
    scalefac_compress >>= 1;

    if (scalefac_compress < 180) {
      slen[0] =  scalefac_compress / 36;
      slen[1] = (scalefac_compress % 36) / 6;
      slen[2] = (scalefac_compress % 36) % 6;
      slen[3] = 0;

      nsfb = nsfb_table[3][index];
    }
    else if (scalefac_compress < 244) {
      scalefac_compress -= 180;

      slen[0] = (scalefac_compress % 64) >> 4;
      slen[1] = (scalefac_compress % 16) >> 2;
      slen[2] =  scalefac_compress %  4;
      slen[3] = 0;

      nsfb = nsfb_table[4][index];
    }
    else {
      scalefac_compress -= 244;

      slen[0] = scalefac_compress / 3;
      slen[1] = scalefac_compress % 3;
      slen[2] = 0;
      slen[3] = 0;

      nsfb = nsfb_table[5][index];
    }

    n = 0;
    for (part = 0; part < 4; ++part) {
      unsigned int max, is_pos;

      max = (1 << slen[part]) - 1;

      for (i = 0; i < nsfb[part]; ++i) {
	is_pos = mad_bit_read(ptr, slen[part]);

	channel->scalefac[n] = is_pos;
	gr1ch->scalefac[n++] = (is_pos == max);
      }
    }

    while (n < 39) {
      channel->scalefac[n] = 0;
      gr1ch->scalefac[n++] = 0;  /* apparently not illegal */
    }
  }

  return mad_bit_length(&start, ptr);
}

/*
 * NAME:	III_scalefactors()
 * DESCRIPTION:	decode channel scalefactors of one granule from a bitstream
 */
static
unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
			      struct channel const *gr0ch, unsigned int scfsi)
{
  struct mad_bitptr start;
  unsigned int slen1, slen2, sfbi;

  start = *ptr;

  slen1 = sflen_table[channel->scalefac_compress].slen1;
  slen2 = sflen_table[channel->scalefac_compress].slen2;

  if (channel->block_type == 2) {
    unsigned int nsfb;

    sfbi = 0;

    nsfb = (channel->flags & mixed_block_flag) ? 8 + 3 * 3 : 6 * 3;
    while (nsfb--)
      channel->scalefac[sfbi++] = mad_bit_read(ptr, slen1);

    nsfb = 6 * 3;
    while (nsfb--)
      channel->scalefac[sfbi++] = mad_bit_read(ptr, slen2);

    nsfb = 1 * 3;
    while (nsfb--)
      channel->scalefac[sfbi++] = 0;
  }
  else {  /* channel->block_type != 2 */
    if (scfsi & 0x8) {
      for (sfbi = 0; sfbi < 6; ++sfbi)
	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
    }
    else {
      for (sfbi = 0; sfbi < 6; ++sfbi)
	channel->scalefac[sfbi] = mad_bit_read(ptr, slen1);
    }

    if (scfsi & 0x4) {
      for (sfbi = 6; sfbi < 11; ++sfbi)
	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
    }
    else {
      for (sfbi = 6; sfbi < 11; ++sfbi)
	channel->scalefac[sfbi] = mad_bit_read(ptr, slen1);
    }

    if (scfsi & 0x2) {
      for (sfbi = 11; sfbi < 16; ++sfbi)
	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
    }
    else {
      for (sfbi = 11; sfbi < 16; ++sfbi)
	channel->scalefac[sfbi] = mad_bit_read(ptr, slen2);
    }

    if (scfsi & 0x1) {
      for (sfbi = 16; sfbi < 21; ++sfbi)
	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
    }
    else {
      for (sfbi = 16; sfbi < 21; ++sfbi)
	channel->scalefac[sfbi] = mad_bit_read(ptr, slen2);
    }

    channel->scalefac[21] = 0;
  }

  return mad_bit_length(&start, ptr);
}

/*
 * The Layer III formula for requantization and scaling is defined by
 * section 2.4.3.4.7.1 of ISO/IEC 11172-3, as follows:
 *
 *   long blocks:
 *   xr[i] = sign(is[i]) * abs(is[i])^(4/3) *
 *           2^((1/4) * (global_gain - 210)) *
 *           2^-(scalefac_multiplier *
 *               (scalefac_l[sfb] + preflag * pretab[sfb]))
 *
 *   short blocks:
 *   xr[i] = sign(is[i]) * abs(is[i])^(4/3) *
 *           2^((1/4) * (global_gain - 210 - 8 * subblock_gain[w])) *
 *           2^-(scalefac_multiplier * scalefac_s[sfb][w])
 *
 *   where:
 *   scalefac_multiplier = (scalefac_scale + 1) / 2
 *
 * The routines III_exponents() and III_requantize() facilitate this
 * calculation.
 */

/*
 * NAME:	III_exponents()
 * DESCRIPTION:	calculate scalefactor exponents
 */
static
void III_exponents(struct channel const *channel,
		   unsigned char const *sfbwidth, signed int exponents[39])
{
  signed int gain;
  unsigned int scalefac_multiplier, sfbi;

  gain = (signed int) channel->global_gain - 210;
  scalefac_multiplier = (channel->flags & scalefac_scale) ? 2 : 1;

  if (channel->block_type == 2) {
    unsigned int l;
    signed int gain0, gain1, gain2;

    sfbi = l = 0;

    if (channel->flags & mixed_block_flag) {
      unsigned int premask;

      premask = (channel->flags & preflag) ? ~0 : 0;

      /* long block subbands 0-1 */

      while (l < 36) {
	exponents[sfbi] = gain -
	  (signed int) ((channel->scalefac[sfbi] + (pretab[sfbi] & premask)) <<
			scalefac_multiplier);

	l += sfbwidth[sfbi++];
      }
    }

    /* this is probably wrong for 8000 Hz short/mixed blocks */

    gain0 = gain - 8 * (signed int) channel->subblock_gain[0];
    gain1 = gain - 8 * (signed int) channel->subblock_gain[1];
    gain2 = gain - 8 * (signed int) channel->subblock_gain[2];

    while (l < 576) {
      exponents[sfbi + 0] = gain0 -
	(signed int) (channel->scalefac[sfbi + 0] << scalefac_multiplier);
      exponents[sfbi + 1] = gain1 -
	(signed int) (channel->scalefac[sfbi + 1] << scalefac_multiplier);
      exponents[sfbi + 2] = gain2 -
	(signed int) (channel->scalefac[sfbi + 2] << scalefac_multiplier);

      l    += 3 * sfbwidth[sfbi];
      sfbi += 3;
    }
  }
  else {  /* channel->block_type != 2 */
    if (channel->flags & preflag) {
      for (sfbi = 0; sfbi < 22; ++sfbi) {
	exponents[sfbi] = gain -
	  (signed int) ((channel->scalefac[sfbi] + pretab[sfbi]) <<
			scalefac_multiplier);
      }
    }
    else {
      for (sfbi = 0; sfbi < 22; ++sfbi) {
	exponents[sfbi] = gain -
	  (signed int) (channel->scalefac[sfbi] << scalefac_multiplier);
      }
    }
  }
}

/*
 * NAME:	III_requantize()
 * DESCRIPTION:	requantize one (positive) value
 */
static
mad_fixed_t III_requantize(unsigned int value, signed int exp)
{
  mad_fixed_t requantized;
  signed int frac;
  struct fixedfloat const *power;

  frac = exp % 4;  /* assumes sign(frac) == sign(exp) */
  exp /= 4;

  power = &rq_table[value];
  requantized = power->mantissa;
  exp += power->exponent;

  if (exp < 0) {
    if (-exp >= sizeof(mad_fixed_t) * CHAR_BIT) {
      /* underflow */
      requantized = 0;
    }
    else {
      requantized += 1L << (-exp - 1);
      requantized >>= -exp;
    }
  }
  else {
    if (exp >= 5) {
      /* overflow */
# if defined(DEBUG)
      fprintf(stderr, "requantize overflow (%f * 2^%d)\n",
	      mad_f_todouble(requantized), exp);
# endif
      requantized = MAD_F_MAX;
    }
    else
      requantized <<= exp;
  }

  return frac ? mad_f_mul(requantized, root_table[3 + frac]) : requantized;
}

/* we must take care that sz >= bits and sz < sizeof(long) lest bits == 0 */
# define MASK(cache, sz, bits)	\
    (((cache) >> ((sz) - (bits))) & ((1 << (bits)) - 1))
# define MASK1BIT(cache, sz)  \
    ((cache) & (1 << ((sz) - 1)))

/*
 * NAME:	III_huffdecode()
 * DESCRIPTION:	decode Huffman code words of one channel of one granule
 */
static
enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
			      struct channel *channel,
			      unsigned char const *sfbwidth,
			      unsigned int part2_length)
{
  signed int exponents[39], exp;
  signed int const *expptr;
  struct mad_bitptr peek;
  signed int bits_left, cachesz;
  register mad_fixed_t *xrptr;
  mad_fixed_t const *sfbound;
  register unsigned long bitcache;

  bits_left = (signed) channel->part2_3_length - (signed) part2_length;
  if (bits_left < 0)
    return MAD_ERROR_BADPART3LEN;

  III_exponents(channel, sfbwidth, exponents);

  peek = *ptr;
  mad_bit_skip(ptr, bits_left);

  /* align bit reads to byte boundaries */
  cachesz  = mad_bit_bitsleft(&peek);
  cachesz += ((32 - 1 - 24) + (24 - cachesz)) & ~7;

  bitcache   = mad_bit_read(&peek, cachesz);
  bits_left -= cachesz;

  xrptr = &xr[0];

  /* big_values */
  {
    unsigned int region, rcount;
    struct hufftable const *entry;
    union huffpair const *table;
    unsigned int linbits, startbits, big_values, reqhits;
    mad_fixed_t reqcache[16];

    sfbound = xrptr + *sfbwidth++;
    rcount  = channel->region0_count + 1;

    entry     = &mad_huff_pair_table[channel->table_select[region = 0]];
    table     = entry->table;
    linbits   = entry->linbits;
    startbits = entry->startbits;

    if (table == 0)
      return MAD_ERROR_BADHUFFTABLE;

    expptr  = &exponents[0];
    exp     = *expptr++;
    reqhits = 0;

    big_values = channel->big_values;

    while (big_values-- && cachesz + bits_left > 0) {
      union huffpair const *pair;
      unsigned int clumpsz, value;
      register mad_fixed_t requantized;

      if (xrptr == sfbound) {