Function mad_bit_crc

modules/data/mp3/libmad/bit.c:202–246

* NAME: bit->crc() * DESCRIPTION: compute CRC-check word */

 * DESCRIPTION:	compute CRC-check word
 */
unsigned short mad_bit_crc(struct mad_bitptr bitptr, unsigned int len,
			   unsigned short init)
{
  unsigned int crc;
stack(__FUNCTION__, __FILE__, __LINE__);

  for (crc = init; len >= 32; len -= 32) {
    unsigned long data;

    data = mad_bit_read(&bitptr, 32);

    crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 24)) & 0xff];
    crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 16)) & 0xff];
    crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >>  8)) & 0xff];
    crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >>  0)) & 0xff];
  }

  switch (len / 8) {
  case 3: crc = (crc << 8) ^
           crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
          /* Falls Through. */
  case 2: crc = (crc << 8) ^
           crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
          /* Falls Through. */
  case 1: crc = (crc << 8) ^
           crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];

  len %= 8;
  /* Falls Through. */

  case 0: break;
  }

  while (len--) {
    unsigned int msb;

    msb = mad_bit_read(&bitptr, 1) ^ (crc >> 15);

    crc <<= 1;
    if (msb & 1)
      crc ^= CRC_POLY;
  }

  return crc & 0xffff;
}