const unsigned short sd_crc16_table_a[16] =
{
0x0000, 0x1231, 0x2462, 0x3653,
0x48c4, 0x5af5, 0x6ca6, 0x7e97,
0x9188, 0x83b9, 0xb5ea, 0xa7db,
0xd94c, 0xcb7d, 0xfd2e, 0xef1f
};

const unsigned short sd_crc16_table_b[16] =
{
0x0000, 0x1021, 0x2042, 0x3063,
0x4084, 0x50a5, 0x60c6, 0x70e7,
0x8108, 0x9129, 0xa14a, 0xb16b,
0xc18c, 0xd1ad, 0xe1ce, 0xf1ef
};

unsigned short sd_crc16(unsigned char *buff, unsigned int len)
{
unsigned char data;
unsigned short crc = 0;

while(len--)
{
data = *buff++ ^ (crc >> 8);
crc = (sd_crc16_table_a[(data & 0xf0) >> 4] ^ sd_crc16_table_b[data & 0x0f]) ^ (crc << 8);
}
return crc;
}

#define CRC16_POLYNOMIAL 0x1021
static unsigned short crc16_syndrome_table[256];

void gen_crc16_syndrome_table(void) {
  unsigned int c;
  unsigned int n;
  unsigned char k;
  unsigned int poly; // polynomial exclusive-or pattern
  
  poly = CRC16_POLYNOMIAL;
  for (n=0; n<256; n++) {
    c = n << 8;
    for(k=0; k<8; k++)
      c = c & (0x8000) ? poly ^ (c << 1) : (c << 1);
    crc16_syndrome_table[n] = c;
  }
}

unsigned short crc16(unsigned char * pcBlock, unsigned short len) {
  unsigned short crc = 0xFFFF;
  while (len--) crc = (crc << 8) ^ crc16_syndrome_table[(crc >> 8) ^ *pcBlock++];
  return crc;
}