CRC

#define POLY        0x1021
/**
 * Calculating CRC-16 in 'C'
 * @para addr, start of data
 * @para num, length of data
 * @para crc, incoming CRC
 */
uint16_t crc16(unsigned char *addr, int num, uint16_t crc)
{
    int i;
    ; num--)              /* Step through bytes in memory */
    {
        crc = crc ^ (*addr++ << );     /* Fetch byte from memory, XOR into CRC top byte*/
        ; i < ; i++)             /* Prepare to rotate 8 bits */
        {
            if (crc & 0x8000)            /* b15 is set... */
                crc = (crc << ) ^ POLY;    /* rotate and XOR with polynomic */
            else                          /* b15 is clear... */
                crc <<= ;                  /* just rotate */
        }                             /* Loop for 8 bits */
        crc &= 0xFFFF;                  /* Ensure CRC remains 16-bit value */
    }                               /* Loop until num=0 */
    return(crc);                    /* Return updated CRC */
}

转自http://blog.csdn.net/liyuanbhu/article/details/7882789