CCITT CRC16 Code

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Sample CCITT CRC Code

// Update the CRC for transmitted and received data using
// the CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1).

    unsigned char ser_data;
    static unsigned int crc;

    crc  = (unsigned char)(crc >> 8) | (crc << 8);
    crc ^= ser_data;
    crc ^= (unsigned char)(crc & 0xff) >> 4;
    crc ^= (crc << 8) << 4;
    crc ^= ((crc & 0xff) << 4) << 1;

Note: It is best not to alter this code. For example, (crc<<8)<<4 does not generate the same code as crc<<12. Although the result of the computation is the same, the latter generates much more code and executes slower.