#define POLYNOMIAL     0x1021

#define WIDTH   (8 * sizeof(resultType))
#define MSb     ((resultType)1 << (WIDTH - 1))

resultType
crc(const readType * data, unsigned n, resultType remainder) {
    unsigned pos;
    unsigned char bitp;

    for (pos = 0; pos != n; pos++) {
        remainder ^= ((resultType)data[pos] << (WIDTH - 8));
        for (bitp = 8; bitp > 0; bitp--) {
            if (remainder & MSb) {
                remainder = (remainder << 1) ^ POLYNOMIAL;
            } else {
                remainder <<= 1;
            }
        }
    }

    return remainder;
}