the crc thus may be checked either by the obvious method of computing the crc on the message, inverting it, and comparing with the crc in the message stream, or by calculating the crc on the entire codeword and comparing it with an expected fixed value formula_45, called the check polynomial, residue or magic number. this may be computed as formula_46, or equivalently by computing the unmodified crc of a message consisting of formula_2 ones, formula_48.