To provide a method of quickly calculating a carry-out word (feedback word) from a shift register, having a feedback tap at a position determined by generating polynomials.

The method of calculating a carry-out word from a register, having a feedback tap at a position determined by generating polynomials, such as CRC encoders, decoders or trap circuits, etc., calculates the carry-out word of a length K according to a formula 'carryout-word = select-word. top-word-matrix'. The carry-out word is a 1×K row vector, the top-word- matrix is calculated from K significant bits of the shift register, and the select- word is 1×K row vector determined by generating polynomials.