Multiplication or division by a power of two (2^{n} say) of a dyadic
digit (*a*,*b*) reduces to simply adding or subtracting *n* to or from
*b*. Provided (*a*,*b*) is not zero (ie. (0,0), for which the zero
digit is returned). Range checking may also be performed on the shift
left (multiplication by positive powers of 2) operation to ensure
that the result remains in the range [-1,1].