When we are to make use of decimal numbers,we can use multiplication by the power of 10 just by a shift,so that is it not really necessary to consider the said multiplication in the evaluation of (M (n).
However,in the evaluation of c1, for the multiplication of large integers,the sum we have from n/2 - digits cannot have n/2 digits,but it can actually have n/2+1.
Note that these assumptions were made for the sake of computational convenience.