The only correct calculation of the DDSword is with 64bit multiplication and LL integers (as above). Some sites show calculation with floating point - bad idea - as the float is not precise enough for the DDSword calculation! (there are even AD DDS chips with 48bit DDSword!).
I would use the libraries, but applying the above LL calc for DDSword.
Also mind when doing sweep with "adding the frequency step" (instead of a freq calculation of each sweep point) the error of the frequency accumulates, when the step is not a precise number.. The same occur when using an encoder as the input dial (and doing adding/subtracting a fixed step).