The selection of the intermediary working type, used for exponential
and logarithmic functions when combining values from different scales,
was implemented too simplistic.
Following the example of the `NumberJoinType`, it seems preferrable
to spell out the decision logic explicitly. This allows to pick `long doubl`
as working type especially in cases where 64bit integral parameters are
involved, either as source or destination.
With these final tweaks, the `verify_valueJoining()` test is not complete,
presumably with path coverage of the conversion functions.
The Scale descriptor and operational logic is now defined to the point
that it can be integrated into the general Parameter implementation machinery.
Ichthyostega
da9b40df03