Scala is not C#

Took a while to debug what was going wrong here

        val tmp = toUnsigned(leftSide.digits(i)) * toUnsigned(rightSide.digits(j)))
           +  toUnsigned(da(k)) + carry

because it compiles, silently discarding the fact that this is two statements, the second with no immediately apparent side-effects.

It should be more like

        val tmp = (
          (toUnsigned(leftSide.digits(i)) * toUnsigned(rightSide.digits(j))) +
          toUnsigned(da(k)) + carry)

where the parentheses and the trailing operators give a belt-and-braces approach to delineating the statement boundaries.