Re: Infinite Interval

Hi Ashutosh,

I've added tests for all the operators and functions involving
intervals and what I think the expected behaviors to be. The
formatting might be slightly off and I've left the contents of the
error messages as TODOs. Hopefully it's a good reference for the
implementation.

> Adding infinite interval to an infinite timestamp with opposite
> direction is not going to yield 0 but some infinity. Since we are adding
> interval to the timestamp the resultant timestamp is an infinity
> preserving the direction.

I think I disagree with this. Tom Lane in one of the previous threads
said:
> tl;dr: we should model it after the behavior of IEEE float infinities,
> except we'll want to throw errors where those produce NaNs.
and I agree with this opinion. I believe that means that adding an
infinite interval to an infinite timestamp with opposite directions
should yield an error instead of some infinity. Since with floats this
would yield a NaN.

> Dividing infinite interval by finite number keeps it infinite.
> TODO: Do we change the sign of infinity if factor is negative?
Again if we model this after the IEEE float behavior, then the answer
is yes, we do change the sign of infinity.

- Joe Koshakow