You can set a thread-local flag to direct Number how to round
non-exact results with the syntax:
Number::rounding_mode prev_mode = Number::setround(Number::towards_zero);
This flag will stay in effect for this thread only until another call
to setround. The previously set rounding mode is returned.
You can also retrieve the current rounding mode with:
Number::rounding_mode current_mode = Number::getround();
The available rounding modes are:
* to_nearest : Rounds to nearest representable value. On tie, rounds
to even.
* towards_zero : Rounds towards zero.
* downward : Rounds towards negative infinity.
* upward : Rounds towards positive infinity.
The default rounding mode is to_nearest.
* Conversions to Number are implicit
* Conversions away from Number are explicit and potentially lossy
* If lossy, round to nearest, and to even on tie
