floorToDouble abstract method
Returns the greatest double integer value no greater than this.
If this is already an integer valued double, including -0.0, or it is a
non-finite double value, the value is returned unmodified.
For the purpose of rounding, -0.0 is considered to be below 0.0.
A number d in the range 0.0 < d < 1.0 will return 0.0.
Implementation
double floorToDouble();