Returns the greatest double integer value no greater than
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
d in the range
0.0 < d < 1.0 will return
The result is always a double. If this is a numerically large integer, the result may be an infinite double.