Returns the next representable neighbor of x in the direction towards y.
Remember to link the math library: valac -X -lm ...
The size of the step between x and the result depends on the type of the result.
If x = y the function simply returns y. If either value is
double.NAN, then double.NAN is returned. Otherwise a value corresponding to the value
of the least significant bit in the mantissa is added or subtracted, depending on the direction.
| x |
A numeric value. |
| y |
A numeric value. |