In addition to this issue:
There is often the need to decide, if a Complex number is a positive or negative integer.
Or if a Complex number is a positive or negative real value.
And depending on the case, convert the number to an int, long or double value within some tolerance.
Are there already some functions in hipparchus planned or available?
The isMathematicalInteger and round functions have been added to Complex (I hesitated to put them in ComplexUtils, but finally decided arbitrarily to let them in Complex).
For other utilities, I think performing the tests directly using the getReal(), getImaginary() and the double functions implemented in both FastMath and Precision should be enough.
If you prefer to have dedicated utilities, you could contribute them to the ComplexUtils class.