Maxima

[John Keith]

If you need higher precision on the 50g you can use the LongFloat library. With DIGITS set to 50, 298257223563 R<->F FINV returns 33528106647474807198455286185205559557326361780098.E-61 which agrees with your first result. With input of 298.257223563, R<->F FINV returns 33528106647474807198455286185205559557326361780098.E-52 which is also correct for all 50 digits, differing only in the exponent.

DIGITS can be set to any number up to 9999 which should be adequate for most purposes.