It is possible to get negative 0.

[Xavienth]

Due to the way the sign is assigned to the result in bigint.add(), it is possible to get a result of -0 when using bigint.subtract().

[Xavienth]

This is easily fixed with a check before the result is given, comparing the result to bigint.new("-0") and changing the sign.

[tayler-king]

Does this impact any future calculations using -0 or is it purely cosmetic?

[Xavienth]

It can affect comparisons, as in comparing a bigint to a 0 bigint. If the first is -0, the output is false.
This could be worked around on the user's end by adding an extra comparison to check 0 AND -0 to be sure.

[tayler-king]

I see. Unfortunately it seems as though the author is no longer active on GitHub - it might be better to fork the repo.