Modulo after operations

[s1na]

FixedBN performs bound-checking in its constructor. Most of the operations return a new BN instance (not a FixedBN), and because they have not been overriden they wouldn't necessarily have the specified width. Does it make sense to override such operations to cast them to FixedBN and do a modulo afterwards if necessary? Or should users of the library take care of this?

[axic]

I think they should return a FixedBN instance. It should be possible to retrieve a BN instance out of a FixedBN instance.