The latest beta includes a number of changes/fixes to bigfloat.
Bigfloat is now passing my 100+ unit tests.
Note that I have not had a chance to update $powmod() with your updated algorithm. This should be in the next beta.
This beta also does not include the /bigfloat -d switch yet as I would like to make sure bigfloat is stable first.
Please let me know how this beta works out for you.