Copyright (c) 2012 10iii All Rights Reserved. This module is released under a BSD license.
This module is modified from Tom Wu's jsbn library. Which is also under a BSD license. See http://www-cs-students.stanford.edu/~tjw/jsbn/
The main change from jsbn is using a buff array instead of hashset member to keep digits, and estimate buff size when create a new BI object during calculating. For detail see https://github.com/10iii/nodebi