Resources

This library draws inspiration from libraries like Java BigInteger, GNU MP Arithmetic Library, Javolution JScience, as well as following literature

Modern Computer Arithmetic
Richard P. Brent and Paul Zimmermann
Version 0.5.9 of 7 October 2010

Hacker`s Delight
Henry S. Warren, Jr.
Second Edition

Art of Computer Programming, Volume 2: Seminumerical Algorithms
Donald E. Knuth
3rd Edition

Refinement of a newton reciprocal algorithm for arbitrary precision numbers
Yiping Cheng, Ze Liu

And many other blogs and posts scattered over the internet.

If you want to try building BigNum library yourself, those are the sources I would recommend to start with.