Soft84 is a calculator app for Android OS devices. You can install it from Google's Android Market. It is hoped to someday provide most of the functionality of the HP 48 calculator. At the moment it is a capable RPN scientific calculator with units and rudimentary programming features.
It uses several libraries for arbitrary precision arithmetic: GNU Multiple Precision (GMP), GNU MP Floating/Rounding (MPFR), and GNU MP Complex (MPC). In principle it can be an arbitrary precision calculator, though at the moment it is hard-coded to 100 decimal digits of precision.
Soft84 is released under the GPL V2. If you are really interested in the source, let me know and I will provide you access to my git repository. But here is a source snapshot from 2012/01/16
Soft84 is a XXX - screenshot of home screen, explanation of displays and buttons there XXX - screenshot of alt screen, explanation of displays and buttons there