I played around with the calculator source code from the Android Open Source Project after a previous submission[1]. I think Google moved it from AOSP to the Google Play Services several years ago, but the old source is still available.

It does solve some real problems that I'd love to have available in a library. The discussion on the previous article links to some libraries, but my recollection is that the calculator code is more accessible to an innumerate person like myself.

Edit: the previous article under discussion doesn't seem to be available, but it's on archive.org[2].

[1] https://news.ycombinator.com/item?id=24700705

[2] https://web.archive.org/web/20250126130328/https://blog.acol...