A modern version of the asop packages/app application which Google has dropped.
To get the original source code of the Google package you need to:
git clone https://android.googlesource.com/platform/packages/apps/ExactCalculator
Then checkout an older version because it has been wiped out by the commit:
8caf6b4a41d462a403c47046ff1399c758613644 "Deprecate ExactCalculator"