The compiler is based on my years-old and heavily-extended fork of LICE with DECUS C preprocessor added, making for a completely "public domain" self-hosting compiler with some additional language extensions.
The compiler source code is distributed with a copy of the UNLICENSE, as per LICE, but the DECUS C preprocessor public domain attribution can be checked separately (and the compiler can be built in more stripped-down forms). New features such as the RV64 backend, object-oriented extensions and command-line frontend have been written by myself (but are mixed in with the LICE code), and the rest has been heavily refactored to match.