The code is actually derived directly from the original PlayStation MIPS machine code and uses that as its basis. I wrote tools to convert this machine code to an assembly-like form of C++ and that was gradually converted to standard C++ with the emulation layers being stripped back over time. I did use the GEC code later on as a reference once that became available (I started before that point) but even then I still had to painstakingly convert and go through every single function and gradually strip away all emulation, piece by piece. It was a very interesting process but basically my goal all along was to maintain working builds at every single point in time so if a problem was introduced I could pinpoint exactly where in the git history it was introduced. Thankfully all that stuff is done now (it was a LOT of work!), so I can just focus on adding improvements and quality of life features etc.