The code's functionality is immediately obvious to me as someone who works a lot with graphics coordinate systems.

I'm sure the code would be immediately obvious to anyone who would be working on it at the time.

Comments aren't unnecessary, they can be very helpful, but they also come with a high maintenance cost that should be considered when using them. They are a long-term maintenance liability because by design the compiler ignores them so its very easy to change/refactor code and miss changing a comment and then having the comment be misleading or just plain wrong.

These days one could make some sort of case (though I wouldn't entirely buy it, yet) that an LLM-based linter could be used to make sure comments do not get disconnected from the code they are documenting, but in 1990? not so much.

Would I have used longer variable names for slightly more clarity? Today, sure. In 1990, probably not. Temporal context is important and compilers/editors/etc have come a long way since then.