How Does "git log --reverse" Work?

I'm trying to understand how 'git log --reverse' displays commits in reverse order (i.e. oldest commit first).

The fact that each commit object has pointer(s) to parent object(s) makes it trivial to go newest to oldest. But, I haven't found a way to go oldest to newest.

I've looked at the code but it's not well commented. Does the answer have something to do with commit lists?

Any advice would be appreciated.

Cordially, Jon Forrest