Very cool algorithm and great write-up!

I was a bit confused initially about what your algorithm actually did, until I got to the pseudo-code. Ideally there would be a high level description of what the algorithm is supposed to do before that.

Something as simple as: “a date algorithm converts a number of days elapsed since the UNIX epoch (1970-01-01) to a Gregorian calendar date consisting of day, month, and year” would help readers understand what they're about to read.