app/player_rating.cpp

Glicko-2 + the on-device rating file (see player_rating.h).

The algorithm is Glickman’s, followed to the letter (glicko.net/glicko/glicko2.pdf): work in the internal (μ, φ) scale, solve for the new volatility with the Illinois variant of regula falsi, then convert back. The only liberty taken is the one-result rating period, which is argued for in the header.

Declarations live in app/player_rating.h.