Module name ending with a number is not correcty underscore-ed

[fungalcofe]

Environment

• Elixir & Erlang/OTP versions: Elixir 1.10.1 (compiled with Erlang/OTP 22)
• Operating system: NixOS 20.09

Current behavior

I wrote a module named SHA512 (and related controller, view, etc.) in my Phoenix project and the view is searching templates under template/sh_a512.

This behaviour can also be noticed when using mix phx.gen.schema Something SHA512 sha512 lorem:string, generated files have many sh_a512 occurrences.

In iex this behaviour can be noticed by running the following:

iex(1)> Macro.underscore "SHA512"     
"sh_a512"
iex(2)> Macro.underscore "LOREMIPSUM512"
"loremipsu_m512"

Expected behavior

To have module's last letter looks unusual (sh_a512).
I'd expect to have the underscore placed between the letters and the numbers (sha_512) or no underscore split at all.