[optional] use math to reduce clarity

[jhheider]

optional reduction in clarity to remove if cases and loops.

turns on testing, and unit tests the two helper functions.

note that this merges up to #17 , so careful with muddying that diff.

updated to split out the github actions work. this now merges to #20

[jhheider]

we should probably migrate to https://github.com/dtolnay/rust-toolchain since the action-rs jobs are 5 years old and archived. they are using set-output which will go away some day, probably sooner than we expect. see: https://www.reddit.com/r/rust/comments/z1mlls/actionsrs_github_actions_need_more_maintainers_or/

Edit: handled in #19

[mxcl]

It’s less clear, but it’s cool if it’s faster. Which I wonder about… you know?

Probs should be rebased.

[jhheider]

the compiler is usually more than capable of figuring out real optimizations. people who care a lot use https://godbolt.org/noscript/rust to check.

[jhheider]

I'll split up the stuff that's not math games