Try out multiversion

[est31]

It would be cool to experiment with adding a feature that uses autovectorization if available: https://github.com/calebzulawski/multiversion

[est31]

I have created a multiversion branch, and see some minor improvements: https://github.com/RustAudio/lewton/tree/multiversion

Time before: 2.9013s,2.9159s,2.8968s

Time after: 2.7436s,2.7662s,2.7524s

Summing up these values gives a 5.4% improvement. Not sure it's worth the overhead to add it.