[saghm]

The time was taken by the code around the assembly language. It was an abstraction someone wrote in a way that happened not to be efficient. The ability of someone to write a costly abstraction doesn't take away from Rust any more than the possibility of doing that in C++ would from whether C++ has them.

[Dylan16807]

It was caused by the code around it, but the actual CPU cycles stalled out in the assembly language, making it much harder to find the problem.

Is how I understood the post.

Anyway there's noting wrong with rust FFI. The overhead was because this function wanted to support two options and didn't implement that in the best way.