is building a vector mathematically with mod and remainder faster that converting to a string and collecting?

really cool! any chance you could write an explanation?

not for very large numbers

This is so nice!

I am not sure what I am supposed to be doing with null bytes

does Null => "<z>" or just "z"?

They are basically the same. As per the documentation:

paste0(..., collapse) is equivalent to paste(..., sep = "", collapse), slightly more efficiently.

I assume you mean that i % 2 returns -1 for negative odd numbers whereas i & 1 is positive. But I fail to see where behavior is different for even numbers. See https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=1ba4abb31460c86f5c426d188672c5bb

It may also be worth adding that this is a good test for unsigned integers, but will not work in general for signed integers when using rust. Since len() always returns a positive number (usize) this is a safe test in the above code.

If you're trying to test odd/even for something that could be positive or negative, the n % 2 == 0 test is a better choice.

It does a bitwise AND. As all odd numbers will have the final bit set and all even numbers not, this is a good test.