Rewrote my totient calculator in C. It’s pretty much a direct translation of the excrement I wrote in Rust. Be gentle, there are obvious points that I miss completely in C that veterans in the ancient language would scoff heartily about. I don’t yet know what the hell a struct is for or the extents of threading. All in good time.

So here’s my uncommented and fully unnecessary data type usage.

Figured I’d write a much quicker varient of the Totient Function in Rust. Excellent language. I don’t have a grasp on the finer points available to Rustaceans, but I can hopefully put concurrency and whatnot to use at some point. The code is quick, but I know it can be quicker if I just spend some time putting it together.

This is the quick crap I dreamt up:

use std::env;

fn gcd(mut m: u64, mut n: u64) -> u64 {
   while m != 0 {
       let old_m = m;
       m = n % m;
       n = old_m;
   }
   n
}

fn totient(mut a: u64) -> u64 {
    let mut y = 0;
    let o = a;
    while a != 0 {
        if gcd(o, a) == 1 {
            y += 1;
        }
        a -= 1;
    }
    y
}

fn main() {
    let args: Vec<_> = env::args().collect();
    let n: u64 = args[1].parse::<u64>().unwrap();
    let m: u64 = args[2].parse::<u64>().unwrap();

    let x = (n..m).collect::<Vec<u64>>();

    for i in &x {
        let o = totient(*i);
        println!("{:?}, {:?}", i, o);
    }
    
}

The code should compile with no problems. Yes, I realize that u64 is overkill. No, my code will never require unsigned 2^64 integers. It may be a quirky choice, but whatever. Change to u32 as needed, though I’m sure it won’t be a problem for anyone.

I’ve taken a few implementations apart and I’ve tried to figure out what the intention of Euler’s Phi function is. I think I’ve got it. I found an interesting implementation in Ruby here but it wasn’t satisfactory. Sure, the code was incredibly minimalistic, but it was also recursive and overflowed the stack for anything over 7704 iterations. I didn’t like the inflexibility of it. So I rewrote it in big ugly moron code that isn’t recursive, but is capable of scaling to some decently large totients. I might see if I can code something similar in Rust, just for shits and giggles.