Use `std::mem::swap` instead of temp variables

[claytonwramsey]

Hi! I just came across your website from the Rust Users forum. It's pretty cool!

I noticed a spot where the code provided for Euclid's GCD algorithm could be improved: you use temporary variables to swap a and b, but we can just use std::mem::swap to more idiomatically (and maybe slightly more quickly) swap the two.

Here's what the simplified code would be:

fn gcd(mut a: usize, mut b: usize) -> usize {
    // If equal, return any of them
    if a == b {
        return a;
    }

    // Swap a with b, if b is greater than a
    if b > a {
        std::mem::swap(&mut a, &mut b);
    }

    while b > 0 {
        a %= b;
        std::mem::swap(&mut a, &mut b);
    }

    // Now, a % b = 0, hence return it
    return a;
}

(I would also substitute the first two checks with match a.cmp(&b) to save time, but this is mostly a matter of taste)

While we're at it, it might be worthwhile that most modern implementations of GCD these days take advantage of O(1) bit-scan operations - in the case of Rust, trailing_zeros() - to quickly implement the binary GCD algorithm. Check out how num does it.

[namanlp]

Hi there,

While it does not affect speed significantly, yes, it will be better idiomatically. I will replace this asap.

Regarding Binary GCD instead of Euclid GCD, I know it is a bit faster, but I will have to write a complete article on it.

I will try to bring it on.

Actually, currently, I am working on other things. Like segment trees and longest palindrome subseqeunce and similar stuff, that you will not find easily anywhere else for rust.

I will try to bring on Binary GCD as well.

Thanks for your opinion.
It is really helpful as well as motivating.
Regards
Naman