const std = @import("std");

fn pgcd(l: u32, r: u32) u32 {
    var a = l;
    var b = r;
    if (a == 0 or b == 0) {
        return 0;
    }
    while (a != b) {
        if (a > b) {
            a = a - b;
        } else {
            b = b - a;
        }
    }
    return a;
}

const expect = @import("std").testing.expect;

fn expectidentical(i: u32) !void {
    try expect(pgcd(i, i) == i);
}

test "identical" {
    try expectidentical(1);
    try expectidentical(7);
    try expectidentical(18);
}

test "primes" {
    try expect(pgcd(4, 13) == 1);
}

test "pgcdexists" {
    try expect(pgcd(15, 35) == 5);
}

test "pgcdlower" {
    try expect(pgcd(15, 5) == 5);
}