UUID v4 in Rust

uuidv4.rs

use rand::Rng;

fn calc_uuid() -> String {

    let mut result: String = "".to_owned();    
    let mut rng = rand::thread_rng();
    
    for x in 0..16 {
    
        let rand_value = if x == 6 {
            64 + rng.gen_range(0, 15)
        } else {
            rng.gen_range(0, 255)
        } as u64;
        
        if x == 4 || x == 6 || x == 8 || x == 10 {
            result.push_str("-");
        }
        
        result.push_str(to_hex(rand_value, 2).as_str());
    }
    
    result
}

fn to_hex(num: u64, length: i32) -> String {
    let mut result: String = "".to_owned();

    let hex_values = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"];

    let mut i = length as i32 - 1;
    while i >= 0 {
        let raise = (16u32).pow(i as u32) as f64;
        let index = (num as f64 / raise).floor() as u32;
        result.push_str(hex_values[(index % 16u32) as usize]);
        i -= 1;
    }

    result
}


fn main() {
    // generate 50 uuids
    for _x in 0..50 {
        println!("{}", calc_uuid());
    }
}