在检查 armstrong 数时如何处理整数溢出？

问：

在解决 exercism 问题时，我未能通过以下测试用例： 测试失败

thread 'properly_handles_overflow' panicked at 'attempt to add with overflow', src/lib.rs:9:9

use std::io;
pub fn is_armstrong_number(mut num: u32) -> bool {
    let check = num;
    let mut sum = 0;
    let length = (num as f64).log(10.0).floor() as u32 + 1;

    while num != 0 {
        let digit = num % 10;
        sum += u32::pow(digit, length);
        num = num / 10;
    }
    if sum == check {
        return true;
    } else {
        return false;
    }
}

fn main() {
    let mut input = String::new();
    io::stdin().read_line(&mut input);
    let number: u32 = input.trim().parse().unwrap();

    is_armstrong_number(number);
}