rust - Hex String 转成 u64

网上只有 "123" 转成 123的例子, 可是我需要 "B8" 转 184 的功能呀, 只能自己撸一个

fn parse_hex_str(str: &String) -> u64 {
    let mut rst: u64 = 0;
    let len = str.len();
    str.to_ascii_uppercase().bytes().enumerate().for_each(|(i, c)| {
        let a = 'A' as u8;
        let zero = '0' as u8;
        let m = if c >= a {
            c - a + 10
        } else {
            c - zero
        };
        rst += ((m as u64) << (len - i - 1) as u64 * 4);
    });
    rst
}