You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: base_n.rs
    path of file: ./repos/kcl/compiler_base/3rdparty/rustc_data_structures/src
    
    the code of the file until where you have to start completion: /// Converts unsigned integers into a string representation with some base.
/// Bases up to and including 36 can be used for case-insensitive things.
use std::str;

pub const MAX_BASE: usize = 64;
pub const ALPHANUMERIC_ONLY: usize = 62;
pub const CASE_INSENSITIVE: usize = 36;

const BASE_64: &[u8; MAX_BASE as usize] =
    b"0123456789abcdefghijklmno
    
pub fn push_str(mut n: u128, base: usize, output: &mut String) {
    debug_assert!(base >= 2 && base <= MAX_BASE);
    let mut s = [0u8; 128];
    let mut index = 0;

    let base = base as u128;

    loop {
        s[index] = BASE_64[(n % base) as usize];
        index += 1;
        n /= base;

        if n == 0 {
            break;
        }
    }
    s[0..index].reverse();

    output.push_str(str::from_utf8(&s[0..index]).unwrap());
}