Rust Fast I/O

main.rs

fn main() {
    let buf = stdin();
    let mut token = buf.split_ascii_whitespace();

    use std::fmt::Write;
    // buf.clear();
    let mut buf = String::new();
    writeln!(buf, "{}", token.next().unwrap()).unwrap();
    print!("{}", buf);
}

extern "C" {
    fn mmap(addr: usize, len: usize, p: i32, f: i32, fd: i32, o: i64) -> *mut u8;
    fn fstat(fd: i32, stat: *mut usize) -> i32;
}
fn stdin() -> &'static str {
    let mut stat = [0; 18];
    unsafe { fstat(0, (&mut stat).as_mut_ptr()) };
    let buffer = unsafe { mmap(0, stat[6], 1, 2, 0, 0) };
    unsafe { std::str::from_utf8_unchecked(std::slice::from_raw_parts(buffer, stat[6])) }
}