lancer / programs / uptime / src / main.rs

#![no_std]
#![no_main]

use lancer_user::syscall;

#[unsafe(no_mangle)]
pub extern "C" fn lancer_main() -> ! {
    let ms = syscall::clock_monotonic_ms();
    let secs = match ms > 0 {
        true => ms as u64 / 1000,
        false => 0,
    };

    let mut buf = [0u8; 22];
    let start = fmt_u64(&mut buf, secs);
    buf[20] = b's';
    buf[21] = b'\n';
    lancer_user::io::write_bytes(&buf[start..]);

    syscall::exit()
}

fn fmt_u64(buf: &mut [u8; 22], n: u64) -> usize {
    match n {
        0 => {
            buf[19] = b'0';
            19
        }
        _ => {
            let mut v = n;
            (0..20).rev().fold(20usize, |pos, _| match v {
                0 => pos,
                _ => {
                    let np = pos - 1;
                    buf[np] = b'0' + (v % 10) as u8;
                    v /= 10;
                    np
                }
            })
        }
    }
}