fn b64(c: u8) -> u8 {
    if c >= 65 && c <= 90 {
        return c - 65
    }
    if c >= 97 && c <= 122 {
        return c - 97 + 26
    }
    if c >= 48 && c <= 57 {
        return c - 48 + 52
    }
    if c == 43 {
        return 62
    }
    return 63
}

fn decodeByte0(a: u8, b: u8) -> u8 {
    return b64(a) * 4 + b64(b) / 16
}

fn decodeByte1(b: u8, c: u8) -> u8 {
    return (b64(b) % 16) * 16 + b64(c) / 4
}

fn decodeByte2(c: u8, d: u8) -> u8 {
    return (b64(c) % 4) * 64 + b64(d)
}

pub fn main(world: World) -> Void raises {
    let ok: Bool = decodeByte0(84, 87) == 77 && decodeByte1(87, 70) == 97 && decodeByte2(70, 117) == 110
    if ok {
        check world.out.write("base64 decode ok\n")
    }
}