pub fn main(world: World) -> Void raises {
    var dst: [16]u8 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    let copied: usize = std.mem.copy(dst, std.mem.span("mem copy fill\n"))
    var i: i32 = 0
    var total: usize = 0
    while i < 20000 {
        total = total + copied
        i = i + 1
    }
    if total == 280000 && dst[0] == 109 as u8 {
        check world.out.write("mem copy fill\n")
    }
}