fn value(c: u8) -> u32 {
    if c >= 48 && c <= 57 {
        return (c - 48) as u32
    }
    if c >= 65 && c <= 90 {
        return (c - 65 + 10) as u32
    }
    return 0
}

fn digitSum(n: u32) -> u32 {
    return n / 10 + n % 10
}

fn checkDigit(text: Span<u8>) -> u32 {
    var sum: u32 = 0
    var i: usize = 0
    while i < 8 {
        var v: u32 = value(text[i])
        if i % 2 == 1 {
            v = v * 2
        }
        sum = sum + digitSum(v)
        i = i + 1
    }
    return (10 - sum % 10) % 10
}

pub fn main(world: World) -> Void raises {
    if checkDigit(std.mem.span("03783310")) == 0 {
        check world.out.write("cusip ok\n")
    }
}