IBAN Validator Swift

Question

I am writing an algorithm to validate IBAN (International Bank Account Number) in Swift 3 and not able to figure one of the validation.

Example IBAN - BE68539007547034

Here are the rules to validate -

1. Input number should be of length 16.
2. First 2 characters are country code (not numeric).
3. Last 14 are numeric.
4. Last 2 characters are the modulo 97 result of the previous 12 numeric characters.

While #1 - #3 are clear I need clarity on #4. If anyone have done this before and know about it then please let me know.

Answer 1

From Wikipedia

let IBAN = "GB82WEST12345698765432" // uppercase, no whitespace !!!!
var a = IBAN.utf8.map{ $0 }
while a.count < 4 {
    a.append(0)
}
let b = a[4..<a.count] + a[0..<4]
let c = b.reduce(0) { (r, u) -> Int in
    let i = Int(u)
    return i > 64 ? (100 * r + i - 55) % 97: (10 * r + i - 48) % 97
}
print( "IBAN \(IBAN) is", c == 1 ? "valid": "invalid")

prints

IBAN GB82WEST12345698765432 is valid

With IBAN from your question it prints

IBAN BE68539007547034 is valid