Validating Israeli ID number

Question

I'm looking for a clean and efficient way to validate an Israeli ID number.

It's basically an implementation of the Luhn algorithm on a 9 digits number.

Note: This question is here for the community because it wasn't on stack overflow yet. You can add answers in different coding languages.

Answer 1

Here's an efficient way to implement it in C# (link):

public static bool IsValidIsraeliID(string israeliID)
    {
        if (israeliID.Length != 9)
            return false;

        long sum = 0;

        for (int i = 0; i < israeliID.Length; i++)
        {
            var digit = israeliID[israeliID.Length - 1 - i] - '0';
            sum += (i % 2 != 0) ? GetDouble(digit) : digit;
        }

        return sum % 10 == 0;

        int GetDouble(long i)
        {
            switch (i)
            {
                case 0: return 0;
                case 1: return 2;
                case 2: return 4;
                case 3: return 6;
                case 4: return 8;
                case 5: return 1;
                case 6: return 3;
                case 7: return 5;
                case 8: return 7;
                case 9: return 9;
                default: return 0;
            }
        }
    }