Ttykuu

I have a small C# program that validates Swedish social security numbers 'Personnummer', https://en.wikipedia.org/wiki/Personal_identity_number_(Sweden)

I chose to use Regex as there are many different ways it can be input

using System;
using System.Globalization;
using System.Linq;
using System.Text.RegularExpressions;

namespace Personnummer

 /// <summary>
 /// Class used to verify Swedish social security numbers.
 /// </summary>
 public static class Personnummer
 
 private static readonly Regex regex;
 private static readonly CultureInfo cultureInfo;

 static Personnummer()
 +]0,1)?(d3)(d0,1)");
 

 /// <summary>
 /// Calculates the checksum value of a given digit-sequence as string by using the luhn/mod10 algorithm.
 /// </summary>
 /// <param name="value">Sequense of digits as a string.</param>
 /// <returns>Resulting checksum value.</returns>
 private static int Luhn(string value)
 
 // Luhm algorithm doubles every other number in the value.
 // To get the correct checksum digit we aught to append a 0 on the sequence.
 // If the result becomes a two digit number, subtract 9 from the value.
 // If the total sum is not a 0, the last checksum value should be subtracted from 10.
 // The resulting value is the check value that we use as control number.

 // The value passed is a string, so we aught to get the actual integer value from each char (i.e., subtract '0' which is 48).
 int[] t = value.ToCharArray().Select(d => d - 48).ToArray();
 int sum = 0;
 int temp;
 for (int i = t.Length; i -->0; )
 
 temp = t[i];
 sum += (i % 2 == t.Length % 2) 
 ? ((temp * 2) % 10) + temp / 5 
 : temp;
 

 return sum % 10;
 

 /// <summary>
 /// Function to make sure that the passed year, month and day is parseable to a date.
 /// </summary>
 /// <param name="year">Years as string.</param>
 /// <param name="month">Month as int.</param>
 /// <param name="day">Day as int.</param>
 /// <returns>Result.</returns>
 private static bool TestDate(string year, int month, int day)
 
 try
 
 DateTime dt = new DateTime(cultureInfo.Calendar.ToFourDigitYear(int.Parse(year)), month, day);
 return true;
 
 catch
 
 return false;
 
 

 /// <summary>
 /// Validate Swedish social security number.
 /// </summary>
 /// <param name="value">Value as string.</param>
 /// <returns>Result.</returns>
 public static bool Valid(string value)
 

 /// <summary>
 /// Validate Swedish social security number.
 /// </summary>
 /// <param name="value">Value as long.</param>
 /// <returns>Result.</returns>
 public static bool Valid(long value)
 
 return Valid(value.ToString());