Use c-sharp to determine whether a given large number is prime or not

C# determines whether a given large number is prime.
When you see this problem, the first reaction is that this is a problem of program complexity, and then the algorithm problem.
Let's first look at the rules for primes:
Link:http://en.wikipedia.org/wiki/Prime_number
C# prime code:

public bool primeNumber(int n){
             int sqr = Convert.ToInt32(Math.Sqrt(n));
             for (int i = sqr; i > 2; i--){
                 if (n % i == 0){
                     b = false;
                 }
             }
             return b;
         }

Obviously, the program complexity of the above code is N
Let's optimize the code and look at the following code:

public bool primeNumber(int n)
         {
             bool b = true;
             if (n == 1 || n == 2)
                 b = true;
             else
             {
                 int sqr = Convert.ToInt32(Math.Sqrt(n));
                 for (int i = sqr; i > 2; i--)
                 {
                     if (n % i == 0)
                     {
                         b = false;
                     }
                 }
             }
             return b;
         }

Reduce the program complexity to N/2 by increasing the initial judgment.
The above two pieces of code can determine whether a large number is prime or not 100% of the time, but for the problem
1. Satisfy the judgment of large Numbers;
2. To get the right result as soon as possible;
Obviously not satisfied. The net looked up the fastest algorithm to get accurate results, a recognized solution is the miller-rabin algorithm
Link:http://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test
The basic principle of miller-rabin is to increase the speed (that is, probability hit) through the judgment method of random number algorithm, but at the expense of accuracy.
Miller-rabin's judgment of the primes of large Numbers is not always accurate, but it is a basic solution for this problem.
Miller-rabin C# code:

public bool IsProbablePrime(BigInteger source) {
             int certainty = 2;
             if (source == 2 || source == 3)
                 return true;
             if (source < 2 || source % 2 == 0)
                 return false;

             BigInteger d = source - 1;
             int s = 0;

             while (d % 2 == 0) {
                 d /= 2;
                 s += 1;
             }

             RandomNumberGenerator rng = RandomNumberGenerator.Create();
             byte[] bytes = new byte[source.ToByteArray().LongLength];
             BigInteger a;

             for (int i = 0; i < certainty; i++) {
                 do {
                     rng.GetBytes(bytes);
                     a = new BigInteger(bytes);
                 }
                 while (a < 2 || a >= source - 2);

                 BigInteger x = BigInteger.ModPow(a, d, source);
                 if (x == 1 || x == source - 1)
                     continue;

                 for (int r = 1; r < s; r++) {
                     x = BigInteger.ModPow(x, 2, source);
                     if (x == 1)
                         return false;
                     if (x == source - 1)
                         break;
                 }

                 if (x != source - 1)
                     return false;
             }

             return true;
         }