Data commit

Task/Miller-Rabin-primality-test/C-sharp/miller-rabin-primality-test-1.cs

@@ -0,0 +1,27 @@
+public static class RabinMiller
+{
+    public static bool IsPrime(int n, int k)
+    {
+        if ((n < 2) || (n % 2 == 0)) return (n == 2);
+
+        int s = n - 1;
+        while (s % 2 == 0)  s >>= 1;
+
+        Random r = new Random();
+        for (int i = 0; i < k; i++)
+        {
+            int a = r.Next(n - 1) + 1;
+            int temp = s;
+            long mod = 1;
+            for (int j = 0; j < temp; ++j)  mod = (mod * a) % n;
+            while (temp != n - 1 && mod != 1 && mod != n - 1)
+            {
+                mod = (mod * mod) % n;
+                temp *= 2;
+            }
+
+            if (mod != n - 1 && temp % 2 == 0) return false;
+        }
+        return true;
+    }
+}

Task/Miller-Rabin-primality-test/C-sharp/miller-rabin-primality-test-2.cs

@@ -0,0 +1,58 @@
+// Miller-Rabin primality test as an extension method on the BigInteger type.
+// Based on the Ruby implementation on this page.
+public static class BigIntegerExtensions
+{
+  public static bool IsProbablePrime(this BigInteger source, int certainty)
+  {
+    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;
+    }
+
+    // There is no built-in method for generating random BigInteger values.
+    // Instead, random BigIntegers are constructed from randomly generated
+    // byte arrays of the same length as the source.
+    RandomNumberGenerator rng = RandomNumberGenerator.Create();
+    byte[] bytes = new byte[source.ToByteArray().LongLength];
+    BigInteger a;
+
+    for(int i = 0; i < certainty; i++)
+    {
+      do
+      {
+        // This may raise an exception in Mono 2.10.8 and earlier.
+        // http://bugzilla.xamarin.com/show_bug.cgi?id=2761
+        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;
+  }
+}