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Miller–Rabin primality test: Difference between revisions
→{{header|C sharp}}
Line 435:
return true;
}
}
</lang>
<lang C sharp|C#>
// 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;
}
}
</lang>
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