/// <summary>
/// Uses the fermat test a given amount of times to test whether or not a supplied interger is probably prime.
/// </summary>
/// <param name="b">Value to test primality of</param>
/// <param name="provider">Random provider used to generate values to test b against</param>
/// <param name="certainty">How many times the test should be performed. More iterations means higher certainty, but at the cost of performance!</param>
/// <returns>Whether or not the given value is probably prime or not</returns>
public static bool IsProbablePrime(BigInteger b, RandomProvider provider, int certainty)
{
BigInteger e = b - 1;
byte[] b1 = b.ToByteArray();
byte last = b1[b1.Length - 1];
int len = b1.Length - 1;
for (int i = 0; i < certainty; ++i)
{
byte[] gen = new byte[provider.NextInt(len) + 1];
provider.GetBytes(gen);
if (last != 0 && gen.Length == len + 1)
{
gen[gen.Length - 1] %= last;
}
else
{
gen[gen.Length - 1] &= 127;
}
BigInteger test = new BigInteger(gen);
if (ModExp(test, e, b) != 1)
{
return(false);
}
}
return(true);
}
