/// <summary>
/// Generate a prime number using with a given approximate length and byte length margin
/// </summary>
/// <param name="threads">How many threads to use to generate primes</param>
/// <param name="approximateByteCount">The byte array length around which the prime generator will select lengths</param>
/// <param name="byteMargin">Allowed deviation of byte length from approximateByteCount</param>
/// <param name="certainty">How many iterations of the fermat test should be run to test primailty for each generated number</param>
/// <param name="provider">Random provider that will be used to generate random primes</param>
/// <returns>A prime number that is aproximately approximateByteCount long</returns>
public static BigInteger GeneratePrime(int threads, int approximateByteCount, int byteMargin, int certainty, RandomProvider provider)
{
var found = false;
BigInteger result = BigInteger.Zero;
for (int i = 0; i < threads; ++i)
{
Task.Factory.StartNew(() =>
{
char left = '\0';
byte rand = 0;
BigInteger b = BigInteger.Zero;
while (!found)
{
if (left == 0)
{
rand = provider.GetBytes(1)[0];
left = (char)8;
}
byte[] b1 = provider.GetBytes(approximateByteCount + (provider.GetBytes(1)[0] % byteMargin) * (rand % 2 == 1 ? 1 : -1));
b1[0] |= 1; // Always odd
b1[b1.Length - 1] &= 127; // Always positive
b = new BigInteger(b1);
rand >>= 1;
--left;
if (IsProbablePrime(b, provider, certainty))
{
found = true;
result = b;
}
}
});
}
while (!found)
{
System.Threading.Thread.Sleep(125);
}
return(result);
}
