public static async Task <BigInteger> GenerateAsync(BigInteger maxExclusive, IRandomProvider randomProvider)
{
if (randomProvider == null)
{
throw new ArgumentNullException(nameof(randomProvider));
}
if (maxExclusive == BigIntegerHelpers.Zero)
{
throw new ArgumentOutOfRangeException(nameof(maxExclusive), "Max exclusive must be above 0.");
}
if (maxExclusive == BigIntegerHelpers.One)
{
return(BigInteger.Zero);
}
if (maxExclusive < new BigInteger(int.MaxValue))
{
return(new BigInteger(randomProvider.NextInt((int)maxExclusive)));
}
var bytes = maxExclusive.ToByteArray();
BigInteger result = 0;
await Task.Run(() =>
{
do
{
randomProvider.NextBytes(bytes);
if (bytes.All(v => v == 0))
{
throw new InvalidOperationException("Zero buffer returned by random provider.");
}
bytes[bytes.Length - 1] &= 0x7F;
result = new BigInteger(bytes);
} while (result >= maxExclusive || result.Equals(BigIntegerHelpers.One) ||
result.Equals(BigIntegerHelpers.Zero));
});
return(result);
}
public static async Task <BigInteger> GeneratePrime(uint bitLength, IRandomProvider randomProvider, IPrimalityTest primalityTest)
{
if (randomProvider == null)
{
throw new ArgumentNullException(nameof(randomProvider));
}
if (bitLength < 8)
{
throw new ArgumentOutOfRangeException(nameof(bitLength), "Bit length must be at least of length 8.");
}
var bytes = bitLength / 8;
var randomNumberBytes = new byte[bytes];
randomProvider.NextBytes(randomNumberBytes);
var result = new BigInteger(randomNumberBytes);
if (result.Sign < 0)
{
result = BigInteger.Negate(result);
}
if (result.IsEven)
{
result = result + 1;
}
while (!await primalityTest.TestAsync(result))
{
result = result + 2;
}
return(result);
}