public void nextNumber()
{
CurrentNumber = random.Next(1, 1000);
if (IsPrime(CurrentNumber))
{
PrimeFound?.Invoke(this, EventArgs.Empty);
}
}
// <summary>
// Starting from 2, keep finding the next larger prime number until cancelled.
// This method uses the "Sieve of Eratosthenes" as explained here: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
// 1. Create a list of consecutive integers from 2 through n: (2, 3, 4, ..., n).
// 2. Initially, let p equal 2, the smallest prime number.
// 3. Enumerate the multiples of p by counting to n from 2p in increments of p, and mark them in the list (these will be 2p, 3p, 4p, ... ; the p itself should not be marked).
// 4. Find the first number greater than p in the list that is not marked. If there was no such number, stop.
// Otherwise, let p now equal this new number(which is the next prime), and repeat from step 3.
/// </summary>
public void FindMaxPrime(CancellationTokenSource cts)
{
MaxPrime = 2;
int currentNumber = 0;
int outerCounter = 0;
var outerTotal = EndPrimeRange - MaxPrime;
// Add the first prime
Primes.Add(MaxPrime);
while (outerCounter++ <= outerTotal)
{
for (currentNumber = MaxPrime; currentNumber <= EndPrimeRange; currentNumber++)
{
if (cts.IsCancellationRequested)
{
return;
}
var notPrime = currentNumber * MaxPrime;
// Don't add it to the list if it's beyond the maximum range, or less than the already known max prime.
if (notPrime > EndPrimeRange)
{
break;
}
if (notPrime < MaxPrime)
{
continue;
}
// Check against some known prime numbers.
if (IsDivisibleByKnownPrimes(notPrime))
{
continue;
}
// Add it to the known list of not primes
NotPrimes.Add(notPrime);
}
// Find the prime candidates greater than MaxPrime
for (currentNumber = MaxPrime + 1; currentNumber <= EndPrimeRange; currentNumber++)
{
if (cts.IsCancellationRequested)
{
return;
}
// Don't add it to the list if it's beyond the maximum range, or less than the already known max prime.
if (currentNumber > EndPrimeRange || currentNumber < MaxPrime)
{
continue;
}
if (IsDivisibleByKnownPrimes(currentNumber))
{
continue;
}
// Check to see if we've found a new maximum prime
if (!NotPrimes.Contains(currentNumber))
{
MaxPrime = currentNumber;
// Only keep a limited list of known primes to reduce checking time.
if (Primes.Count < 30)
{
Primes.Add(MaxPrime);
}
// Notify the view model that it's time for an update.
PrimeFound?.Invoke(this, EventArgs.Empty);
break;
}
}
}
}
