private void SieveOfEratosthenesFactorizer(int limit, int passes, int start, int end)
{
var factorizer = new SieveOfEratosthenesFactorizer(limit);
for (int p = 0; p < passes; ++p)
{
for (int n = start; n <= end; ++n)
{
factorizer.GetPrimeFactors(n).ToArray();
}
}
}
public void GetPrimeFactors_AgreesWithNaiveFactorizer()
{
var sieveFactorizer = new SieveOfEratosthenesFactorizer(3481);
var trialDivisionFactorizer = new TrialDivisionFactorizer(3481);
for (int n = 0; n <= 3481; ++n)
{
CollectionAssert.AreEquivalent(
NaivePrimeDeciderProviderFactorizer.GetPrimeFactors(n).ToArray(),
sieveFactorizer.GetPrimeFactors(n).ToArray());
CollectionAssert.AreEquivalent(
NaivePrimeDeciderProviderFactorizer.GetPrimeFactors(n).ToArray(),
trialDivisionFactorizer.GetPrimeFactors(n).ToArray());
}
}
public void GetPrimeFactors_AgreesWithKnownOutput()
{
var sieveFactorizer = new SieveOfEratosthenesFactorizer(1000);
var trialDivisionFactorizer = new TrialDivisionFactorizer(1000);
foreach (var numberPrimeFactorsPair in _numberPrimeFactorsPairs)
{
int number = numberPrimeFactorsPair.Item1;
int[] primeFactors = numberPrimeFactorsPair.Item2;
CollectionAssert.AreEquivalent(primeFactors, sieveFactorizer.GetPrimeFactors(number).ToArray());
CollectionAssert.AreEquivalent(primeFactors, trialDivisionFactorizer.GetPrimeFactors(number).ToArray());
CollectionAssert.AreEquivalent(primeFactors, NaivePrimeDeciderProviderFactorizer.GetPrimeFactors(number).ToArray());
}
}
public IEnumerable <long> GetPrimeFactors(long n)
{
if (n <= _sieveFactorizer.Limit)
{
foreach (long primeFactor in _sieveFactorizer.GetPrimeFactors((int)n))
{
yield return(primeFactor);
}
}
else
{
foreach (long prime in _sieveFactorizer.Primes)
{
// Check for factors up to sqrt(n), as non-primes with a factor larger than that
// must also have a factor less than that, otherwise they'd multiply together to
// make a number greater than n. The fact that n is getting smaller doesn't matter.
// If this condition stops the loop, what remains of n is a single prime factor.
// All primes less than 'prime' were already divided out, so for n to have multiple
// prime factors they'd have to all be >= 'prime', but in that case the loop
// wouldn't stop here.
if (prime * prime > n)
{
break;
}
while (n % prime == 0)
{
yield return(prime);
n /= prime;
}
// All the prime factors have been extracted, so stop looking.
if (n == 1)
{
yield break;
}
}
// The loop above was broken out of (before n == 1), so the original n, or what
// remains of it, is prime.
yield return(n);
}
}
