public XInt Factorial(int n)
{
if (n < 20)
{
return(XMath.Factorial(n));
}
this.sieve = new PrimeSieve(n);
var pLen = (int)(2.0 * (XMath.FloorSqrt(n)
+ (double)n / (XMath.Log2(n) - 1)));
this.primeList = new int[pLen];
var exp2 = n - XMath.BitCount(n);
return(this.RecFactorial(n) << exp2);
}
private static XInt Swing3(PrimeSieve sieve, int n)
{
var primorial = Task.Factory.StartNew <XInt>(() =>
{
var start = sieve.NextPrime(n / 2);
start = sieve.NextPrime(start);
return(sieve.GetPrimorial(start, n, 2));
});
var count = 0;
var rootN = XMath.FloorSqrt(n);
var startPrime = sieve.NextPrime(rootN);
startPrime = sieve.NextPrime(startPrime);
var aPrimes = sieve.GetPrimeCollectionEveryOther(5, rootN);
var bPrimes = sieve.GetPrimeCollectionEveryOther(startPrime, n / 3);
var primeList = new int[aPrimes.NumberOfPrimes + bPrimes.NumberOfPrimes];
foreach (var prime in aPrimes)
{
int q = n, p = 1;
while ((q /= prime) > 0)
{
if ((q & 1) == 1)
{
p *= prime;
}
}
if (p > 1)
{
primeList[count++] = p;
}
}
foreach (var prime in bPrimes.Where(prime => ((n / prime) & 1) == 1))
{
primeList[count++] = prime;
}
var primeProduct = XMath.Product(primeList, 0, count);
return(primeProduct * primorial.Result);
}
XInt Swing(int n)
{
if (n < 33)
{
return(SmallOddSwing[n]);
}
var primorial = Task.Factory.StartNew <XInt>(() =>
this.sieve.GetPrimorial(n / 2 + 1, n));
var count = 0;
var rootN = XMath.FloorSqrt(n);
var aPrimes = this.sieve.GetPrimeCollection(3, rootN);
var bPrimes = this.sieve.GetPrimeCollection(rootN + 1, n / 3);
var piN = aPrimes.NumberOfPrimes + bPrimes.NumberOfPrimes;
var primeList = new int[piN];
foreach (var prime in aPrimes)
{
int q = n, p = 1;
while ((q /= prime) > 0)
{
if ((q & 1) == 1)
{
p *= prime;
}
}
if (p > 1)
{
primeList[count++] = p;
}
}
foreach (var prime in bPrimes.Where(prime => ((n / prime) & 1) == 1))
{
primeList[count++] = prime;
}
var primeProduct = XMath.Product(primeList, 0, count);
return(primeProduct * primorial.Result);
}
private XInt Swing(int n)
{
if (n < 33)
{
return(SmallOddSwing[n]);
}
int count = 0, rootN = XMath.FloorSqrt(n);
var aPrimes = this.sieve.GetPrimeCollection(3, rootN);
var bPrimes = this.sieve.GetPrimeCollection(rootN + 1, n / 3);
foreach (var prime in aPrimes)
{
int q = n, p = 1;
while ((q /= prime) > 0)
{
if ((q & 1) == 1)
{
p *= prime;
}
}
if (p > 1)
{
this.primeList[count++] = p;
}
}
foreach (var prime in bPrimes.Where(prime => ((n / prime) & 1) == 1))
{
this.primeList[count++] = prime;
}
var primorial = this.sieve.GetPrimorial(n / 2 + 1, n);
return(primorial * XMath.Product(this.primeList, 0, count));
}
public XInt Factorial(int n)
{
if (n < 20)
{
return(XMath.Factorial(n));
}
var rootN = XMath.FloorSqrt(n);
var log2N = XMath.FloorLog2(n);
var section = new XInt[log2N + 1];
for (var i = 0; i < section.Length; i++)
{
section[i] = XInt.One;
}
var sieve = new PrimeSieve(n);
var primes = sieve.GetPrimeCollection(3, rootN);
foreach (var prime in primes)
{
int k = 0, m = 0, q = n;
do
{
m += q /= prime;
} while (q >= 1);
while (m > 0)
{
if ((m & 1) == 1)
{
section[k] *= prime;
}
m = m / 2;
k++;
}
}
var j = 2;
var low = n;
while (low != rootN)
{
var high = low;
low = n / j++;
if (low < rootN)
{
low = rootN;
}
var primorial = sieve.GetPrimorial(low + 1, high);
if (primorial != XInt.One)
{
int k = 0, m = j - 2;
while (m > 0)
{
if ((m & 1) == 1)
{
section[k] *= primorial;
}
m = m / 2;
k++;
}
}
}
var factorial = section[log2N];
for (var i = log2N - 1; i >= 0; --i)
{
factorial = XInt.Pow(factorial, 2) * section[i];
}
var exp2N = n - XMath.BitCount(n);
return(factorial << exp2N);
}