public XInt Factorial(int n)
{
if (n < 0)
{
throw new ArithmeticException(
this.Name + ": " + nameof(n) + " >= 0 required, but was " + n);
}
this.oddFactNdiv4 = this.oddFactNdiv2 = XInt.One;
return(this.OddFactorial(n) << (n - XMath.BitCount(n)));
}
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);
}
public XInt Factorial(int n)
{
if (n < 20)
{
return(XMath.Factorial(n));
}
var sieve = new PrimeSieve(n);
var task2 = Task.Factory.StartNew <XInt>(() =>
{
this.results2 = new IAsyncResult[XMath.FloorLog2(n)];
this.swingDelegate2 = Swing2;
this.taskCounter2 = 0;
var N = n;
// -- It is more efficient to add the big swings
// -- first and the small ones later!
while (N >= Smallswing)
{
this.results2[this.taskCounter2++] = this.swingDelegate2.BeginInvoke(sieve, N, null, null);
N >>= 1;
}
return(this.RecFactorial2(n));
});
this.results3 = new IAsyncResult[XMath.FloorLog2(n)];
this.swingDelegate3 = Swing3;
this.taskCounter3 = 0;
var m = n;
// -- It is more efficient to add the big swings
// -- first and the small ones later!
while (m >= Smallswing)
{
this.results3[this.taskCounter3++] = this.swingDelegate3.BeginInvoke(sieve, m, null, null);
m >>= 1;
}
var task3Result = this.RecFactorial3(n);
return((task2.Result * task3Result) << (n - XMath.BitCount(n)));
}
public XInt Factorial(int n)
{
if (n < 20)
{
return(XMath.Factorial(n));
}
var lgN = XMath.FloorLog2(n);
var piN = 2 + (15 * n) / (8 * (lgN - 1));
this.primeList = new int[piN];
this.multiList = new int[piN];
var len = this.PrimeFactors(n);
var exp2 = n - XMath.BitCount(n);
return(this.NestedSquare(len) << exp2);
}
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);
}