1: package de.luschny.math.factorial;
2:
3: import de.luschny.math.arithmetic.Xint;
4:
5: public class FactorialSquaredDiff implements IFactorialFunction
6: {
7:
8: public FactorialSquaredDiff()
9: {
10: }
11:
12: public String getName()
13: {
14: return "SquaredDifference ";
15: }
16:
17: public Xint factorial(int n)
18: {
19: if (n < 0)
20: {
21: throw new ArithmeticException("Factorial: n has to be >= 0, but was " + n);
22: }
23:
24: if (n < 2)
25: {
26: return Xint.ONE;
27: }
28:
29: long h = n / 2, q = h * h;
30: long r = (n & 1) == 1 ? 2 * q * n : 2 * q;
31: Xint f = Xint.valueOf(r);
32:
33: for (int d = 1; d < n - 2; d += 2)
34: {
35: f = f.multiply(q -= d);
36: }
37:
38: return f;
39: }
40:
41: } // endOfFactorialSquaredDiff