/* mathematically the same: less stable typically, but useful if n-k+1 < 0 : */ static double lfastchoose2(double n, double k, int *s_choose) { double r; r = lgammafn_sign(n - k + 1., s_choose); return lgammafn(n + 1.) - lgammafn(k + 1.) - r; }
double lgammafn(double x) { return lgammafn_sign(x, NULL); }