/* 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);
}