//       algorithm can be used to compute log1p(x) to within a few ULP:
//
//              u = 1+x;
//              if(u==1.0) return x ; else
//                         return log(u)*(x/(u-1.0));
//
//       See HP-15C Advanced Functions Handbook, p.193.

// Log1p returns the natural logarithm of 1 plus its argument x.
// It is more accurate than [Log](1 + x) when x is near zero.
//
// Special cases are:
//
//	Log1p(+Inf) = +Inf