Returns ln(1+x). For small values of x, log1p(x) is more accurate than log(1.0+x). If x is ##NaN or < -1 => ##NaN If x is ##Inf => ##Inf If x is -1 => ##-Inf If x is 0 => 0 with sign matching x See: https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html#log1p-double-