f64 implementation

f64.rs

impl f64 {
    // ...
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn ln(self) -> f64 {
        if self.is_finite() {
            if x > 0.0 {
                return unsafe { intrinsics::logf64(self) }
            }
            return if x == 0.0 {
                NEG_INFINITY // log(0) = -Inf
            } else {
                NAN // log(-ve) = NaN
            }
        } else if self.is_nan() {
            self // log(NaN) = NaN
        } else if x > 0.0 {
            x // log(Inf) = Inf
        } else {
            return NAN // log(-Inf) = NaN
        }
    }
    // ...
}

original impl.rs

impl f64 {
    // ...
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn ln(self) -> f64 {
        unsafe { intrinsics::logf64(self) }
   }
    // ...
}