Check result of NotNan addition for NaN

Fixes #32.

Author: mbrubeck

src/lib.rs

@@ -258,11 +258,14 @@ impl<T: Float> Deref for NotNan<T> {
 
 impl<T: Float + PartialEq> Eq for NotNan<T> {}
 
+/// Adds two NotNans.
+///
+/// Panics if the computation results in NaN
 impl<T: Float> Add for NotNan<T> {
     type Output = Self;
 
     fn add(self, other: Self) -> Self {
-        NotNan(self.0 + other.0)
+        NotNan::new(self.0 + other.0).expect("Addition resulted in NaN")
     }
 }
 

tests/test.rs

@@ -522,3 +522,11 @@ fn hash_is_good_for_fractional_numbers() {
     let pct_unique = set.len() as f64 / limit as f64;
     assert!(0.99f64 < pct_unique, "percent-unique={}", pct_unique);
 }
+
+#[test]
+#[should_panic]
+fn test_add_fails_on_nan() {
+    let a = NotNan::new(std::f32::INFINITY).unwrap();
+    let b = NotNan::new(std::f32::NEG_INFINITY).unwrap();
+    let _c = a + b;
+}