Add test against possible undefined behavior

Author: vks

tests/bool.rs

@@ -0,0 +1,26 @@
+#![cfg(feature = "std")]
+
+extern crate rand;
+extern crate libc;
+
+use rand::{FromEntropy, SmallRng};
+use rand::distributions::{Distribution, Bernoulli};
+
+#[link_name = "m"]
+extern "C" {
+    fn nextafter(x: f64, y: f64) -> f64;
+}
+
+/// This test should make sure that we don't accidentally have undefined
+/// behavior for large propabilties due to
+/// https://github.com/rust-lang/rust/issues/10184.
+#[test]
+fn large_probability() {
+    let p = unsafe { nextafter(1., 0.) };
+    assert!(p < 1.);
+    let d = Bernoulli::new(p);
+    let mut rng = SmallRng::from_entropy();
+    for _ in 0..10 {
+        assert!(d.sample(&mut rng));
+    }
+}