Merge remote-tracking branch 'tarcieri/black-box' into develop

Author: isislovecruft

src/lib.rs

@@ -993,6 +993,13 @@ impl ConstantTimeLess for cmp::Ordering {
 pub struct BlackBox<T: Copy>(T);
 
 impl<T: Copy> BlackBox<T> {
+    /// Constructs a new instance of `BlackBox` which will wrap the specified value.
+    ///
+    /// All access to the inner value will be mediated by a `black_box` optimization barrier.
+    pub const fn new(value: T) -> Self {
+        Self(value)
+    }
+
     /// Read the inner value, applying an optimization barrier on access.
     pub fn get(self) -> T {
         black_box(self.0)

tests/mod.rs

@@ -423,3 +423,10 @@ fn less_than_ordering() {
     assert_eq!(cmp::Ordering::Greater.ct_lt(&cmp::Ordering::Less).unwrap_u8(), 0);
     assert_eq!(cmp::Ordering::Less.ct_lt(&cmp::Ordering::Greater).unwrap_u8(), 1);
 }
+
+#[test]
+fn black_box_round_trip() {
+    let n = 42u64;
+    let black_box = BlackBox::new(n);
+    assert_eq!(n, black_box.get());
+}