Merge pull request #76 from tarcieri/impl-ct-eq-for-choice

Impl ConstantTimeEq for Choice

Author: hdevalence

src/lib.rs

@@ -240,6 +240,13 @@ impl<T: ConstantTimeEq> ConstantTimeEq for [T] {
     }
 }
 
+impl ConstantTimeEq for Choice {
+    #[inline]
+    fn ct_eq(&self, rhs: &Choice) -> Choice {
+        !(*self ^ *rhs)
+    }
+}
+
 /// Given the bit-width `$bit_width` and the corresponding primitive
 /// unsigned and signed types `$t_u` and `$t_i` respectively, generate
 /// an `ConstantTimeEq` implementation.

tests/mod.rs

@@ -135,6 +135,14 @@ fn conditional_select_choice() {
     assert_eq!(bool::from(Choice::conditional_select(&f, &t, t)), true);
 }
 
+#[test]
+fn choice_equal() {
+    assert!(Choice::from(0).ct_eq(&Choice::from(0)).unwrap_u8() == 1);
+    assert!(Choice::from(0).ct_eq(&Choice::from(1)).unwrap_u8() == 0);
+    assert!(Choice::from(1).ct_eq(&Choice::from(0)).unwrap_u8() == 0);
+    assert!(Choice::from(1).ct_eq(&Choice::from(1)).unwrap_u8() == 1);
+}
+
 #[test]
 fn test_ctoption() {
     let a = CtOption::new(10, Choice::from(1));