Fix rotate_{left, right} for multiple of bitsize rotation amounts

Add additional rotation tests

src/libcore/num/mod.rs

@@ -586,14 +586,14 @@ fn trailing_zeros(self) -> $T { unsafe { $cttz(self) } }
             fn rotate_left(self, n: uint) -> $T {
                 // Protect against undefined behaviour for over-long bit shifts
                 let n = n % $BITS;
-                (self << n) | (self >> ($BITS - n))
+                (self << n) | (self >> (($BITS - n) % $BITS))
             }
 
             #[inline]
             fn rotate_right(self, n: uint) -> $T {
                 // Protect against undefined behaviour for over-long bit shifts
                 let n = n % $BITS;
-                (self >> n) | (self << ($BITS - n))
+                (self >> n) | (self << (($BITS - n) % $BITS))
             }
 
             #[inline]

src/libcoretest/num/int_macros.rs

@@ -114,6 +114,15 @@ fn test_rotate() {
         assert_eq!(_1.rotate_left(124), _1);
         assert_eq!(_0.rotate_right(124), _0);
         assert_eq!(_1.rotate_right(124), _1);
+
+        // Rotating by 0 should have no effect
+        assert_eq!(A.rotate_left(0), A);
+        assert_eq!(B.rotate_left(0), B);
+        assert_eq!(C.rotate_left(0), C);
+        // Rotating by a multiple of word size should also have no effect
+        assert_eq!(A.rotate_left(64), A);
+        assert_eq!(B.rotate_left(64), B);
+        assert_eq!(C.rotate_left(64), C);
     }
 
     #[test]

src/libcoretest/num/uint_macros.rs

@@ -74,6 +74,15 @@ fn test_rotate() {
         assert_eq!(_1.rotate_left(124), _1);
         assert_eq!(_0.rotate_right(124), _0);
         assert_eq!(_1.rotate_right(124), _1);
+
+        // Rotating by 0 should have no effect
+        assert_eq!(A.rotate_left(0), A);
+        assert_eq!(B.rotate_left(0), B);
+        assert_eq!(C.rotate_left(0), C);
+        // Rotating by a multiple of word size should also have no effect
+        assert_eq!(A.rotate_left(64), A);
+        assert_eq!(B.rotate_left(64), B);
+        assert_eq!(C.rotate_left(64), C);
     }
 
     #[test]