Note rotate_{left,right} in wrapping_sh{lr} docs

src/libcore/num/mod.rs

@@ -741,6 +741,13 @@ macro_rules! int_impl {
         /// where `mask` removes any high-order bits of `rhs` that
         /// would cause the shift to exceed the bitwidth of the type.
         ///
+        /// Note that this is *not* the same as a rotate-left; the
+        /// RHS of a wrapping shift-left is restricted to the range
+        /// of the type, rather than the bits shifted out of the LHS
+        /// being returned to the other end. The primitive integer
+        /// types all implement a `rotate_left` function, which may
+        /// be what you want instead.
+        ///
         /// # Examples
         ///
         /// Basic usage:
@@ -759,6 +766,13 @@ macro_rules! int_impl {
         /// where `mask` removes any high-order bits of `rhs` that
         /// would cause the shift to exceed the bitwidth of the type.
         ///
+        /// Note that this is *not* the same as a rotate-right; the
+        /// RHS of a wrapping shift-right is restricted to the range
+        /// of the type, rather than the bits shifted out of the LHS
+        /// being returned to the other end. The primitive integer
+        /// types all implement a `rotate_right` function, which may
+        /// be what you want instead.
+        ///
         /// # Examples
         ///
         /// Basic usage: