use slice rotate methods

Signed-off-by: Mohammad AlSaleh <CE.Mohammad.AlSaleh@gmail.com>

Author: MoSal

src/vec/mod.rs

@@ -996,50 +996,11 @@ impl<T, LenT: LenType, S: VecStorage<T> + ?Sized> VecInner<T, LenT, S> {
 
         match remove_index.cmp(&insert_index) {
             Ordering::Equal => (),
-            Ordering::Less => {
-                // SAFETY: `remove_index < length` assertion guarantees the pointer is within
-                // bounds.
-                let remove_at = unsafe { self.as_mut_ptr().add(remove_index) };
-
-                // SAFETY:
-                // Copies from
-                //  (remove_index + 1)..(insert_index + 1)
-                // to
-                //  remove_index..insert_index
-                //
-                // remove_index < insert_index (this match)
-                // remove_index + 1 < insert_index + 1 (can't saturate because <= length)
-                // remove_index + 1 <= insert_index < length
-                // insert_index + 1 <= length
-                //
-                // If `remove_index == 0`, and `insert_index + 1 ==  length`, then we copy from
-                // 1..length to 0..(length-1).
-                unsafe { ptr::copy(remove_at.add(1), remove_at, insert_index - remove_index) };
-            }
-            Ordering::Greater => {
-                // SAFETY: `insert_index < length` assertion guarantees the pointer is within
-                // bounds.
-                let insert_at = unsafe { self.as_mut_ptr().add(insert_index) };
-
-                // SAFETY:
-                // Copies from
-                //  insert_index..remove_index
-                // to
-                //  (insert_index + 1)..(remove_index + 1)
-                //
-                // insert_index < remove_index (this match)
-                // insert_index + 1 < remove_index + 1 (can't saturate because <= length)
-                // insert_index + 1 <= remove_index < length
-                // remove_index + 1 <= length
-                //
-                // If `insert_index == 0`, and `remove_index + 1 ==  length`, then we copy from
-                // 0..(length-1) to 1..(length).
-                unsafe { ptr::copy(insert_at, insert_at.add(1), remove_index - insert_index) };
-            }
+            Ordering::Less => self[remove_index..=insert_index].rotate_left(1),
+            Ordering::Greater => self[insert_index..=remove_index].rotate_right(1),
         }
 
-        // SAFETY: `insert_index < length` assertion guarantees the pointer is within bounds.
-        unsafe { ptr::write(self.as_mut_ptr().add(insert_index), element) };
+        self[insert_index] = element;
         to_remove
     }