wip nth_back on chunks

Signed-off-by: wizAmit <amitforfriends_dns@yahoo.com>

Author: @amit.chandra

src/libcore/slice/mod.rs

@@ -4178,23 +4178,6 @@ impl<'a, T> DoubleEndedIterator for Chunks<'a, T> {
             Some(snd)
         }
     }
-
-    #[inline]
-    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
-        let (end, overflow) = self.v.len().overflowing_sub(n * self.chunk_size);
-        if overflow {
-            self.v = &mut [];
-            None
-        } else {
-            let start = match end.checked_sub(self.chunk_size) {
-                Some(res) => cmp::min(self.v.len(), res),
-                None => 0,
-            };
-            let nth_back = &self.v[start..end];
-            self.v = &self.v[..start];
-            Some(nth_back)
-        }
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/tests/slice.rs

@@ -134,25 +134,6 @@ fn test_chunks_nth() {
     assert_eq!(c2.next(), None);
 }
 
-#[test]
-fn test_chunks_nth_back() {
-    let v: &[i32] = &[0, 1, 2, 3, 4, 5];
-    let mut c = v.chunks(2);
-    assert_eq!(c.nth_back(1).unwrap(), &[2, 3]);
-    assert_eq!(c.next().unwrap(), &[0, 1]);
-    assert_eq!(c.next(), None);
-
-    let v2: &[i32] = &[0, 1, 2, 3, 4];
-    let mut c2 = v2.chunks(3);
-    assert_eq!(c2.nth_back(1).unwrap(), &[0, 1]);
-    assert_eq!(c2.next(), None);
-    assert_eq!(c2.next_back(), None);
-
-    let v3: &[i32] = &[0, 1, 2, 3, 4];
-    let mut c3 = v3.chunks(10);
-    assert_eq!(c3.nth_back(0).unwrap(), &[0, 1, 2, 3, 4]);
-    assert_eq!(c3.next(), None);
-}
 
 #[test]
 fn test_chunks_last() {