wip nth_back on chunks

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

diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index d06d107d32a41cabbe8a3fca7e35bf6ed950d277..54c5285bc495cdeb830f6310eacefe9f7feca250 100644 (file)
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -4178,6 +4178,22 @@ fn next_back(&mut self) -> Option<&'a [T]> {
             Some(snd)
         }
     }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) {
+        let (end, overflow) = self.v.len().overflowing_sub(n);
+        if end < self.v.len()  || overflow {
+            self.v = &[];
+            None
+        } else {
+            let start = match end.checked_sub(self.chunk_size) {
+                Some(sum) => cmp::min(self.v.len(), sum),
+                None => self.v.len(),
+            };
+            let nth = &self.v[start..end];
+            self.v = &self.v[end..];
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs
index acf6b03791f01ad27baed0bcc0ddef31e11985cc..0233b96d3a72d6d08c0f2bfbf29f3d58650489f0 100644 (file)
--- a/src/libcore/tests/slice.rs
+++ b/src/libcore/tests/slice.rs
@@ -134,6 +134,19 @@ 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(), &[4, 5]);
+
+    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);
+}
+
 #[test]
 fn test_chunks_last() {
     let v: &[i32] = &[0, 1, 2, 3, 4, 5];