Auto merge of #90130 - Mark-Simulacrum:revert-namebinding, r=oli-obk

[rust.git] / library / alloc / src / collections / vec_deque / mod.rs

diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index 09ae1f7eebd09b8b6165fffb5247ba574c3a2ddf..de607c8fdab31dd098a5ee88c1f76dd81f41ac85 100644 (file)
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -418,6 +418,25 @@ fn diff(a: usize, b: usize) -> usize {
         }
     }
 
+    /// Copies all values from `src` to `dst`, wrapping around if needed.
+    /// Assumes capacity is sufficient.
+    #[inline]
+    unsafe fn copy_slice(&mut self, dst: usize, src: &[T]) {
+        debug_assert!(src.len() <= self.cap());
+        let head_room = self.cap() - dst;
+        if src.len() <= head_room {
+            unsafe {
+                ptr::copy_nonoverlapping(src.as_ptr(), self.ptr().add(dst), src.len());
+            }
+        } else {
+            let (left, right) = src.split_at(head_room);
+            unsafe {
+                ptr::copy_nonoverlapping(left.as_ptr(), self.ptr().add(dst), left.len());
+                ptr::copy_nonoverlapping(right.as_ptr(), self.ptr(), right.len());
+            }
+        }
+    }
+
     /// Frobs the head and tail sections around to handle the fact that we
     /// just reallocated. Unsafe because it trusts old_capacity.
     #[inline]
@@ -524,9 +543,9 @@ pub fn new_in(alloc: A) -> VecDeque<T, A> {
     /// ```
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub fn with_capacity_in(capacity: usize, alloc: A) -> VecDeque<T, A> {
+        assert!(capacity < 1_usize << usize::BITS - 1, "capacity overflow");
         // +1 since the ringbuffer always leaves one space empty
         let cap = cmp::max(capacity + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
-        assert!(cap > capacity, "capacity overflow");
 
         VecDeque { tail: 0, head: 0, buf: RawVec::with_capacity_in(cap, alloc) }
     }
@@ -2081,8 +2100,17 @@ pub fn split_off(&mut self, at: usize) -> Self
     #[inline]
     #[stable(feature = "append", since = "1.4.0")]
     pub fn append(&mut self, other: &mut Self) {
-        // naive impl
-        self.extend(other.drain(..));
+        self.reserve(other.len());
+        unsafe {
+            let (left, right) = other.as_slices();
+            self.copy_slice(self.head, left);
+            self.copy_slice(self.wrap_add(self.head, left.len()), right);
+        }
+        // SAFETY: Update pointers after copying to avoid leaving doppelganger
+        // in case of panics.
+        self.head = self.wrap_add(self.head, other.len());
+        // Silently drop values in `other`.
+        other.tail = other.head;
     }
 
     /// Retains only the elements specified by the predicate.