diff options
| -rw-r--r-- | library/alloc/src/collections/vec_deque/mod.rs | 32 |
1 files changed, 30 insertions, 2 deletions
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs index 09ae1f7eebd..c890ff4ac5e 100644 --- a/library/alloc/src/collections/vec_deque/mod.rs +++ b/library/alloc/src/collections/vec_deque/mod.rs @@ -418,6 +418,25 @@ impl<T, A: Allocator> VecDeque<T, A> { } } + /// 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] @@ -2081,8 +2100,17 @@ impl<T, A: Allocator> VecDeque<T, A> { #[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. |