diff options
| -rw-r--r-- | library/alloc/src/collections/vec_deque/mod.rs | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs index e4b28204158..e702ddb3f2a 100644 --- a/library/alloc/src/collections/vec_deque/mod.rs +++ b/library/alloc/src/collections/vec_deque/mod.rs @@ -417,6 +417,26 @@ impl<T, A: Allocator> VecDeque<T, A> { } } + /// Append all values from `src` to `self`, wrapping around if needed. + /// Assumes capacity is sufficient. + #[inline] + unsafe fn append_slice(&mut self, src: &[T]) { + debug_assert!(self.len() + src.len() + 1 <= self.cap()); + let head_room = self.cap() - self.head; + if self.head < self.tail || src.len() <= head_room { + unsafe { + ptr::copy_nonoverlapping(src.as_ptr(), self.ptr().add(self.head), src.len()); + } + } else { + let (left, right) = src.split_at(head_room); + unsafe { + ptr::copy_nonoverlapping(left.as_ptr(), self.ptr().add(self.head), left.len()); + ptr::copy_nonoverlapping(right.as_ptr(), self.ptr(), right.len()); + } + } + self.head = self.wrap_add(self.head, src.len()); + } + /// Frobs the head and tail sections around to handle the fact that we /// just reallocated. Unsafe because it trusts old_capacity. #[inline] @@ -2088,8 +2108,14 @@ 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.append_slice(left); + self.append_slice(right); + } + // Silently drop values in `other`. + other.tail = other.head; } /// Retains only the elements specified by the predicate. |