diff options
Diffstat (limited to 'library')
| -rw-r--r-- | library/core/src/slice/iter.rs | 36 |
1 files changed, 2 insertions, 34 deletions
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs index 18bf61aeb16..27fcb8b5332 100644 --- a/library/core/src/slice/iter.rs +++ b/library/core/src/slice/iter.rs @@ -1653,25 +1653,7 @@ impl<'a, T> DoubleEndedIterator for ChunksMut<'a, T> { let sz = if remainder != 0 { remainder } else { self.chunk_size }; let tmp = mem::replace(&mut self.v, &mut []); let tmp_len = tmp.len(); - // SAFETY: split_at_unchecked requires the argument be less than or - // equal to the length. This is guaranteed, but subtle: We need the - // expression `tmp_len - sz` not to overflow, which means we need - // `sz >= tmp_len`. - // - // `sz` will always either be `tmp_or_v.len() % self.chunk_size` - // (where `tmp_or_v` is the slice that at the time was `self.v` but - // now is `tmp`, and thus `tmp_len` and `tmp_or_v.len()` are the - // same), which will always evaluate to strictly less than - // `tmp_or_v.len()` (or panic, in the case that `self.chunk_size` is - // zero), or it can be `self.chunk_size`, in the case that the - // length is exactly divisible by the chunk size. - // - // While it seems like using `self.chunk_size` in this case could - // lead to a value greater than `tmp_len`, it cannot: if - // `self.chunk_size` were greater than `tmp_len`, then - // `tmp_or_v.len() % self.chunk_size` would have returned non-zero - // (note that in this branch of the `if`, we already know that - // `self.v` is non-empty). + // SAFETY: Similar to `Chunks::next_back` let (head, tail) = unsafe { tmp.split_at_mut_unchecked(tmp_len - sz) }; self.v = head; Some(tail) @@ -2691,21 +2673,7 @@ impl<'a, T> DoubleEndedIterator for RChunksMut<'a, T> { let remainder = self.v.len() % self.chunk_size; let sz = if remainder != 0 { remainder } else { self.chunk_size }; let tmp = mem::replace(&mut self.v, &mut []); - // SAFETY: split_at_mut_unchecked requires the argument be less than - // or equal to the length. This is guaranteed, but subtle: `chunksz` - // will always either be `tmp_or_v.len() % self.chunk_size` (where - // `tmp_or_v` is the slice that at the time was `self.v` but now is - // `tmp`), which will always evaluate to strictly less than - // `tmp_or_v.len()` (or panic, in the case that `self.chunk_size` is - // zero), or it can be `self.chunk_size`, in the case that the - // length is exactly divisible by the chunk size. - // - // While it seems like using `self.chunk_size` in this case could - // lead to a value greater than `tmp_or_v.len()`, it cannot: if - // `self.chunk_size` were greater than `tmp_or_v.len()`, then - // `tmp_or_v.len() % self.chunk_size` would return nonzero (note - // that in this branch of the `if`, we already know that `tmp_or_v` - // is non-empty). + // SAFETY: Similar to `Chunks::next_back` let (head, tail) = unsafe { tmp.split_at_mut_unchecked(sz) }; self.v = tail; Some(head) |