diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs index dc5aaa8726032..a85c874d54de1 100644 --- a/library/alloc/src/collections/vec_deque/mod.rs +++ b/library/alloc/src/collections/vec_deque/mod.rs @@ -52,7 +52,7 @@ pub use self::iter::Iter; mod iter; -use self::spec_extend::SpecExtend; +use self::spec_extend::{SpecExtend, SpecExtendFront}; mod spec_extend; @@ -179,6 +179,21 @@ impl VecDeque { self.len += 1; } + /// Prepends an element to the buffer. + /// + /// # Safety + /// + /// May only be called if `deque.len() < deque.capacity()` + #[inline] + unsafe fn push_front_unchecked(&mut self, element: T) { + self.head = self.wrap_sub(self.head, 1); + // SAFETY: Because of the precondition, it's guaranteed that there is space + // in the logical array before the first element (where self.head is now). + unsafe { self.buffer_write(self.head, element) }; + // This can't overflow because `deque.len() < deque.capacity() <= usize::MAX`. + self.len += 1; + } + /// Moves an element out of the buffer #[inline] unsafe fn buffer_read(&mut self, off: usize) -> T { @@ -505,6 +520,35 @@ impl VecDeque { } } + /// Copies all values from `src` to `dst` in reversed order, wrapping around if needed. + /// Assumes capacity is sufficient. + /// Equivalent to calling [`VecDeque::copy_slice`] with a [reversed](https://doc.rust-lang.org/std/primitive.slice.html#method.reverse) slice. + #[inline] + unsafe fn copy_slice_reversed(&mut self, dst: usize, src: &[T]) { + /// # Safety + /// + /// See [`ptr::copy_nonoverlapping`]. + unsafe fn copy_nonoverlapping_reversed(src: *const T, dst: *mut T, count: usize) { + for i in 0..count { + unsafe { ptr::copy_nonoverlapping(src.add(count - 1 - i), dst.add(i), 1) }; + } + } + + debug_assert!(src.len() <= self.capacity()); + let head_room = self.capacity() - dst; + if src.len() <= head_room { + unsafe { + copy_nonoverlapping_reversed(src.as_ptr(), self.ptr().add(dst), src.len()); + } + } else { + let (left, right) = src.split_at(src.len() - head_room); + unsafe { + copy_nonoverlapping_reversed(right.as_ptr(), self.ptr().add(dst), right.len()); + copy_nonoverlapping_reversed(left.as_ptr(), self.ptr(), left.len()); + } + } + } + /// Writes all values from `iter` to `dst`. /// /// # Safety @@ -2122,6 +2166,73 @@ impl VecDeque { unsafe { self.buffer_write(self.to_physical_idx(len), value) } } + /// Prepends all contents of the iterator to the front of the deque. + /// The order of the contents is preserved. + /// + /// To get behavior like [`append`][VecDeque::append] where elements are moved + /// from the other collection to this one, use `self.prepend(other.drain(..))`. + /// + /// # Examples + /// + /// ``` + /// #![feature(deque_extend_front)] + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::from([4, 5, 6]); + /// deque.prepend([1, 2, 3]); + /// assert_eq!(deque, [1, 2, 3, 4, 5, 6]); + /// ``` + /// + /// Move values between collections like [`append`][VecDeque::append] does but prepend to the front: + /// + /// ``` + /// #![feature(deque_extend_front)] + /// use std::collections::VecDeque; + /// + /// let mut deque1 = VecDeque::from([4, 5, 6]); + /// let mut deque2 = VecDeque::from([1, 2, 3]); + /// deque1.prepend(deque2.drain(..)); + /// assert_eq!(deque1, [1, 2, 3, 4, 5, 6]); + /// assert!(deque2.is_empty()); + /// ``` + #[unstable(feature = "deque_extend_front", issue = "146975")] + #[track_caller] + pub fn prepend>(&mut self, other: I) { + self.extend_front(other.into_iter().rev()) + } + + /// Prepends all contents of the iterator to the front of the deque, + /// as if [`push_front`][VecDeque::push_front] was called repeatedly with + /// the values yielded by the iterator. + /// + /// # Examples + /// + /// ``` + /// #![feature(deque_extend_front)] + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::from([4, 5, 6]); + /// deque.extend_front([3, 2, 1]); + /// assert_eq!(deque, [1, 2, 3, 4, 5, 6]); + /// ``` + /// + /// This behaves like [`push_front`][VecDeque::push_front] was called repeatedly: + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::from([4, 5, 6]); + /// for v in [3, 2, 1] { + /// deque.push_front(v); + /// } + /// assert_eq!(deque, [1, 2, 3, 4, 5, 6]); + /// ``` + #[unstable(feature = "deque_extend_front", issue = "146975")] + #[track_caller] + pub fn extend_front>(&mut self, iter: I) { + >::spec_extend_front(self, iter.into_iter()); + } + #[inline] fn is_contiguous(&self) -> bool { // Do the calculation like this to avoid overflowing if len + head > usize::MAX diff --git a/library/alloc/src/collections/vec_deque/spec_extend.rs b/library/alloc/src/collections/vec_deque/spec_extend.rs index 6c2199135e08a..f73ba795cbea4 100644 --- a/library/alloc/src/collections/vec_deque/spec_extend.rs +++ b/library/alloc/src/collections/vec_deque/spec_extend.rs @@ -1,4 +1,4 @@ -use core::iter::TrustedLen; +use core::iter::{Copied, Rev, TrustedLen}; use core::slice; use super::VecDeque; @@ -114,3 +114,113 @@ where } } } + +// Specialization trait used for VecDeque::extend_front +pub(super) trait SpecExtendFront { + #[track_caller] + fn spec_extend_front(&mut self, iter: I); +} + +impl SpecExtendFront for VecDeque +where + I: Iterator, +{ + #[track_caller] + default fn spec_extend_front(&mut self, mut iter: I) { + // This function should be the moral equivalent of: + // + // for item in iter { + // self.push_front(item); + // } + + while let Some(element) = iter.next() { + let (lower, _) = iter.size_hint(); + self.reserve(lower.saturating_add(1)); + + // SAFETY: We just reserved space for at least one element. + unsafe { self.push_front_unchecked(element) }; + + // Inner loop to avoid repeatedly calling `reserve`. + while self.len < self.capacity() { + let Some(element) = iter.next() else { + return; + }; + // SAFETY: The loop condition guarantees that `self.len() < self.capacity()`. + unsafe { self.push_front_unchecked(element) }; + } + } + } +} + +#[cfg(not(test))] +impl SpecExtendFront> for VecDeque { + #[track_caller] + fn spec_extend_front(&mut self, mut iterator: vec::IntoIter) { + let slice = iterator.as_slice(); + // SAFETY: elements in the slice are forgotten after this call + unsafe { prepend_reversed(self, slice) }; + iterator.forget_remaining_elements(); + } +} + +#[cfg(not(test))] +impl SpecExtendFront>> for VecDeque { + #[track_caller] + fn spec_extend_front(&mut self, iterator: Rev>) { + let mut iterator = iterator.into_inner(); + let slice = iterator.as_slice(); + // SAFETY: elements in the slice are forgotten after this call + unsafe { prepend(self, slice) }; + iterator.forget_remaining_elements(); + } +} + +impl<'a, T, A: Allocator> SpecExtendFront>> for VecDeque +where + Copied>: Iterator, +{ + #[track_caller] + fn spec_extend_front(&mut self, iter: Copied>) { + let slice = iter.into_inner().as_slice(); + // SAFETY: T is Copy because Copied> is Iterator + unsafe { prepend_reversed(self, slice) }; + } +} + +impl<'a, T, A: Allocator> SpecExtendFront>>> for VecDeque +where + Rev>>: Iterator, +{ + #[track_caller] + fn spec_extend_front(&mut self, iter: Rev>>) { + let slice = iter.into_inner().into_inner().as_slice(); + // SAFETY: T is Copy because Rev>> is Iterator + unsafe { prepend(self, slice) }; + } +} + +/// # Safety +/// +/// Elements of `slice` will be copied into the deque, make sure to forget the items if `T` is not `Copy`. +unsafe fn prepend(deque: &mut VecDeque, slice: &[T]) { + deque.reserve(slice.len()); + + unsafe { + deque.head = deque.wrap_sub(deque.head, slice.len()); + deque.copy_slice(deque.head, slice); + deque.len += slice.len(); + } +} + +/// # Safety +/// +/// Elements of `slice` will be copied into the deque, make sure to forget the items if `T` is not `Copy`. +unsafe fn prepend_reversed(deque: &mut VecDeque, slice: &[T]) { + deque.reserve(slice.len()); + + unsafe { + deque.head = deque.wrap_sub(deque.head, slice.len()); + deque.copy_slice_reversed(deque.head, slice); + deque.len += slice.len(); + } +} diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs index 786f88c29ef46..73197d021f1a3 100644 --- a/library/alloc/src/lib.rs +++ b/library/alloc/src/lib.rs @@ -106,6 +106,7 @@ #![feature(const_default)] #![feature(const_eval_select)] #![feature(const_heap)] +#![feature(copied_into_inner)] #![feature(core_intrinsics)] #![feature(deprecated_suggestion)] #![feature(deref_pure_trait)] @@ -134,6 +135,7 @@ #![feature(ptr_alignment_type)] #![feature(ptr_internals)] #![feature(ptr_metadata)] +#![feature(rev_into_inner)] #![feature(set_ptr_value)] #![feature(sized_type_properties)] #![feature(slice_from_ptr_range)] diff --git a/library/alloctests/lib.rs b/library/alloctests/lib.rs index 0201c8752210c..efdcb893bfeef 100644 --- a/library/alloctests/lib.rs +++ b/library/alloctests/lib.rs @@ -20,6 +20,7 @@ #![feature(assert_matches)] #![feature(char_internals)] #![feature(char_max_len)] +#![feature(copied_into_inner)] #![feature(core_intrinsics)] #![feature(exact_size_is_empty)] #![feature(extend_one)] @@ -32,6 +33,7 @@ #![feature(maybe_uninit_uninit_array_transpose)] #![feature(ptr_alignment_type)] #![feature(ptr_internals)] +#![feature(rev_into_inner)] #![feature(sized_type_properties)] #![feature(slice_iter_mut_as_mut_slice)] #![feature(slice_ptr_get)] diff --git a/library/alloctests/tests/vec_deque.rs b/library/alloctests/tests/vec_deque.rs index 0a4a0e0cac4d7..cf31613577f74 100644 --- a/library/alloctests/tests/vec_deque.rs +++ b/library/alloctests/tests/vec_deque.rs @@ -2081,3 +2081,77 @@ fn test_extend_and_prepend_from_within() { v.extend_from_within(..); assert_eq!(v.iter().map(|s| &**s).collect::(), "123123123123"); } + +#[test] +fn test_extend_front() { + let mut v = VecDeque::new(); + v.extend_front(0..3); + assert_eq!(v, [2, 1, 0]); + v.extend_front(3..6); + assert_eq!(v, [5, 4, 3, 2, 1, 0]); + v.prepend([1; 4]); + assert_eq!(v, [1, 1, 1, 1, 5, 4, 3, 2, 1, 0]); + + let mut v = VecDeque::with_capacity(8); + let cap = v.capacity(); + v.extend(0..4); + v.truncate_front(2); + v.extend_front(4..8); + assert_eq!(v.as_slices(), ([7, 6].as_slice(), [5, 4, 2, 3].as_slice())); + assert_eq!(v.capacity(), cap); + + let mut v = VecDeque::new(); + v.extend_front([]); + v.extend_front(None); + v.extend_front(vec![]); + v.prepend([]); + v.prepend(None); + v.prepend(vec![]); + assert_eq!(v.capacity(), 0); + v.extend_front(Some(123)); + assert_eq!(v, [123]); +} + +#[test] +fn test_extend_front_specialization_vec_into_iter() { + // trigger 4 code paths: all combinations of prepend and extend_front, wrap and no wrap + let mut v = VecDeque::with_capacity(4); + v.prepend(vec![1, 2, 3]); + assert_eq!(v, [1, 2, 3]); + v.pop_back(); + // this should wrap around the physical buffer + v.prepend(vec![-1, 0]); + // check it really wrapped + assert_eq!(v.as_slices(), ([-1].as_slice(), [0, 1, 2].as_slice())); + + let mut v = VecDeque::with_capacity(4); + v.extend_front(vec![1, 2, 3]); + assert_eq!(v, [3, 2, 1]); + v.pop_back(); + // this should wrap around the physical buffer + v.extend_front(vec![4, 5]); + // check it really wrapped + assert_eq!(v.as_slices(), ([5].as_slice(), [4, 3, 2].as_slice())); +} + +#[test] +fn test_extend_front_specialization_copy_slice() { + // trigger 4 code paths: all combinations of prepend and extend_front, wrap and no wrap + let mut v = VecDeque::with_capacity(4); + v.prepend([1, 2, 3].as_slice().iter().copied()); + assert_eq!(v, [1, 2, 3]); + v.pop_back(); + // this should wrap around the physical buffer + v.prepend([-1, 0].as_slice().iter().copied()); + // check it really wrapped + assert_eq!(v.as_slices(), ([-1].as_slice(), [0, 1, 2].as_slice())); + + let mut v = VecDeque::with_capacity(4); + v.extend_front([1, 2, 3].as_slice().iter().copied()); + assert_eq!(v, [3, 2, 1]); + v.pop_back(); + // this should wrap around the physical buffer + v.extend_front([4, 5].as_slice().iter().copied()); + // check it really wrapped + assert_eq!(v.as_slices(), ([5].as_slice(), [4, 3, 2].as_slice())); +} diff --git a/library/core/src/iter/adapters/copied.rs b/library/core/src/iter/adapters/copied.rs index 23e4e25ab5388..9627ace29795c 100644 --- a/library/core/src/iter/adapters/copied.rs +++ b/library/core/src/iter/adapters/copied.rs @@ -24,6 +24,12 @@ impl Copied { pub(in crate::iter) fn new(it: I) -> Copied { Copied { it } } + + #[doc(hidden)] + #[unstable(feature = "copied_into_inner", issue = "none")] + pub fn into_inner(self) -> I { + self.it + } } fn copy_fold(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, &T) -> Acc {