diff options
Diffstat (limited to 'library/alloc/src/collections/vec_deque/mod.rs')
| -rw-r--r-- | library/alloc/src/collections/vec_deque/mod.rs | 1283 |
1 files changed, 510 insertions, 773 deletions
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs index 2a57dad89..4866c53e7 100644 --- a/library/alloc/src/collections/vec_deque/mod.rs +++ b/library/alloc/src/collections/vec_deque/mod.rs @@ -10,11 +10,10 @@ use core::cmp::{self, Ordering}; use core::fmt; use core::hash::{Hash, Hasher}; -use core::iter::{repeat_with, FromIterator}; -use core::marker::PhantomData; -use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties}; +use core::iter::{repeat_n, repeat_with, ByRefSized, FromIterator}; +use core::mem::{ManuallyDrop, SizedTypeProperties}; use core::ops::{Index, IndexMut, Range, RangeBounds}; -use core::ptr::{self, NonNull}; +use core::ptr; use core::slice; // This is used in a bunch of intra-doc links. @@ -52,14 +51,6 @@ pub use self::iter::Iter; mod iter; -use self::pair_slices::PairSlices; - -mod pair_slices; - -use self::ring_slices::RingSlices; - -mod ring_slices; - use self::spec_extend::SpecExtend; mod spec_extend; @@ -67,11 +58,6 @@ mod spec_extend; #[cfg(test)] mod tests; -const INITIAL_CAPACITY: usize = 7; // 2^3 - 1 -const MINIMUM_CAPACITY: usize = 1; // 2 - 1 - -const MAXIMUM_ZST_CAPACITY: usize = 1 << (usize::BITS - 1); // Largest possible power of two - /// A double-ended queue implemented with a growable ring buffer. /// /// The "default" usage of this type as a queue is to use [`push_back`] to add to @@ -105,13 +91,13 @@ pub struct VecDeque< T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global, > { - // tail and head are pointers into the buffer. Tail always points - // to the first element that could be read, Head always points - // to where data should be written. - // If tail == head the buffer is empty. The length of the ringbuffer - // is defined as the distance between the two. - tail: usize, + // `self[0]`, if it exists, is `buf[head]`. + // `head < buf.capacity()`, unless `buf.capacity() == 0` when `head == 0`. head: usize, + // the number of initialized elements, starting from the one at `head` and potentially wrapping around. + // if `len == 0`, the exact value of `head` is unimportant. + // if `T` is zero-Sized, then `self.len <= usize::MAX`, otherwise `self.len <= isize::MAX as usize`. + len: usize, buf: RawVec<T, A>, } @@ -124,18 +110,8 @@ impl<T: Clone, A: Allocator + Clone> Clone for VecDeque<T, A> { } fn clone_from(&mut self, other: &Self) { - self.truncate(other.len()); - - let mut iter = PairSlices::from(self, other); - while let Some((dst, src)) = iter.next() { - dst.clone_from_slice(&src); - } - - if iter.has_remainder() { - for remainder in iter.remainder() { - self.extend(remainder.iter().cloned()); - } - } + self.clear(); + self.extend(other.iter().cloned()); } } @@ -180,41 +156,6 @@ impl<T, A: Allocator> VecDeque<T, A> { self.buf.ptr() } - /// Marginally more convenient - #[inline] - fn cap(&self) -> usize { - if T::IS_ZST { - // For zero sized types, we are always at maximum capacity - MAXIMUM_ZST_CAPACITY - } else { - self.buf.capacity() - } - } - - /// Turn ptr into a slice, since the elements of the backing buffer may be uninitialized, - /// we will return a slice of [`MaybeUninit<T>`]. - /// - /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and - /// incorrect usage of this method. - /// - /// [zeroed]: mem::MaybeUninit::zeroed - #[inline] - unsafe fn buffer_as_slice(&self) -> &[MaybeUninit<T>] { - unsafe { slice::from_raw_parts(self.ptr() as *mut MaybeUninit<T>, self.cap()) } - } - - /// Turn ptr into a mut slice, since the elements of the backing buffer may be uninitialized, - /// we will return a slice of [`MaybeUninit<T>`]. - /// - /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and - /// incorrect usage of this method. - /// - /// [zeroed]: mem::MaybeUninit::zeroed - #[inline] - unsafe fn buffer_as_mut_slice(&mut self) -> &mut [MaybeUninit<T>] { - unsafe { slice::from_raw_parts_mut(self.ptr() as *mut MaybeUninit<T>, self.cap()) } - } - /// Moves an element out of the buffer #[inline] unsafe fn buffer_read(&mut self, off: usize) -> T { @@ -229,51 +170,58 @@ impl<T, A: Allocator> VecDeque<T, A> { } } - /// Returns `true` if the buffer is at full capacity. + /// Returns a slice pointer into the buffer. + /// `range` must lie inside `0..self.capacity()`. #[inline] - fn is_full(&self) -> bool { - self.cap() - self.len() == 1 + unsafe fn buffer_range(&self, range: Range<usize>) -> *mut [T] { + unsafe { + ptr::slice_from_raw_parts_mut(self.ptr().add(range.start), range.end - range.start) + } } - /// Returns the index in the underlying buffer for a given logical element - /// index. + /// Returns `true` if the buffer is at full capacity. #[inline] - fn wrap_index(&self, idx: usize) -> usize { - wrap_index(idx, self.cap()) + fn is_full(&self) -> bool { + self.len == self.capacity() } /// Returns the index in the underlying buffer for a given logical element /// index + addend. #[inline] fn wrap_add(&self, idx: usize, addend: usize) -> usize { - wrap_index(idx.wrapping_add(addend), self.cap()) + wrap_index(idx.wrapping_add(addend), self.capacity()) + } + + #[inline] + fn to_physical_idx(&self, idx: usize) -> usize { + self.wrap_add(self.head, idx) } /// Returns the index in the underlying buffer for a given logical element /// index - subtrahend. #[inline] fn wrap_sub(&self, idx: usize, subtrahend: usize) -> usize { - wrap_index(idx.wrapping_sub(subtrahend), self.cap()) + wrap_index(idx.wrapping_sub(subtrahend).wrapping_add(self.capacity()), self.capacity()) } /// Copies a contiguous block of memory len long from src to dst #[inline] - unsafe fn copy(&self, dst: usize, src: usize, len: usize) { + unsafe fn copy(&mut self, src: usize, dst: usize, len: usize) { debug_assert!( - dst + len <= self.cap(), + dst + len <= self.capacity(), "cpy dst={} src={} len={} cap={}", dst, src, len, - self.cap() + self.capacity() ); debug_assert!( - src + len <= self.cap(), + src + len <= self.capacity(), "cpy dst={} src={} len={} cap={}", dst, src, len, - self.cap() + self.capacity() ); unsafe { ptr::copy(self.ptr().add(src), self.ptr().add(dst), len); @@ -282,22 +230,22 @@ impl<T, A: Allocator> VecDeque<T, A> { /// Copies a contiguous block of memory len long from src to dst #[inline] - unsafe fn copy_nonoverlapping(&self, dst: usize, src: usize, len: usize) { + unsafe fn copy_nonoverlapping(&mut self, src: usize, dst: usize, len: usize) { debug_assert!( - dst + len <= self.cap(), + dst + len <= self.capacity(), "cno dst={} src={} len={} cap={}", dst, src, len, - self.cap() + self.capacity() ); debug_assert!( - src + len <= self.cap(), + src + len <= self.capacity(), "cno dst={} src={} len={} cap={}", dst, src, len, - self.cap() + self.capacity() ); unsafe { ptr::copy_nonoverlapping(self.ptr().add(src), self.ptr().add(dst), len); @@ -305,30 +253,28 @@ impl<T, A: Allocator> VecDeque<T, A> { } /// Copies a potentially wrapping block of memory len long from src to dest. - /// (abs(dst - src) + len) must be no larger than cap() (There must be at + /// (abs(dst - src) + len) must be no larger than capacity() (There must be at /// most one continuous overlapping region between src and dest). - unsafe fn wrap_copy(&self, dst: usize, src: usize, len: usize) { - #[allow(dead_code)] - fn diff(a: usize, b: usize) -> usize { - if a <= b { b - a } else { a - b } - } + unsafe fn wrap_copy(&mut self, src: usize, dst: usize, len: usize) { debug_assert!( - cmp::min(diff(dst, src), self.cap() - diff(dst, src)) + len <= self.cap(), + cmp::min(src.abs_diff(dst), self.capacity() - src.abs_diff(dst)) + len + <= self.capacity(), "wrc dst={} src={} len={} cap={}", dst, src, len, - self.cap() + self.capacity() ); - if src == dst || len == 0 { + // If T is a ZST, don't do any copying. + if T::IS_ZST || src == dst || len == 0 { return; } let dst_after_src = self.wrap_sub(dst, src) < len; - let src_pre_wrap_len = self.cap() - src; - let dst_pre_wrap_len = self.cap() - dst; + let src_pre_wrap_len = self.capacity() - src; + let dst_pre_wrap_len = self.capacity() - dst; let src_wraps = src_pre_wrap_len < len; let dst_wraps = dst_pre_wrap_len < len; @@ -342,7 +288,7 @@ impl<T, A: Allocator> VecDeque<T, A> { // D . . . // unsafe { - self.copy(dst, src, len); + self.copy(src, dst, len); } } (false, false, true) => { @@ -355,8 +301,8 @@ impl<T, A: Allocator> VecDeque<T, A> { // . . D . // unsafe { - self.copy(dst, src, dst_pre_wrap_len); - self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len); + self.copy(src, dst, dst_pre_wrap_len); + self.copy(src + dst_pre_wrap_len, 0, len - dst_pre_wrap_len); } } (true, false, true) => { @@ -369,8 +315,8 @@ impl<T, A: Allocator> VecDeque<T, A> { // . . D . // unsafe { - self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len); - self.copy(dst, src, dst_pre_wrap_len); + self.copy(src + dst_pre_wrap_len, 0, len - dst_pre_wrap_len); + self.copy(src, dst, dst_pre_wrap_len); } } (false, true, false) => { @@ -383,8 +329,8 @@ impl<T, A: Allocator> VecDeque<T, A> { // D . . . // unsafe { - self.copy(dst, src, src_pre_wrap_len); - self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len); + self.copy(src, dst, src_pre_wrap_len); + self.copy(0, dst + src_pre_wrap_len, len - src_pre_wrap_len); } } (true, true, false) => { @@ -397,8 +343,8 @@ impl<T, A: Allocator> VecDeque<T, A> { // D . . . // unsafe { - self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len); - self.copy(dst, src, src_pre_wrap_len); + self.copy(0, dst + src_pre_wrap_len, len - src_pre_wrap_len); + self.copy(src, dst, src_pre_wrap_len); } } (false, true, true) => { @@ -414,9 +360,9 @@ impl<T, A: Allocator> VecDeque<T, A> { debug_assert!(dst_pre_wrap_len > src_pre_wrap_len); let delta = dst_pre_wrap_len - src_pre_wrap_len; unsafe { - self.copy(dst, src, src_pre_wrap_len); - self.copy(dst + src_pre_wrap_len, 0, delta); - self.copy(0, delta, len - dst_pre_wrap_len); + self.copy(src, dst, src_pre_wrap_len); + self.copy(0, dst + src_pre_wrap_len, delta); + self.copy(delta, 0, len - dst_pre_wrap_len); } } (true, true, true) => { @@ -432,9 +378,9 @@ impl<T, A: Allocator> VecDeque<T, A> { debug_assert!(src_pre_wrap_len > dst_pre_wrap_len); let delta = src_pre_wrap_len - dst_pre_wrap_len; unsafe { - self.copy(delta, 0, len - src_pre_wrap_len); - self.copy(0, self.cap() - delta, delta); - self.copy(dst, src, dst_pre_wrap_len); + self.copy(0, delta, len - src_pre_wrap_len); + self.copy(self.capacity() - delta, 0, delta); + self.copy(src, dst, dst_pre_wrap_len); } } } @@ -444,8 +390,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// 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; + debug_assert!(src.len() <= self.capacity()); + let head_room = self.capacity() - dst; if src.len() <= head_room { unsafe { ptr::copy_nonoverlapping(src.as_ptr(), self.ptr().add(dst), src.len()); @@ -478,48 +424,100 @@ impl<T, A: Allocator> VecDeque<T, A> { }); } + /// Writes all values from `iter` to `dst`, wrapping + /// at the end of the buffer and returns the number + /// of written values. + /// + /// # Safety + /// + /// Assumes that `iter` yields at most `len` items. + /// Assumes capacity is sufficient. + unsafe fn write_iter_wrapping( + &mut self, + dst: usize, + mut iter: impl Iterator<Item = T>, + len: usize, + ) -> usize { + struct Guard<'a, T, A: Allocator> { + deque: &'a mut VecDeque<T, A>, + written: usize, + } + + impl<'a, T, A: Allocator> Drop for Guard<'a, T, A> { + fn drop(&mut self) { + self.deque.len += self.written; + } + } + + let head_room = self.capacity() - dst; + + let mut guard = Guard { deque: self, written: 0 }; + + if head_room >= len { + unsafe { guard.deque.write_iter(dst, iter, &mut guard.written) }; + } else { + unsafe { + guard.deque.write_iter( + dst, + ByRefSized(&mut iter).take(head_room), + &mut guard.written, + ); + guard.deque.write_iter(0, iter, &mut guard.written) + }; + } + + guard.written + } + /// Frobs the head and tail sections around to handle the fact that we /// just reallocated. Unsafe because it trusts old_capacity. #[inline] unsafe fn handle_capacity_increase(&mut self, old_capacity: usize) { - let new_capacity = self.cap(); + let new_capacity = self.capacity(); + debug_assert!(new_capacity >= old_capacity); // Move the shortest contiguous section of the ring buffer - // T H + // + // H := head + // L := last element (`self.to_physical_idx(self.len - 1)`) + // + // H L // [o o o o o o o . ] - // T H + // H L // A [o o o o o o o . . . . . . . . . ] - // H T - // [o o . o o o o o ] - // T H + // L H + // [o o o o o o o o ] + // H L // B [. . . o o o o o o o . . . . . . ] - // H T - // [o o o o o . o o ] - // H T + // L H + // [o o o o o o o o ] + // L H // C [o o o o o . . . . . . . . . o o ] - if self.tail <= self.head { + // can't use is_contiguous() because the capacity is already updated. + if self.head <= old_capacity - self.len { // A // Nop - } else if self.head < old_capacity - self.tail { - // B - unsafe { - self.copy_nonoverlapping(old_capacity, 0, self.head); - } - self.head += old_capacity; - debug_assert!(self.head > self.tail); } else { - // C - let new_tail = new_capacity - (old_capacity - self.tail); - unsafe { - self.copy_nonoverlapping(new_tail, self.tail, old_capacity - self.tail); + let head_len = old_capacity - self.head; + let tail_len = self.len - head_len; + if head_len > tail_len && new_capacity - old_capacity >= tail_len { + // B + unsafe { + self.copy_nonoverlapping(0, old_capacity, tail_len); + } + } else { + // C + let new_head = new_capacity - head_len; + unsafe { + // can't use copy_nonoverlapping here, because if e.g. head_len = 2 + // and new_capacity = old_capacity + 1, then the heads overlap. + self.copy(self.head, new_head, head_len); + } + self.head = new_head; } - self.tail = new_tail; - debug_assert!(self.head < self.tail); } - debug_assert!(self.head < self.cap()); - debug_assert!(self.tail < self.cap()); - debug_assert!(self.cap().count_ones() == 1); + debug_assert!(self.head < self.capacity() || self.capacity() == 0); } } @@ -533,6 +531,7 @@ impl<T> VecDeque<T> { /// /// let deque: VecDeque<u32> = VecDeque::new(); /// ``` + // FIXME: This should probably be const #[inline] #[stable(feature = "rust1", since = "1.0.0")] #[must_use] @@ -569,8 +568,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[inline] #[unstable(feature = "allocator_api", issue = "32838")] - pub fn new_in(alloc: A) -> VecDeque<T, A> { - VecDeque::with_capacity_in(INITIAL_CAPACITY, alloc) + pub const fn new_in(alloc: A) -> VecDeque<T, A> { + VecDeque { head: 0, len: 0, buf: RawVec::new_in(alloc) } } /// Creates an empty deque with space for at least `capacity` elements. @@ -584,11 +583,7 @@ impl<T, A: Allocator> 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(); - - VecDeque { tail: 0, head: 0, buf: RawVec::with_capacity_in(cap, alloc) } + VecDeque { head: 0, len: 0, buf: RawVec::with_capacity_in(capacity, alloc) } } /// Provides a reference to the element at the given index. @@ -608,8 +603,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get(&self, index: usize) -> Option<&T> { - if index < self.len() { - let idx = self.wrap_add(self.tail, index); + if index < self.len { + let idx = self.to_physical_idx(index); unsafe { Some(&*self.ptr().add(idx)) } } else { None @@ -637,8 +632,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_mut(&mut self, index: usize) -> Option<&mut T> { - if index < self.len() { - let idx = self.wrap_add(self.tail, index); + if index < self.len { + let idx = self.to_physical_idx(index); unsafe { Some(&mut *self.ptr().add(idx)) } } else { None @@ -672,8 +667,8 @@ impl<T, A: Allocator> VecDeque<T, A> { pub fn swap(&mut self, i: usize, j: usize) { assert!(i < self.len()); assert!(j < self.len()); - let ri = self.wrap_add(self.tail, i); - let rj = self.wrap_add(self.tail, j); + let ri = self.to_physical_idx(i); + let rj = self.to_physical_idx(j); unsafe { ptr::swap(self.ptr().add(ri), self.ptr().add(rj)) } } @@ -691,7 +686,7 @@ impl<T, A: Allocator> VecDeque<T, A> { #[inline] #[stable(feature = "rust1", since = "1.0.0")] pub fn capacity(&self) -> usize { - self.cap() - 1 + if T::IS_ZST { usize::MAX } else { self.buf.capacity() } } /// Reserves the minimum capacity for at least `additional` more elements to be inserted in the @@ -718,7 +713,15 @@ impl<T, A: Allocator> VecDeque<T, A> { /// [`reserve`]: VecDeque::reserve #[stable(feature = "rust1", since = "1.0.0")] pub fn reserve_exact(&mut self, additional: usize) { - self.reserve(additional); + let new_cap = self.len.checked_add(additional).expect("capacity overflow"); + let old_cap = self.capacity(); + + if new_cap > old_cap { + self.buf.reserve_exact(self.len, additional); + unsafe { + self.handle_capacity_increase(old_cap); + } + } } /// Reserves capacity for at least `additional` more elements to be inserted in the given @@ -739,15 +742,13 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn reserve(&mut self, additional: usize) { - let old_cap = self.cap(); - let used_cap = self.len() + 1; - let new_cap = used_cap - .checked_add(additional) - .and_then(|needed_cap| needed_cap.checked_next_power_of_two()) - .expect("capacity overflow"); + let new_cap = self.len.checked_add(additional).expect("capacity overflow"); + let old_cap = self.capacity(); if new_cap > old_cap { - self.buf.reserve_exact(used_cap, new_cap - used_cap); + // we don't need to reserve_exact(), as the size doesn't have + // to be a power of 2. + self.buf.reserve(self.len, additional); unsafe { self.handle_capacity_increase(old_cap); } @@ -793,7 +794,17 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "try_reserve", since = "1.57.0")] pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> { - self.try_reserve(additional) + let new_cap = + self.len.checked_add(additional).ok_or(TryReserveErrorKind::CapacityOverflow)?; + let old_cap = self.capacity(); + + if new_cap > old_cap { + self.buf.try_reserve_exact(self.len, additional)?; + unsafe { + self.handle_capacity_increase(old_cap); + } + } + Ok(()) } /// Tries to reserve capacity for at least `additional` more elements to be inserted @@ -831,15 +842,12 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "try_reserve", since = "1.57.0")] pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> { - let old_cap = self.cap(); - let used_cap = self.len() + 1; - let new_cap = used_cap - .checked_add(additional) - .and_then(|needed_cap| needed_cap.checked_next_power_of_two()) - .ok_or(TryReserveErrorKind::CapacityOverflow)?; + let new_cap = + self.len.checked_add(additional).ok_or(TryReserveErrorKind::CapacityOverflow)?; + let old_cap = self.capacity(); if new_cap > old_cap { - self.buf.try_reserve_exact(used_cap, new_cap - used_cap)?; + self.buf.try_reserve(self.len, additional)?; unsafe { self.handle_capacity_increase(old_cap); } @@ -890,13 +898,14 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "shrink_to", since = "1.56.0")] pub fn shrink_to(&mut self, min_capacity: usize) { - let min_capacity = cmp::min(min_capacity, self.capacity()); - // We don't have to worry about an overflow as neither `self.len()` nor `self.capacity()` - // can ever be `usize::MAX`. +1 as the ringbuffer always leaves one space empty. - let target_cap = cmp::max(cmp::max(min_capacity, self.len()) + 1, MINIMUM_CAPACITY + 1) - .next_power_of_two(); + let target_cap = min_capacity.max(self.len); - if target_cap < self.cap() { + // never shrink ZSTs + if T::IS_ZST || self.capacity() <= target_cap { + return; + } + + if target_cap < self.capacity() { // There are three cases of interest: // All elements are out of desired bounds // Elements are contiguous, and head is out of desired bounds @@ -905,49 +914,55 @@ impl<T, A: Allocator> VecDeque<T, A> { // At all other times, element positions are unaffected. // // Indicates that elements at the head should be moved. - let head_outside = self.head == 0 || self.head >= target_cap; + + let tail_outside = (target_cap + 1..=self.capacity()).contains(&(self.head + self.len)); // Move elements from out of desired bounds (positions after target_cap) - if self.tail >= target_cap && head_outside { - // T H + if self.len == 0 { + self.head = 0; + } else if self.head >= target_cap && tail_outside { + // H := head + // L := last element + // H L // [. . . . . . . . o o o o o o o . ] - // T H + // H L // [o o o o o o o . ] unsafe { - self.copy_nonoverlapping(0, self.tail, self.len()); + // nonoverlapping because self.head >= target_cap >= self.len + self.copy_nonoverlapping(self.head, 0, self.len); } - self.head = self.len(); - self.tail = 0; - } else if self.tail != 0 && self.tail < target_cap && head_outside { - // T H + self.head = 0; + } else if self.head < target_cap && tail_outside { + // H := head + // L := last element + // H L // [. . . o o o o o o o . . . . . . ] - // H T + // L H // [o o . o o o o o ] - let len = self.wrap_sub(self.head, target_cap); + let len = self.head + self.len - target_cap; unsafe { - self.copy_nonoverlapping(0, target_cap, len); + self.copy_nonoverlapping(target_cap, 0, len); } - self.head = len; - debug_assert!(self.head < self.tail); - } else if self.tail >= target_cap { - // H T + } else if self.head >= target_cap { + // H := head + // L := last element + // L H // [o o o o o . . . . . . . . . o o ] - // H T + // L H // [o o o o o . o o ] - debug_assert!(self.wrap_sub(self.head, 1) < target_cap); - let len = self.cap() - self.tail; - let new_tail = target_cap - len; + let len = self.capacity() - self.head; + let new_head = target_cap - len; unsafe { - self.copy_nonoverlapping(new_tail, self.tail, len); + // can't use copy_nonoverlapping here for the same reason + // as in `handle_capacity_increase()` + self.copy(self.head, new_head, len); } - self.tail = new_tail; - debug_assert!(self.head < self.tail); + self.head = new_head; } self.buf.shrink_to_fit(target_cap); - debug_assert!(self.head < self.cap()); - debug_assert!(self.tail < self.cap()); - debug_assert!(self.cap().count_ones() == 1); + debug_assert!(self.head < self.capacity() || self.capacity() == 0); + debug_assert!(self.len <= self.capacity()); } } @@ -992,20 +1007,20 @@ impl<T, A: Allocator> VecDeque<T, A> { // * The head of the VecDeque is moved before calling `drop_in_place`, // so no value is dropped twice if `drop_in_place` panics unsafe { - if len > self.len() { + if len >= self.len { return; } - let num_dropped = self.len() - len; + let (front, back) = self.as_mut_slices(); if len > front.len() { let begin = len - front.len(); let drop_back = back.get_unchecked_mut(begin..) as *mut _; - self.head = self.wrap_sub(self.head, num_dropped); + self.len = len; ptr::drop_in_place(drop_back); } else { let drop_back = back as *mut _; let drop_front = front.get_unchecked_mut(len..) as *mut _; - self.head = self.wrap_sub(self.head, num_dropped); + self.len = len; // Make sure the second half is dropped even when a destructor // in the first one panics. @@ -1039,7 +1054,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn iter(&self) -> Iter<'_, T> { - Iter::new(unsafe { self.buffer_as_slice() }, self.tail, self.head) + let (a, b) = self.as_slices(); + Iter::new(a.iter(), b.iter()) } /// Returns a front-to-back iterator that returns mutable references. @@ -1061,11 +1077,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn iter_mut(&mut self) -> IterMut<'_, T> { - // SAFETY: The internal `IterMut` safety invariant is established because the - // `ring` we create is a dereferenceable slice for lifetime '_. - let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()); - - unsafe { IterMut::new(ring, self.tail, self.head, PhantomData) } + let (a, b) = self.as_mut_slices(); + IterMut::new(a.iter_mut(), b.iter_mut()) } /// Returns a pair of slices which contain, in order, the contents of the @@ -1097,14 +1110,10 @@ impl<T, A: Allocator> VecDeque<T, A> { #[inline] #[stable(feature = "deque_extras_15", since = "1.5.0")] pub fn as_slices(&self) -> (&[T], &[T]) { - // Safety: - // - `self.head` and `self.tail` in a ring buffer are always valid indices. - // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. - unsafe { - let buf = self.buffer_as_slice(); - let (front, back) = RingSlices::ring_slices(buf, self.head, self.tail); - (MaybeUninit::slice_assume_init_ref(front), MaybeUninit::slice_assume_init_ref(back)) - } + let (a_range, b_range) = self.slice_ranges(..); + // SAFETY: `slice_ranges` always returns valid ranges into + // the physical buffer. + unsafe { (&*self.buffer_range(a_range), &*self.buffer_range(b_range)) } } /// Returns a pair of slices which contain, in order, the contents of the @@ -1135,16 +1144,10 @@ impl<T, A: Allocator> VecDeque<T, A> { #[inline] #[stable(feature = "deque_extras_15", since = "1.5.0")] pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) { - // Safety: - // - `self.head` and `self.tail` in a ring buffer are always valid indices. - // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. - unsafe { - let head = self.head; - let tail = self.tail; - let buf = self.buffer_as_mut_slice(); - let (front, back) = RingSlices::ring_slices(buf, head, tail); - (MaybeUninit::slice_assume_init_mut(front), MaybeUninit::slice_assume_init_mut(back)) - } + let (a_range, b_range) = self.slice_ranges(..); + // SAFETY: `slice_ranges` always returns valid ranges into + // the physical buffer. + unsafe { (&mut *self.buffer_range(a_range), &mut *self.buffer_range(b_range)) } } /// Returns the number of elements in the deque. @@ -1161,7 +1164,7 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn len(&self) -> usize { - count(self.tail, self.head, self.cap()) + self.len } /// Returns `true` if the deque is empty. @@ -1178,17 +1181,41 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn is_empty(&self) -> bool { - self.tail == self.head + self.len == 0 } - fn range_tail_head<R>(&self, range: R) -> (usize, usize) + /// Given a range into the logical buffer of the deque, this function + /// return two ranges into the physical buffer that correspond to + /// the given range. + fn slice_ranges<R>(&self, range: R) -> (Range<usize>, Range<usize>) where R: RangeBounds<usize>, { - let Range { start, end } = slice::range(range, ..self.len()); - let tail = self.wrap_add(self.tail, start); - let head = self.wrap_add(self.tail, end); - (tail, head) + let Range { start, end } = slice::range(range, ..self.len); + let len = end - start; + + if len == 0 { + (0..0, 0..0) + } else { + // `slice::range` guarantees that `start <= end <= self.len`. + // because `len != 0`, we know that `start < end`, so `start < self.len` + // and the indexing is valid. + let wrapped_start = self.to_physical_idx(start); + + // this subtraction can never overflow because `wrapped_start` is + // at most `self.capacity()` (and if `self.capacity != 0`, then `wrapped_start` is strictly less + // than `self.capacity`). + let head_len = self.capacity() - wrapped_start; + + if head_len >= len { + // we know that `len + wrapped_start <= self.capacity <= usize::MAX`, so this addition can't overflow + (wrapped_start..wrapped_start + len, 0..0) + } else { + // can't overflow because of the if condition + let tail_len = len - head_len; + (wrapped_start..self.capacity(), 0..tail_len) + } + } } /// Creates an iterator that covers the specified range in the deque. @@ -1217,9 +1244,14 @@ impl<T, A: Allocator> VecDeque<T, A> { where R: RangeBounds<usize>, { - let (tail, head) = self.range_tail_head(range); - // The shared reference we have in &self is maintained in the '_ of Iter. - Iter::new(unsafe { self.buffer_as_slice() }, tail, head) + let (a_range, b_range) = self.slice_ranges(range); + // SAFETY: The ranges returned by `slice_ranges` + // are valid ranges into the physical buffer, so + // it's ok to pass them to `buffer_range` and + // dereference the result. + let a = unsafe { &*self.buffer_range(a_range) }; + let b = unsafe { &*self.buffer_range(b_range) }; + Iter::new(a.iter(), b.iter()) } /// Creates an iterator that covers the specified mutable range in the deque. @@ -1252,13 +1284,14 @@ impl<T, A: Allocator> VecDeque<T, A> { where R: RangeBounds<usize>, { - let (tail, head) = self.range_tail_head(range); - - // SAFETY: The internal `IterMut` safety invariant is established because the - // `ring` we create is a dereferenceable slice for lifetime '_. - let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()); - - unsafe { IterMut::new(ring, tail, head, PhantomData) } + let (a_range, b_range) = self.slice_ranges(range); + // SAFETY: The ranges returned by `slice_ranges` + // are valid ranges into the physical buffer, so + // it's ok to pass them to `buffer_range` and + // dereference the result. + let a = unsafe { &mut *self.buffer_range(a_range) }; + let b = unsafe { &mut *self.buffer_range(b_range) }; + IterMut::new(a.iter_mut(), b.iter_mut()) } /// Removes the specified range from the deque in bulk, returning all @@ -1310,39 +1343,30 @@ impl<T, A: Allocator> VecDeque<T, A> { // When finished, the remaining data will be copied back to cover the hole, // and the head/tail values will be restored correctly. // - let (drain_tail, drain_head) = self.range_tail_head(range); + let Range { start, end } = slice::range(range, ..self.len); + let drain_start = start; + let drain_len = end - start; // The deque's elements are parted into three segments: - // * self.tail -> drain_tail - // * drain_tail -> drain_head - // * drain_head -> self.head + // * 0 -> drain_start + // * drain_start -> drain_start+drain_len + // * drain_start+drain_len -> self.len // - // T = self.tail; H = self.head; t = drain_tail; h = drain_head + // H = self.head; T = self.head+self.len; t = drain_start+drain_len; h = drain_head // - // We store drain_tail as self.head, and drain_head and self.head as - // after_tail and after_head respectively on the Drain. This also + // We store drain_start as self.len, and drain_len and self.len as + // drain_len and orig_len respectively on the Drain. This also // truncates the effective array such that if the Drain is leaked, we // have forgotten about the potentially moved values after the start of // the drain. // - // T t h H + // H h t T // [. . . o o x x o o . . .] // - let head = self.head; - // "forget" about the values after the start of the drain until after // the drain is complete and the Drain destructor is run. - self.head = drain_tail; - let deque = NonNull::from(&mut *self); - unsafe { - // Crucially, we only create shared references from `self` here and read from - // it. We do not write to `self` nor reborrow to a mutable reference. - // Hence the raw pointer we created above, for `deque`, remains valid. - let ring = self.buffer_as_slice(); - - Drain::new(drain_head, head, ring, drain_tail, drain_head, deque) - } + unsafe { Drain::new(self, drain_start, drain_len) } } /// Clears the deque, removing all values. @@ -1361,6 +1385,8 @@ impl<T, A: Allocator> VecDeque<T, A> { #[inline] pub fn clear(&mut self) { self.truncate(0); + // Not strictly necessary, but leaves things in a more consistent/predictable state. + self.head = 0; } /// Returns `true` if the deque contains an element equal to the @@ -1455,7 +1481,7 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn back(&self) -> Option<&T> { - self.get(self.len().wrapping_sub(1)) + self.get(self.len.wrapping_sub(1)) } /// Provides a mutable reference to the back element, or `None` if the @@ -1479,7 +1505,7 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn back_mut(&mut self) -> Option<&mut T> { - self.get_mut(self.len().wrapping_sub(1)) + self.get_mut(self.len.wrapping_sub(1)) } /// Removes the first element and returns it, or `None` if the deque is @@ -1503,9 +1529,10 @@ impl<T, A: Allocator> VecDeque<T, A> { if self.is_empty() { None } else { - let tail = self.tail; - self.tail = self.wrap_add(self.tail, 1); - unsafe { Some(self.buffer_read(tail)) } + let old_head = self.head; + self.head = self.to_physical_idx(1); + self.len -= 1; + Some(unsafe { self.buffer_read(old_head) }) } } @@ -1528,9 +1555,8 @@ impl<T, A: Allocator> VecDeque<T, A> { if self.is_empty() { None } else { - self.head = self.wrap_sub(self.head, 1); - let head = self.head; - unsafe { Some(self.buffer_read(head)) } + self.len -= 1; + Some(unsafe { self.buffer_read(self.to_physical_idx(self.len)) }) } } @@ -1552,10 +1578,11 @@ impl<T, A: Allocator> VecDeque<T, A> { self.grow(); } - self.tail = self.wrap_sub(self.tail, 1); - let tail = self.tail; + self.head = self.wrap_sub(self.head, 1); + self.len += 1; + unsafe { - self.buffer_write(tail, value); + self.buffer_write(self.head, value); } } @@ -1577,16 +1604,14 @@ impl<T, A: Allocator> VecDeque<T, A> { self.grow(); } - let head = self.head; - self.head = self.wrap_add(self.head, 1); - unsafe { self.buffer_write(head, value) } + unsafe { self.buffer_write(self.to_physical_idx(self.len), value) } + self.len += 1; } #[inline] fn is_contiguous(&self) -> bool { - // FIXME: Should we consider `head == 0` to mean - // that `self` is contiguous? - self.tail <= self.head + // Do the calculation like this to avoid overflowing if len + head > usize::MAX + self.head <= self.capacity() - self.len } /// Removes an element from anywhere in the deque and returns it, @@ -1615,8 +1640,8 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "deque_extras_15", since = "1.5.0")] pub fn swap_remove_front(&mut self, index: usize) -> Option<T> { - let length = self.len(); - if length > 0 && index < length && index != 0 { + let length = self.len; + if index < length && index != 0 { self.swap(index, 0); } else if index >= length { return None; @@ -1650,7 +1675,7 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "deque_extras_15", since = "1.5.0")] pub fn swap_remove_back(&mut self, index: usize) -> Option<T> { - let length = self.len(); + let length = self.len; if length > 0 && index < length - 1 { self.swap(index, length - 1); } else if index >= length { @@ -1689,198 +1714,26 @@ impl<T, A: Allocator> VecDeque<T, A> { self.grow(); } - // Move the least number of elements in the ring buffer and insert - // the given object - // - // At most len/2 - 1 elements will be moved. O(min(n, n-i)) - // - // There are three main cases: - // Elements are contiguous - // - special case when tail is 0 - // Elements are discontiguous and the insert is in the tail section - // Elements are discontiguous and the insert is in the head section - // - // For each of those there are two more cases: - // Insert is closer to tail - // Insert is closer to head - // - // Key: H - self.head - // T - self.tail - // o - Valid element - // I - Insertion element - // A - The element that should be after the insertion point - // M - Indicates element was moved - - let idx = self.wrap_add(self.tail, index); - - let distance_to_tail = index; - let distance_to_head = self.len() - index; - - let contiguous = self.is_contiguous(); - - match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) { - (true, true, _) if index == 0 => { - // push_front - // - // T - // I H - // [A o o o o o o . . . . . . . . .] - // - // H T - // [A o o o o o o o . . . . . I] - // - - self.tail = self.wrap_sub(self.tail, 1); - } - (true, true, _) => { - unsafe { - // contiguous, insert closer to tail: - // - // T I H - // [. . . o o A o o o o . . . . . .] - // - // T H - // [. . o o I A o o o o . . . . . .] - // M M - // - // contiguous, insert closer to tail and tail is 0: - // - // - // T I H - // [o o A o o o o . . . . . . . . .] - // - // H T - // [o I A o o o o o . . . . . . . o] - // M M - - let new_tail = self.wrap_sub(self.tail, 1); - - self.copy(new_tail, self.tail, 1); - // Already moved the tail, so we only copy `index - 1` elements. - self.copy(self.tail, self.tail + 1, index - 1); - - self.tail = new_tail; - } - } - (true, false, _) => { - unsafe { - // contiguous, insert closer to head: - // - // T I H - // [. . . o o o o A o o . . . . . .] - // - // T H - // [. . . o o o o I A o o . . . . .] - // M M M - - self.copy(idx + 1, idx, self.head - idx); - self.head = self.wrap_add(self.head, 1); - } - } - (false, true, true) => { - unsafe { - // discontiguous, insert closer to tail, tail section: - // - // H T I - // [o o o o o o . . . . . o o A o o] - // - // H T - // [o o o o o o . . . . o o I A o o] - // M M - - self.copy(self.tail - 1, self.tail, index); - self.tail -= 1; - } - } - (false, false, true) => { - unsafe { - // discontiguous, insert closer to head, tail section: - // - // H T I - // [o o . . . . . . . o o o o o A o] - // - // H T - // [o o o . . . . . . o o o o o I A] - // M M M M - - // copy elements up to new head - self.copy(1, 0, self.head); - - // copy last element into empty spot at bottom of buffer - self.copy(0, self.cap() - 1, 1); - - // move elements from idx to end forward not including ^ element - self.copy(idx + 1, idx, self.cap() - 1 - idx); - - self.head += 1; - } - } - (false, true, false) if idx == 0 => { - unsafe { - // discontiguous, insert is closer to tail, head section, - // and is at index zero in the internal buffer: - // - // I H T - // [A o o o o o o o o o . . . o o o] - // - // H T - // [A o o o o o o o o o . . o o o I] - // M M M - - // copy elements up to new tail - self.copy(self.tail - 1, self.tail, self.cap() - self.tail); - - // copy last element into empty spot at bottom of buffer - self.copy(self.cap() - 1, 0, 1); - - self.tail -= 1; - } - } - (false, true, false) => { - unsafe { - // discontiguous, insert closer to tail, head section: - // - // I H T - // [o o o A o o o o o o . . . o o o] - // - // H T - // [o o I A o o o o o o . . o o o o] - // M M M M M M - - // copy elements up to new tail - self.copy(self.tail - 1, self.tail, self.cap() - self.tail); - - // copy last element into empty spot at bottom of buffer - self.copy(self.cap() - 1, 0, 1); - - // move elements from idx-1 to end forward not including ^ element - self.copy(0, 1, idx - 1); - - self.tail -= 1; - } + let k = self.len - index; + if k < index { + // `index + 1` can't overflow, because if index was usize::MAX, then either the + // assert would've failed, or the deque would've tried to grow past usize::MAX + // and panicked. + unsafe { + // see `remove()` for explanation why this wrap_copy() call is safe. + self.wrap_copy(self.to_physical_idx(index), self.to_physical_idx(index + 1), k); + self.buffer_write(self.to_physical_idx(index), value); + self.len += 1; } - (false, false, false) => { - unsafe { - // discontiguous, insert closer to head, head section: - // - // I H T - // [o o o o A o o . . . . . . o o o] - // - // H T - // [o o o o I A o o . . . . . o o o] - // M M M - - self.copy(idx + 1, idx, self.head - idx); - self.head += 1; - } + } else { + let old_head = self.head; + self.head = self.wrap_sub(self.head, 1); + unsafe { + self.wrap_copy(old_head, self.head, index); + self.buffer_write(self.to_physical_idx(index), value); + self.len += 1; } } - - // tail might've been changed so we need to recalculate - let new_idx = self.wrap_add(self.tail, index); - unsafe { - self.buffer_write(new_idx, value); - } } /// Removes and returns the element at `index` from the deque. @@ -1906,156 +1759,26 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn remove(&mut self, index: usize) -> Option<T> { - if self.is_empty() || self.len() <= index { + if self.len <= index { return None; } - // There are three main cases: - // Elements are contiguous - // Elements are discontiguous and the removal is in the tail section - // Elements are discontiguous and the removal is in the head section - // - special case when elements are technically contiguous, - // but self.head = 0 - // - // For each of those there are two more cases: - // Insert is closer to tail - // Insert is closer to head - // - // Key: H - self.head - // T - self.tail - // o - Valid element - // x - Element marked for removal - // R - Indicates element that is being removed - // M - Indicates element was moved - - let idx = self.wrap_add(self.tail, index); - - let elem = unsafe { Some(self.buffer_read(idx)) }; + let wrapped_idx = self.to_physical_idx(index); - let distance_to_tail = index; - let distance_to_head = self.len() - index; + let elem = unsafe { Some(self.buffer_read(wrapped_idx)) }; - let contiguous = self.is_contiguous(); - - match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) { - (true, true, _) => { - unsafe { - // contiguous, remove closer to tail: - // - // T R H - // [. . . o o x o o o o . . . . . .] - // - // T H - // [. . . . o o o o o o . . . . . .] - // M M - - self.copy(self.tail + 1, self.tail, index); - self.tail += 1; - } - } - (true, false, _) => { - unsafe { - // contiguous, remove closer to head: - // - // T R H - // [. . . o o o o x o o . . . . . .] - // - // T H - // [. . . o o o o o o . . . . . . .] - // M M - - self.copy(idx, idx + 1, self.head - idx - 1); - self.head -= 1; - } - } - (false, true, true) => { - unsafe { - // discontiguous, remove closer to tail, tail section: - // - // H T R - // [o o o o o o . . . . . o o x o o] - // - // H T - // [o o o o o o . . . . . . o o o o] - // M M - - self.copy(self.tail + 1, self.tail, index); - self.tail = self.wrap_add(self.tail, 1); - } - } - (false, false, false) => { - unsafe { - // discontiguous, remove closer to head, head section: - // - // R H T - // [o o o o x o o . . . . . . o o o] - // - // H T - // [o o o o o o . . . . . . . o o o] - // M M - - self.copy(idx, idx + 1, self.head - idx - 1); - self.head -= 1; - } - } - (false, false, true) => { - unsafe { - // discontiguous, remove closer to head, tail section: - // - // H T R - // [o o o . . . . . . o o o o o x o] - // - // H T - // [o o . . . . . . . o o o o o o o] - // M M M M - // - // or quasi-discontiguous, remove next to head, tail section: - // - // H T R - // [. . . . . . . . . o o o o o x o] - // - // T H - // [. . . . . . . . . o o o o o o .] - // M - - // draw in elements in the tail section - self.copy(idx, idx + 1, self.cap() - idx - 1); - - // Prevents underflow. - if self.head != 0 { - // copy first element into empty spot - self.copy(self.cap() - 1, 0, 1); - - // move elements in the head section backwards - self.copy(0, 1, self.head - 1); - } - - self.head = self.wrap_sub(self.head, 1); - } - } - (false, true, false) => { - unsafe { - // discontiguous, remove closer to tail, head section: - // - // R H T - // [o o x o o o o o o o . . . o o o] - // - // H T - // [o o o o o o o o o o . . . . o o] - // M M M M M - - // draw in elements up to idx - self.copy(1, 0, idx); - - // copy last element into empty spot - self.copy(0, self.cap() - 1, 1); - - // move elements from tail to end forward, excluding the last one - self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1); - - self.tail = self.wrap_add(self.tail, 1); - } - } + let k = self.len - index - 1; + // safety: due to the nature of the if-condition, whichever wrap_copy gets called, + // its length argument will be at most `self.len / 2`, so there can't be more than + // one overlapping area. + if k < index { + unsafe { self.wrap_copy(self.wrap_add(wrapped_idx, 1), wrapped_idx, k) }; + self.len -= 1; + } else { + let old_head = self.head; + self.head = self.to_physical_idx(1); + unsafe { self.wrap_copy(old_head, self.head, index) }; + self.len -= 1; } elem @@ -2091,7 +1814,7 @@ impl<T, A: Allocator> VecDeque<T, A> { where A: Clone, { - let len = self.len(); + let len = self.len; assert!(at <= len, "`at` out of bounds"); let other_len = len - at; @@ -2128,8 +1851,8 @@ impl<T, A: Allocator> VecDeque<T, A> { } // Cleanup where the ends of the buffers are - self.head = self.wrap_sub(self.head, other_len); - other.head = other.wrap_index(other_len); + self.len = at; + other.len = other_len; other } @@ -2154,17 +1877,26 @@ impl<T, A: Allocator> VecDeque<T, A> { #[inline] #[stable(feature = "append", since = "1.4.0")] pub fn append(&mut self, other: &mut Self) { - self.reserve(other.len()); + if T::IS_ZST { + self.len += other.len; + other.len = 0; + other.head = 0; + return; + } + + 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); + self.copy_slice(self.to_physical_idx(self.len), left); + // no overflow, because self.capacity() >= old_cap + left.len() >= self.len + left.len() + self.copy_slice(self.to_physical_idx(self.len + 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; + self.len += other.len; + // Now that we own its values, forget everything in `other`. + other.len = 0; + other.head = 0; } /// Retains only the elements specified by the predicate. @@ -2232,7 +1964,7 @@ impl<T, A: Allocator> VecDeque<T, A> { where F: FnMut(&mut T) -> bool, { - let len = self.len(); + let len = self.len; let mut idx = 0; let mut cur = 0; @@ -2270,9 +2002,8 @@ impl<T, A: Allocator> VecDeque<T, A> { // Extend or possibly remove this assertion when valid use-cases for growing the // buffer without it being full emerge debug_assert!(self.is_full()); - let old_cap = self.cap(); - self.buf.reserve_exact(old_cap, old_cap); - assert!(self.cap() == old_cap * 2); + let old_cap = self.capacity(); + self.buf.reserve_for_push(old_cap); unsafe { self.handle_capacity_increase(old_cap); } @@ -2306,7 +2037,7 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "vec_resize_with", since = "1.33.0")] pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T) { - let len = self.len(); + let len = self.len; if new_len > len { self.extend(repeat_with(generator).take(new_len - len)) @@ -2372,110 +2103,129 @@ impl<T, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "deque_make_contiguous", since = "1.48.0")] pub fn make_contiguous(&mut self) -> &mut [T] { + if T::IS_ZST { + self.head = 0; + } + if self.is_contiguous() { - let tail = self.tail; - let head = self.head; - // Safety: - // - `self.head` and `self.tail` in a ring buffer are always valid indices. - // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. - return unsafe { - MaybeUninit::slice_assume_init_mut( - RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0, - ) - }; + unsafe { return slice::from_raw_parts_mut(self.ptr().add(self.head), self.len) } } - let buf = self.buf.ptr(); - let cap = self.cap(); - let len = self.len(); + let &mut Self { head, len, .. } = self; + let ptr = self.ptr(); + let cap = self.capacity(); - let free = self.tail - self.head; - let tail_len = cap - self.tail; + let free = cap - len; + let head_len = cap - head; + let tail = len - head_len; + let tail_len = tail; - if free >= tail_len { - // there is enough free space to copy the tail in one go, - // this means that we first shift the head backwards, and then - // copy the tail to the correct position. + if free >= head_len { + // there is enough free space to copy the head in one go, + // this means that we first shift the tail backwards, and then + // copy the head to the correct position. // // from: DEFGH....ABC // to: ABCDEFGH.... unsafe { - ptr::copy(buf, buf.add(tail_len), self.head); + self.copy(0, head_len, tail_len); // ...DEFGH.ABC - ptr::copy_nonoverlapping(buf.add(self.tail), buf, tail_len); + self.copy_nonoverlapping(head, 0, head_len); // ABCDEFGH.... - - self.tail = 0; - self.head = len; } - } else if free > self.head { - // FIXME: We currently do not consider ....ABCDEFGH - // to be contiguous because `head` would be `0` in this - // case. While we probably want to change this it - // isn't trivial as a few places expect `is_contiguous` - // to mean that we can just slice using `buf[tail..head]`. - // there is enough free space to copy the head in one go, - // this means that we first shift the tail forwards, and then - // copy the head to the correct position. + self.head = 0; + } else if free >= tail_len { + // there is enough free space to copy the tail in one go, + // this means that we first shift the head forwards, and then + // copy the tail to the correct position. // // from: FGH....ABCDE // to: ...ABCDEFGH. unsafe { - ptr::copy(buf.add(self.tail), buf.add(self.head), tail_len); + self.copy(head, tail, head_len); // FGHABCDE.... - ptr::copy_nonoverlapping(buf, buf.add(self.head + tail_len), self.head); + self.copy_nonoverlapping(0, tail + head_len, tail_len); // ...ABCDEFGH. - - self.tail = self.head; - self.head = self.wrap_add(self.tail, len); } + + self.head = tail; } else { - // free is smaller than both head and tail, - // this means we have to slowly "swap" the tail and the head. + // `free` is smaller than both `head_len` and `tail_len`. + // the general algorithm for this first moves the slices + // right next to each other and then uses `slice::rotate` + // to rotate them into place: // - // from: EFGHI...ABCD or HIJK.ABCDEFG - // to: ABCDEFGHI... or ABCDEFGHIJK. - let mut left_edge: usize = 0; - let mut right_edge: usize = self.tail; - unsafe { - // The general problem looks like this - // GHIJKLM...ABCDEF - before any swaps - // ABCDEFM...GHIJKL - after 1 pass of swaps - // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store - // - then restart the algorithm with a new (smaller) store - // Sometimes the temp store is reached when the right edge is at the end - // of the buffer - this means we've hit the right order with fewer swaps! - // E.g - // EF..ABCD - // ABCDEF.. - after four only swaps we've finished - while left_edge < len && right_edge != cap { - let mut right_offset = 0; - for i in left_edge..right_edge { - right_offset = (i - left_edge) % (cap - right_edge); - let src = right_edge + right_offset; - ptr::swap(buf.add(i), buf.add(src)); + // initially: HIJK..ABCDEFG + // step 1: ..HIJKABCDEFG + // step 2: ..ABCDEFGHIJK + // + // or: + // + // initially: FGHIJK..ABCDE + // step 1: FGHIJKABCDE.. + // step 2: ABCDEFGHIJK.. + + // pick the shorter of the 2 slices to reduce the amount + // of memory that needs to be moved around. + if head_len > tail_len { + // tail is shorter, so: + // 1. copy tail forwards + // 2. rotate used part of the buffer + // 3. update head to point to the new beginning (which is just `free`) + + unsafe { + // if there is no free space in the buffer, then the slices are already + // right next to each other and we don't need to move any memory. + if free != 0 { + // because we only move the tail forward as much as there's free space + // behind it, we don't overwrite any elements of the head slice, and + // the slices end up right next to each other. + self.copy(0, free, tail_len); } - let n_ops = right_edge - left_edge; - left_edge += n_ops; - right_edge += right_offset + 1; + + // We just copied the tail right next to the head slice, + // so all of the elements in the range are initialized + let slice = &mut *self.buffer_range(free..self.capacity()); + + // because the deque wasn't contiguous, we know that `tail_len < self.len == slice.len()`, + // so this will never panic. + slice.rotate_left(tail_len); + + // the used part of the buffer now is `free..self.capacity()`, so set + // `head` to the beginning of that range. + self.head = free; } + } else { + // head is shorter so: + // 1. copy head backwards + // 2. rotate used part of the buffer + // 3. update head to point to the new beginning (which is the beginning of the buffer) + + unsafe { + // if there is no free space in the buffer, then the slices are already + // right next to each other and we don't need to move any memory. + if free != 0 { + // copy the head slice to lie right behind the tail slice. + self.copy(self.head, tail_len, head_len); + } - self.tail = 0; - self.head = len; + // because we copied the head slice so that both slices lie right + // next to each other, all the elements in the range are initialized. + let slice = &mut *self.buffer_range(0..self.len); + + // because the deque wasn't contiguous, we know that `head_len < self.len == slice.len()` + // so this will never panic. + slice.rotate_right(head_len); + + // the used part of the buffer now is `0..self.len`, so set + // `head` to the beginning of that range. + self.head = 0; + } } } - let tail = self.tail; - let head = self.head; - // Safety: - // - `self.head` and `self.tail` in a ring buffer are always valid indices. - // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. - unsafe { - MaybeUninit::slice_assume_init_mut( - RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0, - ) - } + unsafe { slice::from_raw_parts_mut(ptr.add(self.head), self.len) } } /// Rotates the double-ended queue `mid` places to the left. @@ -2513,7 +2263,7 @@ impl<T, A: Allocator> VecDeque<T, A> { #[stable(feature = "vecdeque_rotate", since = "1.36.0")] pub fn rotate_left(&mut self, mid: usize) { assert!(mid <= self.len()); - let k = self.len() - mid; + let k = self.len - mid; if mid <= k { unsafe { self.rotate_left_inner(mid) } } else { @@ -2556,7 +2306,7 @@ impl<T, A: Allocator> VecDeque<T, A> { #[stable(feature = "vecdeque_rotate", since = "1.36.0")] pub fn rotate_right(&mut self, k: usize) { assert!(k <= self.len()); - let mid = self.len() - k; + let mid = self.len - k; if k <= mid { unsafe { self.rotate_right_inner(k) } } else { @@ -2567,26 +2317,24 @@ impl<T, A: Allocator> VecDeque<T, A> { // SAFETY: the following two methods require that the rotation amount // be less than half the length of the deque. // - // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`, - // but than `min` is never more than half the capacity, regardless of x, + // `wrap_copy` requires that `min(x, capacity() - x) + copy_len <= capacity()`, + // but then `min` is never more than half the capacity, regardless of x, // so it's sound to call here because we're calling with something // less than half the length, which is never above half the capacity. unsafe fn rotate_left_inner(&mut self, mid: usize) { debug_assert!(mid * 2 <= self.len()); unsafe { - self.wrap_copy(self.head, self.tail, mid); + self.wrap_copy(self.head, self.to_physical_idx(self.len), mid); } - self.head = self.wrap_add(self.head, mid); - self.tail = self.wrap_add(self.tail, mid); + self.head = self.to_physical_idx(mid); } unsafe fn rotate_right_inner(&mut self, k: usize) { debug_assert!(k * 2 <= self.len()); self.head = self.wrap_sub(self.head, k); - self.tail = self.wrap_sub(self.tail, k); unsafe { - self.wrap_copy(self.tail, self.head, k); + self.wrap_copy(self.to_physical_idx(self.len), self.head, k); } } @@ -2833,29 +2581,30 @@ impl<T: Clone, A: Allocator> VecDeque<T, A> { /// ``` #[stable(feature = "deque_extras", since = "1.16.0")] pub fn resize(&mut self, new_len: usize, value: T) { - self.resize_with(new_len, || value.clone()); + if new_len > self.len() { + let extra = new_len - self.len(); + self.extend(repeat_n(value, extra)) + } else { + self.truncate(new_len); + } } } /// Returns the index in the underlying buffer for a given logical element index. #[inline] -fn wrap_index(index: usize, size: usize) -> usize { - // size is always a power of 2 - debug_assert!(size.is_power_of_two()); - index & (size - 1) -} - -/// Calculate the number of elements left to be read in the buffer -#[inline] -fn count(tail: usize, head: usize, size: usize) -> usize { - // size is always a power of 2 - (head.wrapping_sub(tail)) & (size - 1) +fn wrap_index(logical_index: usize, capacity: usize) -> usize { + debug_assert!( + (logical_index == 0 && capacity == 0) + || logical_index < capacity + || (logical_index - capacity) < capacity + ); + if logical_index >= capacity { logical_index - capacity } else { logical_index } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: PartialEq, A: Allocator> PartialEq for VecDeque<T, A> { fn eq(&self, other: &Self) -> bool { - if self.len() != other.len() { + if self.len != other.len() { return false; } let (sa, sb) = self.as_slices(); @@ -2919,7 +2668,7 @@ impl<T: Ord, A: Allocator> Ord for VecDeque<T, A> { #[stable(feature = "rust1", since = "1.0.0")] impl<T: Hash, A: Allocator> Hash for VecDeque<T, A> { fn hash<H: Hasher>(&self, state: &mut H) { - state.write_length_prefix(self.len()); + state.write_length_prefix(self.len); // It's not possible to use Hash::hash_slice on slices // returned by as_slices method as their length can vary // in otherwise identical deques. @@ -2950,12 +2699,18 @@ impl<T, A: Allocator> IndexMut<usize> for VecDeque<T, A> { #[stable(feature = "rust1", since = "1.0.0")] impl<T> FromIterator<T> for VecDeque<T> { + #[inline] fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> VecDeque<T> { - let iterator = iter.into_iter(); - let (lower, _) = iterator.size_hint(); - let mut deq = VecDeque::with_capacity(lower); - deq.extend(iterator); - deq + // Since converting is O(1) now, might as well re-use that logic + // (including things like the `vec::IntoIter`→`Vec` specialization) + // especially as that could save us some monomorphiziation work + // if one uses the same iterators (like slice ones) with both. + return from_iter_via_vec(iter.into_iter()); + + #[inline] + fn from_iter_via_vec<U>(iter: impl Iterator<Item = U>) -> VecDeque<U> { + Vec::from_iter(iter).into() + } } } @@ -3028,7 +2783,7 @@ impl<'a, T: 'a + Copy, A: Allocator> Extend<&'a T> for VecDeque<T, A> { #[stable(feature = "rust1", since = "1.0.0")] impl<T: fmt::Debug, A: Allocator> fmt::Debug for VecDeque<T, A> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_list().entries(self).finish() + f.debug_list().entries(self.iter()).finish() } } @@ -3039,31 +2794,13 @@ impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> { /// [`Vec<T>`]: crate::vec::Vec /// [`VecDeque<T>`]: crate::collections::VecDeque /// - /// This avoids reallocating where possible, but the conditions for that are - /// strict, and subject to change, and so shouldn't be relied upon unless the - /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated. - fn from(mut other: Vec<T, A>) -> Self { - let len = other.len(); - if T::IS_ZST { - // There's no actual allocation for ZSTs to worry about capacity, - // but `VecDeque` can't handle as much length as `Vec`. - assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow"); - } else { - // We need to resize if the capacity is not a power of two, too small or - // doesn't have at least one free space. We do this while it's still in - // the `Vec` so the items will drop on panic. - let min_cap = cmp::max(MINIMUM_CAPACITY, len) + 1; - let cap = cmp::max(min_cap, other.capacity()).next_power_of_two(); - if other.capacity() != cap { - other.reserve_exact(cap - len); - } - } - - unsafe { - let (other_buf, len, capacity, alloc) = other.into_raw_parts_with_alloc(); - let buf = RawVec::from_raw_parts_in(other_buf, capacity, alloc); - VecDeque { tail: 0, head: len, buf } - } + /// In its current implementation, this is a very cheap + /// conversion. This isn't yet a guarantee though, and + /// shouldn't be relied on. + #[inline] + fn from(other: Vec<T, A>) -> Self { + let (ptr, len, cap, alloc) = other.into_raw_parts_with_alloc(); + Self { head: 0, len, buf: unsafe { RawVec::from_raw_parts_in(ptr, cap, alloc) } } } } @@ -3105,11 +2842,11 @@ impl<T, A: Allocator> From<VecDeque<T, A>> for Vec<T, A> { let other = ManuallyDrop::new(other); let buf = other.buf.ptr(); let len = other.len(); - let cap = other.cap(); + let cap = other.capacity(); let alloc = ptr::read(other.allocator()); - if other.tail != 0 { - ptr::copy(buf.add(other.tail), buf, len); + if other.head != 0 { + ptr::copy(buf.add(other.head), buf, len); } Vec::from_raw_parts_in(buf, len, cap, alloc) } @@ -3136,8 +2873,8 @@ impl<T, const N: usize> From<[T; N]> for VecDeque<T> { ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N); } } - deq.tail = 0; - deq.head = N; + deq.head = 0; + deq.len = N; deq } } |