| // This Source Code Form is subject to the terms of the Mozilla Public |
| // License, v. 2.0. If a copy of the MPL was not distributed with this |
| // file, You can obtain one at http://mozilla.org/MPL/2.0/. |
| |
| //! A fixed capacity array sized to match some other type `T`. |
| //! |
| //! See [`InlineArray`](struct.InlineArray.html) |
| |
| use std::borrow::{Borrow, BorrowMut}; |
| use std::cmp::Ordering; |
| use std::fmt::{Debug, Error, Formatter}; |
| use std::hash::{Hash, Hasher}; |
| use std::iter::{FromIterator, FusedIterator}; |
| use std::marker::PhantomData; |
| use std::mem::{self, ManuallyDrop}; |
| use std::ops::{Deref, DerefMut}; |
| use std::ptr; |
| use std::slice::{from_raw_parts, from_raw_parts_mut, Iter as SliceIter, IterMut as SliceIterMut}; |
| |
| /// A fixed capacity array sized to match some other type `T`. |
| /// |
| /// This works like a vector, but allocated on the stack (and thus marginally |
| /// faster than `Vec`), with the allocated space exactly matching the size of |
| /// the given type `T`. The vector consists of a `usize` tracking its current |
| /// length, followed by zero or more elements of type `A`. The capacity is thus |
| /// `( size_of::<T>() - size_of::<usize>() ) / size_of::<A>()`. This could lead |
| /// to situations where the capacity is zero, if `size_of::<A>()` is greater |
| /// than `size_of::<T>() - size_of::<usize>()`, which is not an error and |
| /// handled properly by the data structure. |
| /// |
| /// If `size_of::<T>()` is less than `size_of::<usize>()`, meaning the vector |
| /// has no space to store its length, `InlineArray::new()` will panic. |
| /// |
| /// This is meant to facilitate optimisations where a list data structure |
| /// allocates a fairly large struct for itself, allowing you to replace it with |
| /// an `InlineArray` until it grows beyond its capacity. This not only gives you |
| /// a performance boost at very small sizes, it also saves you from having to |
| /// allocate anything on the heap until absolutely necessary. |
| /// |
| /// For instance, `im::Vector<A>` in its final form currently looks like this |
| /// (approximately): |
| /// |
| /// ```rust, ignore |
| /// struct RRB<A> { |
| /// length: usize, |
| /// tree_height: usize, |
| /// outer_head: Rc<Chunk<A>>, |
| /// inner_head: Rc<Chunk<A>>, |
| /// tree: Rc<TreeNode<A>>, |
| /// inner_tail: Rc<Chunk<A>>, |
| /// outer_tail: Rc<Chunk<A>>, |
| /// } |
| /// ``` |
| /// |
| /// That's two `usize`s and five `Rc`s, which comes in at 56 bytes on x86_64 |
| /// architectures. With `InlineArray`, that leaves us with 56 - |
| /// `size_of::<usize>()` = 48 bytes we can use before having to expand into the |
| /// full data struture. If `A` is `u8`, that's 48 elements, and even if `A` is a |
| /// pointer we can still keep 6 of them inline before we run out of capacity. |
| /// |
| /// We can declare an enum like this: |
| /// |
| /// ```rust, ignore |
| /// enum VectorWrapper<A> { |
| /// Inline(InlineArray<A, RRB<A>>), |
| /// Full(RRB<A>), |
| /// } |
| /// ``` |
| /// |
| /// Both of these will have the same size, and we can swap the `Inline` case out |
| /// with the `Full` case once the `InlineArray` runs out of capacity. |
| pub struct InlineArray<A, T> { |
| data: ManuallyDrop<T>, |
| phantom: PhantomData<A>, |
| } |
| |
| impl<A, T> InlineArray<A, T> { |
| const HOST_SIZE: usize = mem::size_of::<T>(); |
| const ELEMENT_SIZE: usize = mem::size_of::<A>(); |
| const HEADER_SIZE: usize = mem::size_of::<usize>(); |
| |
| pub const CAPACITY: usize = (Self::HOST_SIZE - Self::HEADER_SIZE) / Self::ELEMENT_SIZE; |
| |
| #[inline] |
| #[must_use] |
| unsafe fn len_const(&self) -> *const usize { |
| (&self.data) as *const _ as *const usize |
| } |
| |
| #[inline] |
| #[must_use] |
| pub(crate) unsafe fn len_mut(&mut self) -> *mut usize { |
| (&mut self.data) as *mut _ as *mut usize |
| } |
| |
| #[inline] |
| #[must_use] |
| pub(crate) unsafe fn data(&self) -> *const A { |
| self.len_const().add(1) as *const _ as *const A |
| } |
| |
| #[inline] |
| #[must_use] |
| unsafe fn data_mut(&mut self) -> *mut A { |
| self.len_mut().add(1) as *mut _ as *mut A |
| } |
| |
| #[inline] |
| #[must_use] |
| unsafe fn ptr_at(&self, index: usize) -> *const A { |
| self.data().add(index) |
| } |
| |
| #[inline] |
| #[must_use] |
| unsafe fn ptr_at_mut(&mut self, index: usize) -> *mut A { |
| self.data_mut().add(index) |
| } |
| |
| #[inline] |
| unsafe fn read_at(&self, index: usize) -> A { |
| ptr::read(self.ptr_at(index)) |
| } |
| |
| #[inline] |
| unsafe fn write_at(&mut self, index: usize, value: A) { |
| ptr::write(self.ptr_at_mut(index), value); |
| } |
| |
| /// Get the length of the array. |
| #[inline] |
| #[must_use] |
| pub fn len(&self) -> usize { |
| unsafe { *self.len_const() } |
| } |
| |
| /// Test if the array is empty. |
| #[inline] |
| #[must_use] |
| pub fn is_empty(&self) -> bool { |
| self.len() == 0 |
| } |
| |
| /// Test if the array is at capacity. |
| #[inline] |
| #[must_use] |
| pub fn is_full(&self) -> bool { |
| self.len() >= Self::CAPACITY |
| } |
| |
| /// Construct a new empty array. |
| #[inline] |
| #[must_use] |
| pub fn new() -> Self { |
| debug_assert!(Self::HOST_SIZE > Self::HEADER_SIZE); |
| unsafe { mem::zeroed() } |
| } |
| |
| #[inline] |
| #[must_use] |
| fn get_unchecked(&self, index: usize) -> &A { |
| unsafe { &*self.data().add(index) } |
| } |
| |
| /// Push an item to the back of the array. |
| /// |
| /// Panics if the capacity of the array is exceeded. |
| /// |
| /// Time: O(1) |
| pub fn push(&mut self, value: A) { |
| if self.is_full() { |
| panic!("InlineArray::push: chunk size overflow"); |
| } |
| unsafe { |
| self.write_at(self.len(), value); |
| *self.len_mut() += 1; |
| } |
| } |
| |
| /// Pop an item from the back of the array. |
| /// |
| /// Returns `None` if the array is empty. |
| /// |
| /// Time: O(1) |
| pub fn pop(&mut self) -> Option<A> { |
| if self.is_empty() { |
| None |
| } else { |
| unsafe { |
| *self.len_mut() -= 1; |
| } |
| Some(unsafe { self.read_at(self.len()) }) |
| } |
| } |
| |
| /// Insert a new value at index `index`, shifting all the following values |
| /// to the right. |
| /// |
| /// Panics if the index is out of bounds or the array is at capacity. |
| /// |
| /// Time: O(n) for the number of items shifted |
| pub fn insert(&mut self, index: usize, value: A) { |
| if self.is_full() { |
| panic!("InlineArray::push: chunk size overflow"); |
| } |
| if index > self.len() { |
| panic!("InlineArray::insert: index out of bounds"); |
| } |
| unsafe { |
| let src = self.ptr_at_mut(index); |
| ptr::copy(src, src.add(1), self.len() - index); |
| ptr::write(src, value); |
| *self.len_mut() += 1; |
| } |
| } |
| |
| /// Remove the value at index `index`, shifting all the following values to |
| /// the left. |
| /// |
| /// Returns the removed value, or `None` if the array is empty or the index |
| /// is out of bounds. |
| /// |
| /// Time: O(n) for the number of items shifted |
| pub fn remove(&mut self, index: usize) -> Option<A> { |
| if index >= self.len() { |
| None |
| } else { |
| unsafe { |
| let src = self.ptr_at_mut(index); |
| let value = ptr::read(src); |
| *self.len_mut() -= 1; |
| ptr::copy(src.add(1), src, self.len() - index); |
| Some(value) |
| } |
| } |
| } |
| |
| /// Split an array into two, the original array containing |
| /// everything up to `index` and the returned array containing |
| /// everything from `index` onwards. |
| /// |
| /// Panics if `index` is out of bounds. |
| /// |
| /// Time: O(n) for the number of items in the new chunk |
| pub fn split_off(&mut self, index: usize) -> Self { |
| if index > self.len() { |
| panic!("InlineArray::split_off: index out of bounds"); |
| } |
| let mut out = Self::new(); |
| if index < self.len() { |
| unsafe { |
| ptr::copy(self.ptr_at(index), out.data_mut(), self.len() - index); |
| *out.len_mut() = self.len() - index; |
| *self.len_mut() = index; |
| } |
| } |
| out |
| } |
| |
| #[inline] |
| fn drop_contents(&mut self) { |
| unsafe { |
| let data = self.data_mut(); |
| for i in 0..self.len() { |
| ptr::drop_in_place(data.add(i)); |
| } |
| } |
| } |
| |
| /// Discard the contents of the array. |
| /// |
| /// Time: O(n) |
| pub fn clear(&mut self) { |
| self.drop_contents(); |
| unsafe { |
| *self.len_mut() = 0; |
| } |
| } |
| |
| /// Construct an iterator that drains values from the front of the array. |
| pub fn drain(&mut self) -> Drain<A, T> { |
| Drain { array: self } |
| } |
| } |
| |
| impl<A, T> Drop for InlineArray<A, T> { |
| fn drop(&mut self) { |
| self.drop_contents() |
| } |
| } |
| |
| impl<A, T> Default for InlineArray<A, T> { |
| fn default() -> Self { |
| Self::new() |
| } |
| } |
| |
| // WANT: |
| // impl<A, T> Copy for InlineArray<A, T> where A: Copy {} |
| |
| impl<A, T> Clone for InlineArray<A, T> |
| where |
| A: Clone, |
| { |
| fn clone(&self) -> Self { |
| let mut copy = Self::new(); |
| for i in 0..self.len() { |
| unsafe { |
| copy.write_at(i, self.get_unchecked(i).clone()); |
| } |
| } |
| unsafe { |
| *copy.len_mut() = self.len(); |
| } |
| copy |
| } |
| } |
| |
| impl<A, T> Deref for InlineArray<A, T> { |
| type Target = [A]; |
| fn deref(&self) -> &Self::Target { |
| unsafe { from_raw_parts(self.data(), self.len()) } |
| } |
| } |
| |
| impl<A, T> DerefMut for InlineArray<A, T> { |
| fn deref_mut(&mut self) -> &mut Self::Target { |
| unsafe { from_raw_parts_mut(self.data_mut(), self.len()) } |
| } |
| } |
| |
| impl<A, T> Borrow<[A]> for InlineArray<A, T> { |
| fn borrow(&self) -> &[A] { |
| self.deref() |
| } |
| } |
| |
| impl<A, T> BorrowMut<[A]> for InlineArray<A, T> { |
| fn borrow_mut(&mut self) -> &mut [A] { |
| self.deref_mut() |
| } |
| } |
| |
| impl<A, T> AsRef<[A]> for InlineArray<A, T> { |
| fn as_ref(&self) -> &[A] { |
| self.deref() |
| } |
| } |
| |
| impl<A, T> AsMut<[A]> for InlineArray<A, T> { |
| fn as_mut(&mut self) -> &mut [A] { |
| self.deref_mut() |
| } |
| } |
| impl<A, T, Slice> PartialEq<Slice> for InlineArray<A, T> |
| where |
| Slice: Borrow<[A]>, |
| A: PartialEq, |
| { |
| fn eq(&self, other: &Slice) -> bool { |
| self.deref() == other.borrow() |
| } |
| } |
| |
| impl<A, T> Eq for InlineArray<A, T> where A: Eq {} |
| |
| impl<A, T> PartialOrd for InlineArray<A, T> |
| where |
| A: PartialOrd, |
| { |
| fn partial_cmp(&self, other: &Self) -> Option<Ordering> { |
| self.iter().partial_cmp(other.iter()) |
| } |
| } |
| |
| impl<A, T> Ord for InlineArray<A, T> |
| where |
| A: Ord, |
| { |
| fn cmp(&self, other: &Self) -> Ordering { |
| self.iter().cmp(other.iter()) |
| } |
| } |
| |
| impl<A, T> Debug for InlineArray<A, T> |
| where |
| A: Debug, |
| { |
| fn fmt(&self, f: &mut Formatter) -> Result<(), Error> { |
| f.write_str("Chunk")?; |
| f.debug_list().entries(self.iter()).finish() |
| } |
| } |
| |
| impl<A, T> Hash for InlineArray<A, T> |
| where |
| A: Hash, |
| { |
| fn hash<H>(&self, hasher: &mut H) |
| where |
| H: Hasher, |
| { |
| for item in self { |
| item.hash(hasher) |
| } |
| } |
| } |
| |
| impl<A, T> IntoIterator for InlineArray<A, T> { |
| type Item = A; |
| type IntoIter = Iter<A, T>; |
| fn into_iter(self) -> Self::IntoIter { |
| Iter { array: self } |
| } |
| } |
| |
| impl<A, T> FromIterator<A> for InlineArray<A, T> { |
| fn from_iter<I>(it: I) -> Self |
| where |
| I: IntoIterator<Item = A>, |
| { |
| let mut chunk = Self::new(); |
| for item in it { |
| chunk.push(item); |
| } |
| chunk |
| } |
| } |
| |
| impl<'a, A, T> IntoIterator for &'a InlineArray<A, T> { |
| type Item = &'a A; |
| type IntoIter = SliceIter<'a, A>; |
| fn into_iter(self) -> Self::IntoIter { |
| self.iter() |
| } |
| } |
| |
| impl<'a, A, T> IntoIterator for &'a mut InlineArray<A, T> { |
| type Item = &'a mut A; |
| type IntoIter = SliceIterMut<'a, A>; |
| fn into_iter(self) -> Self::IntoIter { |
| self.iter_mut() |
| } |
| } |
| |
| impl<A, T> Extend<A> for InlineArray<A, T> { |
| /// Append the contents of the iterator to the back of the array. |
| /// |
| /// Panics if the array exceeds its capacity. |
| /// |
| /// Time: O(n) for the length of the iterator |
| fn extend<I>(&mut self, it: I) |
| where |
| I: IntoIterator<Item = A>, |
| { |
| for item in it { |
| self.push(item); |
| } |
| } |
| } |
| |
| impl<'a, A, T> Extend<&'a A> for InlineArray<A, T> |
| where |
| A: 'a + Copy, |
| { |
| /// Append the contents of the iterator to the back of the array. |
| /// |
| /// Panics if the array exceeds its capacity. |
| /// |
| /// Time: O(n) for the length of the iterator |
| fn extend<I>(&mut self, it: I) |
| where |
| I: IntoIterator<Item = &'a A>, |
| { |
| for item in it { |
| self.push(*item); |
| } |
| } |
| } |
| |
| pub struct Iter<A, T> { |
| array: InlineArray<A, T>, |
| } |
| |
| impl<A, T> Iterator for Iter<A, T> { |
| type Item = A; |
| |
| fn next(&mut self) -> Option<Self::Item> { |
| self.array.remove(0) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| (self.array.len(), Some(self.array.len())) |
| } |
| } |
| |
| impl<A, T> DoubleEndedIterator for Iter<A, T> { |
| fn next_back(&mut self) -> Option<Self::Item> { |
| self.array.pop() |
| } |
| } |
| |
| impl<A, T> ExactSizeIterator for Iter<A, T> {} |
| |
| impl<A, T> FusedIterator for Iter<A, T> {} |
| |
| pub struct Drain<'a, A, T> { |
| array: &'a mut InlineArray<A, T>, |
| } |
| |
| impl<'a, A, T> Iterator for Drain<'a, A, T> { |
| type Item = A; |
| |
| fn next(&mut self) -> Option<Self::Item> { |
| self.array.remove(0) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| (self.array.len(), Some(self.array.len())) |
| } |
| } |
| |
| impl<'a, A, T> DoubleEndedIterator for Drain<'a, A, T> { |
| fn next_back(&mut self) -> Option<Self::Item> { |
| self.array.pop() |
| } |
| } |
| |
| impl<'a, A, T> ExactSizeIterator for Drain<'a, A, T> {} |
| |
| impl<'a, A, T> FusedIterator for Drain<'a, A, T> {} |