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use {
super::{
Allocator,
CollectionAllocErr,
taggedlen::TaggedLen
},
core::{
alloc::Layout,
mem::{
ManuallyDrop,
MaybeUninit
},
ptr::{
NonNull,
copy_nonoverlapping
}
}
};
#[repr(C)]
pub(crate) union RawSmallVecInner<T, const N: usize> {
pub(crate) inline: ManuallyDrop<MaybeUninit<[T; N]>>,
pub(crate) heap: (NonNull<T>, usize)
}
/// Either a stack array with `length <= N` or a heap array
/// whose pointer and capacity are stored here.
///
/// We store a `NonNull<T>` instead of a `*mut T` so that type is covariant
/// with respect to `T`, and since the heap pointer is never null.
pub struct RawSmallVec<T, const N: usize, A> {
pub(crate) inner: RawSmallVecInner<T, N>,
pub(crate) alloc: A
}
impl<T, const N: usize, A: Allocator> RawSmallVec<T, N, A> {
pub const INLINE_CAP: usize = if Self::IS_ZST { usize::MAX } else { N };
const IS_ZST: bool = size_of::<T>() == 0;
#[inline]
pub const fn new(alloc: A) -> Self {
Self::new_inline(MaybeUninit::uninit(), alloc)
}
#[inline]
pub const fn new_inline(inline: MaybeUninit<[T; N]>, alloc: A) -> Self {
Self {
inner: RawSmallVecInner {
inline: ManuallyDrop::new(inline)
},
alloc
}
}
#[inline]
pub const fn new_heap(ptr: NonNull<T>, capacity: usize, alloc: A) -> Self {
Self {
inner: RawSmallVecInner {
heap: (ptr, capacity)
},
alloc
}
}
#[inline]
pub const fn as_ptr_inline(&self) -> *const T {
// SAFETY: it is safe because we aren't reading the value, just getting
// a reference to it. reading it would be UB potentially, but
// for that downstream unsafe is required
#[allow(unused_unsafe, reason = "Unsafe in MSRV")]
(unsafe { &raw const self.inner.inline }).cast()
}
#[inline]
pub const fn as_mut_ptr_inline(&mut self) -> *mut T {
// SAFETY: same as above
#[allow(unused_unsafe, reason = "Unsafe in MSRV")]
(unsafe { &raw mut self.inner.inline }).cast()
}
/// # Safety
///
/// `on_heap` must be true if and only if `self.heap` is the active member.
#[inline(always)]
pub const unsafe fn as_ptr(&self, on_heap: bool) -> *const T {
if on_heap {
unsafe { self.inner.heap.0.as_ptr() }
} else {
self.as_ptr_inline()
}
}
/// # Safety
///
/// `on_heap` must be true if and only if `self.heap` is the active member.
#[inline(always)]
pub const unsafe fn as_mut_ptr(&mut self, on_heap: bool) -> *mut T {
if on_heap {
unsafe { self.inner.heap.0.as_ptr() }
} else {
self.as_mut_ptr_inline()
}
}
/// # Safety
///
/// `on_heap` must be true if and only if `self.heap` is the active member.
#[inline(always)]
pub const unsafe fn capacity(&self, on_heap: bool) -> usize {
if on_heap {
unsafe { self.inner.heap.1 }
} else {
Self::INLINE_CAP
}
}
/// # Safety
///
/// `new_capacity` must be non zero, and greater or equal to the length.
/// T must not be a ZST.
pub unsafe fn try_grow_raw(
&mut self,
len: TaggedLen<T>,
new_capacity: usize
) -> Result<(), CollectionAllocErr> {
let (len, was_on_heap) = len.parts();
debug_assert!(!Self::IS_ZST);
debug_assert!(new_capacity > 0 && new_capacity >= len);
// SAFETY: the tag tells which member is active
let ptr = unsafe { self.as_mut_ptr(was_on_heap) };
let new_layout =
Layout::array::<T>(new_capacity).map_err(|_| CollectionAllocErr::CapacityOverflow)?;
if new_layout.size() > isize::MAX as usize {
return Err(CollectionAllocErr::CapacityOverflow);
}
let new_ptr = if !was_on_heap {
// get a fresh allocation
// `new_layout` has nonzero size.
let new_ptr = self
.alloc
.allocate(new_layout)
.map_err(|_| CollectionAllocErr::AllocErr {
layout: new_layout
})?
.cast();
unsafe { copy_nonoverlapping(ptr, new_ptr.as_ptr(), len) };
new_ptr
} else {
// use grow
// this can't overflow since we already constructed an equivalent
// layout during the previous allocation
let old_layout = unsafe {
Layout::from_size_align_unchecked(
self.inner.heap.1 * size_of::<T>(),
align_of::<T>()
)
};
// SAFETY: ptr was allocated with this allocator
// old_layout is the same as the layout used to allocate the
// previous memory block new_layout.size() is greater
// than zero does not overflow when rounded up to
// alignment. since it was constructed
// with Layout::array
unsafe {
(if self.inner.heap.1 < new_capacity {
A::grow
} else {
A::shrink
})(
&self.alloc,
NonNull::new(ptr as *mut u8).unwrap(),
old_layout,
new_layout
)
}
.map_err(|_| CollectionAllocErr::AllocErr {
layout: new_layout
})?
.cast()
};
self.inner.heap = (new_ptr, new_capacity);
Ok(())
}
}