528 lines
20 KiB
Rust
528 lines
20 KiB
Rust
// SPDX-License-Identifier: Apache-2.0 OR MIT
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#![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
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use core::alloc::LayoutError;
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use core::cmp;
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use core::intrinsics;
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use core::mem::{self, ManuallyDrop, MaybeUninit};
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use core::ops::Drop;
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use core::ptr::{self, NonNull, Unique};
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use core::slice;
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#[cfg(not(no_global_oom_handling))]
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use crate::alloc::handle_alloc_error;
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use crate::alloc::{Allocator, Global, Layout};
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use crate::boxed::Box;
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use crate::collections::TryReserveError;
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use crate::collections::TryReserveErrorKind::*;
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#[cfg(test)]
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mod tests;
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#[cfg(not(no_global_oom_handling))]
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enum AllocInit {
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/// The contents of the new memory are uninitialized.
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Uninitialized,
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/// The new memory is guaranteed to be zeroed.
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Zeroed,
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}
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/// A low-level utility for more ergonomically allocating, reallocating, and deallocating
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/// a buffer of memory on the heap without having to worry about all the corner cases
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/// involved. This type is excellent for building your own data structures like Vec and VecDeque.
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/// In particular:
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///
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/// * Produces `Unique::dangling()` on zero-sized types.
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/// * Produces `Unique::dangling()` on zero-length allocations.
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/// * Avoids freeing `Unique::dangling()`.
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/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics).
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/// * Guards against 32-bit systems allocating more than isize::MAX bytes.
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/// * Guards against overflowing your length.
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/// * Calls `handle_alloc_error` for fallible allocations.
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/// * Contains a `ptr::Unique` and thus endows the user with all related benefits.
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/// * Uses the excess returned from the allocator to use the largest available capacity.
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///
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/// This type does not in anyway inspect the memory that it manages. When dropped it *will*
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/// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec`
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/// to handle the actual things *stored* inside of a `RawVec`.
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///
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/// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns
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/// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
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/// `Box<[T]>`, since `capacity()` won't yield the length.
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#[allow(missing_debug_implementations)]
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pub(crate) struct RawVec<T, A: Allocator = Global> {
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ptr: Unique<T>,
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cap: usize,
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alloc: A,
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}
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impl<T> RawVec<T, Global> {
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/// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
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/// they cannot call `Self::new()`.
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///
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/// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
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/// that would truly const-call something unstable.
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pub const NEW: Self = Self::new();
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/// Creates the biggest possible `RawVec` (on the system heap)
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/// without allocating. If `T` has positive size, then this makes a
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/// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
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/// `RawVec` with capacity `usize::MAX`. Useful for implementing
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/// delayed allocation.
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#[must_use]
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pub const fn new() -> Self {
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Self::new_in(Global)
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}
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/// Creates a `RawVec` (on the system heap) with exactly the
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/// capacity and alignment requirements for a `[T; capacity]`. This is
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/// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
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/// zero-sized. Note that if `T` is zero-sized this means you will
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/// *not* get a `RawVec` with the requested capacity.
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///
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/// # Panics
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///
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/// Panics if the requested capacity exceeds `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM.
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#[cfg(not(any(no_global_oom_handling, test)))]
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#[must_use]
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#[inline]
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pub fn with_capacity(capacity: usize) -> Self {
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Self::with_capacity_in(capacity, Global)
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}
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/// Like `with_capacity`, but guarantees the buffer is zeroed.
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#[cfg(not(any(no_global_oom_handling, test)))]
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#[must_use]
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#[inline]
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pub fn with_capacity_zeroed(capacity: usize) -> Self {
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Self::with_capacity_zeroed_in(capacity, Global)
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}
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}
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impl<T, A: Allocator> RawVec<T, A> {
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// Tiny Vecs are dumb. Skip to:
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// - 8 if the element size is 1, because any heap allocators is likely
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// to round up a request of less than 8 bytes to at least 8 bytes.
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// - 4 if elements are moderate-sized (<= 1 KiB).
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// - 1 otherwise, to avoid wasting too much space for very short Vecs.
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pub(crate) const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 {
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8
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} else if mem::size_of::<T>() <= 1024 {
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4
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} else {
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1
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};
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/// Like `new`, but parameterized over the choice of allocator for
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/// the returned `RawVec`.
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pub const fn new_in(alloc: A) -> Self {
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// `cap: 0` means "unallocated". zero-sized types are ignored.
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Self { ptr: Unique::dangling(), cap: 0, alloc }
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}
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/// Like `with_capacity`, but parameterized over the choice of
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/// allocator for the returned `RawVec`.
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#[cfg(not(no_global_oom_handling))]
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#[inline]
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pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
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Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
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}
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/// Like `with_capacity_zeroed`, but parameterized over the choice
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/// of allocator for the returned `RawVec`.
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#[cfg(not(no_global_oom_handling))]
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#[inline]
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pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
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Self::allocate_in(capacity, AllocInit::Zeroed, alloc)
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}
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/// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
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///
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/// Note that this will correctly reconstitute any `cap` changes
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/// that may have been performed. (See description of type for details.)
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///
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/// # Safety
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///
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/// * `len` must be greater than or equal to the most recently requested capacity, and
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/// * `len` must be less than or equal to `self.capacity()`.
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///
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/// Note, that the requested capacity and `self.capacity()` could differ, as
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/// an allocator could overallocate and return a greater memory block than requested.
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pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
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// Sanity-check one half of the safety requirement (we cannot check the other half).
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debug_assert!(
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len <= self.capacity(),
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"`len` must be smaller than or equal to `self.capacity()`"
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);
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let me = ManuallyDrop::new(self);
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unsafe {
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let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
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Box::from_raw_in(slice, ptr::read(&me.alloc))
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}
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}
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#[cfg(not(no_global_oom_handling))]
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fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self {
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// Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
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if mem::size_of::<T>() == 0 || capacity == 0 {
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Self::new_in(alloc)
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} else {
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// We avoid `unwrap_or_else` here because it bloats the amount of
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// LLVM IR generated.
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let layout = match Layout::array::<T>(capacity) {
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Ok(layout) => layout,
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Err(_) => capacity_overflow(),
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};
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match alloc_guard(layout.size()) {
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Ok(_) => {}
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Err(_) => capacity_overflow(),
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}
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let result = match init {
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AllocInit::Uninitialized => alloc.allocate(layout),
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AllocInit::Zeroed => alloc.allocate_zeroed(layout),
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};
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let ptr = match result {
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Ok(ptr) => ptr,
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Err(_) => handle_alloc_error(layout),
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};
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// Allocators currently return a `NonNull<[u8]>` whose length
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// matches the size requested. If that ever changes, the capacity
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// here should change to `ptr.len() / mem::size_of::<T>()`.
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Self {
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ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
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cap: capacity,
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alloc,
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}
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}
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}
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/// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
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///
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/// # Safety
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///
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/// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
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/// `capacity`.
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/// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
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/// systems). ZST vectors may have a capacity up to `usize::MAX`.
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/// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
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/// guaranteed.
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#[inline]
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pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
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Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc }
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}
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/// Gets a raw pointer to the start of the allocation. Note that this is
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/// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
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/// be careful.
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#[inline]
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pub fn ptr(&self) -> *mut T {
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self.ptr.as_ptr()
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}
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/// Gets the capacity of the allocation.
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///
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/// This will always be `usize::MAX` if `T` is zero-sized.
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#[inline(always)]
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pub fn capacity(&self) -> usize {
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if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap }
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}
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/// Returns a shared reference to the allocator backing this `RawVec`.
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pub fn allocator(&self) -> &A {
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&self.alloc
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}
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fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
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if mem::size_of::<T>() == 0 || self.cap == 0 {
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None
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} else {
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// We have an allocated chunk of memory, so we can bypass runtime
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// checks to get our current layout.
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unsafe {
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let layout = Layout::array::<T>(self.cap).unwrap_unchecked();
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Some((self.ptr.cast().into(), layout))
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}
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}
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}
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/// Ensures that the buffer contains at least enough space to hold `len +
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/// additional` elements. If it doesn't already have enough capacity, will
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/// reallocate enough space plus comfortable slack space to get amortized
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/// *O*(1) behavior. Will limit this behavior if it would needlessly cause
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/// itself to panic.
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///
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/// If `len` exceeds `self.capacity()`, this may fail to actually allocate
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/// the requested space. This is not really unsafe, but the unsafe
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/// code *you* write that relies on the behavior of this function may break.
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///
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/// This is ideal for implementing a bulk-push operation like `extend`.
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///
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/// # Panics
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///
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/// Panics if the new capacity exceeds `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM.
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#[cfg(not(no_global_oom_handling))]
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#[inline]
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pub fn reserve(&mut self, len: usize, additional: usize) {
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// Callers expect this function to be very cheap when there is already sufficient capacity.
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// Therefore, we move all the resizing and error-handling logic from grow_amortized and
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// handle_reserve behind a call, while making sure that this function is likely to be
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// inlined as just a comparison and a call if the comparison fails.
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#[cold]
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fn do_reserve_and_handle<T, A: Allocator>(
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slf: &mut RawVec<T, A>,
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len: usize,
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additional: usize,
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) {
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handle_reserve(slf.grow_amortized(len, additional));
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}
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if self.needs_to_grow(len, additional) {
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do_reserve_and_handle(self, len, additional);
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}
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}
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/// A specialized version of `reserve()` used only by the hot and
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/// oft-instantiated `Vec::push()`, which does its own capacity check.
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#[cfg(not(no_global_oom_handling))]
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#[inline(never)]
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pub fn reserve_for_push(&mut self, len: usize) {
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handle_reserve(self.grow_amortized(len, 1));
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}
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/// The same as `reserve`, but returns on errors instead of panicking or aborting.
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pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
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if self.needs_to_grow(len, additional) {
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self.grow_amortized(len, additional)
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} else {
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Ok(())
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}
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}
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/// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting.
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#[inline(never)]
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pub fn try_reserve_for_push(&mut self, len: usize) -> Result<(), TryReserveError> {
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self.grow_amortized(len, 1)
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}
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/// Ensures that the buffer contains at least enough space to hold `len +
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/// additional` elements. If it doesn't already, will reallocate the
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/// minimum possible amount of memory necessary. Generally this will be
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/// exactly the amount of memory necessary, but in principle the allocator
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/// is free to give back more than we asked for.
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///
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/// If `len` exceeds `self.capacity()`, this may fail to actually allocate
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/// the requested space. This is not really unsafe, but the unsafe code
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/// *you* write that relies on the behavior of this function may break.
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///
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/// # Panics
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///
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/// Panics if the new capacity exceeds `isize::MAX` bytes.
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///
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/// # Aborts
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///
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/// Aborts on OOM.
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#[cfg(not(no_global_oom_handling))]
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pub fn reserve_exact(&mut self, len: usize, additional: usize) {
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handle_reserve(self.try_reserve_exact(len, additional));
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}
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/// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
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pub fn try_reserve_exact(
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&mut self,
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len: usize,
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additional: usize,
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) -> Result<(), TryReserveError> {
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if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
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}
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/// Shrinks the buffer down to the specified capacity. If the given amount
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/// is 0, actually completely deallocates.
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///
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/// # Panics
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///
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/// Panics if the given amount is *larger* than the current capacity.
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///
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/// # Aborts
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///
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/// Aborts on OOM.
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#[cfg(not(no_global_oom_handling))]
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pub fn shrink_to_fit(&mut self, cap: usize) {
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handle_reserve(self.shrink(cap));
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}
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}
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impl<T, A: Allocator> RawVec<T, A> {
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/// Returns if the buffer needs to grow to fulfill the needed extra capacity.
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/// Mainly used to make inlining reserve-calls possible without inlining `grow`.
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fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
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additional > self.capacity().wrapping_sub(len)
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}
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fn set_ptr_and_cap(&mut self, ptr: NonNull<[u8]>, cap: usize) {
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// Allocators currently return a `NonNull<[u8]>` whose length matches
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// the size requested. If that ever changes, the capacity here should
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// change to `ptr.len() / mem::size_of::<T>()`.
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self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) };
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self.cap = cap;
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}
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// This method is usually instantiated many times. So we want it to be as
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// small as possible, to improve compile times. But we also want as much of
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// its contents to be statically computable as possible, to make the
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// generated code run faster. Therefore, this method is carefully written
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// so that all of the code that depends on `T` is within it, while as much
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// of the code that doesn't depend on `T` as possible is in functions that
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// are non-generic over `T`.
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fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
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// This is ensured by the calling contexts.
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debug_assert!(additional > 0);
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if mem::size_of::<T>() == 0 {
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// Since we return a capacity of `usize::MAX` when `elem_size` is
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// 0, getting to here necessarily means the `RawVec` is overfull.
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return Err(CapacityOverflow.into());
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}
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// Nothing we can really do about these checks, sadly.
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let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
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// This guarantees exponential growth. The doubling cannot overflow
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// because `cap <= isize::MAX` and the type of `cap` is `usize`.
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let cap = cmp::max(self.cap * 2, required_cap);
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let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap);
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let new_layout = Layout::array::<T>(cap);
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// `finish_grow` is non-generic over `T`.
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let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
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self.set_ptr_and_cap(ptr, cap);
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Ok(())
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}
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// The constraints on this method are much the same as those on
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// `grow_amortized`, but this method is usually instantiated less often so
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// it's less critical.
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fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
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if mem::size_of::<T>() == 0 {
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// Since we return a capacity of `usize::MAX` when the type size is
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// 0, getting to here necessarily means the `RawVec` is overfull.
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return Err(CapacityOverflow.into());
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}
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let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
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let new_layout = Layout::array::<T>(cap);
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// `finish_grow` is non-generic over `T`.
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let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
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self.set_ptr_and_cap(ptr, cap);
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Ok(())
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}
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#[allow(dead_code)]
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fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
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assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity");
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let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
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let ptr = unsafe {
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// `Layout::array` cannot overflow here because it would have
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// overflowed earlier when capacity was larger.
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let new_layout = Layout::array::<T>(cap).unwrap_unchecked();
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self.alloc
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.shrink(ptr, layout, new_layout)
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.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
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};
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self.set_ptr_and_cap(ptr, cap);
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Ok(())
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}
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}
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// This function is outside `RawVec` to minimize compile times. See the comment
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// above `RawVec::grow_amortized` for details. (The `A` parameter isn't
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// significant, because the number of different `A` types seen in practice is
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// much smaller than the number of `T` types.)
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#[inline(never)]
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fn finish_grow<A>(
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new_layout: Result<Layout, LayoutError>,
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current_memory: Option<(NonNull<u8>, Layout)>,
|
|
alloc: &mut A,
|
|
) -> Result<NonNull<[u8]>, TryReserveError>
|
|
where
|
|
A: Allocator,
|
|
{
|
|
// Check for the error here to minimize the size of `RawVec::grow_*`.
|
|
let new_layout = new_layout.map_err(|_| CapacityOverflow)?;
|
|
|
|
alloc_guard(new_layout.size())?;
|
|
|
|
let memory = if let Some((ptr, old_layout)) = current_memory {
|
|
debug_assert_eq!(old_layout.align(), new_layout.align());
|
|
unsafe {
|
|
// The allocator checks for alignment equality
|
|
intrinsics::assume(old_layout.align() == new_layout.align());
|
|
alloc.grow(ptr, old_layout, new_layout)
|
|
}
|
|
} else {
|
|
alloc.allocate(new_layout)
|
|
};
|
|
|
|
memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into())
|
|
}
|
|
|
|
unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
|
|
/// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
|
|
fn drop(&mut self) {
|
|
if let Some((ptr, layout)) = self.current_memory() {
|
|
unsafe { self.alloc.deallocate(ptr, layout) }
|
|
}
|
|
}
|
|
}
|
|
|
|
// Central function for reserve error handling.
|
|
#[cfg(not(no_global_oom_handling))]
|
|
#[inline]
|
|
fn handle_reserve(result: Result<(), TryReserveError>) {
|
|
match result.map_err(|e| e.kind()) {
|
|
Err(CapacityOverflow) => capacity_overflow(),
|
|
Err(AllocError { layout, .. }) => handle_alloc_error(layout),
|
|
Ok(()) => { /* yay */ }
|
|
}
|
|
}
|
|
|
|
// We need to guarantee the following:
|
|
// * We don't ever allocate `> isize::MAX` byte-size objects.
|
|
// * We don't overflow `usize::MAX` and actually allocate too little.
|
|
//
|
|
// On 64-bit we just need to check for overflow since trying to allocate
|
|
// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
|
|
// an extra guard for this in case we're running on a platform which can use
|
|
// all 4GB in user-space, e.g., PAE or x32.
|
|
|
|
#[inline]
|
|
fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
|
|
if usize::BITS < 64 && alloc_size > isize::MAX as usize {
|
|
Err(CapacityOverflow.into())
|
|
} else {
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
// One central function responsible for reporting capacity overflows. This'll
|
|
// ensure that the code generation related to these panics is minimal as there's
|
|
// only one location which panics rather than a bunch throughout the module.
|
|
#[cfg(not(no_global_oom_handling))]
|
|
fn capacity_overflow() -> ! {
|
|
panic!("capacity overflow");
|
|
}
|