1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
14 use core::ptr::{self, NonNull, Unique};
17 use alloc::{Alloc, Layout, Global, oom};
18 use alloc::CollectionAllocErr;
19 use alloc::CollectionAllocErr::*;
22 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
23 /// a buffer of memory on the heap without having to worry about all the corner cases
24 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
27 /// * Produces Unique::empty() on zero-sized types
28 /// * Produces Unique::empty() on zero-length allocations
29 /// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics)
30 /// * Guards against 32-bit systems allocating more than isize::MAX bytes
31 /// * Guards against overflowing your length
33 /// * Avoids freeing Unique::empty()
34 /// * Contains a ptr::Unique and thus endows the user with all related benefits
36 /// This type does not in anyway inspect the memory that it manages. When dropped it *will*
37 /// free its memory, but it *won't* try to Drop its contents. It is up to the user of RawVec
38 /// to handle the actual things *stored* inside of a RawVec.
40 /// Note that a RawVec always forces its capacity to be usize::MAX for zero-sized types.
41 /// This enables you to use capacity growing logic catch the overflows in your length
42 /// that might occur with zero-sized types.
44 /// However this means that you need to be careful when roundtripping this type
45 /// with a `Box<[T]>`: `cap()` won't yield the len. However `with_capacity`,
46 /// `shrink_to_fit`, and `from_box` will actually set RawVec's private capacity
47 /// field. This allows zero-sized types to not be special-cased by consumers of
49 #[allow(missing_debug_implementations)]
50 pub struct RawVec<T, A: Alloc = Global> {
56 impl<T, A: Alloc> RawVec<T, A> {
57 /// Like `new` but parameterized over the choice of allocator for
58 /// the returned RawVec.
59 pub fn new_in(a: A) -> Self {
60 // !0 is usize::MAX. This branch should be stripped at compile time.
61 let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
63 // Unique::empty() doubles as "unallocated" and "zero-sized allocation"
71 /// Like `empty` but parametrized over the choice of allocator for the returned `RawVec`.
72 pub const fn empty_in(a: A) -> Self {
73 // Unique::empty() doubles as "unallocated" and "zero-sized allocation"
81 /// Like `with_capacity` but parameterized over the choice of
82 /// allocator for the returned RawVec.
84 pub fn with_capacity_in(cap: usize, a: A) -> Self {
85 RawVec::allocate_in(cap, false, a)
88 /// Like `with_capacity_zeroed` but parameterized over the choice
89 /// of allocator for the returned RawVec.
91 pub fn with_capacity_zeroed_in(cap: usize, a: A) -> Self {
92 RawVec::allocate_in(cap, true, a)
95 fn allocate_in(cap: usize, zeroed: bool, mut a: A) -> Self {
97 let elem_size = mem::size_of::<T>();
99 let alloc_size = cap.checked_mul(elem_size).unwrap_or_else(|| capacity_overflow());
100 alloc_guard(alloc_size).unwrap_or_else(|_| capacity_overflow());
102 // handles ZSTs and `cap = 0` alike
103 let ptr = if alloc_size == 0 {
104 NonNull::<T>::dangling().as_opaque()
106 let align = mem::align_of::<T>();
107 let result = if zeroed {
108 a.alloc_zeroed(Layout::from_size_align(alloc_size, align).unwrap())
110 a.alloc(Layout::from_size_align(alloc_size, align).unwrap())
119 ptr: ptr.cast().into(),
127 impl<T> RawVec<T, Global> {
128 /// Creates the biggest possible RawVec (on the system heap)
129 /// without allocating. If T has positive size, then this makes a
130 /// RawVec with capacity 0. If T has 0 size, then it makes a
131 /// RawVec with capacity `usize::MAX`. Useful for implementing
132 /// delayed allocation.
133 pub fn new() -> Self {
137 /// Create a `RawVec` with capcity 0 (on the system heap), regardless of `T`, without
139 pub fn empty() -> Self {
140 Self::empty_in(Global)
143 /// Creates a RawVec (on the system heap) with exactly the
144 /// capacity and alignment requirements for a `[T; cap]`. This is
145 /// equivalent to calling RawVec::new when `cap` is 0 or T is
146 /// zero-sized. Note that if `T` is zero-sized this means you will
147 /// *not* get a RawVec with the requested capacity!
151 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
152 /// * Panics on 32-bit platforms if the requested capacity exceeds
153 /// `isize::MAX` bytes.
159 pub fn with_capacity(cap: usize) -> Self {
160 RawVec::allocate_in(cap, false, Global)
163 /// Like `with_capacity` but guarantees the buffer is zeroed.
165 pub fn with_capacity_zeroed(cap: usize) -> Self {
166 RawVec::allocate_in(cap, true, Global)
170 impl<T, A: Alloc> RawVec<T, A> {
171 /// Reconstitutes a RawVec from a pointer, capacity, and allocator.
173 /// # Undefined Behavior
175 /// The ptr must be allocated (via the given allocator `a`), and with the given capacity. The
176 /// capacity cannot exceed `isize::MAX` (only a concern on 32-bit systems).
177 /// If the ptr and capacity come from a RawVec created via `a`, then this is guaranteed.
178 pub unsafe fn from_raw_parts_in(ptr: *mut T, cap: usize, a: A) -> Self {
180 ptr: Unique::new_unchecked(ptr),
187 impl<T> RawVec<T, Global> {
188 /// Reconstitutes a RawVec from a pointer, capacity.
190 /// # Undefined Behavior
192 /// The ptr must be allocated (on the system heap), and with the given capacity. The
193 /// capacity cannot exceed `isize::MAX` (only a concern on 32-bit systems).
194 /// If the ptr and capacity come from a RawVec, then this is guaranteed.
195 pub unsafe fn from_raw_parts(ptr: *mut T, cap: usize) -> Self {
197 ptr: Unique::new_unchecked(ptr),
203 /// Converts a `Box<[T]>` into a `RawVec<T>`.
204 pub fn from_box(mut slice: Box<[T]>) -> Self {
206 let result = RawVec::from_raw_parts(slice.as_mut_ptr(), slice.len());
213 impl<T, A: Alloc> RawVec<T, A> {
214 /// Gets a raw pointer to the start of the allocation. Note that this is
215 /// Unique::empty() if `cap = 0` or T is zero-sized. In the former case, you must
217 pub fn ptr(&self) -> *mut T {
221 /// Gets the capacity of the allocation.
223 /// This will always be `usize::MAX` if `T` is zero-sized.
225 pub fn cap(&self) -> usize {
226 if mem::size_of::<T>() == 0 {
233 /// Returns a shared reference to the allocator backing this RawVec.
234 pub fn alloc(&self) -> &A {
238 /// Returns a mutable reference to the allocator backing this RawVec.
239 pub fn alloc_mut(&mut self) -> &mut A {
243 fn current_layout(&self) -> Option<Layout> {
247 // We have an allocated chunk of memory, so we can bypass runtime
248 // checks to get our current layout.
250 let align = mem::align_of::<T>();
251 let size = mem::size_of::<T>() * self.cap;
252 Some(Layout::from_size_align_unchecked(size, align))
257 /// Doubles the size of the type's backing allocation. This is common enough
258 /// to want to do that it's easiest to just have a dedicated method. Slightly
259 /// more efficient logic can be provided for this than the general case.
261 /// This function is ideal for when pushing elements one-at-a-time because
262 /// you don't need to incur the costs of the more general computations
263 /// reserve needs to do to guard against overflow. You do however need to
264 /// manually check if your `len == cap`.
268 /// * Panics if T is zero-sized on the assumption that you managed to exhaust
269 /// all `usize::MAX` slots in your imaginary buffer.
270 /// * Panics on 32-bit platforms if the requested capacity exceeds
271 /// `isize::MAX` bytes.
280 /// # #![feature(alloc)]
281 /// # extern crate alloc;
283 /// # use alloc::raw_vec::RawVec;
284 /// struct MyVec<T> {
289 /// impl<T> MyVec<T> {
290 /// pub fn push(&mut self, elem: T) {
291 /// if self.len == self.buf.cap() { self.buf.double(); }
292 /// // double would have aborted or panicked if the len exceeded
293 /// // `isize::MAX` so this is safe to do unchecked now.
295 /// ptr::write(self.buf.ptr().offset(self.len as isize), elem);
301 /// # let mut vec = MyVec { buf: RawVec::new(), len: 0 };
307 pub fn double(&mut self) {
309 let elem_size = mem::size_of::<T>();
311 // since we set the capacity to usize::MAX when elem_size is
312 // 0, getting to here necessarily means the RawVec is overfull.
313 assert!(elem_size != 0, "capacity overflow");
315 let (new_cap, uniq) = match self.current_layout() {
317 // Since we guarantee that we never allocate more than
318 // isize::MAX bytes, `elem_size * self.cap <= isize::MAX` as
319 // a precondition, so this can't overflow. Additionally the
320 // alignment will never be too large as to "not be
321 // satisfiable", so `Layout::from_size_align` will always
324 // tl;dr; we bypass runtime checks due to dynamic assertions
325 // in this module, allowing us to use
326 // `from_size_align_unchecked`.
327 let new_cap = 2 * self.cap;
328 let new_size = new_cap * elem_size;
329 alloc_guard(new_size).unwrap_or_else(|_| capacity_overflow());
330 let ptr_res = self.a.realloc(NonNull::from(self.ptr).as_opaque(),
334 Ok(ptr) => (new_cap, ptr.cast().into()),
339 // skip to 4 because tiny Vec's are dumb; but not if that
340 // would cause overflow
341 let new_cap = if elem_size > (!0) / 8 { 1 } else { 4 };
342 match self.a.alloc_array::<T>(new_cap) {
343 Ok(ptr) => (new_cap, ptr.into()),
353 /// Attempts to double the size of the type's backing allocation in place. This is common
354 /// enough to want to do that it's easiest to just have a dedicated method. Slightly
355 /// more efficient logic can be provided for this than the general case.
357 /// Returns true if the reallocation attempt has succeeded, or false otherwise.
361 /// * Panics if T is zero-sized on the assumption that you managed to exhaust
362 /// all `usize::MAX` slots in your imaginary buffer.
363 /// * Panics on 32-bit platforms if the requested capacity exceeds
364 /// `isize::MAX` bytes.
367 pub fn double_in_place(&mut self) -> bool {
369 let elem_size = mem::size_of::<T>();
370 let old_layout = match self.current_layout() {
371 Some(layout) => layout,
372 None => return false, // nothing to double
375 // since we set the capacity to usize::MAX when elem_size is
376 // 0, getting to here necessarily means the RawVec is overfull.
377 assert!(elem_size != 0, "capacity overflow");
379 // Since we guarantee that we never allocate more than isize::MAX
380 // bytes, `elem_size * self.cap <= isize::MAX` as a precondition, so
381 // this can't overflow.
383 // Similarly like with `double` above we can go straight to
384 // `Layout::from_size_align_unchecked` as we know this won't
385 // overflow and the alignment is sufficiently small.
386 let new_cap = 2 * self.cap;
387 let new_size = new_cap * elem_size;
388 alloc_guard(new_size).unwrap_or_else(|_| capacity_overflow());
389 match self.a.grow_in_place(NonNull::from(self.ptr).as_opaque(), old_layout, new_size) {
391 // We can't directly divide `size`.
402 /// Ensures that the buffer contains at least enough space to hold
403 /// `used_cap + needed_extra_cap` elements. If it doesn't already,
404 /// will reallocate the minimum possible amount of memory necessary.
405 /// Generally this will be exactly the amount of memory necessary,
406 /// but in principle the allocator is free to give back more than
409 /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
410 /// the requested space. This is not really unsafe, but the unsafe
411 /// code *you* write that relies on the behavior of this function may break.
415 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
416 /// * Panics on 32-bit platforms if the requested capacity exceeds
417 /// `isize::MAX` bytes.
422 pub fn try_reserve_exact(&mut self, used_cap: usize, needed_extra_cap: usize)
423 -> Result<(), CollectionAllocErr> {
426 // NOTE: we don't early branch on ZSTs here because we want this
427 // to actually catch "asking for more than usize::MAX" in that case.
428 // If we make it past the first branch then we are guaranteed to
431 // Don't actually need any more capacity.
432 // Wrapping in case they gave a bad `used_cap`.
433 if self.cap().wrapping_sub(used_cap) >= needed_extra_cap {
437 // Nothing we can really do about these checks :(
438 let new_cap = used_cap.checked_add(needed_extra_cap).ok_or(CapacityOverflow)?;
439 let new_layout = Layout::array::<T>(new_cap).map_err(|_| CapacityOverflow)?;
441 alloc_guard(new_layout.size())?;
443 let res = match self.current_layout() {
445 debug_assert!(new_layout.align() == layout.align());
446 self.a.realloc(NonNull::from(self.ptr).as_opaque(), layout, new_layout.size())
448 None => self.a.alloc(new_layout),
451 self.ptr = res?.cast().into();
458 pub fn reserve_exact(&mut self, used_cap: usize, needed_extra_cap: usize) {
459 match self.try_reserve_exact(used_cap, needed_extra_cap) {
460 Err(CapacityOverflow) => capacity_overflow(),
461 Err(AllocErr) => oom(),
462 Ok(()) => { /* yay */ }
466 /// Calculates the buffer's new size given that it'll hold `used_cap +
467 /// needed_extra_cap` elements. This logic is used in amortized reserve methods.
468 /// Returns `(new_capacity, new_alloc_size)`.
469 fn amortized_new_size(&self, used_cap: usize, needed_extra_cap: usize)
470 -> Result<usize, CollectionAllocErr> {
472 // Nothing we can really do about these checks :(
473 let required_cap = used_cap.checked_add(needed_extra_cap).ok_or(CapacityOverflow)?;
474 // Cannot overflow, because `cap <= isize::MAX`, and type of `cap` is `usize`.
475 let double_cap = self.cap * 2;
476 // `double_cap` guarantees exponential growth.
477 Ok(cmp::max(double_cap, required_cap))
480 /// Ensures that the buffer contains at least enough space to hold
481 /// `used_cap + needed_extra_cap` elements. If it doesn't already have
482 /// enough capacity, will reallocate enough space plus comfortable slack
483 /// space to get amortized `O(1)` behavior. Will limit this behavior
484 /// if it would needlessly cause itself to panic.
486 /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
487 /// the requested space. This is not really unsafe, but the unsafe
488 /// code *you* write that relies on the behavior of this function may break.
490 /// This is ideal for implementing a bulk-push operation like `extend`.
494 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
495 /// * Panics on 32-bit platforms if the requested capacity exceeds
496 /// `isize::MAX` bytes.
505 /// # #![feature(alloc)]
506 /// # extern crate alloc;
508 /// # use alloc::raw_vec::RawVec;
509 /// struct MyVec<T> {
514 /// impl<T: Clone> MyVec<T> {
515 /// pub fn push_all(&mut self, elems: &[T]) {
516 /// self.buf.reserve(self.len, elems.len());
517 /// // reserve would have aborted or panicked if the len exceeded
518 /// // `isize::MAX` so this is safe to do unchecked now.
521 /// ptr::write(self.buf.ptr().offset(self.len as isize), x.clone());
528 /// # let mut vector = MyVec { buf: RawVec::new(), len: 0 };
529 /// # vector.push_all(&[1, 3, 5, 7, 9]);
532 pub fn try_reserve(&mut self, used_cap: usize, needed_extra_cap: usize)
533 -> Result<(), CollectionAllocErr> {
535 // NOTE: we don't early branch on ZSTs here because we want this
536 // to actually catch "asking for more than usize::MAX" in that case.
537 // If we make it past the first branch then we are guaranteed to
540 // Don't actually need any more capacity.
541 // Wrapping in case they give a bad `used_cap`
542 if self.cap().wrapping_sub(used_cap) >= needed_extra_cap {
546 let new_cap = self.amortized_new_size(used_cap, needed_extra_cap)?;
547 let new_layout = Layout::array::<T>(new_cap).map_err(|_| CapacityOverflow)?;
549 // FIXME: may crash and burn on over-reserve
550 alloc_guard(new_layout.size())?;
552 let res = match self.current_layout() {
554 debug_assert!(new_layout.align() == layout.align());
555 self.a.realloc(NonNull::from(self.ptr).as_opaque(), layout, new_layout.size())
557 None => self.a.alloc(new_layout),
560 self.ptr = res?.cast().into();
567 /// The same as try_reserve, but errors are lowered to a call to oom().
568 pub fn reserve(&mut self, used_cap: usize, needed_extra_cap: usize) {
569 match self.try_reserve(used_cap, needed_extra_cap) {
570 Err(CapacityOverflow) => capacity_overflow(),
571 Err(AllocErr) => oom(),
572 Ok(()) => { /* yay */ }
575 /// Attempts to ensure that the buffer contains at least enough space to hold
576 /// `used_cap + needed_extra_cap` elements. If it doesn't already have
577 /// enough capacity, will reallocate in place enough space plus comfortable slack
578 /// space to get amortized `O(1)` behavior. Will limit this behaviour
579 /// if it would needlessly cause itself to panic.
581 /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
582 /// the requested space. This is not really unsafe, but the unsafe
583 /// code *you* write that relies on the behavior of this function may break.
585 /// Returns true if the reallocation attempt has succeeded, or false otherwise.
589 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
590 /// * Panics on 32-bit platforms if the requested capacity exceeds
591 /// `isize::MAX` bytes.
592 pub fn reserve_in_place(&mut self, used_cap: usize, needed_extra_cap: usize) -> bool {
594 // NOTE: we don't early branch on ZSTs here because we want this
595 // to actually catch "asking for more than usize::MAX" in that case.
596 // If we make it past the first branch then we are guaranteed to
599 // Don't actually need any more capacity. If the current `cap` is 0, we can't
600 // reallocate in place.
601 // Wrapping in case they give a bad `used_cap`
602 let old_layout = match self.current_layout() {
603 Some(layout) => layout,
604 None => return false,
606 if self.cap().wrapping_sub(used_cap) >= needed_extra_cap {
610 let new_cap = self.amortized_new_size(used_cap, needed_extra_cap)
611 .unwrap_or_else(|_| capacity_overflow());
613 // Here, `cap < used_cap + needed_extra_cap <= new_cap`
614 // (regardless of whether `self.cap - used_cap` wrapped).
615 // Therefore we can safely call grow_in_place.
617 let new_layout = Layout::new::<T>().repeat(new_cap).unwrap().0;
618 // FIXME: may crash and burn on over-reserve
619 alloc_guard(new_layout.size()).unwrap_or_else(|_| capacity_overflow());
620 match self.a.grow_in_place(
621 NonNull::from(self.ptr).as_opaque(), old_layout, new_layout.size(),
634 /// Shrinks the allocation down to the specified amount. If the given amount
635 /// is 0, actually completely deallocates.
639 /// Panics if the given amount is *larger* than the current capacity.
644 pub fn shrink_to_fit(&mut self, amount: usize) {
645 let elem_size = mem::size_of::<T>();
647 // Set the `cap` because they might be about to promote to a `Box<[T]>`
653 // This check is my waterloo; it's the only thing Vec wouldn't have to do.
654 assert!(self.cap >= amount, "Tried to shrink to a larger capacity");
657 // We want to create a new zero-length vector within the
658 // same allocator. We use ptr::write to avoid an
659 // erroneous attempt to drop the contents, and we use
660 // ptr::read to sidestep condition against destructuring
661 // types that implement Drop.
664 let a = ptr::read(&self.a as *const A);
665 self.dealloc_buffer();
666 ptr::write(self, RawVec::new_in(a));
668 } else if self.cap != amount {
670 // We know here that our `amount` is greater than zero. This
671 // implies, via the assert above, that capacity is also greater
672 // than zero, which means that we've got a current layout that
675 // We also know that `self.cap` is greater than `amount`, and
676 // consequently we don't need runtime checks for creating either
678 let old_size = elem_size * self.cap;
679 let new_size = elem_size * amount;
680 let align = mem::align_of::<T>();
681 let old_layout = Layout::from_size_align_unchecked(old_size, align);
682 match self.a.realloc(NonNull::from(self.ptr).as_opaque(),
685 Ok(p) => self.ptr = p.cast().into(),
694 impl<T> RawVec<T, Global> {
695 /// Converts the entire buffer into `Box<[T]>`.
697 /// While it is not *strictly* Undefined Behavior to call
698 /// this procedure while some of the RawVec is uninitialized,
699 /// it certainly makes it trivial to trigger it.
701 /// Note that this will correctly reconstitute any `cap` changes
702 /// that may have been performed. (see description of type for details)
703 pub unsafe fn into_box(self) -> Box<[T]> {
704 // NOTE: not calling `cap()` here, actually using the real `cap` field!
705 let slice = slice::from_raw_parts_mut(self.ptr(), self.cap);
706 let output: Box<[T]> = Box::from_raw(slice);
712 impl<T, A: Alloc> RawVec<T, A> {
713 /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
714 pub unsafe fn dealloc_buffer(&mut self) {
715 let elem_size = mem::size_of::<T>();
717 if let Some(layout) = self.current_layout() {
718 self.a.dealloc(NonNull::from(self.ptr).as_opaque(), layout);
724 unsafe impl<#[may_dangle] T, A: Alloc> Drop for RawVec<T, A> {
725 /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
727 unsafe { self.dealloc_buffer(); }
733 // We need to guarantee the following:
734 // * We don't ever allocate `> isize::MAX` byte-size objects
735 // * We don't overflow `usize::MAX` and actually allocate too little
737 // On 64-bit we just need to check for overflow since trying to allocate
738 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
739 // an extra guard for this in case we're running on a platform which can use
740 // all 4GB in user-space. e.g. PAE or x32
743 fn alloc_guard(alloc_size: usize) -> Result<(), CollectionAllocErr> {
744 if mem::size_of::<usize>() < 8 && alloc_size > ::core::isize::MAX as usize {
745 Err(CapacityOverflow)
751 // One central function responsible for reporting capacity overflows. This'll
752 // ensure that the code generation related to these panics is minimal as there's
753 // only one location which panics rather than a bunch throughout the module.
754 fn capacity_overflow() -> ! {
755 panic!("capacity overflow")
764 fn allocator_param() {
765 use allocator::{Alloc, AllocErr};
767 // Writing a test of integration between third-party
768 // allocators and RawVec is a little tricky because the RawVec
769 // API does not expose fallible allocation methods, so we
770 // cannot check what happens when allocator is exhausted
771 // (beyond detecting a panic).
773 // Instead, this just checks that the RawVec methods do at
774 // least go through the Allocator API when it reserves
777 // A dumb allocator that consumes a fixed amount of fuel
778 // before allocation attempts start failing.
779 struct BoundedAlloc { fuel: usize }
780 unsafe impl Alloc for BoundedAlloc {
781 unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<Opaque>, AllocErr> {
782 let size = layout.size();
783 if size > self.fuel {
784 return Err(AllocErr);
786 match Global.alloc(layout) {
787 ok @ Ok(_) => { self.fuel -= size; ok }
791 unsafe fn dealloc(&mut self, ptr: NonNull<Opaque>, layout: Layout) {
792 Global.dealloc(ptr, layout)
796 let a = BoundedAlloc { fuel: 500 };
797 let mut v: RawVec<u8, _> = RawVec::with_capacity_in(50, a);
798 assert_eq!(v.a.fuel, 450);
799 v.reserve(50, 150); // (causes a realloc, thus using 50 + 150 = 200 units of fuel)
800 assert_eq!(v.a.fuel, 250);
804 fn reserve_does_not_overallocate() {
806 let mut v: RawVec<u32> = RawVec::new();
807 // First `reserve` allocates like `reserve_exact`
809 assert_eq!(9, v.cap());
813 let mut v: RawVec<u32> = RawVec::new();
815 assert_eq!(7, v.cap());
816 // 97 if more than double of 7, so `reserve` should work
817 // like `reserve_exact`.
819 assert_eq!(97, v.cap());
823 let mut v: RawVec<u32> = RawVec::new();
825 assert_eq!(12, v.cap());
827 // 3 is less than half of 12, so `reserve` must grow
828 // exponentially. At the time of writing this test grow
829 // factor is 2, so new capacity is 24, however, grow factor
830 // of 1.5 is OK too. Hence `>= 18` in assert.
831 assert!(v.cap() >= 12 + 12 / 2);