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Add try_zeroed_vec and zeroed_vec #117

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merged 3 commits into from
Jul 7, 2022
Merged

Add try_zeroed_vec and zeroed_vec #117

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28e14fa
add `try_zeroed_vec` and `zeroed_vec`, adjust impl of `try_zeroed_sli…
fu5ha Jul 4, 2022
0f6bb79
go back to returning an error rather than calling handle_alloc_error
fu5ha Jul 4, 2022
3a4e116
use boxed slice .into_vec instead :)
fu5ha Jul 4, 2022
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30 changes: 22 additions & 8 deletions src/allocation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,25 @@ pub fn zeroed_box<T: Zeroable>() -> Box<T> {
try_zeroed_box().unwrap()
}

/// Allocates a `Vec<T>` of length and capacity exactly equal to `length` and all elements zeroed.
///
/// ## Failure
///
/// This fails if the allocation fails, or if a layout cannot be calculated for the allocation.
pub fn try_zeroed_vec<T: Zeroable>(length: usize) -> Result<Vec<T>, ()> {
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if length == 0 {
Ok(Vec::new())
} else {
let boxed_slice = try_zeroed_slice_box(length)?;
Ok(boxed_slice.into_vec())
}
}

/// As [`try_zeroed_vec`] but unwraps for you
pub fn zeroed_vec<T: Zeroable>(length: usize) -> Vec<T> {
try_zeroed_vec(length).unwrap()
}

/// Allocates a `Box<[T]>` with all contents being zeroed out.
///
/// This uses the global allocator to create a zeroed allocation and _then_
Expand All @@ -102,7 +121,7 @@ pub fn zeroed_box<T: Zeroable>() -> Box<T> {
///
/// ## Failure
///
/// This fails if the allocation fails.
/// This fails if the allocation fails, or if a layout cannot be calculated for the allocation.
#[inline]
pub fn try_zeroed_slice_box<T: Zeroable>(
length: usize,
Expand All @@ -117,12 +136,7 @@ pub fn try_zeroed_slice_box<T: Zeroable>(
// This will also not allocate.
return Ok(Vec::new().into_boxed_slice());
}
// For Pod types, the layout of the array/slice is equivalent to repeating the
// type.
let layout_length = size_of::<T>().checked_mul(length).ok_or(())?;
assert!(layout_length != 0);
let layout =
Layout::from_size_align(layout_length, align_of::<T>()).map_err(|_| ())?;
let layout = core::alloc::Layout::array::<T>(length).map_err(|_| ())?;
let ptr = unsafe { alloc_zeroed(layout) };
if ptr.is_null() {
// we don't know what the error is because `alloc_zeroed` is a dumb API
Expand All @@ -131,7 +145,7 @@ pub fn try_zeroed_slice_box<T: Zeroable>(
let slice =
unsafe { core::slice::from_raw_parts_mut(ptr as *mut T, length) };
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This should be core::ptr::slice_from_raw_parts_mut() to avoid creating an intermediate reference (also also reduces the amount of unsafe by one line).

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That's a possible change, but in this case the intermediate reference is fine, because the allocation is initialized anyway.

Ok(unsafe { Box::<[T]>::from_raw(slice) })
}
}
}

/// As [`try_zeroed_slice_box`](try_zeroed_slice_box), but unwraps for you.
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