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use core::alloc::Layout as StdLayout;
use core::mem;
/// Aborts the process.
///
/// To abort, this function simply panics while panicking.
pub(crate) fn abort() -> ! {
struct Panic;
impl Drop for Panic {
fn drop(&mut self) {
panic!("aborting the process");
}
}
let _panic = Panic;
panic!("aborting the process");
}
/// Calls a function and aborts if it panics.
///
/// This is useful in unsafe code where we can't recover from panics.
#[inline]
pub(crate) fn abort_on_panic<T>(f: impl FnOnce() -> T) -> T {
struct Bomb;
impl Drop for Bomb {
fn drop(&mut self) {
abort();
}
}
let bomb = Bomb;
let t = f();
mem::forget(bomb);
t
}
/// A version of `alloc::alloc::Layout` that can be used in the const
/// position.
#[derive(Clone, Copy, Debug)]
pub(crate) struct Layout {
size: usize,
align: usize,
}
impl Layout {
/// Creates a new `Layout` with the given size and alignment.
#[inline]
pub(crate) const fn from_size_align(size: usize, align: usize) -> Self {
Self { size, align }
}
/// Creates a new `Layout` for the given sized type.
#[inline]
pub(crate) const fn new<T>() -> Self {
Self::from_size_align(mem::size_of::<T>(), mem::align_of::<T>())
}
/// Convert this into the standard library's layout type.
///
/// # Safety
///
/// - `align` must be non-zero and a power of two.
/// - When rounded up to the nearest multiple of `align`, the size
/// must not overflow.
#[inline]
pub(crate) const unsafe fn into_std(self) -> StdLayout {
StdLayout::from_size_align_unchecked(self.size, self.align)
}
/// Get the alignment of this layout.
#[inline]
pub(crate) const fn align(&self) -> usize {
self.align
}
/// Get the size of this layout.
#[inline]
pub(crate) const fn size(&self) -> usize {
self.size
}
/// Returns the layout for `a` followed by `b` and the offset of `b`.
///
/// This function was adapted from the currently unstable `Layout::extend()`:
/// https://doc.rust-lang.org/nightly/std/alloc/struct.Layout.html#method.extend
#[inline]
pub(crate) const fn extend(self, other: Layout) -> Option<(Layout, usize)> {
let new_align = max(self.align(), other.align());
let pad = self.padding_needed_for(other.align());
let offset = leap!(self.size().checked_add(pad));
let new_size = leap!(offset.checked_add(other.size()));
// return None if any of the following are true:
// - align is 0 (implied false by is_power_of_two())
// - align is not a power of 2
// - size rounded up to align overflows
if !new_align.is_power_of_two() || new_size > core::usize::MAX - (new_align - 1) {
return None;
}
let layout = Layout::from_size_align(new_size, new_align);
Some((layout, offset))
}
/// Returns the padding after `layout` that aligns the following address to `align`.
///
/// This function was adapted from the currently unstable `Layout::padding_needed_for()`:
/// https://doc.rust-lang.org/nightly/std/alloc/struct.Layout.html#method.padding_needed_for
#[inline]
pub(crate) const fn padding_needed_for(self, align: usize) -> usize {
let len = self.size();
let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
len_rounded_up.wrapping_sub(len)
}
}
#[inline]
pub(crate) const fn max(left: usize, right: usize) -> usize {
if left > right {
left
} else {
right
}
}
|
