Lines
100 %
Functions
#![allow(clippy::enum_clike_unportable_variant)]
#[cfg(not(feature = "ferrocene_certified"))]
use crate::num::NonZero;
use crate::ub_checks::assert_unsafe_precondition;
use crate::{cmp, fmt, hash, mem, num};
// Ferrocene addition: imports used by certified subset
#[cfg(feature = "ferrocene_certified")]
use crate::{mem, ub_checks::assert_unsafe_precondition};
/// A type storing a `usize` which is a power of two, and thus
/// represents a possible alignment in the Rust abstract machine.
///
/// Note that particularly large alignments, while representable in this type,
/// are likely not to be supported by actual allocators and linkers.
#[unstable(feature = "ptr_alignment_type", issue = "102070")]
#[cfg_attr(not(feature = "ferrocene_certified"), derive(Copy, Clone, PartialEq, Eq))]
#[cfg_attr(feature = "ferrocene_certified", derive(Copy, Clone))]
#[repr(transparent)]
pub struct Alignment(AlignmentEnum);
// Alignment is `repr(usize)`, but via extra steps.
const _: () = assert!(size_of::<Alignment>() == size_of::<usize>());
const _: () = assert!(align_of::<Alignment>() == align_of::<usize>());
fn _alignment_can_be_structurally_matched(a: Alignment) -> bool {
matches!(a, Alignment::MIN)
}
impl Alignment {
/// The smallest possible alignment, 1.
/// All addresses are always aligned at least this much.
/// # Examples
/// ```
/// #![feature(ptr_alignment_type)]
/// use std::ptr::Alignment;
/// assert_eq!(Alignment::MIN.as_usize(), 1);
pub const MIN: Self = Self(AlignmentEnum::_Align1Shl0);
/// Returns the alignment for a type.
/// This provides the same numerical value as [`align_of`],
/// but in an `Alignment` instead of a `usize`.
#[inline]
#[must_use]
pub const fn of<T>() -> Self {
// This can't actually panic since type alignment is always a power of two.
const { Alignment::new(align_of::<T>()).unwrap() }
/// Creates an `Alignment` from a `usize`, or returns `None` if it's
/// not a power of two.
/// Note that `0` is not a power of two, nor a valid alignment.
pub const fn new(align: usize) -> Option<Self> {
if align.is_power_of_two() {
// SAFETY: Just checked it only has one bit set
Some(unsafe { Self::new_unchecked(align) })
} else {
None
/// Creates an `Alignment` from a power-of-two `usize`.
/// # Safety
/// `align` must be a power of two.
/// Equivalently, it must be `1 << exp` for some `exp` in `0..usize::BITS`.
/// It must *not* be zero.
#[track_caller]
pub const unsafe fn new_unchecked(align: usize) -> Self {
assert_unsafe_precondition!(
check_language_ub,
"Alignment::new_unchecked requires a power of two",
(align: usize = align) => align.is_power_of_two()
);
// SAFETY: By precondition, this must be a power of two, and
// our variants encompass all possible powers of two.
unsafe { mem::transmute::<usize, Alignment>(align) }
/// Returns the alignment as a [`usize`].
pub const fn as_usize(self) -> usize {
self.0 as usize
/// Returns the alignment as a <code>[NonZero]<[usize]></code>.
pub const fn as_nonzero(self) -> NonZero<usize> {
// This transmutes directly to avoid the UbCheck in `NonZero::new_unchecked`
// since there's no way for the user to trip that check anyway -- the
// validity invariant of the type would have to have been broken earlier --
// and emitting it in an otherwise simple method is bad for compile time.
// SAFETY: All the discriminants are non-zero.
unsafe { mem::transmute::<Alignment, NonZero<usize>>(self) }
/// Returns the base-2 logarithm of the alignment.
/// This is always exact, as `self` represents a power of two.
/// assert_eq!(Alignment::of::<u8>().log2(), 0);
/// assert_eq!(Alignment::new(1024).unwrap().log2(), 10);
pub const fn log2(self) -> u32 {
self.as_nonzero().trailing_zeros()
/// Returns a bit mask that can be used to match this alignment.
/// This is equivalent to `!(self.as_usize() - 1)`.
/// #![feature(ptr_mask)]
/// use std::ptr::{Alignment, NonNull};
/// #[repr(align(1))] struct Align1(u8);
/// #[repr(align(2))] struct Align2(u16);
/// #[repr(align(4))] struct Align4(u32);
/// let one = <NonNull<Align1>>::dangling().as_ptr();
/// let two = <NonNull<Align2>>::dangling().as_ptr();
/// let four = <NonNull<Align4>>::dangling().as_ptr();
/// assert_eq!(four.mask(Alignment::of::<Align1>().mask()), four);
/// assert_eq!(four.mask(Alignment::of::<Align2>().mask()), four);
/// assert_eq!(four.mask(Alignment::of::<Align4>().mask()), four);
/// assert_ne!(one.mask(Alignment::of::<Align4>().mask()), one);
pub const fn mask(self) -> usize {
// SAFETY: The alignment is always nonzero, and therefore decrementing won't overflow.
!(unsafe { self.as_usize().unchecked_sub(1) })
// FIXME(const-hack) Remove me once `Ord::max` is usable in const
pub(crate) const fn max(a: Self, b: Self) -> Self {
if a.as_usize() > b.as_usize() { a } else { b }
impl fmt::Debug for Alignment {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{:?} (1 << {:?})", self.as_nonzero(), self.log2())
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl const TryFrom<NonZero<usize>> for Alignment {
type Error = num::TryFromIntError;
fn try_from(align: NonZero<usize>) -> Result<Alignment, Self::Error> {
align.get().try_into()
impl const TryFrom<usize> for Alignment {
fn try_from(align: usize) -> Result<Alignment, Self::Error> {
Self::new(align).ok_or(num::TryFromIntError(()))
impl const From<Alignment> for NonZero<usize> {
fn from(align: Alignment) -> NonZero<usize> {
align.as_nonzero()
impl const From<Alignment> for usize {
fn from(align: Alignment) -> usize {
align.as_usize()
impl cmp::Ord for Alignment {
fn cmp(&self, other: &Self) -> cmp::Ordering {
self.as_nonzero().get().cmp(&other.as_nonzero().get())
impl cmp::PartialOrd for Alignment {
fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
Some(self.cmp(other))
impl hash::Hash for Alignment {
fn hash<H: hash::Hasher>(&self, state: &mut H) {
self.as_nonzero().hash(state)
/// Returns [`Alignment::MIN`], which is valid for any type.
#[rustc_const_unstable(feature = "const_default", issue = "143894")]
impl const Default for Alignment {
fn default() -> Alignment {
Alignment::MIN
#[cfg(target_pointer_width = "16")]
#[cfg_attr(not(feature = "ferrocene_certified"), derive(PartialEq, Eq))]
#[derive(Copy, Clone)]
#[repr(usize)]
enum AlignmentEnum {
_Align1Shl0 = 1 << 0,
_Align1Shl1 = 1 << 1,
_Align1Shl2 = 1 << 2,
_Align1Shl3 = 1 << 3,
_Align1Shl4 = 1 << 4,
_Align1Shl5 = 1 << 5,
_Align1Shl6 = 1 << 6,
_Align1Shl7 = 1 << 7,
_Align1Shl8 = 1 << 8,
_Align1Shl9 = 1 << 9,
_Align1Shl10 = 1 << 10,
_Align1Shl11 = 1 << 11,
_Align1Shl12 = 1 << 12,
_Align1Shl13 = 1 << 13,
_Align1Shl14 = 1 << 14,
_Align1Shl15 = 1 << 15,
#[cfg(target_pointer_width = "32")]
_Align1Shl16 = 1 << 16,
_Align1Shl17 = 1 << 17,
_Align1Shl18 = 1 << 18,
_Align1Shl19 = 1 << 19,
_Align1Shl20 = 1 << 20,
_Align1Shl21 = 1 << 21,
_Align1Shl22 = 1 << 22,
_Align1Shl23 = 1 << 23,
_Align1Shl24 = 1 << 24,
_Align1Shl25 = 1 << 25,
_Align1Shl26 = 1 << 26,
_Align1Shl27 = 1 << 27,
_Align1Shl28 = 1 << 28,
_Align1Shl29 = 1 << 29,
_Align1Shl30 = 1 << 30,
_Align1Shl31 = 1 << 31,
#[cfg(target_pointer_width = "64")]
_Align1Shl32 = 1 << 32,
_Align1Shl33 = 1 << 33,
_Align1Shl34 = 1 << 34,
_Align1Shl35 = 1 << 35,
_Align1Shl36 = 1 << 36,
_Align1Shl37 = 1 << 37,
_Align1Shl38 = 1 << 38,
_Align1Shl39 = 1 << 39,
_Align1Shl40 = 1 << 40,
_Align1Shl41 = 1 << 41,
_Align1Shl42 = 1 << 42,
_Align1Shl43 = 1 << 43,
_Align1Shl44 = 1 << 44,
_Align1Shl45 = 1 << 45,
_Align1Shl46 = 1 << 46,
_Align1Shl47 = 1 << 47,
_Align1Shl48 = 1 << 48,
_Align1Shl49 = 1 << 49,
_Align1Shl50 = 1 << 50,
_Align1Shl51 = 1 << 51,
_Align1Shl52 = 1 << 52,
_Align1Shl53 = 1 << 53,
_Align1Shl54 = 1 << 54,
_Align1Shl55 = 1 << 55,
_Align1Shl56 = 1 << 56,
_Align1Shl57 = 1 << 57,
_Align1Shl58 = 1 << 58,
_Align1Shl59 = 1 << 59,
_Align1Shl60 = 1 << 60,
_Align1Shl61 = 1 << 61,
_Align1Shl62 = 1 << 62,
_Align1Shl63 = 1 << 63,