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refactor: Add
AlignedBytes
types (#19308)
Co-authored-by: Orson Peters <[email protected]>
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,112 @@ | ||
use bytemuck::{Pod, Zeroable}; | ||
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use super::{days_ms, f16, i256, months_days_ns}; | ||
use crate::array::View; | ||
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/// Define that a type has the same byte alignment and size as `B`. | ||
/// | ||
/// # Safety | ||
/// | ||
/// This is safe to implement if both types have the same alignment and size. | ||
pub unsafe trait AlignedBytesCast<B: AlignedBytes>: Pod {} | ||
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/// A representation of a type as raw bytes with the same alignment as the original type. | ||
pub trait AlignedBytes: Pod + Zeroable + Copy + Default + Eq { | ||
const ALIGNMENT: usize; | ||
const SIZE: usize; | ||
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type Unaligned: AsRef<[u8]> | ||
+ AsMut<[u8]> | ||
+ std::ops::Index<usize, Output = u8> | ||
+ std::ops::IndexMut<usize, Output = u8> | ||
+ for<'a> TryFrom<&'a [u8]> | ||
+ std::fmt::Debug | ||
+ Default | ||
+ IntoIterator<Item = u8> | ||
+ Pod; | ||
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fn to_unaligned(&self) -> Self::Unaligned; | ||
fn from_unaligned(unaligned: Self::Unaligned) -> Self; | ||
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/// Safely cast a mutable reference to a [`Vec`] of `T` to a mutable reference of `Self`. | ||
fn cast_vec_ref_mut<T: AlignedBytesCast<Self>>(vec: &mut Vec<T>) -> &mut Vec<Self> { | ||
if cfg!(debug_assertions) { | ||
assert_eq!(size_of::<T>(), size_of::<Self>()); | ||
assert_eq!(align_of::<T>(), align_of::<Self>()); | ||
} | ||
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// SAFETY: SameBytes guarantees that T: | ||
// 1. has the same size | ||
// 2. has the same alignment | ||
// 3. is Pod (therefore has no life-time issues) | ||
unsafe { std::mem::transmute(vec) } | ||
} | ||
} | ||
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macro_rules! impl_aligned_bytes { | ||
( | ||
$(($name:ident, $size:literal, $alignment:literal, [$($eq_type:ty),*]),)+ | ||
) => { | ||
$( | ||
/// Bytes with a size and alignment. | ||
/// | ||
/// This is used to reduce the monomorphizations for routines that solely rely on the size | ||
/// and alignment of types. | ||
#[derive(Debug, Copy, Clone, PartialEq, Eq, Default, Pod, Zeroable)] | ||
#[repr(C, align($alignment))] | ||
pub struct $name([u8; $size]); | ||
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impl AlignedBytes for $name { | ||
const ALIGNMENT: usize = $alignment; | ||
const SIZE: usize = $size; | ||
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type Unaligned = [u8; $size]; | ||
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#[inline(always)] | ||
fn to_unaligned(&self) -> Self::Unaligned { | ||
self.0 | ||
} | ||
#[inline(always)] | ||
fn from_unaligned(unaligned: Self::Unaligned) -> Self { | ||
Self(unaligned) | ||
} | ||
} | ||
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impl AsRef<[u8; $size]> for $name { | ||
#[inline(always)] | ||
fn as_ref(&self) -> &[u8; $size] { | ||
&self.0 | ||
} | ||
} | ||
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$( | ||
impl From<$eq_type> for $name { | ||
#[inline(always)] | ||
fn from(value: $eq_type) -> Self { | ||
bytemuck::must_cast(value) | ||
} | ||
} | ||
impl From<$name> for $eq_type { | ||
#[inline(always)] | ||
fn from(value: $name) -> Self { | ||
bytemuck::must_cast(value) | ||
} | ||
} | ||
unsafe impl AlignedBytesCast<$name> for $eq_type {} | ||
)* | ||
)+ | ||
} | ||
} | ||
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impl_aligned_bytes! { | ||
(Bytes1Alignment1, 1, 1, [u8, i8]), | ||
(Bytes2Alignment2, 2, 2, [u16, i16, f16]), | ||
(Bytes4Alignment4, 4, 4, [u32, i32, f32]), | ||
(Bytes8Alignment8, 8, 8, [u64, i64, f64]), | ||
(Bytes8Alignment4, 8, 4, [days_ms]), | ||
(Bytes12Alignment4, 12, 4, [[u32; 3]]), | ||
(Bytes16Alignment4, 16, 4, [View]), | ||
(Bytes16Alignment8, 16, 8, [months_days_ns]), | ||
(Bytes16Alignment16, 16, 16, [u128, i128]), | ||
(Bytes32Alignment16, 32, 16, [i256]), | ||
} |
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