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Allow memcmp for more array comparisons

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This way comparing `[NonZeroU8; 8]` is just as fast as comparing `[u8; 8]`.
This commit is contained in:
Scott McMurray 2021-12-10 17:30:39 -08:00
parent f0448f44bc
commit 24affba02e
1 changed files with 49 additions and 5 deletions
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54
library/core/src/array/equality.rs
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@ -1,3 +1,6 @@
use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize};
use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[B; N]> for [A; N]
where
@ -124,7 +127,7 @@ impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
}
}
impl<T: PartialEq<U> + IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T {
impl<T: IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T {
fn spec_eq(a: &[T; N], b: &[U; N]) -> bool {
// SAFETY: This is why `IsRawEqComparable` is an `unsafe trait`.
unsafe {
@ -145,11 +148,52 @@ impl<T: PartialEq<U> + IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N
/// - `Self` and `U` have the same layout.
/// - `Self: PartialEq<U>` is byte-wise (this means no floats, among other things)
#[rustc_specialization_trait]
unsafe trait IsRawEqComparable<U> {}
unsafe trait IsRawEqComparable<U>: PartialEq<U> {}
macro_rules! is_raw_comparable {
($($t:ty),+) => {$(
macro_rules! is_raw_eq_comparable {
($($t:ty),+ $(,)?) => {$(
unsafe impl IsRawEqComparable<$t> for $t {}
)+};
}
is_raw_comparable!(bool, char, u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
// SAFETY: All the ordinary integer types allow all bit patterns as distinct values
is_raw_eq_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
// SAFETY: bool and char have *niches*, but no *padding*, so this is sound
is_raw_eq_comparable!(bool, char);
// SAFETY: Similarly, the non-zero types have a niche, but no undef,
// and they compare like their underlying numeric type.
is_raw_eq_comparable!(
NonZeroU8,
NonZeroU16,
NonZeroU32,
NonZeroU64,
NonZeroU128,
NonZeroUsize,
NonZeroI8,
NonZeroI16,
NonZeroI32,
NonZeroI64,
NonZeroI128,
NonZeroIsize,
);
// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus
// are also safe to equality-compare bitwise inside an `Option`.
// The way `PartialOrd` is defined for `Option` means that this wouldn't work
// for `<` or `>` on the signed types, but since we only do `==` it's fine.
is_raw_eq_comparable!(
Option<NonZeroU8>,
Option<NonZeroU16>,
Option<NonZeroU32>,
Option<NonZeroU64>,
Option<NonZeroU128>,
Option<NonZeroUsize>,
Option<NonZeroI8>,
Option<NonZeroI16>,
Option<NonZeroI32>,
Option<NonZeroI64>,
Option<NonZeroI128>,
Option<NonZeroIsize>,
);