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Document alternatives to Mask<T, LANES> that guarantee layout. Fixes #332 #333

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5 changes: 5 additions & 0 deletions crates/core_simd/src/masks.rs
Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,11 @@ impl_element! { isize }
/// The layout of this type is unspecified, and may change between platforms
/// and/or Rust versions, and code should not assume that it is equivalent to
/// `[T; LANES]`.
///
/// For a type with size guaranteed equal to `[T; LANES]`, use
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Suggested change
/// For a type with size guaranteed equal to `[T; LANES]`, use
/// For a type with size guaranteed equal-or-greater-than `[T; LANES]`, use

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Suggested change
/// For a type with size guaranteed equal to `[T; LANES]`, use
/// For a type equivalent to `[T; LANES]` (with possible trailing padding for alignment purposes), use

maybe equivalent is too strong? ideas?

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/// For a type with size guaranteed equal-or-greater-than `[T; LANES]`, use

imho that loses most meaning, e.g. [u8; 5000] fits but is unlikely to be desired.

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"equivalent" is indeed too strong.

/// `Simd<T, LANES>`. For a type with size guaranteed to use 1 bit per
/// lane (padded up to the next integer type or), use [`ToBitMask::BitMask`]
/// or (with crate feature `generic_const_exprs`) `ToBitMaskArray::BitMaskArray`.
#[repr(transparent)]
pub struct Mask<T, const LANES: usize>(mask_impl::Mask<T, LANES>)
where
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