Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

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

Open
wants to merge 6 commits into
base: master
Choose a base branch
from
Open

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

Changes from 2 commits
Commits
Show all changes
6 commits
Select commit Hold shift + click to select a range
6c926f4
Document alternatives to Mask<T, LANES> that guarantee layout.
reinerp Mar 8, 2023
9805f7c
Format code
reinerp Mar 8, 2023
b44a0de
Spelling
reinerp Mar 9, 2023
c4e2ae5
Update wording
reinerp Mar 13, 2023
84bc197
s/layout/size. Mention BitMaskArray.
reinerp Mar 13, 2023
ecb9703
Wording
reinerp Mar 13, 2023
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 4 additions & 0 deletions crates/core_simd/src/masks.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,10 @@ 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 layout guaranteed equivalent to `[T; LANES]`, use
/// `SIMD<T, LANES>`. For a type with layout guaranteed to use 1 bit per
reinerp marked this conversation as resolved.
Show resolved Hide resolved
/// lane (padded up to full bytes), use `LANES::BitMask`.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

So, the exact number of bytes is an implementation detail (we've used u64 before and we might choose it again... basically we want to retain the freedom to use an integer of a reasonable size, OR to use a byte array, depending on what strikes the best ergonomics/codegen balance). Right now, this seems like it might suggest it uses exactly the next byte in size. I am not sure what would be most clear to express our desired reservation while providing you the minimum of guarantees you want (or if you even consider that acceptable).

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The type is actually ToBitMask::BitMask: https://doc.rust-lang.org/std/simd/trait.ToBitMask.html#associatedtype.BitMask. It's not padded up to the next byte, but the next integer.

#[repr(transparent)]
pub struct Mask<T, const LANES: usize>(mask_impl::Mask<T, LANES>)
where
Expand Down