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WIP: Add sized_str crate #6446

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WIP: Add sized_str crate #6446

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a8b2beb
Add sized_str crate
rtfeldman Jan 27, 2024
1113bd9
Try out copy_lane! macro
rtfeldman Jan 28, 2024
9f5f78b
Optimize sized_str using godbolt.org
rtfeldman Jan 28, 2024
1261a47
Add Str4Chunks::as_slice
rtfeldman Jan 28, 2024
9714eb0
Update some docs
rtfeldman Jan 28, 2024
9b680fb
Rename NonEmptyStr4 to just Str4
rtfeldman Jan 28, 2024
b1eedbe
Add Str8
rtfeldman Jan 28, 2024
3d3845a
Avoid a memcpy when creating Str4/Str8
rtfeldman Jan 28, 2024
72e6c70
Clippy
rtfeldman Jan 28, 2024
e261836
Make Str4::first_index_in accept `&[Str4]`
rtfeldman Jan 29, 2024
541e1fd
Make sized_str be no_std in release builds
rtfeldman Jan 31, 2024
5ad6259
wip garbage_lanes
rtfeldman Jan 31, 2024
ed6b563
Fix implementation
rtfeldman Feb 1, 2024
919d53f
Add allow(unused) to silence test helper warnings
rtfeldman Feb 2, 2024
d2e0a42
Add str_finder
rtfeldman Feb 2, 2024
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Add Str4Chunks::as_slice
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@rtfeldman
rtfeldman committed Jan 28, 2024
commit 1261a4792ab8ae254509e6cef4b2b3a53e4e4f5b
22 changes: 16 additions & 6 deletions crates/sized_str/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,24 7,34 @@ use std::num::{NonZeroU32, NonZeroU8};
pub struct NonEmptyStr4(NonZeroU32);

#[repr(align(16))]
pub struct Str4Chunk([NonZeroU32; 4]);
pub struct Str4Chunk([NonZeroU32; Str4Chunks::NUM_LANES]);

pub struct Str4Chunks<'a>(&'a [Str4Chunk]);

impl<'a> Str4Chunks<'a> {
const NUM_LANES: usize = 4;
const ALIGN: usize = Self::NUM_LANES * std::mem::align_of::<NonEmptyStr4>();

/// Safety: The given slice must:
/// - have a nonzero length that's a multiple of 4
/// - point to a memory address that's disible by 16
pub unsafe fn new_unchecked(slice: &'a [NonEmptyStr4]) -> Self {
const NUM_LANES: usize = 4;
const ALIGN: usize = NUM_LANES * std::mem::align_of::<NonEmptyStr4>();

debug_assert!(!slice.is_empty());
debug_assert_eq!(slice.len() % NUM_LANES, 0);
debug_assert_eq!(0, ((slice as *const _) as *const u32) as usize % ALIGN);
debug_assert_eq!(slice.len() % Self::NUM_LANES, 0);
debug_assert_eq!(
0,
((slice as *const _) as *const u32) as usize % Self::ALIGN
);

std::mem::transmute(slice)
}

pub fn as_slice(&self) -> &[NonEmptyStr4] {
// Internally, we have chunks of 4; adjust the returned slice's length accordingly.
unsafe {
std::slice::from_raw_parts(self.0.as_ptr().cast(), self.0.len() * Self::NUM_LANES)
}
}
}

impl NonEmptyStr4 {
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