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swizzle_dyn: 64 byte swizzle_dyn for AVX2 #480

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swizzle_dyn: 64 byte swizzle_dyn for AVX2 #480

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c045fbe
swizzle_dyn: 64 byte swizzle_dyn for AVX2
87flowers Sep 8, 2025
3bb811b
Add safety comment for mem::transmute
87flowers Sep 11, 2025
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2 changes: 2 additions & 0 deletions crates/core_simd/src/swizzle_dyn.rs
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Expand Up @@ -220,6 +220,8 @@ unsafe fn avx2_pshufb512(bytes: Simd<u8, 64>, idxs: Simd<u8, 64>) -> Simd<u8, 64

let z0 = half_swizzler(bytes0, bytes1, idxs0);
let z1 = half_swizzler(bytes0, bytes1, idxs1);

// SAFETY: Concatenation of two 32-element vectors to one 64-element vector
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this says what your doing, what it should say is why it's safe to use transmute like this. e.g.:
[Simd<u8, 32>; 2] and Simd<u8, 64> both have the same size (64) and no padding bytes, so transmuting is safe

let z = mem::transmute::<[Simd<u8, 32>; 2], Simd<u8, 64>>([z0.into(), z1.into()]);

idxs.simd_lt(high).select(z, Simd::splat(0u8))
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