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Optimize swizzle_dyn on AVX-512 VBMI #545

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Merged
programmerjake merged 1 commit into from
Jul 30, 2026
Merged

Optimize swizzle_dyn on AVX-512 VBMI #545

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22 changes: 10 additions & 12 deletions crates/core_simd/src/swizzle_dyn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,13 +73,12 @@ impl<const N: usize> Simd<u8, N> {
16 => transize(x86::_mm_shuffle_epi8, self, zeroing_idxs(idxs)),
#[cfg(all(target_feature = "avx512vl", target_feature = "avx512vbmi"))]
32 => {
// Unlike vpshufb, vpermb doesn't zero out values in the result based on the index high bit
let swizzler = |bytes, idxs| {
let mask = x86::_mm256_cmp_epu8_mask::<{ x86::_MM_CMPINT_LT }>(
idxs,
Simd::<u8, 32>::splat(N as u8).into(),
);
x86::_mm256_maskz_permutexvar_epi8(mask, idxs, bytes)
// Clamp out-of-range indices to the first byte of a
// second, all-zero table.
let idxs =
x86::_mm256_min_epu8(idxs, Simd::<u8, 32>::splat(N as u8).into());
x86::_mm256_permutex2var_epi8(bytes, idxs, x86::_mm256_setzero_si256())
};
transize(swizzler, self, idxs)
}
Expand All @@ -90,13 +89,12 @@ impl<const N: usize> Simd<u8, N> {
// Notable absence: avx512bw pshufb shuffle
#[cfg(all(target_feature = "avx512vl", target_feature = "avx512vbmi"))]
64 => {
// Unlike vpshufb, vpermb doesn't zero out values in the result based on the index high bit
let swizzler = |bytes, idxs| {
let mask = x86::_mm512_cmp_epu8_mask::<{ x86::_MM_CMPINT_LT }>(
idxs,
Simd::<u8, 64>::splat(N as u8).into(),
);
x86::_mm512_maskz_permutexvar_epi8(mask, idxs, bytes)
// Clamp out-of-range indices to the first byte of a
// second, all-zero table.
let idxs =
x86::_mm512_min_epu8(idxs, Simd::<u8, 64>::splat(N as u8).into());
x86::_mm512_permutex2var_epi8(bytes, idxs, x86::_mm512_setzero_si512())
};
transize(swizzler, self, idxs)
}
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