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## _mm256_castsi128_si256

# Function _mm256_castsi128_si256

1.27.0 (const: unstable) · Source

    pub fn _mm256_castsi128_si256(a: __m128i) -> __m256i

Available on x86-64 and target feature `avx` and (x86 or x86-64) only.
Expand description

Casts vector of type __m128i to type __m256i; the upper 128 bits of the result are indeterminate.

In the Intel documentation, the upper bits are declared to be “undefined”. This is not equivalent to `mem::MaybeUninit`; instead, these bits are non-deterministically set to some valid value. In practice, this is typically equivalent to `mem::zeroed`.

Intel’s documentation