# Function core::arch::x86::_mm256_maskz_gf2p8affineinv_epi64_epi8

source · ```
pub unsafe fn _mm256_maskz_gf2p8affineinv_epi64_epi8(
k: __mmask32,
x: __m256i,
a: __m256i,
const B: i32
) -> __m256i
```

🔬This is a nightly-only experimental API. (

`stdsimd`

#48556)Available on

**(x86 or x86-64) and target feature**only.`gfni,avx512bw,avx512vl`

and x86## Expand description

Performs an affine transformation on the inverted packed bytes in x. That is computes a*inv(x)+b over the Galois Field 2^8 for each packed byte with a being a 8x8 bit matrix and b being a constant 8-bit immediate value. The inverse of a byte is defined with respect to the reduction polynomial x^8+x^4+x^3+x+1. The inverse of 0 is 0. Each pack of 8 bytes in x is paired with the 64-bit word at the same position in a.

Uses the writemask in k - elements are zeroed in the result if the corresponding mask bit is not set. Otherwise the computation result is written into the result.