Function _mm256_mask_popcnt_epi64 

pub fn _mm256_mask_popcnt_epi64(
    src: __m256i,
    k: __mmask8,
    a: __m256i,
) -> __m256i

Available on x86 and target feature avx512vpopcntdq and target feature avx512vl only.

For each packed 64-bit integer maps the value to the number of logical 1 bits.

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

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