pub unsafe fn _mm_mask_popcnt_epi64(
    src: __m128i,
    k: __mmask8,
    a: __m128i
) -> __m128i
🔬 This is a nightly-only experimental API. (stdsimd #48556)
Available on x86 and target feature avx512vpopcntdq,avx512vl only.
Expand description

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.

Intel’s documentation