`_mm256_cmpeq_epi32` produces `0xFFFFFFFF`, the article suggests shifting to produce a `1` and then add.

Instead you can interpret `0xFFFFFFFF` as negative one, and subtract. That saves a shift. So you're counting -1, -2, -3, etc.

Flip the sign when accumulating.

In general I think this is a pretty common counting trick. I don't think those shift operations even exists for epi8, so there you really need to use it to avoid reduction to a narrow register. Also, in the case of epi8 you need to deal with overflow, so the pattern is like this in pseudo code:

    v[1:32] = 0
    total = 0
    for j = 0 to N / 256
        for i = 0 to 255
            v[1:32] -= cmpeq(..., ...)
        end
        total -= sum(v)
    end