Calculating "triple" dot products

General Usage Performance
2

Have you already tried some approach that we can compare to?

A straightforward implementation:

function dot3(x, y, z)
  s = zero(promote_type(eltype(x), eltype(y), eltype(z)))
  @simd for i in eachindex(x, y, z)
    s += x[i] * y[i] * z[i]
  end
  return s
end

I am getting

julia> x = rand(1000); y = rand(1000); z = rand(1000);

julia> @btime dot3($x, $y, $z);
  118.453 ns (0 allocations: 0 bytes)
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