So... SIMD intrinsics? You also need to take into account that a huge chunk of the work in SIMD is the need to rearrange your data to be more amenable to the C

So... SIMD intrinsics? You also need to take into account that a huge chunk of the work in SIMD is the need to rearrange your data to be more amenable to the CPU. C++ compilers are very restricted in what they can do for you there.