Port to non-SSE

In my standard 8 thread test of section 44444554, the SSE speedups are

  overall: 15.4334 s / 10.4560 s = 1.476
  compute only: 50.7098 s / 25.6764 s = 1.975

1.975 is a pretty good speedup for 128 bit SSE over 64 bit ops.