title: SSE instruction sanity check
body: <p>The code below has me slightly perplexed:</p>
  
  <pre><code>
  function(__m128 foo)
  {
    __m128 bar = _mm_shuffle_ps(foo, foo, _MM_SHUFFLE(2,2,2,2))
  }
  </code></pre>
  
  <p>Is it just taking the 2nd word of foo and pasting it 4 times into bar or does it do something else as well?</p>