title: Usage of _mm_shuffle_epi8 intrinsic
body: <p>Can someone please explain the <code>_mm_shuffle_epi8</code> SSSE3 intrinsic? 
  I know it shuffles 16 8-bit integers in an <code>__m128i</code> but not sure how I could use this. </p>
  
  <p>I basically want to use <code>_mm_shuffle_epi8</code> to modify the function below to get better performance.</p>
  
  <pre><code>while(not done)
      dest[i+0] = (src+j).a;
      dest[i+1] = (src+j).b;
      dest[i+2] = (src+j).c;
      dest[i+3] = (src+j+1).a;
      dest[i+4] = (src+j+1).b;
      dest[i+5] = (src+j+1).c;
      i+=6;
      j+=2;
  </code></pre>