title: Shift a __m128i of n bits
body: <p>I have a <code>__m128i</code> variable and I need to shift its 128 bit value of n bits, i.e. like <code>_mm_srli_si128</code> and <code>_mm_slli_si128</code> work, but on bits instead of bytes. What is the most efficient way of doing this?</p>