Switch to SSE2 for the hottest loop.
Break out the second hottest loop too. We're not enabling SSE, though; I'm not seeing any improvements from that. I suspect the low number of iterations in that loop outweighs the advantages of SSEing it.
MSVC compat.
Match the type declaration in GCC.
Increase size of ignored buffer space at the end. 16 bytes at the time means 16 bytes of buffer space.
Nit.
Even if SSE doesn't gain us anything, going 32bit is a clear win.