From: "H. Peter Anvin" <hpa@zytor.com>

As expected, when it hit mainline I started getting real bug reports... 
the attached patch does the following:

- Fixes a few x86-64 specific bugs;

- Removes MMX and SSE-1 from x86-64 (if we have x86-64 we have SSE-2);

- Slightly astracts the integer code to make it easier to add
  architecture-specific optimizations later (e.g.  IA64 once gcc gets
  better IA64 intrinsics support);

- Resurrects the user-space testbench, and makes it not output the known
  false positive of the D+Q case (D+Q is equivalent to a RAID-5 recovery,
  so I didn't implement it in the user-space testbench.)