Thanks much for this performance improvement.  I puzzled for a while to 
figure out what was going on, and was confused by that tricky macro 
expansion.  Nowadays functions are typically not significantly slower 
than macros, so unless there's a major performance difference I'd prefer 
to use functions.  I installed the performance improvement patch and 
followed up with the attached patch, which uses C functions instead of 
macros and which coalesces some of the near-duplicate code.  The 
followup patch also includes some comments to try to explain the new 
functions.