Concerning r6385, things that are apparent from the svn log: hresdiff should equal hres now, no need to shift; pixdiff should always be 1 now; replace ^1 by ^WORD_ADDR_XOR or something; it's better to eliminate Lsw, hresdiff and pixdiff; no more need for trickery like
leftuppix = ((leftuppix ^ 2) + 2) ^ 2;
in case you still have it, just
leftuppix++;
Cool, I'll submit an update to that effect shortly, please let me know if I've done it correctly.