Speed Freak

The code size would increase but using a vector table such as follows would allow you to unroll your (remainder) loops . With normal code, four states would be required but for MMX all eight would be best.

 mov      eax,ecx           ; Get Width         and      eax,0000111b         jmp      $SetTbl[eax*4]     ; At bottom of assembly source file insert the vector table so ; it doesn't interfere with your memory caches.             Align 16 $SetTbl:dd       $SetQ           ; (n mod 8) = 0         dd       $Set1           ; (n mod 4) = 1         dd       $Set2           ; (n mod 4) = 2         dd       $Set3           ; (n mod 4) = 3         dd       $SetD           ; (n mod 4) = 0         dd       $Set1           ; (n mod 4) = 1         dd       $Set2           ; (n mod 4) = 2         dd       $Set3           ; (n mod 4) = 3