The recent discussion about Research choosing BSD's paging over Reiser-London's brought to mind a stunning program by Reiser that Research did adopt. A critical primitive in the Blit terminal was bitblt (block transfer of a rectangular area). It was used ubiquitously, for example to refresh data when window-stacking changed, to move data within a window, or to pop up a menu.. The display memory was word-oriented, so bitblt was fraught with niggling details about bit alignment and overlap of source and destination. A general bitblt subroutine was a rats' nest of conditionals--grossly inefficient for important special cases like scrolling. Bitblt got refined (i.e. elaborated) several times before Reiser did away with it entirely. Instead he wrote a just-in-time generator of optimal code. Thousands of distinct variants, which varied in size from 16 to 72 bytes, could be produced by the same 400 lines of assembler code. Doug