Re: [TUHS] A Reiser tour de force

[David Barto <david@kdbarto.org>]

> On Apr 1, 2022, at 8:59 AM, Douglas McIlroy <douglas.mcilroy@dartmouth.edu> wrote:
> 
> 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

Does this exist for the rest of us to study?

	David