1 Apr
2022
1 Apr
'22
7:15 p.m.
On Apr 1, 2022, at 8:59 AM, Douglas McIlroy
<douglas.mcilroy(a)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