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Timing bug in C-V, M-V
- To: (BUG ZWEI) at MIT-AI
- Subject: Timing bug in C-V, M-V
- From: GLS at MIT-AI (Guy L. Steele, Jr.)
- Date: Mon ,7 Jul 80 15:31:00 EDT
- Cc: GLS at MIT-AI
In the version of ZWEI on system 29.95 NWS, with microcode 669, on LISP Machine Eight:
The C-V (Next Screen) and M-V (Previous Screen) commands have a severe bug.
If you type them ahead, then they perform relative to the last screen display
rather than to what the screen would be after the preceding command.
Example: I search for something a long way away, then type C-V before
it has been found (I know that what I want will be on the next screenfull).
The result is that when the search terminates, I see the screenfull after
the point I started the search from, not after the found thing. This also
happens if you substitute M-< for searching--it's not a search bug.
I would surmise that ZWEI is checking for typeahead for immediate eecution
before updating its idea of what ought to be on the screen. This idea
of where the screen-window into the buffer is within the buffer should be
updated even though none of it has a chance to actually be put up on the
screen. That is, ZWEI needs two ideas of what is going on--what IS on
the screen, and what OUGHT to be (but is not necessarily)--and the second
should be updated with higher priority than processing typeahead if C-V
is to work properly without timing screws like this one.