Re: [jed-users] del_region() tremendously slow

["John E. Davis" <jed@xxxxxxxxxxx>]

Morten Bo Johansen <mbj@xxxxxxxxx> wrote:
> I just happened to stumble into this rather abnormal use case: mark and
> delete about two million lines in a file. With del_region(), it takes about
> 8 seconds to do so on my oldish computer. With the competition (Emacs), it
> happens in the blink of an eye. Why is del_region() so slow?

I rewrote the delete_region function to improve its peformance.
Testing shows that it is now about 150 times faster than before.  The
updated version is pre0.99.20-188, which you can find at
<http://snapshots.jedsoft.org/snapshots/>.  (I will update the github
repository next week with the recent updates; until then use the
tarfile or <git://git.jedsoft.org/git/jed.git>)

Emacs and jed have very different representations of a buffer.  Jed
represents a buffer as a linked list of lines, whereas Emacs uses a
simple character buffer with a gap where insertions/deletions take
place.  Each has its advantages and disadvantages.  Deleting a region
using the buffer gap approach is a trivial operation that simply
involves updating the size of the gap (assuming the gap does not have
to be moved).

Thanks for reporting this.
--John

>
> The following function does the job in 1 sec flat - still slower than
> Emacs, but 8 times faster than del_region():
>
>   define delete_region()
>  {
>     variable reg_end;
>
>     ifnot (is_visible_mark)
>       return flush("no region is marked");
>
>     check_region(1);
>     reg_end = what_line;
>     exchange_point_and_mark();
>
>     loop (reg_end - what_line())
>       delete_line();
>
>     pop_spot(); pop_mark_0();
>  }
>
> If this function doesn't deviate from the intrinsic function in its workings
> or has some other shortcomings unbeknownst to me, why not just make this a
> library function in site.sl and call it del_region to replace the very slow
> intrinsic?
>
> I know it is an abnormal use case, but still ...
>
> Regards,
> Morten
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