bug#6671: moving point and scroll-conservatively

[Chong Yidong]

Eli Zaretskii <eliz@gnu.org> writes:

>> That should make the 100619/100620 changes unnecessary.
>
> Please don't revert these changes.  They took a lot of effort to
> arrive at, and generally DTRT in a way that is easy to understand and
> maintain.
>
> The problem with performance for large moves of point is IMO
> straightforward to fix: when point is "far away" (which could be set
> back to those proverbial 10 screen lines), then, instead of moving one
> line at a time, move to point in one go, and then compute the window
> start so that point is at the proper place relative to window start.

These change you propose would also necessitate reverting 100619/100620.
Anytime the iterator is forced to traverse thousands (or in this case
tens of thousands) of lines, that's clearly the wrong thing.