Re: emacs takes exhorbitantly long to read long, one-line files.

[Dmitry Antipov]

On 05/20/2013 07:59 PM, Eli Zaretskii wrote:

> But it won't succeed to make Emacs usable with such files.  E.g., try
> this:
>
>    M->
>    C-p
>
> and count the seconds it takes to perform the second command.
>
> What Emacs does behind the scenes is go to the beginning of the
> previous _physical_ line (which is quite fast in this case), and the
> go all the way down the humongously long line, one character at a
> time, until it finds the place to put the cursor.  Unless we make
> radical changes in this algorithm, how can anyone expect reasonable
> performance from this?

This is pretty ugly because both previous-line and next-line uses
Fforward_line, which uses scan_newline, which _does not_ use newline
cache :-(. Due to the above, I believe that the use of scan_newline
should be limited to *Messages* buffer tricks, and other users should
be converted to use find_newline instead.

Dmitry