bug#20154: 25.0.50; json-encode-string is too slow for large strings

[Eli Zaretskii]

> Date: Fri, 20 Mar 2015 18:52:26 +0200
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 20154@debbugs.gnu.org
> 
> On 03/20/2015 06:44 PM, Eli Zaretskii wrote:
> 
> > To see how much of the time is taken by json-encode-char, replace it
> > with something trivial, like 1+, and see what speedup you get.
> 
> Yep. Replacing the second definition with
> 
> (defun json-encode-big-string (str)
>    (with-temp-buffer
>      (insert str)
>      (goto-char (point-min))
>      (while (re-search-forward "[\"\\/\b\f\b\r\t]\\|[^ -~]" nil t)
>        (replace-match "z" t t))
>      (format "\"%s\"" (buffer-string))))
> 
> still makes it take ~100ms on the example string (as opposed to 2ms in 
> the optimized Python implementation).

That's not what I see here.  I cannot get the time above 1 sec even
with a 1000 time longer input string, if I replace json-encode-char
with 1+.

So I think your 100ms is the constant overhead of some kind.