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

[Dmitry Gutov <dgutov@yandex.ru>]

On 03/20/2015 04:34 PM, Eli Zaretskii wrote:

> I suggest to start with a detailed profile of the current
> implementation,

Any suggestions there? By the way, I've included the example, so you can 
also profile it yourself.

Here's the output of the built-in profiler, after using the current 
implementation:

CPU:

- command-execute                                   1147  79%
  - call-interactively                               1147  79%
   - funcall-interactively                           1082  74%
    - eval-last-sexp                                 1035  71%
     - elisp--eval-last-sexp                         1035  71%
      - eval                                         1035  71%
       - length                                      1035  71%
        - json-encode-string                         1035  71%
         - mapconcat                                  874  60%
            json-encode-char                          571  39%
    + execute-extended-command                         40   2%
    + previous-line                                     7   0%
   + byte-code                                         65   4%
- ...                                                298  20%
    Automatic GC                                      298  20%

Memory:

- command-execute                            255,362,537  99%
  - call-interactively                        255,362,537  99%
   - funcall-interactively                    255,349,159  99%
    - eval-last-sexp                          248,605,484  97%
     - elisp--eval-last-sexp                  248,605,484  97%
      - eval                                  217,011,432  84%
       - length                               217,011,432  84%
        - json-encode-string                  217,011,432  84%
         - mapconcat                           93,689,099  36%
            json-encode-char                   81,784,197  32%
           format                                     814   0%
        elisp--eval-last-sexp-print-value          11,954   0%
      + elisp--preceding-sexp                       2,048   0%
    + execute-extended-command                  6,743,643   2%
    + previous-line                                    32   0%
   + byte-code                                     13,378   0%
+ xselect-convert-to-string                          176   0%
   ...                                                  0   0%