bug#31138: Native json slower than json.el

[Dmitry Gutov]

On 23.04.2019 15:15, Eli Zaretskii wrote:
> I thought about this.  It could make sense to have a UTF-8 specific
> function to encode and decode strings.  With encodings other than
> UTF-8 it becomes trickier, and probably likewise with buffer text,
> where we need to take the gap into account.

Doing that for buffer text as well might be helpful. Other encodings are 
much less of a priority, I would say.

> What applications do we have where en/decoding strings has critical
> effect on performance?

It wouldn't be critical most of the time, but even a few % performance 
improvement across the board, basically for free, might be welcome.

So that's why I mentioned decode-coding-string (though 
code_convert_string would be a better choice; or decode_coding_object?), 
as opposed to creating a new specialized function.

What I can understand from our testing, this kind of change improves 
performance for all kinds of strings when the source encoding is 
utf_8_unix. Even for large ones (despite you expecting otherwise). The 
only kinds of input where this should result in a (likely minor) 
slowdown would be ones where the contents do not correspond to the 
declared encoding.

Again, the patch, or several, shouldn't be particularly hard to write, 
and we can try them out with different scenarios.