bug#31138: Native json slower than json.el

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Cc: sebastien@chapu.is, yyoncho@gmail.com, 31138@debbugs.gnu.org
> Date: Wed, 24 Apr 2019 18:55:45 +0300
> 
> On 23.04.2019 17:58, Eli Zaretskii wrote:
> 
> >> Doing that for buffer text as well might be helpful.
> > 
> > In what use cases would this be helpful?  Most cases of decoding text
> > in a buffer happen when we read text from files, where we already have
> > an internal optimization for plain ASCII files.
> 
> HTTP request response buffers? They can be as large as several 
> megabytes, as we have established in this discussion.

Please point me to examples of this, I don't think I understand what
you have in mind.

> > We could perhaps try
> > a similar optimization for UTF-8 instead of just ASCII.
> 
> I think so.

Turns out we already do, I just missed that.

> But it did increase the performance of json-serialize, by more than 2x, 
> on the same test data I've been using.
> 
> Like 3.8s to 1.6s for 10 iterations.
> 
> Can we do something like that? Removing conversion altogether is 
> probably not an option, but even using Fstring_as_unibyte instead lead 
> to a significant improvement (2,43s with this approach).

What does libjansson do if it receives strings with bytes it cannot
interpret?  Like raw bytes or UTF-8 sequences whose length is more
than 4 bytes?