bug#31138: Native json slower than json.el

[Eli Zaretskii]

> Cc: p.stephani2@gmail.com, sebastien@chapu.is, yyoncho@gmail.com,
>  31138@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Mon, 22 Apr 2019 20:05:46 +0300
> 
> > I meant make a loop that literally checks only for
> > ASCII_CHAR_P, and nothing more.
> 
> Is this (attached) what you had in mind?

Yes, but I'm slightly surprised why you loop from the end of the
string and not from the beginning.

> It's a bit faster again (naturally). At this point I don't see any 
> statistically significant performance difference from the no_validation 
> patch.

I guess that's expected when the strings in JSON are short enough.

The next question is what speedup you will see from the optimized
decoding version I just posted.  Then we could decide whether testing
for valid UTF-8 non-ASCII text is justified.