bug#31138: Native json slower than json.el

[Dmitry Gutov]

On 22.04.2019 10:16, Eli Zaretskii wrote:
> Please don't forget that json-parse-string first_encodes_  the input
> string in UTF-8, then passes it to libjansson, then_decodes_  each
> string element it receives back.  So we do some non-trivial processing
> besides make_specified_string, and removing decoding only saves part
> of that.

That actually means that speeding up code_convert_string might 
*potentially* (e.g. if it's infinitely fast) yield more than 50% 
performance improvement.