On Tue, Jan 15, 2013 at 3:26 AM, Stefan Monnier <monnier@iro.umontreal.ca>wrote:

> You mean that json.elc is only 5 to 25 times slower than
> a C implementation?  I actually expected significantly worse.
>

Both share quite a few code paths actually, for example number-to-string
conversion (and vice versa) and multibyte handling. I wrote the code a
little
while ago but IIRC data conversion between Emacs-land and native land
accounts
for a non-negligible share of the runtime, and of course the same goes for
building Emacs data structures from parsed data. (It doesn't help that with
JSON, you don't know how big an array or map will be until you're finished
parsing it.)

Also, although performance is my primary objective, I didn't pick the C
library
on that aspect alone. For example, libjson bills itself as a "JSON reader
and
writer which is super-effiecient [sic] and usually runs circles around other
JSON libraries." But it doesn't support streaming and thus would add a
significant memory overhead for large documents, and also it's not nearly as
portable.

I did spend some time making sure that the interface performs well and
there are
no obvious low-hanging-fruit-type optimizations left, but any help with
making
it even faster is welcome! I think that an order of magnitude is a good
start
though, it certainly takes my other app from "painfully slow" to "perfectly
usable".