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? 狢 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".