Re: string-for-each vs. for-each+string->list performance

[Aleix Conchillo Flaqué]

On Sat, Jun 6, 2020 at 11:27 PM Aleix Conchillo Flaqué <aconchillo@gmail.com>
wrote:

> Hi,
>
> in the latest guile-json, 4.1.0. I changed some code to use
> for-each+string->list. The performance seemed nice and I released it.
>
> Christopher Lam pointed out that I could have used string-for-each
> instead. I made the change but the performance degraded a lot:
>
> string-for-each:
>
> scheme@(json parser)> ,t (->bool (scm->json-string json))
> $19 = #t
> ;; 17.909537s real time, 18.063382s run time.  0.207281s spent in GC.
>
> vs
>
> for-each + string->list:
>
> scheme@(json parser)> ,t (->bool (scm->json-string json))
> $20 = #t
> ;; 2.998381s real time, 3.319349s run time.  0.471969s spent in GC.
>
> string-for-each is implemented in scheme here, if Im not wrong:
>
> http://git.savannah.gnu.org/cgit/guile.git/tree/module/rnrs/base.scm#n89
>
> string->list and for-each would use C.
>
> Is that huge gap expected?
>
> This is with Guile 3.0.2.
>
>
Forgot to mention that Chritopher also pointed out that string->list has an
optimization for narrow strings:

http://git.savannah.gnu.org/cgit/guile.git/tree/libguile/srfi-13.c#n294

which means it doesn't use string_ref where the scheme code has to do it.
So, it might be due to this?

Aleix