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

[Linus Björnstam]

You can cut another 15-ish % from that loop by making an inline loop, btw

(let loop ((pos 0))
  (when (< pos (string-length str))
    ...
    (loop (1+ pos)))

I have been looking at the disassembly, even for simpler cases, but I haven't 
been able to understand enough of it. 

BTW: string-for-each is in the default environment, and is probably the same as 
the srfi-13 C implementation.

-- 
  Linus Björnstam

On Sun, 7 Jun 2020, at 08:27, Aleix Conchillo Flaqué 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.
> 
> Best,
> 
> Aleix
>