From: Bart Schaefer <schaefer@brasslantern.com>
To: "zsh-workers@zsh.org" <zsh-workers@zsh.org>
Subject: Re: Idea for optimization (use case: iterate string with index parameter)
Date: Fri, 5 Jan 2018 14:23:57 -0800 [thread overview]
Message-ID: <CAH+w=7ZyKsNCqfO=EQPapmrSh+VPb-EFFhTXvBbt85fOR4DjAw@mail.gmail.com> (raw)
In-Reply-To: <etPan.5a4f7fdd.52e15119.14e5a@zdharma.org>
On Fri, Jan 5, 2018 at 5:38 AM, Sebastian Gniazdowski
<psprint@zdharma.org> wrote:
> iterating string with index parameter is quite slow, because unicode characters are skipped and counted using mbrtowc().
I can't remember the last time I needed to do that kind of iteration.
> For example, I saw z-sy-h uses such loops, my projects sometimes use them too. The point is that iterating a string and doing something with letters, e.g. counting brackets, is a very common use case, and the optimization would be triggered often.
Hmm. Whether this is worthwhile depends on the size of the typical
processed string. I can see this affecting z-sy-h when e.g. running
zed on a big function, but probably not when editing a typical command
line.
Maybe it would be reasonable to do something in shell code, e.g.:
typeset -a iter=(${(s//)string})
for ((i=1; i <= $#iter; i++)); do something with $iter[i]; done
string=${(j//)iter} # if needed
That is more memory-intensive, of course, but it also assists with
cases of unordered access into the array of characters.
> In general, the array would hold #N (5-10 or so) last string-index requests. If new request would target the same string, but index greater by 1, getarg() would call mbrtowc() once (via MB_METACHARLEN macro) reusing the previous in-string pointer.
Why only when greater by 1? If greater, scan to and record the next
needed position. Same number of mbrtowc() conversions, overall.
next prev parent reply other threads:[~2018-01-05 22:24 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-05 13:38 Sebastian Gniazdowski
2018-01-05 22:23 ` Bart Schaefer [this message]
2018-01-06 5:16 ` Sebastian Gniazdowski
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