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Re: Is Elisp really that slow?

From: tomas
Subject: Re: Is Elisp really that slow?
Date: Tue, 14 May 2019 16:44:07 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, May 14, 2019 at 03:21:54PM +0200, Emanuel Berg wrote:
> tomas wrote:
> >> 1) Identify what is slow in Elisp.
> >> 
> >> 2) Rewrite it in C?
> >
> > 3) Write a regexp-to-assembler compiler.
> > Bonus points if that runs on the GPU, using
> > its SIMD features.
> Please DIY Mr. Zerolo, personally I'd be happy
> to try out translating Elisp into C.

But regexp match /was/ the bottleneck in the code sample
you posted, whose core loop is:

  (while (re-search-forward regexp end t)
          (replace-match to-string) )

(go benchmark it, Emacs offers great facilities for that).
So no amount of Elisp -> C translation or other Elisp
speedup will make your code noticeably faster.


> I know how to write C in general, but how does
> one integrate it into Emacs?

Again, Emacs is happy to tell you. Just do C-f (aka
describe-function), enter re-search-forward <ENTER> and
you get a small blurb:

    re-search-forward is an interactive built-in function in
    ‘C source code’.

    (re-search-forward REGEXP &optional BOUND NOERROR COUNT)

    Probably introduced at or before Emacs version 19.29.

    Search forward from point for regular expression REGEXP.
    [...more interesting text here...]

Notice how this ‘C source code’ above is a link? Follow it,
either by putting point on it and hitting ENTER or by mouse-
clicking on it, and presto, you are in the middle of a C
function written to be called from Elisp (you compile your
Emacs from source code, do you?).

In the manual, there is "E7. Writing Emacs Primitives".

Have fun...

-- t

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