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Re: Which is faster: narrow-to-region or delete-region?
From: |
Arthur Miller |
Subject: |
Re: Which is faster: narrow-to-region or delete-region? |
Date: |
Wed, 22 Sep 2021 09:00:54 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
Eli Zaretskii <eliz@gnu.org> writes:
>> From: Arthur Miller <arthur.miller@live.com>
>> Date: Tue, 21 Sep 2021 22:10:09 +0200
>>
>>
>> I have a DEFUN in the middle of a temporary buffer; which is faster to use to
>> eliminate the rest of the code from the calculations for font lock:
>>
>> (narrow-to-region defun-begin defun-end)
>>
>> or
>>
>> (delete-region (point-min) defun-begin) +
>> (delete-region defun-end (point-max))
>
> The narrow-to-region method must be much faster, since it only sets a
> bunch of variables and does little else.
Thought so when saw the code, but wasn't sure.
> bunch of variables and does little else. Moreover, it cannot trigger
> GC, whereas delete-region method very well can.
That too, wasn't even thinking about that. I am not so familiar how GC works
with code in C.
>> I have tried both and notice no differences.
>
> Maybe in a very small buffer.
I was just tested in help buffers with that patch I made. But it is interactive
so it is hard to see the difference; I haven't benchmarked.
Thank you. That was educative. And helpful.