Re: [dev] [sandy] [PATCH] VIM key bindings.

From: <>
Date: Fri, 11 Jul 2014 03:04:44 +0200

> Another thing you can do is to only preallocate a fixed size buffer
> and add to a list of buffers. Every time you cross block boundary, you alloc
> a new buffer and attach it at the end of your list.
> There are many ways to do this, I'd go for the simplest approach in terms of code
> readability and stop worrying about performance.
> If it is slow or memory hungry, it can be fixed later incrementally.

My 2 cents.

Array of gap buffers is simple, imperative and efficient. I implemented
what looks like a VI clone at this point to which I plan to add ACME like
features. The data structure I used is a linked list of gap buffers, to
stress the performance I use gap buffers of at most 11 runes. If these
buffers are scaled up to 4k, I can enjoy real time edition in a file of
5 megs. When the file gets real big, seeking forward is nice and
fast (because I use a cache that memorizes the last gap buffer accessed),
but seeking backwards is slow. One solution to this is to move to a
doubly linked list instead. Another solution is simply an array, and
moreover, we enjoy locality (which is the most important property of a
data structure with the current processors).

  This is why I recommend an array of gap buffers.

If you want some real good inspiration I recommend reading QEmacs' source
code ( It is awesome C written by a super
skilled hacker. It uses mmap to seamlessly edit files of several gigabytes,
basically, the address space is the limit. Of course, this is overkill, and
I do not advocate this but it shows that combined with caching (read the
code to understand what I mean), an array of gap buffers is enough for all
our purposes.

Functional languages have ropes, I like functional languages, but in this
case I find the imperative solution more pragmatic and elegant by its

-- mpu
Received on Fri Jul 11 2014 - 03:04:44 CEST

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