Same-size chunk replacements (was RunRev vs RealBasic)

Dar Scott dsc at swcp.com
Thu Jan 20 16:58:43 CST 2005


On Jan 19, 2005, at 11:33 PM, Richard Gaskin wrote:

> > I did write some compositing and blur/sharpen filters in
> > transcript some time ago, but I don't know the details of
> > the 'same-size chunk' replacements. Where can I find more info?
>
> All I know is what Dar posted here, but it sounded really tasty. 
> Apparently he made a suggestion to Scott Raney about ways to optimize 
> operations in which a string of a given length is used to replace a 
> substring of the same length within a larger chunk.
>
> In previous versions a very generalized approach was used for all 
> replacement operations, requiring that the data be copied during the 
> replacement, which can be computationally expensive with large chunks.
>
> Since the data being inserted is the same length as the data being 
> removed the handle size doesn't change, allowing the operation to work 
> in-place, without copying.
>
> IIRC, Raney reported that the new method should improve speed by 
> roughly 4000 times for those cases.
>
> Dar - got the details for us?

You got the important parts.

For building a large string such as an image, the put-after command is 
fastest (1 or 2 microseconds on my Mac).  So, if you are doing color 
shifting on an image, that is the best to go.

    put newPixel after imageSoFar

But if you are putting a small image over a large image or drawing onto 
an image or doing something that needs random access or a change to 
only part, then use same-size put-into (6 microseconds on my Mac).

    put newPixel into char p to p+3 of imageSoFar

This used to take very long on large images.  Now both of these are 
small fixed time.  (Well, there is a tiny growth time every once in a 
while for 'after' but it is only a microsecond on my computer, that is, 
it is fixed, too.)

Anyway, use 'after' if you can, and make sure the chunk sizes match if 
you can't.

This also very handy for binary arrays and matrices and such.

I thought I had entered that as an enhancement into bugzilla, but 
either I goofed or it was changed.

This is one of those things in which a fundamental enhancement or 
performance improvement might open the doors to a scripting solution to 
what is on folks' wish lists.

Dar

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