squeeze out some performance

Joel Goldstick joel.goldstick at gmail.com
Fri Dec 6 23:07:56 CET 2013

On Fri, Dec 6, 2013 at 11:52 AM, John Ladasky <john_ladasky at sbcglobal.net>wrote:

> On Friday, December 6, 2013 12:47:54 AM UTC-8, Robert Voigtländer wrote:
> > I try to squeeze out some performance of the code pasted on the link
> below.
> > http://pastebin.com/gMnqprST

Not that this will speed up your code but you have this:

    if not clockwise:
        s = start
        start = end
        end = s

Python people would write:
    end, start = start, end

You have quite a few if statements that involve multiple comparisons of the
same variable.  Did you know you can do things like this in python:

>>> x = 4
>>> 2 < x < 7
>>> x = 55
>>> 2 < x < 7

> Several comments:
> 1) I find this program to be very difficult to read, largely because
> there's a whole LOT of duplicated code.  Look at lines 53-80, and lines
> 108-287, and lines 294-311.  It makes it harder to see what this algorithm
> actually does.  Is there a way to refactor some of this code to use some
> shared function calls?
> 2) I looked up the "Bresenham algorithm", and found two references which
> may be relevant.  The original algorithm was one which computed good raster
> approximations to straight lines.  The second algorithm described may be
> more pertinent to you, because it draws arcs of circles.
>     http://en.wikipedia.org/wiki/Bresenham's_line_algorithm
>     http://en.wikipedia.org/wiki/Midpoint_circle_algorithm
> Both of these algorithms are old, from the 1960's, and can be implemented
> using very simple CPU register operations and minimal memory.  Both of the
> web pages I referenced have extensive example code and pseudocode, and
> discuss optimization.  If you need speed, is this really a job for Python?
> 3) I THINK that I see some code -- those duplicated parts -- which might
> benefit from the use of multiprocessing (assuming that you have a
> multi-core CPU).  But I would have to read more deeply to be sure.  I need
> to understand the algorithm more completely, and exactly how you have
> modified it for your needs.
> --
> https://mail.python.org/mailman/listinfo/python-list

Joel Goldstick
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