RE: Vectorizing simple loops

[Jose Marcos Ferraro]

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of pawelz
Sent: domingo, 6 de dezembro de 2015 21:03
To: address@hidden
Subject: RE: Vectorizing simple loops

Jose, Thank you very much for working on it. I just tested your solution and 
its results match perfectly with the original function even on big data sets. 
The performance is over 200 times better, so it is exactly what I needed.
Now, would you be so kind to explain the train of thought in this algorithm?
I'd very much like to understand it better.
        



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Pawel,
your finite state machine is very peculiar, to the point that I though I had 
misunderstood it.
If the accumulator is positive and the input is -1 or -2, it forgets the old 
value and start again from zero. The same thing happens if the acc is negative 
and input is +1 or +2.
So we can separate in two parts , a positive and a negative one. That's why the 
intermediate variables have a positive"up" and negative "down" version.
Each of this two parts is independent and can be calculated separetedly. 
Finally, inside each part there is a certain number of "runs" inside which the 
accumulator simply goes up till it reaches top. 
When it reaches top it will not change anymore till the end of the run, so one 
can simply ignore it and later clean the values that go higher (or lower) then 
allowed.
So inside each run it behaves as a simple accumulator increasing at 2 and doing 
nothing at 0 or 1.
If you are really concerned about performance, it can most likely be improved. 
This is simply the first version that I wrote and that I believe is simpler to 
understand.
The code can certainly also be factored, as someone pointed on this list and as 
the evident analogy between the up and down variables show the duplication of 
code.
Jose Marcos Ferraro     
www.LOGITeng.com