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Re: [Discuss-gnuradio] Moving average and history

From: Martin Braun
Subject: Re: [Discuss-gnuradio] Moving average and history
Date: Tue, 10 Feb 2009 16:02:53 +0100
User-agent: Mutt/1.5.17 (2007-11-01)

On Mon, Feb 09, 2009 at 01:43:41PM +0100, Martin Braun wrote:
> [code]
> Here's what I don't understand: the state for the MA (as for all
> filters) is saved implicitly in the history. However, in this special
> case, the state is simply one scalar value (saved in 'sum'). The way
> this is implemented, that state has to be recalculated every time work()
> is called. So, why bother with history() and not simply make 'sum' a
> class property? Would that screw up the scheduling?
> The reason I ask is if I write a MA block for vectors, using history()
> means keeping vector_length x MA_length samples in some buffer and
> running as many extra multiplications every time work() is called. Of
> course, I'd prefer to solve this the GNU Radio way, but in this case it
> would seem a waste of memory and CPU cycles.

forget about skipping the history(), of course it couldn't work.
However, by adding a state buffer to the class, the first for() loop
can be skipped. For long MAs, this would save some multiplications and
only increase memory usage by one item_size.

Next time I'll think about it twice :)


Dipl.-Ing. Martin Braun           Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik  Fax:   +49-(0)721-608 6071
Universitaet Karlsruhe (TH)       http://www.int.uni-karlsruhe.de/

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