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Re: [Discuss-gnuradio] blocks.complex_to_arg() implementation

From: Daniele Nicolodi
Subject: Re: [Discuss-gnuradio] blocks.complex_to_arg() implementation
Date: Thu, 14 Aug 2014 11:15:40 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

On 13/08/2014 16:37, Tom Rondeau wrote:
> The version we have in there is much (MUCH) faster than the libm atan2
> function. So yes, we trade off a bit of error for a massive
> computational gain. The error is very small from what I recall, expect
> in a few instances (near 0 or near pi/2 or something like that). Having
> a graph of the error somewhere would be helpful.

I think it depends on the point of view, for me it is a bit of
computational gain for a massive error :)

> The fast atan method we use is still faster than what we have in VOLK. I
> remember testing this out myself, which included putting that code into
> the constructor. However, take a look at this post:
> http://www.trondeau.com/blog/2012/2/17/volk-benchmarking.html

I don't see anything specific to the atan2() and alignment there.

> We see an improvement in speed of blocks by doing the alignment.
> Actually, I think that all blocks should probably have their alignment
> set whether or not they use VOLK. But that would be a lot of work to do
> correctly with all of our blocks to make sure it's done right and is
> actually giving us a benefit. But having test this one in particular,
> no, I don't see any need to remove this code.

I see. Probably a comment in the code mentioning this, to avoid other
being puzzled, is in order here :)


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