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Re: [Discuss-gnuradio] bug in gr_rotate and patch

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] bug in gr_rotate and patch
Date: Sun, 11 Jan 2004 18:07:53 -0800
User-agent: Mutt/1.4.1i

On Sun, Jan 11, 2004 at 04:35:11PM -0800, Joshua Lackey wrote:
> I've found a trivial but fairly annoying bug in the gr_rotator class.
> The bug affects anything using a frequency translating filter and that
> includes almost all the programs in src/gnu/examples.
> It is caused by rounding error and manifests as slowly decreasing signal
> amplitude.  Essentially, the output from the filter is rotated through a
> certain phase which is incremented each time.  The initial phase and
> phase increment both have magnitude 1 yet, because of rounding error,
> their product does not.  My fix is to normalize the phase after each
> increment.
> The following patch is against the latest version of gr_rotator.h in cvs.

Thanks Josh,

I've applied the patch.

Even though it adds approximately 74 cycles (P4), it's still about
twice as fast as computing FSINCOS, and it has the wonderful benefit
of working ;-)


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