Thanks Doug. I ended up implementing my own solution using a volk call. I
hadn't realized the built in filters were wrappers for volk, thank you for
pointing that out. Glad to know I did it in a gnuradio centric way.
Rich
Sent from my iPhone
> On Sep 15, 2015, at 8:14 AM, Douglas Geiger <doug.gei...@bioradiation.net>
> wrote:
>
> Rich,
> If you look in gr-filter/lib/fir_filter.cc you'll see all the filter kernel
> implementations. Since it looks like you're only interested in floats (and
> therefore, I assume real - not complex - signals and taps), if you look at
> fir_filter_fff::filter(const float input[]) you can see that it really is
> just a wrapper for the volk_32f_x2_dot_prod_32f kernel from VOLK. Note that
> this call is the inner kernel, which gets called either by filterN (for the
> non-decimating case) or filterNdec (for the decimating case) inside the
> work(...) function by the corresponding block (i.e. fir_filter_fff_impl.cc
> for the all-floats case). If you are interested in complex signals/taps,
> fir_filter.cc has all the other variants as well, but you'll notice that
> pretty much all the filter(...) calls are just wrappers for VOLK functions
> (e.g. volk_32fc_x2_dot_prod_32fc for the all complex float case). All the
> rest of the code relating to the FIR filters has to do with setup and things
> like updating taps, so if all you need is a simple dot product function for
> implementing your own FIR filter, I highly recommend looking through the VOLK
> documentation. Note that if you have lots of taps, it becomes desirable at
> some point to move into the Fourier domain, and do a simple element-wise
> multiply rather than a time domain convolution. I'll leave walking through
> fft_filter.cc as an exercise for the reader...
>
> Regards,
> Doug
>
>> On Mon, Sep 14, 2015 at 1:24 AM, Richard Bell <richard.be...@gmail.com>
>> wrote:
>> Hi all,
>>
>> I'm not sure how to implement a simple FIR filter within C++ code that does
>> not act directly on the OOT blocks input array. I would appreciate it if
>> someone would demonstrate a simple example of how to use fir_filter_fff
>> assuming the following:
>>
>> float[N] my_input_array = {N float values}; <---- This is not the OOT
>> modules input port array
>> float[M] taps = {my taps};
>> float[N+M-1] my_output_array = {N+M-1 float values}; <---- This is not the
>> OOT modules output port
>>
>> What is the code that will convolve my_input_array with taps and store it in
>> my_output_array using gnuradio builtins? I've tried this myself but can't
>> get it to work. I'm not interested in writing my own convolution code when
>> gnuradio has optimized implementations.
>>
>> Thanks,
>> Rich
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> Discuss-gnuradio@gnu.org
>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
>
> --
> Doug Geiger
> doug.gei...@bioradiation.net
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