[Discuss-gnuradio] Analysis_filterbank

[Sebastiaan Heunis]

Hi

I think I have found what might be my problem with the
analysis_filterbank.  When using it as a polyphase channeliser, you
need to start feeding samples in from the bottom channel, upwards.
The gr.analysis_filterbank uses gr.stream_to_streams to split the
input into a number of streams starting at the top.  For a polyphase
channeliser, this should be the other way round.  I guess I need to
make a different version of stream_to_streams to do this.  Can someone
please just help me with some c++ code?  In particular the work()
function of gr_stream_to_streams:

const char *in = (const char *) input_items[0];
  char **outv = (char **) &output_items[0];
  int nstreams = output_items.size();

  for (int i = 0; i < noutput_items; i++){
    for (int j = 0; j < nstreams; j++){
      memcpy(outv[j], in, item_size);
      outv[j] += item_size;
      in += item_size;
    }
  }

Firstly, why do we use a pointer to a pointer for the output data?
For what I intend to do, I need to do the following, right?

memcpy(outv[nstreams-j-1],in,item_size);
outv[nstreams-j-1] -= item_size;       //or out[nstreams-j-1] += item_size?
in += item_size;

Thanks

Sebastiaan