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Re: [Discuss-gnuradio] gnuradio block for boolean operations

From: Tim Meehan
Subject: Re: [Discuss-gnuradio] gnuradio block for boolean operations
Date: Mon, 18 Feb 2008 09:07:42 -0800

Thanks for the input Ed.  Some comments below

Purely from the point of view of "cohesion" I would recommend
the "gr_xor_bb" form instead of passing in a selector that
determines the behavior.  Although I must admit, I wrestled
for quite a while with writing so much infrastructure code
for something as simple an an "xor".

[tim] I think the auto code generators in gengen is a good compromise

[tim] One note on your nrzi_to_nrz code below.  I don't know much about
compiler optimization but I suspect
    nrz_bit = ! nrzi_bit ^ d_prev_nrzi_bit

might give you better performance than the if else.  Then again I have been wrong more than I have been right
on this sort of thing :-)

Here's the code for gr_nrzi_to_nrz_bb.  The code for xor
is similar.

@(^.^)@  Ed

/* -*- c++ -*- */
 * Copyright 2006 Free Software Foundation, Inc.
 * This file is part of GNU Radio
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.

#include "config.h"

#include <gr_nrzi_to_nrz_bb.h>
#include <gr_io_signature.h>
#include <stdexcept>

gr_make_nrzi_to_nrz_bb (bool preload)
  return gr_nrzi_to_nrz_bb_sptr (new gr_nrzi_to_nrz_bb (preload));

gr_nrzi_to_nrz_bb::gr_nrzi_to_nrz_bb (bool preload)
  : gr_sync_block ("nrzi_to_nrz_bb",
           gr_make_io_signature (1, 1, sizeof (unsigned char)),
           gr_make_io_signature (1, 1, sizeof (unsigned char))),

gr_nrzi_to_nrz_bb::work (int                       noutput_items,
                         gr_vector_const_void_star &input_items,
                         gr_vector_void_star       &output_items)
  const unsigned char* in  = (const unsigned char *) input_items[0];
  unsigned char*       out = (unsigned char *) output_items[0];
  unsigned char        nrzi_bit;
  unsigned char        nrz_bit;

  for (int i = 0; i < noutput_items; i++)
        nrzi_bit = in[i];
        // Convert NRZI to NRZ.
        if(nrzi_bit != d_prev_nrzi_bit)
            nrz_bit = 0;
            nrz_bit = 1;
        out[i] = nrz_bit;
        d_prev_nrzi_bit = nrzi_bit;
  return noutput_items;

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