qa_gr_math.cc			\

	qa_gri_lfsr.cc

/* -*- c++ -*- */

/*

 * Copyright 2007 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 3, 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

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * 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.

 */

#ifndef INCLUDED_GRI_LFSR_H

#define INCLUDED_GRI_LFSR_H

#include <stdexcept>

#include <stdint.h>

/*!

 * \brief Fibonacci Linear Feedback Shift Register using specified polynomial mask

 * \ingroup math

 *

 * Generates a maximal length pseudo-random sequence of length 2^degree-1

 * 

 * Constructor: gri_lfsr(int mask, int seed, int reg_len);

 *  

 *      mask - polynomial coefficients representing the locations

 *             of feedback taps from a shift register which are xor'ed

 *             together to form the new high order bit.

 *

 *             Some common masks might be:

 *              x^4 + x^3 + x^0 = 0x19

 *              x^5 + x^3 + x^0 = 0x29

 *              x^6 + x^5 + x^0 = 0x61

 *

 *      seed - the initialization vector placed into the register

 *             durring initialization.   Low order bit corresponds

 *             to x^0 coefficient -- the first to be shifted as output.

 *

 *   reg_len - specifies the length of the feedback shift register 

 *             to be used.   Durring each iteration, the register

 *             is rightshifted one and the new bit is placed in bit reg_len.

 *             reg_len should generally be at least order(mask) + 1

 *

 *

 * see http://en.wikipedia.org/wiki/Linear_feedback_shift_register 

 * for more explanation.

 *

 *

 *

 *  next_bit() - performs once cycle of the lfsr,

 *               generating the new high order bit from the mask

 *               and returning the low order bit which has been

 *               shifted out of the register.

 *

 *

 */

class gri_lfsr

{

 private:

  uint32_t d_shift_register;

  uint32_t d_mask;

  uint32_t d_shift_register_length;	// less than 32

  static uint32_t

  popCount(uint32_t x)

  {

    uint32_t r = x - ((x >> 1) & 033333333333)

                   - ((x >> 2) & 011111111111);

    return ((r + (r >> 3)) & 030707070707) % 63;

  }

 public:

  gri_lfsr(uint32_t mask, uint32_t seed, uint32_t reg_len)

    : d_shift_register(seed), d_mask(mask), d_shift_register_length(reg_len)

  {

    if (reg_len > 31)

      throw std::invalid_argument("reg_len must be <= 31");

  }

  unsigned char next_bit() {

    unsigned char bit = d_shift_register & 1;

    unsigned char newbit = popCount( d_shift_register & d_mask )%2;

    d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length));

    return bit;

  }

  int mask() const { return d_mask; }

};

#endif /* INCLUDED_GRI_LFSR_H */

#include <qa_gri_lfsr.h>

  s->addTest (qa_gri_lfsr::suite ());

/*

 * Copyright 2008 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 3, 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

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * 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 <gri_lfsr.h>

#include <qa_gri_lfsr.h>

#include <cppunit/TestAssert.h>

#include <stdio.h>

void

qa_gri_lfsr::test_lfsr ()

{

  int mask = 0x19;

  int seed = 0x01;

  int length = 5;

  gri_lfsr lfsr1(mask,seed,length);

  gri_lfsr lfsr2(mask,seed,length);

  unsigned char expected[] = {1, 0, 1, 1, 0, 1, 0, 1, 0, 0};

  for(unsigned int i=0; i<31; i++){

    lfsr1.next_bit();

  }

  // test that after one lfsr cycle we still match out uncycled lfsr

  for (unsigned int i = 0; i < 41; i++) {

    CPPUNIT_ASSERT_EQUAL((int) lfsr1.next_bit(), (int) lfsr2.next_bit());

  }

  // test the known correct values at the given shift offset

  for(unsigned int i=0; i<10; i++){

    CPPUNIT_ASSERT_EQUAL((int) lfsr1.next_bit(), (int) expected[i]);

  }

  // test for register length too long

  CPPUNIT_ASSERT_THROW(gri_lfsr(mask, seed, 32), std::invalid_argument);

}

/* -*- c++ -*- */

/*

 * Copyright 2008 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 3, 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

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * 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.

 */

#ifndef _QA_GRI_LFSR_H_

#define _QA_GRI_LFSR_H_

#include <cppunit/extensions/HelperMacros.h>

#include <cppunit/TestCase.h>

class qa_gri_lfsr : public CppUnit::TestCase {

  CPPUNIT_TEST_SUITE(qa_gri_lfsr);

  CPPUNIT_TEST(test_lfsr);

  CPPUNIT_TEST_SUITE_END();

 private:

  void test_lfsr();

};

#endif /* _QA_GRI_LFSR_H_ */