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

/*

 * Copyright 2004,2006 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

 * 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., 59 Temple Place - Suite 330,

 * Boston, MA 02111-1307, USA.

 */

#ifdef HAVE_CONFIG_H

#include "config.h"

#endif

#include <gr_correlate_access_code_bb.h>

#include <gr_io_signature.h>

#include <stdexcept>

#include <gr_count_bits.h>

#define VERBOSE 0

gr_correlate_access_code_bb_sptr

gr_make_correlate_access_code_bb (const std::string &access_code, int threshold)

{

  return gr_correlate_access_code_bb_sptr (new gr_correlate_access_code_bb (access_code, threshold));

}

gr_correlate_access_code_bb::gr_correlate_access_code_bb (

  const std::string &access_code, int threshold)

  : gr_sync_block ("correlate_access_code_bb",

                   gr_make_io_signature (1, 1, sizeof(char)),

                   gr_make_io_signature (1, 1, sizeof(char))),

    d_data_reg(0), d_flag_reg(0), d_flag_bit(0), d_mask(0),

    d_threshold(threshold), d_flip(0)

{

  if (!set_access_code(access_code)){

    fprintf(stderr, "gr_correlate_access_code_bb: access_code is > 64 bits\n");

    throw std::out_of_range ("access_code is > 64 bits");

  }

}

gr_correlate_access_code_bb::~gr_correlate_access_code_bb ()

{

}

bool

gr_correlate_access_code_bb::set_access_code(

  const std::string &access_code)

{

  unsigned len = access_code.length();        // # of bytes in string

  if (len > 64)

    return false;

  // set len top bits to 1.

  d_mask = ((~0ULL) >> (64 - len)) << (64 - len);

  d_flag_bit = 1LL << (64 - len);        // Where we or-in new flag values.

                                        // new data always goes in 0x0000000000000001

  d_access_code = 0;

  for (unsigned i=0; i < 64; i++){

    d_access_code <<= 1;

    if (i < len)

      d_access_code |= access_code[i] & 1;        // look at LSB only

  }

  return true;

}

int

gr_correlate_access_code_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];

  for (int i = 0; i < noutput_items; i++){

    // compute output value

    unsigned int t = 0;

    t |= d_flip ^ (((d_data_reg >> 63) & 0x1) << 0);

    t |= ((d_flag_reg >> 63) & 0x1) << 1;        // flag bit

    out[i] = t;

    // compute hamming distance between desired access code and current data

    unsigned long long wrong_bits = 0;

    unsigned int nwrong = d_threshold+1;

    int new_flag = 0;

    wrong_bits  = (d_data_reg ^ d_access_code) & d_mask;

    nwrong = gr_count_bits64(wrong_bits);

    // test for access code with up to threshold errors or its compelement

    new_flag = (nwrong <= d_threshold) || (nwrong >= (64-d_threshold));

#if 0   

    if(new_flag) {

      printf("%llx  ==>  %llx  :  d_flip=%u\n", d_access_code, d_data_reg, d_flip);

    }

#endif

    // shift in new data and new flag

    d_data_reg = (d_data_reg << 1) | (in[i] & 0x1);

    d_flag_reg = (d_flag_reg << 1);

    if (new_flag) {

      d_flag_reg |= d_flag_bit;

      d_flip = nwrong >= (64-d_threshold);   // flip bits if this is true

    }

  }

  return noutput_items;

}