/*---------------------------------------------------------------------------*
 *                                   IT++			             *
 *---------------------------------------------------------------------------*
 * Copyright (c) 1995-2003 by Tony Ottosson, Thomas Eriksson, Pål Frenger,   *
 * Tobias Ringström, and Jonas Samuelsson.                                   *
 *                                                                           *
 * Permission to use, copy, modify, and distribute this software and its     *
 * documentation under the terms of the GNU General Public License is hereby *
 * granted. No representations are made about the suitability of this        *
 * software for any purpose. It is provided "as is" without expressed or     *
 * implied warranty. See the GNU General Public License for more details.    *
 *---------------------------------------------------------------------------*/

/*! 
  \file 
  \brief Implementation of Class for the Extended Golay Code (24,12,8).
  \author Tony Ottosson

  1.4

  2003/05/22 08:55:20
*/

#include "base/specmat.h"
#include "comm/egolay.h"
#include "comm/commfunc.h"
#include <iostream>

namespace itpp { 

  Extended_Golay::Extended_Golay(void)
  {	
    B="0 1 1 1 1 1 1 1 1 1 1 1;1 1 1 0 1 1 1 0 0 0 1 0;1 1 0 1 1 1 0 0 0 1 0 1;1 0 1 1 1 0 0 0 1 0 1 1;1 1 1 1 0 0 0 1 0 1 1 0;1 1 1 0 0 0 1 0 1 1 0 1;1 1 0 0 0 1 0 1 1 0 1 1;1 0 0 0 1 0 1 1 0 1 1 1;1 0 0 1 0 1 1 0 1 1 1 0;1 0 1 0 1 1 0 1 1 1 0 0;1 1 0 1 1 0 1 1 1 0 0 0;1 0 1 1 0 1 1 1 0 0 0 1";

    G = concat_horizontal(eye_b(12), B);
  }

  bvec Extended_Golay::encode(const bvec &uncoded_bits)
  {
    int no_bits = uncoded_bits.length();
    int no_blocks = (int)floor((double)no_bits/12);
    bvec output(24*no_blocks);
    bmat Gt = G.T();
    int i;
	
    for (i=0; i<no_blocks; i++) 
      output.replace_mid(24*i, Gt * uncoded_bits.mid(i*12,12));

    return output;
  }

  bvec Extended_Golay::decode(const bvec &coded_bits)
  {
    int no_bits = coded_bits.length();
    int no_blocks = (int)floor((double)no_bits/24);
    bvec output(12*no_blocks);
    int i;
    int j;
    bvec S(12),BS(12),r(12),temp(12),e(24),c(24);
    bmat eyetemp = eye_b(12);

    for (i=0; i<no_blocks; i++) {
      r = coded_bits.mid(i*24,24);
      // Step 1. Compute S=G*r.
      S = G*r;
      // Step 2. w(S)<=3. e=(S,0). Goto 8.
      if( weight(S) <= 3 ) {
	e = concat(S, zeros_b(12)); goto Step8;
      }
	  
      // Step 3. w(S+Ii)<=2. e=(S+Ii,yi). Goto 8.
      for (j=0; j<12; j++) {
			
	temp = S + B.get_col(j);
	if ( weight(temp) <=2 ) {
	  e = concat(temp, eyetemp.get_row(j)); goto Step8;
	}
      }

      // STEP 4. Compute B*S
      BS = B*S;

      // Step 5. w(B*S)<=3. e=(0,BS). Goto8.
      if ( weight(BS) <=3 ) {
	e = concat(zeros_b(12), BS); goto Step8;
      }

      // Step 6. w(BS+Ri)<=2. e=(xi,BS+Ri). Goto 8.
      for (j=0; j<12; j++) {
	temp = BS + B.get_row(j);
	if ( weight(temp) <=2 ) {
	  e = concat(eyetemp.get_row(j), temp); goto Step8;
	}
      }

      // Step 7. Uncorrectable erreor pattern. Choose the first 12 bits.
      e = zeros_b(24); goto Step8;
	  
    Step8: // Step 8. c=r+e. STOP
      c = r + e;
      output.replace_mid(i*12, c.left(12));
    }
  
    return output;
  }

} //namespace itpp