% Hnew=par_binconv(H,m)
% Converts parity matrix H of size 1xn (corresponding to (n-1)/n
% convolutional codes), with elements expressed in octal form,
% into matrix Hnew. The new matrix has size 1x(n(m+1)), where 
% the elements are binary values. Every m+1 elements correspond to
% the binary description of the original element of H expressed in octal
% form. The argument m is the maximum degree of the polynomials of
% H (and is equal to the log2 the number of states of the (n-1)/n code). 
% Note that the ordering of the binary entries of Hnew is LSB to MSB. 
% 
% George Ginis, June 2001

function Hnew=par_binconv(H,m)
  
  n=size(H,2); % determine rate of code from dimensions of parity matrix
  if (size(H,1) ~= 1) 
    disp('Code does not have rate (n-1)/n!'); 
    break;
  end
  k=n-1;
  
  % matrix defining mapping from octal values to binary values
  map=[0 0 0;
       1 0 0;
       0 1 0;
       1 1 0;
       0 0 1;
       1 0 1;
       0 1 1;
       1 1 1];
  
  for j=1:n   % for all columns

    % each entry of H has at most ceil((m+1)/3) octal digits      
    for digit=0:ceil((m+1)/3)-1
            
      r = mod(H(1,j),10);
      H(1,j) = floor(H(1,j)/10);

      % each digit corresponds to 3 binary entries, unless the
      % maximum number of binary entries has been reached
      if (digit*3+3 <= m+1) 
	Hnew(1,(j-1)*(m+1)+digit*3+1:(j-1)*(m+1)+digit*3+3) = map(r+1,:);  
      else
	Hnew(1,(j-1)*(m+1)+digit*3+1:(j-1)*(m+1)+(m+1)) = ...
	    map(r+1,1:m-digit*3+1);
      end
	
    end
    
  end