function y = rsc_encode(g, x, terminated)
% Copyright Nov. 1998 Yufei Wu
% MPRG lab, Virginia Tech.
% for academic use only

% encodes a block of data x (0/1)with a recursive systematic
% convolutional code with generator vectors in g, and
% returns the output in y (0/1).
% if terminated>0, the trellis is perfectly terminated
% if terminated<0, it is left unterminated;

% determine the constraint length (K), memory (m), and rate (1/n)
% and number of information bits.
[n,K] = size(g);
m = K - 1;
if terminated>0
  L_info = length(x);   % L_info: lenght of information sequence?  -yzh
  L_total = L_info + m; % L_total:m additional bits is used to terminate?  -yzh
else
  L_total = length(x);
  L_info = L_total - m; % see the sequence for untermated in function encoderm for reason. length of x is L_total  --yzh
end  


% initialize the state vector
state = zeros(1,m);

% generate the codeword
for i = 1:L_total
   if terminated<0 | (terminated>0 & i<=L_info)
      d_k = x(1,i);     % d_k: information sequence -yzh
   elseif terminated>0 & i>L_info
      % terminate the trellis
      d_k = rem( g(1,2:K)*state', 2 ); % g(1,2:K): why is g(1,2:K)? not other recursive polynomial?  -yzh
   end
   % a_k??feedback polynomial is g(1:)? --yzh
   % for terminated>0 & i>L_info, a_k will be zero(heihei)  -yzh 
   % recursive encoding?right!    --yzh
   a_k = rem( g(1,:)*[d_k state]', 2 );     % a_k: the bit to be put into the register    -yzh
   [output_bits, state] = encode_bit(g, a_k, state);
   % since systematic, first output is input bit
   output_bits(1,1) = d_k;
   y(n*(i-1)+1:n*i) = output_bits;  % n output bits for 1 input bit(recursiv encoder)  --yzh
end