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function [sys, x0, str, ts] = simbchdc(t, x, u, flag, n, k, tp, dim); 
%SIMBCHDC SIMULINK S-function for BCH decode. 
%       The m-dile is designed to be used in a SIMULINK S-Function block. 
%       This function will decode the cyclic code using BCH decod method. 
%       Parameters: n -- length of code word. 
%                   k -- length of message. 
%                   t -- error-correction capability. 
%                   tp-- list of all GF(2^M) elements. n=2^M-1. 
% 
%       The output has length n+1, the last digit is the error signal err. 
%       A non-negative err indicates number of errors have been corrected. 
%       A nagative err indicates that more than t error have been found in 
%       in the code, the routine cannot correct such error. 
 
%       Wes Wang 
%       Copyright (c) 1995-96 by The MathWorks, Inc. 
 
if (flag == 3) 
    % refresh the state only when there is a trigger signal 
    len_u = length(u); 
    if u(len_u) 
        % output the decode result. 
        % main calculation 
        code_word = bi2de(vec2mat(u(1:len_u-1), dim)) - 1; 
        [sys, err] = rscore(code_word, k, tp, dim, n); 
        % output is the combination of message and error information. 
        sys = sys +1; 
        indx = find(~(sys>=0)); 
        sys(indx) = indx-indx; 
        sys = de2bi(sys, dim)'; 
        sys = [sys(:); err]; 
%        disp(['should output ', num2str(k * dim + 1), 'it is now ', num2str(length(sys))]) 
    else 
        % if there is no trigger, no calculation. 
        if t <= 0 
            sys = zeros(m*k+1, 1); 
        end; 
    end; 
elseif flag == 0 
    if 2^dim-1 ~= n 
        error('Reed-Solomon decode has illegal code word length') 
    end; 
    sys(1) = 0; % no continuous state 
    sys(2) = 0; 
    sys(3) = k * dim + 1;   % number of output, code word length plus one. 
    sys(4) = n * dim + 1;       % number of input, message length. 
    sys(5) = 0; 
    sys(6) = 1;       % direct through flag. 
    sys(7) = 1;       % one sample rate 
    x0 = []; 
    ts = [-1, 0]; 
else 
    sys = []; 
end;