gfdiv.m

数字通信第四版原书的例程

function q = gfdiv(b, a, p)
%GFDIV  Element-by-element division in GF(P) or GF(P^M).
%       Q = GFDIV(B, A)  divides B by A resulting in the quotient Q in GF(2).
%       A zero element in A will result in an NaN solution.
%
%       Q = GFDIV(B, A, P) divides B by A resulting in the quotient Q in
%       GF(P), where P must be a prime number. When P is a list of all the
%       elements in GF(P^M), and P is a prime number, Q is the result of the
%       dividing operation in the GF(P^M) field.
%
%       See also GFADD, GFMUL, GFTUPLE, GFPRETTY

%       Wes Wang 6/8/94, 7/19/94, 10/7/95
%       Copyright (c) 1995-96 by The MathWorks, Inc.
%       $Revision: 1.1 $  $Date: 1996/04/01 17:58:35 $

if nargin < 2
  error('Not enough input for GFADD')
elseif nargin < 3
    p = 2;
end
a = a(:);
b = b(:);
if length(p) <= 1
    if ~isempty([find(a~=floor(a)), find(a<0), find(a>=p)])
         error('The polynomial coeficients must be in GF(P)')
    elseif ~isempty([find(b~=floor(b)), find(b<0), find(b>=p)])
     error('The polynomial coeficients must be in GF(P)')
    end;

    len_a = length(a);
    len_b = length(b);
    x = a;
    if p > 2
       x = a .^ (p-2);
       if floor(x) ~= x
          disp('Warning: The prime number is too big to be handled by gfdiv');
       end;
    end;
    indx = find(~(x > 0));
    if (len_a == len_b) | (len_b == 1)
        q = rem(b .* x, p);
        q(indx) = indx + NaN;
    elseif len_a == 1
        if isempty(indx)
            q = rem(b .* x, p);
        else
            q = b + NaN;
        end;
    elseif len_a > len_b
        x = a(1:len_b);
        indx = find(~(x > 0));
        q = rem(b .* x, p);
        q(indx) = indx + NaN;
    else
        q = b;
        q(1:len_a) = rem(b(1:len_a) .* x, p);
        q(indx) = indx + NaN;
    end;
else
    % GF(P^M) field computation.
    prim = max(max(p)) + 1;
    [n_p, m_p] = size(p);
    indxa = find(~(a>=0));
    indxb = find(~(b >=0));
    len_a = length(a);
    len_b = length(b);
    if (len_a == len_b) | (len_a == 1) | (len_b == 1)
        q = rem(b + n_p - 1 - a, n_p - 1);
    else
        cal_len = min(len_a, len_b);
        q = rem(b(1 : cal_len) + n_p - 1 - a(1 : cal_len), n_p - 1);
    end;
    q(indxb) = indxb - Inf;
    q(indxa) = indxa + NaN;
end;
q=q(:);
%--end of GFDIV--