Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / hammgen.m

diff --git a/octave_packages/communications-1.1.1/hammgen.m b/octave_packages/communications-1.1.1/hammgen.m
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+## Copyright (C) 2003 David Bateman
+##
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{h} = } hammgen (@var{m})
+## @deftypefnx {Function File} {@var{h} = } hammgen (@var{m},@var{p})
+## @deftypefnx {Function File} {[@var{h},@var{g}] = } hammgen (@var{...})
+## @deftypefnx {Function File} {[@var{h},@var{g},@var{n},@var{k}] = } hammgen (@var{...})
+##
+## Produce the parity check and generator matrices of a Hamming code. The
+## variable @var{m} defines the [@var{n},@var{k}] Hamming code where 
+## @code{@var{n} = 2 ^ @var{m} - 1} and @code{@var{k} = @var{n} - @var{m}}.
+## @var{m} must be between 3 and 16.
+##
+## The parity check matrix is generated relative to the primitive polynomial
+## of GF(2^@var{m}). If @var{p} is specified the default primitive polynomial
+## of GF(2^@var{m}) is overridden. @var{p} must be a valid primitive 
+## polynomial of the correct order for GF(2^@var{m}).
+##
+## The parity check matrix is returned in the @var{m} by @var{n} matrix 
+## @var{h}, and if requested the generator matrix is returned in the @var{k}
+## by @var{n} matrix @var{g}.
+##
+## @end deftypefn
+## @seealso{gen2par}
+
+function [h, g, n, k] = hammgen(m, p)
+
+  if ((nargin < 1) || (nargin > 2))
+    usage ("[h [, g [, n, k]]] = hammgen (m [, p])");
+  endif
+
+  if (!isscalar(m) || (floor(m) != m) || (m < 3) || (m > 16))
+    error ("hammgen: m must be an integer between 3 and 16");
+  endif
+
+  if (nargin > 1)
+    if (!isscalar(p))
+      p = bi2de(p);
+    endif
+    if ((floor(p) != p) || (p < 2^m) || (p > 2^(m+1)) || !isprimitive(p))
+      error ("hammgen: p must be a primitive polynomial of GF(2^m)");
+    endif
+  else
+    ## Get the primitive polynomial of GF(2^M). Note that the default
+    ## primitive polynomial is not necessarily primpoly(m,"min"), so
+    ## have to create a Galois variable to extract the default primitive.
+    ## The problem is, this limits m to be less than or equal to 16,
+    ## as the Galois type itself is limited to this value
+    p = gf(0,m).prim_poly;
+  endif
+
+  n = 2^m -1;
+  k = n - m;
+  if (nargout > 1)
+    [h, g] = cyclgen(n, p);
+  else
+    h = cyclgen(n,p);
+  endif
+  
+endfunction