Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/communications-1.1.1/rsdecof.m b/octave_packages/communications-1.1.1/rsdecof.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} {} rsdecof (@var{in},@var{out})
+## @deftypefnx {Function File} {} rsdecof (@var{in},@var{out},@var{t})
+##
+## Decodes an ascii file using a Reed-Solomon coder. The input file is
+## defined by @var{in} and the result is written to the output file @var{out}.
+## The type of coding to use is determined by whether the input file is 7-
+## or 8-bit. If the input file is 7-bit, the default coding is [127,117].
+## while the default coding for an 8-bit file is a [255, 235]. This allows
+## for 5 or 10 error characters in 127 or 255 symbols to be corrected 
+## respectively. The number of errors that can be corrected can be overridden 
+## by the variable @var{t}.
+##
+## If the file is not an integer multiple of the message size (127 or 255)
+## in length, then the file is padded with the EOT (ascii character 4)
+## character before decoding.
+##
+## @end deftypefn
+## @seealso{rsencof}
+
+function rsdecof(in, out, t)
+
+  if ((nargin < 2) || (nargin > 3))
+    usage("rsdecof (in, out [, t])");
+  endif
+
+  if (!ischar(in) || !ischar(out))
+    error ("rsdecof: input and output filenames must be strings");
+  endif
+
+  if (nargin != 3)
+    t = 0;
+  else
+    if (!isscalar(t) || (t != floor(d)) || (t < 1))
+      error ("rsdecof: t must be a postive, non-zero integer");
+    endif
+  endif
+
+  try fid = fopen(in, "rt");
+  catch
+    error ("rsdecof: can not open input file");
+  end
+  [code, count] = fread(fid, Inf, "char");
+  fclose(fid);
+
+  is8bit = (max(code) > 127);
+
+  if (is8bit)
+    m = 8;
+    n = 255;
+    if (t == 0)
+      t = 10;
+    endif
+  else
+    m = 7;
+    n = 127;
+    if (t == 0)
+      t = 5;
+    endif
+  endif
+  k = n - 2 * t;
+
+  ncodewords = ceil(count / n);
+  npad = n * ncodewords - count;
+  code = reshape([code ; 4 * ones(npad,1)],n,ncodewords)';
+
+  msg = rsdec(gf(code,m), n, k, "beginning")';
+  msg = msg(:);
+
+  try fid = fopen(out, "w+t");
+  catch
+    error ("rsdecof; can not open output file");
+  end
+  fwrite(fid, msg(1:(ncodewords*k-npad)), "char");
+  fclose(fid);
+
+endfunction