Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / lz77deco.m

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+## Copyright (C) 2007 Gorka Lertxundi
+##
+## 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{m} =} lz77deco (@var{c}, @var{alph}, @var{la}, @var{n})
+## Lempel-Ziv 77 source algorithm decoding implementation. Where
+##
+## @table @asis
+## @item @var{m}
+## message decoded (1xN).
+## @item @var{c}
+## encoded message (Mx3).
+## @item @var{alph}
+## size of alphabet.
+## @item @var{la}
+## lookahead buffer size.
+## @item @var{n}
+## sliding window buffer size.
+## @end table
+## @seealso{lz77enco}
+## @end deftypefn
+
+function m = lz77deco(c, alph, la, n)
+  if (la <= 0 || n <= 0)
+    error("lz77deco: Lookahead buffer size and window size must be higher than 0.");
+  endif
+  if n - la < la
+    error("lz77deco: Unreachable configuration: n - la >= la.");
+  endif
+  if alph < 2
+    error("lz77deco: Alphabet size within less than 2 symbols? Is that possible?.");
+  endif
+  if columns(c) != 3
+    error("lz77deco: Encoded message must be a Nx3 matrix.");
+  endif
+
+  window = zeros(1,n);
+  x = length(c);
+  len = length(c);
+
+  for x=1:len
+    ## update window
+    temp = n-la+c(x,2)-c(x,1);
+    for y=1:temp
+      window(n-la+y) = window(c(x,1)+y);
+    endfor
+    window(n-la+c(x,2)+1) = c(x,3);
+       
+    ## decoded message
+    m_deco = window(n-la+1:n-la+c(x,2)+1);
+    if x == 1
+      m = m_deco;
+    else
+      m = [m m_deco];
+    endif
+       
+    ## CCW shift
+    temp = c(x,2)+1;
+    window(1:n-la) = window(temp+1:n-la+temp);
+  endfor
+
+endfunction
+
+%!demo
+%! lz77deco([8 2 1 ; 7 3 2 ; 6 7 2 ; 2 8 0],3,9,18)