Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / lz77enco.m

diff --git a/octave_packages/communications-1.1.1/lz77enco.m b/octave_packages/communications-1.1.1/lz77enco.m
new file mode 100644 (file)
index 0000000..4a1b299
--- /dev/null
+++ b/octave_packages/communications-1.1.1/lz77enco.m
@@ -0,0 +1,93 @@
+## 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{c} =} lz77enco (@var{m}, @var{alph}, @var{la}, @var{n})
+## Lempel-Ziv 77 source algorithm implementation. Where
+##
+## @table @asis
+## @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{lz77deco}
+## @end deftypefn
+
+function c = lz77enco(m, alph, la, n)
+
+  if (la <= 0 || n <= 0)
+    error("lz77enco: Lookahead buffer size and window size must be higher than 0.2");
+  endif
+  if n - la < la
+    error("lz77enco: Unreachable configuration: n - la >= la.");
+  endif
+  if alph < 2
+    error("lz77enco: Alphabet size within less than 2 symbols?");
+  endif
+  if max(m)+1 > alph
+    error("lz77enco: It is not possible to codify the message, too small alphabet size.");
+  endif
+  if rows(m) != 1
+    error("lz77enco: Message to encode must be a 1xN matrix.");
+  endif
+
+  c = zeros(1,3);
+  enco = zeros(1,3);
+  window = zeros(1,n);
+  x = length(m);
+  len = length(m);
+
+  while x ~= 0
+    ## update window
+    window(1:n-la) = window(enco(2)+2:n-la+enco(2)+1);
+    if x < la
+      window(n-la+1:n) = [m(len-x+1:len) zeros(1,la-x)];
+    else
+      window(n-la+1:n) = m(len-x+1:len-x+la);
+    endif
+       
+    ## get a reference (position ,length) to longest match, and next symbol
+    enco = [0 0 0];
+    for y=(n-la):-1:1
+      z = 0;
+      while(z ~= la && (window(y+z) == window(n-la+z+1)))
+       z += 1;
+      endwhile
+               
+      if enco(2) < z
+       enco(1) = y-1;
+       enco(2) = z;
+       enco(3) = window(n-la+z+1);
+      endif
+    endfor
+
+    ## encoded message
+    if x == len
+      c = enco;
+    else
+      c = [c ; enco];
+    endif
+
+    x -= enco(2)+1;
+  endwhile
+endfunction
+
+%!demo
+%! lz77enco([0 0 1 0 1 0 2 1 0 2 1 0 2 1 2 0 2 1 0 2 1 2 0 0],3,9,18)