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view main/comm/inst/lz77enco.m @ 9666:67d4cfc5eeb3 octave-forge
comm: update license to GPLv3+
author | carandraug |
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date | Tue, 13 Mar 2012 04:31:21 +0000 |
parents | 90a46621a91d |
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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{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)