/usr/share/octave/packages/communications-1.2.1/lz77enco.m is in octave-communications-common 1.2.1-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 | ## 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: LA and N must be positive integers");
endif
if (n - la < la)
error ("lz77deco: N must be >= 2*LA");
endif
if (alph < 2)
error ("lz77enco: ALPH must be >= 2");
endif
if (max (m) + 1 > alph)
error ("lz77enco: ALPH must be greater than the largest element of M");
endif
if (rows (m) != 1)
error ("lz77enco: M must be a row vector");
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)
%% Test input validation
%!error lz77enco (1, 1, 1, 1)
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