This file is indexed.

/usr/share/octave/packages/communications-1.2.1/bchpoly.m is in octave-communications-common 1.2.1-5.

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
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
## 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} {@var{p} =} bchpoly ()
## @deftypefnx {Function File} {@var{p} =} bchpoly (@var{n})
## @deftypefnx {Function File} {@var{p} =} bchpoly (@var{n}, @var{k})
## @deftypefnx {Function File} {@var{p} =} bchpoly (@var{prim}, @var{k})
## @deftypefnx {Function File} {@var{p} =} bchpoly (@var{n}, @var{k}, @var{prim})
## @deftypefnx {Function File} {@var{p} =} bchpoly (@dots{}, @var{probe})
## @deftypefnx {Function File} {[@var{p}, @var{f}] =} bchpoly (@dots{})
## @deftypefnx {Function File} {[@var{p}, @var{f}, @var{c}] =} bchpoly (@dots{})
## @deftypefnx {Function File} {[@var{p}, @var{f}, @var{c}, @var{par}] =} bchpoly (@dots{})
## @deftypefnx {Function File} {[@var{p}, @var{f}, @var{c}, @var{par}, @var{t}] =} bchpoly (@dots{})
##
## Calculates the generator polynomials for a BCH coder. Called with no input
## arguments @code{bchpoly} returns a list of all of the valid BCH codes for
## the codeword length 7, 15, 31, 63, 127, 255 and 511. A three column matrix
## is returned with each row representing a separate valid BCH code. The first
## column is the codeword length, the second the message length and the third
## the error correction capability of the code.
##
## Called with a single input argument, @code{bchpoly} returns the valid BCH
## codes for the specified codeword length @var{n}. The output format is the
## same as above.
##
## When called with two or more arguments, @code{bchpoly} calculates the
## generator polynomial of a particular BCH code. The generator polynomial
## is returned in @var{p} as a vector representation of a polynomial in
## GF(2). The terms of the polynomial are listed least-significant term
## first.
##
## The desired BCH code can be specified by its codeword length @var{n}
## and its message length @var{k}. Alternatively, the primitive polynomial
## over which to calculate the polynomial can be specified as @var{prim}.
## If a vector representation of the primitive polynomial is given, then
## @var{prim} can be specified as the first argument of two arguments,
## or as the third argument. However, if an integer representation of the
## primitive polynomial is used, then the primitive polynomial must be
## specified as the third argument.
##
## When called with two or more arguments, @code{bchpoly} can also return the
## factors @var{f} of the generator polynomial @var{p}, the cyclotomic coset
## for the Galois field over which the BCH code is calculated, the parity
## check matrix @var{par} and the error correction capability @var{t}. It
## should be noted that the parity check matrix is calculated with
## @code{cyclgen} and limitations in this function means that the parity
## check matrix is only available for codeword length up to 63. For
## codeword length longer than this @var{par} returns an empty matrix.
##
## With a string argument @var{probe} defined, the action of @code{bchpoly}
## is to calculate the error correcting capability of the BCH code defined
## by @var{n}, @var{k} and @var{prim} and return it in @var{p}. This is
## similar to a call to @code{bchpoly} with zero or one argument, except that
## only a single code is checked. Any string value for @var{probe} will
## force this action.
##
## In general the codeword length @var{n} can be expressed as
## @code{2^@var{m}-1}, where @var{m} is an integer. However, if
## [@var{n},@var{k}] is a valid BCH code, then a shortened BCH code of
## the form [@var{n}-@var{x},@var{k}-@var{x}] can be created with the
## same generator polynomial
##
## @seealso{cyclpoly, encode, decode, cosets}
## @end deftypefn

function [p, f, c, par, t] = bchpoly (nn, k, varargin)

  if (nargin < 0 || nargin > 4)
    print_usage ();
  endif

  probe = 0;
  prim = 0;    ## Set to zero to use default primitive polynomial
  if (nargin == 0)
    m = [3:9];
    n = 2.^m - 1;
    nn = n;
  elseif (isscalar (nn))
    m = ceil (log2 (nn+1));
    n = 2.^m - 1;
    if (! (n == fix (n) && n >= 7 && m == fix (m)))
      error ("bchpoly: N must be a integer greater than 3");
    endif
  else
    prim = bi2de (n);
    if (!isprimitive (prim))
      error ("bchpoly: PRIM must be a primitive polynomial of GF(2^M)");
    endif
    m = length (n) - 1;
    n = 2^m - 1;
  endif

  if (nargin > 1 && ! (isscalar (k) && k == fix (k) && k <= n))
    error ("bchpoly: K must be an integer less than N");
  endif

  for i = 1:length (varargin)
    arg = varargin{i};
    if (ischar (arg))
      probe = 1;
      if (nargout > 1)
        error ("bchpoly: only one output argument allowed when probing valid codes");
      endif
    else
      if (prim != 0)
        error ("bchpoly: primitive polynomial already defined");
      endif
      prim = arg;
      if (!isscalar (prim))
        prim = bi2de (prim);
      endif
      if (! (prim == fix (prim) && prim >= 2^m && prim <= 2^(m+1)
             && isprimitive (prim)))
        error ("bchpoly: PRIM must be a primitive polynomial of GF(2^M)");
      endif
    endif
  endfor

  ## Am I using the right algo to calculate the correction capability?
  if (nargin < 2)
    if (nargout > 1)
      error ("bchpoly: only one output argument allowed when probing valid codes");
    endif

    p = [];
    for ni = 1:length (n)
      c = cosets (m(ni), prim);
      nc = length (c);
      fc = zeros (1, nc);
      f = [];

      for t = 1:floor (n(ni)/2)
        for i = 1:nc
          if (fc(i) != 1)
            cl = log (c{i});
            for j = 2*(t-1)+1:2*t
              if (find (cl == j))
                f = [f, c{i}.x];
                fc(i) = 1;
                break;
              endif
            endfor
          endif
        endfor

        k = nn(ni) - length (f);
        if (k < 2)
          break;
        endif

        if (!isempty (p) && (k == p(size (p, 1),2)))
          p(size (p, 1),:) = [nn(ni), k, t];
        else
          p = [p; [nn(ni), k, t]];
        endif
      endfor
    endfor
  else
    c = cosets (m, prim);
    nc = length (c);
    fc = zeros (1, nc);
    f = [];
    fl = 0;
    f0 = [];
    f1 = [];
    t = 0;
    do
      t++;
      f0 = f1;
      for i = 1:nc
        if (fc(i) != 1)
          cl = log (c{i});
          for j = 2*(t-1)+1:2*t
            if (find (cl == j))
              f1 = [f1, c{i}.x];
              fc(i) = 1;
              ptmp = gf ([c{i}(1), 1], m, prim);
              for l = 2:length (c{i})
                ptmp = conv (ptmp, [c{i}(l), 1]);
              endfor
              f = [f; [ptmp.x, zeros(1, m - length (ptmp) + 1)]];
              fl = fl + length (ptmp);
              break;
            endif
          endfor
        endif
      endfor
    until (length (f1) > nn - k)
    t--;

    if (nn - length (f0) != k)
      error ("bchpoly: could not find valid generator polynomial for parameters");
    endif

    if (probe)
      p = [nn, k, t];
    else

      ## Have to delete a line from the list of minimum polynomials
      ## since we've gone one past in calculating f1 above to be
      ## sure or the error correcting capability
      f = f(1:size (f, 1) - 1,:);

      p = gf ([f0(1), 1], m, prim);
      for i = 2:length (f0)
        p = conv (p, [f0(i), 1]);
      endfor
      p = p.x;

      if (nargout > 3)
        if (n > 64)
          warning ("bchpoly: could not create parity matrix");
          par = [];
        else
          par = cyclgen (n, p);
        endif
      endif
    endif
  endif

endfunction

%% Test input validation
%!error bchpoly (1)
%!error bchpoly (1, 2, 3, 4, 5)
%!error bchpoly (5, 10)