This file is indexed.

/usr/share/octave/packages/communications-1.2.1/decode.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
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
## 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{msg} =} decode (@var{code}, @var{n}, @var{k})
## @deftypefnx {Function File} {@var{msg} =} decode (@var{code}, @var{n}, @var{k}, @var{typ})
## @deftypefnx {Function File} {@var{msg} =} decode (@var{code}, @var{n}, @var{k}, @var{typ}, @var{opt1})
## @deftypefnx {Function File} {@var{msg} =} decode (@var{code}, @var{n}, @var{k}, @var{typ}, @var{opt1}, @var{opt2})
## @deftypefnx {Function File} {[@var{msg}, @var{err}] =} decode (@dots{})
## @deftypefnx {Function File} {[@var{msg}, @var{err}, @var{ccode}] =} decode (@dots{})
## @deftypefnx {Function File} {[@var{msg}, @var{err}, @var{ccode}, @var{cerr}] =} decode (@dots{})
##
## Top level block decoder. This function makes use of the lower level
## functions such as @code{cyclpoly}, @code{cyclgen}, @code{hammgen}, and
## @code{bchenco}. The coded message to decode is pass in @var{code}, the
## codeword length is @var{n} and the message length is @var{k}. This
## function is used to decode messages using either:
##
## @table @asis
## @item A [n,k] linear block code defined by a generator matrix
## @item A [n,k] cyclic code defined by a generator polynomial
## @item A [n,k] Hamming code defined by a primitive polynomial
## @item A [n,k] BCH code code defined by a generator polynomial
## @end table
##
## The type of coding to use is defined by the variable @var{typ}. This
## variable is a string taking one of the values
##
## @table @code
## @item  "linear"
## @itemx "linear/binary"
## A linear block code is assumed with the message @var{msg} being in a
## binary format. In this case the argument @var{opt1} is the generator
## matrix, and is required. Additionally, @var{opt2} containing the
## syndrome lookup table (see @code{syndtable}) can also be passed.
## @item  "cyclic"
## @itemx "cyclic/binary"
## A cyclic code is assumed with the message @var{msg} being in a binary
## format. The generator polynomial to use can be defined in @var{opt1}.
## The default generator polynomial to use will be
## @code{cyclpoly (@var{n}, @var{k})}. Additionally, @var{opt2} containing the
## syndrome lookup table (see @code{syndtable}) can also be passed.
## @item  "hamming"
## @itemx "hamming/binary"
## A Hamming code is assumed with the message @var{msg} being in a binary
## format. In this case @var{n} must be of an integer of the form
## @code{2^@var{m}-1}, where @var{m} is an integer. In addition @var{k}
## must be @code{@var{n}-@var{m}}. The primitive polynomial to use can
## be defined in @var{opt1}. The default primitive polynomial to use is
## the same as defined by @code{hammgen}. The variable @var{opt2} should
## not be defined.
## @item  "bch"
## @itemx "bch/binary"
## A BCH code is assumed with the message @var{msg} being in a binary
## format. The primitive polynomial to use can be defined in @var{opt2}.
## The error correction capability of the code can also be defined in
## @var{opt1}. Use the empty matrix [] to let the error correction
## capability take the default value.
## @end table
##
## In addition the argument "binary" above can be replaced with "decimal",
## in which case the message is assumed to be a decimal vector, with each
## value representing a symbol to be coded. The binary format can be in two
## forms
##
## @table @code
## @item An @var{x}-by-@var{n} matrix
## Each row of this matrix represents a symbol to be decoded
## @item A vector with length divisible by @var{n}
## The coded symbols are created from groups of @var{n} elements of this vector
## @end table
##
## The decoded message is return in @var{msg}. The number of errors encountered
## is returned in @var{err}. If the coded message format is "decimal" or a
## "binary" matrix, then @var{err} is a column vector having a length equal
## to the number of decoded symbols. If @var{code} is a "binary" vector, then
## @var{err} is the same length as @var{msg} and indicated the number of
## errors in each symbol. If the value @var{err} is positive it indicates the
## number of errors corrected in the corresponding symbol. A negative value
## indicates an uncorrectable error. The corrected code is returned in
## @var{ccode} in a similar format to the coded message @var{msg}. The
## variable @var{cerr} contains similar data to @var{err} for @var{ccode}.
##
## It should be noted that all internal calculations are performed in the
## binary format. Therefore for large values of @var{n}, it is preferable
## to use the binary format to pass the messages to avoid possible rounding
## errors. Additionally, if repeated calls to @code{decode} will be performed,
## it is often faster to create a generator matrix externally with the
## functions @code{hammgen} or @code{cyclgen}, rather than let @code{decode}
## recalculate this matrix at each iteration. In this case @var{typ} should
## be "linear". The exception to this case is BCH codes, where the required
## syndrome table is too large. The BCH decoder, decodes directly from the
## polynomial never explicitly forming the syndrome table.
##
## @seealso{encode, cyclgen, cyclpoly, hammgen, bchdeco, bchpoly, syndtable}
## @end deftypefn

function [msg, err, ccode, cerr] = decode (code, n, k, typ, opt1, opt2)

  if (nargin < 3 || nargin > 6)
    print_usage ();
  endif

  if (! (isscalar (n) && n == fix (n) && n >= 3))
    error ("decode: N must be an integer greater than 3");
  endif

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

  if (nargin > 3)
    if (!ischar (typ))
      error ("decode: TYP must be a string");
    else
      ## Why the hell did matlab decide on such an ugly way of passing 2 args!
      if (strcmp (typ, "linear") || strcmp (typ, "linear/binary"))
        coding = "linear";
        msgtyp = "binary";
      elseif (strcmp (typ, "linear/decimal"))
        coding = "linear";
        msgtyp = "decimal";
      elseif (strcmp (typ, "cyclic") || strcmp (typ, "cyclic/binary"))
        coding = "cyclic";
        msgtyp = "binary";
      elseif (strcmp (typ, "cyclic/decimal"))
        coding = "cyclic";
        msgtyp = "decimal";
      elseif (strcmp (typ, "bch") || strcmp (typ, "bch/binary"))
        coding = "bch";
        msgtyp = "binary";
      elseif (strcmp (typ, "bch/decimal"))
        coding = "bch";
        msgtyp = "decimal";
      elseif (strcmp (typ, "hamming") || strcmp (typ, "hamming/binary"))
        coding = "hamming";
        msgtyp = "binary";
      elseif (strcmp (typ, "hamming/decimal"))
        coding = "hamming";
        msgtyp = "decimal";
      else
        error ("decode: invalid coding and/or message TYP '%s'", typ);
      endif
    endif
  else
    coding = "hamming";
    msgtyp = "binary";
  endif

  if (strcmp (msgtyp, "binary"))
    vecttyp = 0;
    if ((max (code(:)) > 1) || (min (code(:)) < 0))
      error ("decode: CODE must be a binary matrix");
    endif
    [ncodewords, n2] = size (code);
    len = n2*ncodewords;
    if (len/n != fix (len/n))
      error ("decode: size of CODE must be a multiple of N");
    endif
    if (min (n2, ncodewords) == 1)
      vecttyp = 1;
      ncodewords = len / n;
      code = reshape (code, n, ncodewords);
      code = code';
    elseif (n2 != n)
      error ("decode: CODE must be a matrix with N columns");
    endif
  else
    if (!isvector (code))
      error ("decode: decimal CODE type must be a vector");
    endif
    if (max (code) > 2^n-1 || min (code) < 0)
      error ("decode: all elements of CODE must be in the range [0,2^N-1]");
    endif
    ncodewords = length (code);
    code = de2bi (code(:), n);
  endif

  if (strcmp (coding, "bch"))
    if (nargin < 5 || isempty (opt1))
      tmp = bchpoly (n, k, "probe");
      t = tmp(3);
    else
      t = opt1;
    endif

    if (nargin > 5)
      [msg err ccode] = bchdeco (code, k, t, opt2);
    else
      [msg err ccode] = bchdeco (code, k, t);
    endif
    cerr = err;
  else
    if (strcmp (coding, "linear"))
      if (nargin > 4)
        gen = opt1;
        if ((size (gen, 1) != k) || (size (gen, 2) != n))
          error ("decode: generator matrix must be of size KxN");
        endif
        par = gen2par (gen);
        if (nargin > 5)
          st = opt2;
        else
          st = syndtable (par);
        endif
      else
        error ("decode: linear coding requires a generator matrix");
      endif
    elseif (strcmp (coding, "cyclic"))
      if (nargin > 4)
        [par, gen] = cyclgen (n, opt1);
      else
        [par, gen] = cyclgen (n, cyclpoly (n, k));
      endif
      if (nargin > 5)
        ## FIXME: Should we check that the generator polynomial is
        ## consistent with the syndrome table. Where is the acceleration in
        ## this case???
        st = opt2;
      else
        st = syndtable (par);
      endif
    else
      m = log2 (n + 1);
      if (! (m == fix (m) && m >= 3 && m <= 16))
        error ("decode: N must be equal to 2^M-1 for integer M in the range [3,16]");
      endif
      if (k != (n-m))
        error ("decode: K must be equal to N-M for Hamming decoder");
      endif
      if (nargin > 4)
        [par, gen] = hammgen (m, opt1);
      else
        [par, gen] = hammgen (m);
      endif
      if (nargin > 5)
        error ("decode: too many arguments for Hamming decoder");
      else
        st = syndtable (par);
      endif
    endif

    errvec = st(bi2de ((mod (par * code', 2))', "left-msb") + 1,:);
    ccode = mod (code+errvec, 2);
    err = sum (errvec');
    cerr = err;
    if (isequal (gen(:,1:k), eye (k)))
      msg = ccode(:,1:k);
    elseif (isequal (gen(:,n-k+1:n), eye (k)))
      msg = ccode(:,n-k+1:n);
    else
      error ("decode: generator matrix must be in standard form");
    endif
  endif

  if (strcmp (msgtyp, "binary") && vecttyp == 1)
    msg = msg';
    msg = msg(:);
    ccode = ccode';
    ccode = ccode(:);
    err = ones (k, 1) * err;
    err = err(:);
    cerr = ones (n, 1) * cerr;
    cerr = cerr(:);
  else
    err = err(:);
    cerr = cerr(:);
    if (strcmp (msgtyp, "decimal"))
      msg = bi2de (msg);
      ccode = bi2de (ccode);
    endif
  endif

endfunction

%% Test input validation
%!error decode ()
%!error decode (1)
%!error decode (1, 2)
%!error decode (1, 2, 3, 4, 5, 6, 7)
%!error decode (1, 2, 3)
%!error decode (1, 5, 6)
%!error decode (1, 5, 3, "invalid")