string/strfry.c

   1 /* Copyright (C) 1992, 1996, 1999, 2002, 2007 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <string.h>
  20 #include <stdlib.h>
  21 #include <time.h>
  22 #include <unistd.h>
  23
  24 char *
  25 strfry (char *string)
  26 {
  27   static int init;
  28   static struct random_data rdata;
  29
  30   if (!init)
  31     {
  32       static char state[32];
  33       rdata.state = NULL;
  34       __initstate_r (time ((time_t *) NULL) ^ getpid (),
  35                      state, sizeof (state), &rdata);
  36       init = 1;
  37     }
  38
  39   size_t len = strlen (string);
  40   if (len > 0)
  41     for (size_t i = 0; i < len - 1; ++i)
  42       {
  43         int32_t j;
  44         __random_r (&rdata, &j);
  45         j = j % (len - i) + i;
  46
  47         char c = string[i];
  48         string[i] = string[j];
  49         string[j] = c;
  50       }
  51
  52   return string;
  53 }