string/strfry.c

   1 /* Copyright (C) 1992-2020 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, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <string.h>
  19 #include <stdlib.h>
  20 #include <random-bits.h>
  21 #include <unistd.h>
  22
  23 char *
  24 strfry (char *string)
  25 {
  26   static int init;
  27   static struct random_data rdata;
  28
  29   if (!init)
  30     {
  31       static char state[32];
  32       rdata.state = NULL;
  33       __initstate_r (random_bits (),
  34                      state, sizeof (state), &rdata);
  35       init = 1;
  36     }
  37
  38   size_t len = strlen (string);
  39   if (len > 0)
  40     for (size_t i = 0; i < len - 1; ++i)
  41       {
  42         int32_t j;
  43         __random_r (&rdata, &j);
  44         j = j % (len - i) + i;
  45
  46         char c = string[i];
  47         string[i] = string[j];
  48         string[j] = c;
  49       }
  50
  51   return string;
  52 }