stdlib/rand_r.c

   1 /* Reentrant random function from POSIX.1c.
   2    Copyright (C) 1996-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <stdlib.h>
  21
  22
  23 /* This algorithm is mentioned in the ISO C standard, here extended
  24    for 32 bits.  */
  25 int
  26 rand_r (unsigned int *seed)
  27 {
  28   unsigned int next = *seed;
  29   int result;
  30
  31   next *= 1103515245;
  32   next += 12345;
  33   result = (unsigned int) (next / 65536) % 2048;
  34
  35   next *= 1103515245;
  36   next += 12345;
  37   result <<= 10;
  38   result ^= (unsigned int) (next / 65536) % 1024;
  39
  40   next *= 1103515245;
  41   next += 12345;
  42   result <<= 10;
  43   result ^= (unsigned int) (next / 65536) % 1024;
  44
  45   *seed = next;
  46
  47   return result;
  48 }