libc/stdlib/rand_r.c

   1 /* Reentrant random function frm POSIX.1c.
   2    Copyright (C) 1996, 1999 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com <mailto: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 rand_r (unsigned int *seed)
  26 {
  27     unsigned int next = *seed;
  28     int result;
  29
  30     next *= 1103515245;
  31     next += 12345;
  32     result = (unsigned int) (next / 65536) % 2048;
  33
  34     next *= 1103515245;
  35     next += 12345;
  36     result <<= 10;
  37     result ^= (unsigned int) (next / 65536) % 1024;
  38
  39     next *= 1103515245;
  40     next += 12345;
  41     result <<= 10;
  42     result ^= (unsigned int) (next / 65536) % 1024;
  43
  44     *seed = next;
  45
  46     return result;
  47 }