stdlib/rand_r.c

   1 /* Reentrant random function from POSIX.1c.
   2    Copyright (C) 1996-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <stdlib.h>
  20
  21
  22 /* This algorithm is mentioned in the ISO C standard, here extended
  23    for 32 bits.  */
  24 int
  25 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 }