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glibc  2.9
rand_r.c
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00001 /* Reentrant random function frm POSIX.1c.
00002    Copyright (C) 1996, 1999 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
00005 
00006    The GNU C Library is free software; you can redistribute it and/or
00007    modify it under the terms of the GNU Lesser General Public
00008    License as published by the Free Software Foundation; either
00009    version 2.1 of the License, or (at your option) any later version.
00010 
00011    The GNU C Library is distributed in the hope that it will be useful,
00012    but WITHOUT ANY WARRANTY; without even the implied warranty of
00013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014    Lesser General Public License for more details.
00015 
00016    You should have received a copy of the GNU Lesser General Public
00017    License along with the GNU C Library; if not, write to the Free
00018    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00019    02111-1307 USA.  */
00020 
00021 #include <stdlib.h>
00022 
00023 
00024 /* This algorithm is mentioned in the ISO C standard, here extended
00025    for 32 bits.  */
00026 int
00027 rand_r (unsigned int *seed)
00028 {
00029   unsigned int next = *seed;
00030   int result;
00031 
00032   next *= 1103515245;
00033   next += 12345;
00034   result = (unsigned int) (next / 65536) % 2048;
00035 
00036   next *= 1103515245;
00037   next += 12345;
00038   result <<= 10;
00039   result ^= (unsigned int) (next / 65536) % 1024;
00040 
00041   next *= 1103515245;
00042   next += 12345;
00043   result <<= 10;
00044   result ^= (unsigned int) (next / 65536) % 1024;
00045 
00046   *seed = next;
00047 
00048   return result;
00049 }