lib/carta_random32.c

   1 /*
   2  * Copyright (c) 2002-2006 Hewlett-Packard Development Company, L.P.
   3  *      Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of version 2 of the GNU General Public
   7  * License as published by the Free Software Foundation.
   8  *
   9  * This program 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  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17  * 02111-1307 USA
  18  */
  19 #include <linux/types.h>
  20 #include <linux/module.h>
  21
  22 /*
  23  * Fast, simple, yet decent quality random number generator based on
  24  * a paper by David G. Carta ("Two Fast Implementations of the
  25  * `Minimal Standard' Random Number Generator," Communications of the
  26  * ACM, January, 1990).
  27  */
  28 u64 carta_random32 (u64 seed)
  29 {
  30 #       define A 16807
  31 #       define M ((u32) 1 << 31)
  32         u64 s, prod = A * seed, p, q;
  33
  34         p = (prod >> 31) & (M - 1);
  35         q = (prod >>  0) & (M - 1);
  36         s = p + q;
  37         if (s >= M)
  38                 s -= M - 1;
  39         return s;
  40 }
  41 EXPORT_SYMBOL_GPL(carta_random32);