Stephane Eranian | e0ab292 | 2006-10-11 01:21:45 -0700 | [diff] [blame] | 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); |