next_prime.c revision 25b3c049e70834cf33790a28643ab058b507b35c
1/* Determine prime number.
2   Copyright (C) 2006 Red Hat, Inc.
3   This file is part of Red Hat elfutils.
4   Written by Ulrich Drepper <drepper@redhat.com>, 2000.
5
6   Red Hat elfutils is free software; you can redistribute it and/or modify
7   it under the terms of the GNU General Public License as published by the
8   Free Software Foundation; version 2 of the License.
9
10   Red Hat elfutils is distributed in the hope that it will be useful, but
11   WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   General Public License for more details.
14
15   You should have received a copy of the GNU General Public License along
16   with Red Hat elfutils; if not, write to the Free Software Foundation,
17   Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.
18
19   In addition, as a special exception, Red Hat, Inc. gives You the
20   additional right to link the code of Red Hat elfutils with code licensed
21   under an Open Source Initiative certified open source license
22   (http://www.opensource.org/licenses/index.php) and to distribute linked
23   combinations including the two.  Non-GPL Code permitted under this
24   exception must only link to the code of Red Hat elfutils through those
25   well defined interfaces identified in the file named EXCEPTION found in
26   the source code files (the "Approved Interfaces").  The files of Non-GPL
27   Code may instantiate templates or use macros or inline functions from
28   the Approved Interfaces without causing the resulting work to be covered
29   by the GNU General Public License.  Only Red Hat, Inc. may make changes
30   or additions to the list of Approved Interfaces.  Red Hat's grant of
31   this exception is conditioned upon your not adding any new exceptions.
32   If you wish to add a new Approved Interface or exception, please contact
33   Red Hat.  You must obey the GNU General Public License in all respects
34   for all of the Red Hat elfutils code and other code used in conjunction
35   with Red Hat elfutils except the Non-GPL Code covered by this exception.
36   If you modify this file, you may extend this exception to your version
37   of the file, but you are not obligated to do so.  If you do not wish to
38   provide this exception without modification, you must delete this
39   exception statement from your version and license this file solely under
40   the GPL without exception.
41
42   Red Hat elfutils is an included package of the Open Invention Network.
43   An included package of the Open Invention Network is a package for which
44   Open Invention Network licensees cross-license their patents.  No patent
45   license is granted, either expressly or impliedly, by designation as an
46   included package.  Should you wish to participate in the Open Invention
47   Network licensing program, please visit www.openinventionnetwork.com
48   <http://www.openinventionnetwork.com>.  */
49
50#include <stddef.h>
51
52
53/* Test whether CANDIDATE is a prime.  */
54static int
55is_prime (size_t candidate)
56{
57  /* No even number and none less than 10 will be passed here.  */
58  size_t divn = 3;
59  size_t sq = divn * divn;
60
61  while (sq < candidate && candidate % divn != 0)
62    {
63      size_t old_sq = sq;
64      ++divn;
65      sq += 4 * divn;
66      if (sq < old_sq)
67	return 1;
68      ++divn;
69    }
70
71  return candidate % divn != 0;
72}
73
74
75/* We need primes for the table size.  */
76size_t
77next_prime (size_t seed)
78{
79  /* Make it definitely odd.  */
80  seed |= 1;
81
82  while (!is_prime (seed))
83    seed += 2;
84
85  return seed;
86}
87