lib/next_prime.c

/* Determine prime number.
   Copyright (C) 2006 Red Hat, Inc.
   This file is part of Red Hat elfutils.
   Written by Ulrich Drepper <drepper@redhat.com>, 2000.

   Red Hat elfutils is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by the
   Free Software Foundation; version 2 of the License.

   Red Hat elfutils is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

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   with Red Hat elfutils; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.

   In addition, as a special exception, Red Hat, Inc. gives You the
   additional right to link the code of Red Hat elfutils with code licensed
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   for all of the Red Hat elfutils code and other code used in conjunction
   with Red Hat elfutils except the Non-GPL Code covered by this exception.
   If you modify this file, you may extend this exception to your version
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   exception statement from your version and license this file solely under
   the GPL without exception.

   Red Hat elfutils is an included package of the Open Invention Network.
   An included package of the Open Invention Network is a package for which
   Open Invention Network licensees cross-license their patents.  No patent
   license is granted, either expressly or impliedly, by designation as an
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#include <stddef.h>


/* Test whether CANDIDATE is a prime.  */
static int
is_prime (size_t candidate)
{
  /* No even number and none less than 10 will be passed here.  */
  size_t divn = 3;
  size_t sq = divn * divn;

  while (sq < candidate && candidate % divn != 0)
    {
      size_t old_sq = sq;
      ++divn;
      sq += 4 * divn;
      if (sq < old_sq)
	return 1;
      ++divn;
    }

  return candidate % divn != 0;
}


/* We need primes for the table size.  */
size_t
next_prime (size_t seed)
{
  /* Make it definitely odd.  */
  seed |= 1;

  while (!is_prime (seed))
    seed += 2;

  return seed;
}