glib/gprimes.c

/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

/*
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GLib at ftp://ftp.gtk.org/pub/gtk/.
 */

/*
 * MT safe
 */

#include "config.h"

#include "gprimes.h"


static const guint g_primes[] =
{
  11,
  19,
  37,
  73,
  109,
  163,
  251,
  367,
  557,
  823,
  1237,
  1861,
  2777,
  4177,
  6247,
  9371,
  14057,
  21089,
  31627,
  47431,
  71143,
  106721,
  160073,
  240101,
  360163,
  540217,
  810343,
  1215497,
  1823231,
  2734867,
  4102283,
  6153409,
  9230113,
  13845163,
};

/**
 * g_spaced_primes_closest:
 * @num: a #guint
 *
 * Gets the smallest prime number from a built-in array of primes which
 * is larger than @num. This is used within GLib to calculate the optimum
 * size of a #GHashTable.
 *
 * The built-in array of primes ranges from 11 to 13845163 such that
 * each prime is approximately 1.5-2 times the previous prime.
 *
 * Returns: the smallest prime number from a built-in array of primes
 *     which is larger than @num
 */
guint
g_spaced_primes_closest (guint num)
{
  gsize i;

  for (i = 0; i < G_N_ELEMENTS (g_primes); i++)
    if (g_primes[i] > num)
      return g_primes[i];

  return g_primes[G_N_ELEMENTS (g_primes) - 1];
}