/* * Copyright (c) Contributors, http://opensimulator.org/ * See CONTRIBUTORS.TXT for a full list of copyright holders. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * Neither the name of the OpenSimulator Project nor the * names of its contributors may be used to endorse or promote products * derived from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ using System; namespace OpenSim.Framework { /// <summary> /// Utility class that is used to find small prime numbers and test is number prime number. /// </summary> public static class PrimeNumberHelper { /// <summary> /// Precalculated prime numbers. /// </summary> private static readonly int[] Primes = new int[] { 3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919, 1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591, 17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437, 187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263, 1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369 }; /// <summary> /// Get prime number that is equal or larger than <see cref="min"/>. /// </summary> /// <param name="min"> /// Minimal returned prime number. /// </param> /// <returns> /// Primer number that is equal or larger than <see cref="min"/>. If <see cref="min"/> is too large, return -1. /// </returns> public static int GetPrime(int min) { if (min <= 2) return 2; if (Primes[ Primes.Length - 1 ] < min) { for (int i = min | 1 ; i < 0x7FFFFFFF ; i += 2) { if (IsPrime(i)) return i; } return -1; } for (int i = Primes.Length - 2 ; i >= 0 ; i--) { if (min == Primes[ i ]) return min; if (min > Primes[ i ]) return Primes[ i + 1 ]; } return 2; } /// <summary> /// Just basic Sieve of Eratosthenes prime number test. /// </summary> /// <param name="candinate"> /// Number that is tested. /// </param> /// <returns> /// true, if <see cref="candinate"/> is prime number; otherwise false. /// </returns> public static bool IsPrime(int candinate) { if ((candinate & 1) == 0) // Even number - only prime if 2 return candinate == 2; int upperBound = (int) Math.Sqrt(candinate); for (int i = 3 ; i < upperBound ; i += 2) { if (candinate % i == 0) return false; } return true; } } }