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