107 lines
2.3 KiB
C#
107 lines
2.3 KiB
C#
//
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// HashPrimeNumbers.cs
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//
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// Author:
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// Sergey Chaban (serge@wildwestsoftware.com)
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//
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// Copyright (C) 2004-2005 Novell, Inc (http://www.novell.com)
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//
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// Permission is hereby granted, free of charge, to any person obtaining
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// a copy of this software and associated documentation files (the
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// "Software"), to deal in the Software without restriction, including
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// without limitation the rights to use, copy, modify, merge, publish,
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// distribute, sublicense, and/or sell copies of the Software, and to
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// permit persons to whom the Software is furnished to do so, subject to
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// the following conditions:
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//
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// The above copyright notice and this permission notice shall be
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// included in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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//
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namespace System.Collections
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{
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static class HashPrimeNumbers
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{
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static readonly int [] primeTbl = {
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11,
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19,
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37,
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73,
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109,
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163,
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251,
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367,
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557,
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823,
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1237,
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1861,
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2777,
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4177,
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6247,
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9371,
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14057,
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21089,
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31627,
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47431,
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71143,
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106721,
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160073,
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240101,
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360163,
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540217,
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810343,
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1215497,
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1823231,
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2734867,
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4102283,
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6153409,
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9230113,
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13845163
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};
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//
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// Private static methods
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//
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public static bool TestPrime (int x)
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{
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if ((x & 1) != 0) {
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int top = (int)Math.Sqrt (x);
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for (int n = 3; n < top; n += 2) {
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if ((x % n) == 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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// There is only one even prime - 2.
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return (x == 2);
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}
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public static int CalcPrime (int x)
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{
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for (int i = (x & (~1))-1; i< Int32.MaxValue; i += 2) {
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if (TestPrime (i)) return i;
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}
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return x;
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}
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public static int ToPrime (int x)
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{
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for (int i = 0; i < primeTbl.Length; i++) {
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if (x <= primeTbl [i])
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return primeTbl [i];
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}
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return CalcPrime (x);
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}
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}
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} |