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