92 lines
2.8 KiB
C#
92 lines
2.8 KiB
C#
using System;
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namespace Bright.Common
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{
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/// <summary>
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/// 从 System.Collections.HashTable 源码抄来
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/// </summary>
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public static class HashUtil
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{
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private static readonly int[] primes = {
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3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919,
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1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591,
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17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437,
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187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263,
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1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369};
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private const int HashPrime = 101;
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private const int MaxPrimeArrayLength = 0x7FEFFFFD;
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public static int GetPrime(int min)
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{
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if (min < 0)
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throw new ArgumentException();
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for (int i = 0; i < primes.Length; i++)
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{
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int prime = primes[i];
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if (prime >= min) return prime;
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}
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//outside of our predefined table.
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//compute the hard way.
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for (int i = (min | 1); i < int.MaxValue; i += 2)
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{
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if (IsPrime(i) && ((i - 1) % HashPrime != 0))
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return i;
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}
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return min;
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}
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public static bool IsPrime(int candidate)
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{
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if ((candidate & 1) != 0)
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{
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int limit = (int)Math.Sqrt(candidate);
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for (int divisor = 3; divisor <= limit; divisor += 2)
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{
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if ((candidate % divisor) == 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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return (candidate == 2);
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}
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public static int GetMinPrime()
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{
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return primes[0];
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}
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// Returns size of hashtable to grow to.
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public static int ExpandPrime(int oldSize)
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{
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int newSize = 2 * oldSize;
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// Allow the hashtables to grow to maximum possible size (~2G elements) before encoutering capacity overflow.
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// Note that this check works even when _items.Length overflowed thanks to the (uint) cast
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if ((uint)newSize > MaxPrimeArrayLength && MaxPrimeArrayLength > oldSize)
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{
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return MaxPrimeArrayLength;
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}
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return GetPrime(newSize);
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}
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public static int CalcHash(int x)
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{
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int hash = 17;
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return hash * 23 + x;
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}
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public static int CalcHash(int x, int y)
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{
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int hash = 17;
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hash = hash * 23 + x;
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return hash * 23 + y;
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}
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}
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}
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