107 lines
4.2 KiB
C#
107 lines
4.2 KiB
C#
using System;
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using System.Diagnostics.Contracts;
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using System.Runtime.CompilerServices;
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using System.Runtime.ConstrainedExecution;
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using System.Runtime.Serialization;
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using System.Threading;
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namespace Cryville.Common.Collections {
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internal static class HashHelpers {
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#if FEATURE_RANDOMIZED_STRING_HASHING
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public const int HashCollisionThreshold = 100;
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public static bool s_UseRandomizedStringHashing = String.UseRandomizedHashing();
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#endif
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// Table of prime numbers to use as hash table sizes.
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// A typical resize algorithm would pick the smallest prime number in this array
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// that is larger than twice the previous capacity.
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// Suppose our Hashtable currently has capacity x and enough elements are added
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// such that a resize needs to occur. Resizing first computes 2x then finds the
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// first prime in the table greater than 2x, i.e. if primes are ordered
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// p_1, p_2, ..., p_i, ..., it finds p_n such that p_n-1 < 2x < p_n.
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// Doubling is important for preserving the asymptotic complexity of the
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// hashtable operations such as add. Having a prime guarantees that double
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// hashing does not lead to infinite loops. IE, your hash function will be
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// h1(key) + i*h2(key), 0 <= i < size. h2 and the size must be relatively prime.
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public 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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// Used by Hashtable and Dictionary's SeralizationInfo .ctor's to store the SeralizationInfo
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// object until OnDeserialization is called.
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private static ConditionalWeakTable<object, SerializationInfo> s_SerializationInfoTable;
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internal static ConditionalWeakTable<object, SerializationInfo> SerializationInfoTable {
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get {
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if (s_SerializationInfoTable == null) {
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ConditionalWeakTable<object, SerializationInfo> newTable = new ConditionalWeakTable<object, SerializationInfo>();
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Interlocked.CompareExchange(ref s_SerializationInfoTable, newTable, null);
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}
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return s_SerializationInfoTable;
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}
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}
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[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
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public static bool IsPrime(int candidate) {
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if ((candidate & 1) != 0) {
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int limit = (int)System.Math.Sqrt (candidate);
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for (int divisor = 3; divisor <= limit; divisor += 2) {
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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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internal const Int32 HashPrime = 101;
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[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
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public static int GetPrime(int min) {
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if (min < 0)
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throw new ArgumentException("Hashtable's capacity overflowed and went negative. Check load factor, capacity and the current size of the table.");
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Contract.EndContractBlock();
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for (int i = 0; i < primes.Length; i++) {
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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 < Int32.MaxValue; i += 2) {
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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 int GetMinPrime() {
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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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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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Contract.Assert(MaxPrimeArrayLength == GetPrime(MaxPrimeArrayLength), "Invalid MaxPrimeArrayLength");
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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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// This is the maximum prime smaller than Array.MaxArrayLength
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public const int MaxPrimeArrayLength = 0x7FEFFFFD;
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}
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}
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