90 lines
2.8 KiB
C#
90 lines
2.8 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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namespace Duplicati.Library.Main.ForestHash.Database
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{
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/// <summary>
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/// Provides a simple hash-table like lookup,
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/// similar to a MRU cache
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/// </summary>
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internal class HashLookup<T>
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{
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private const long MAX_MEMORY = 32 * 1024 * 1024; //32mb
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/// <summary>
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/// The lookup table with all values
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/// </summary>
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private T[] m_lookup;
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/// <summary>
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/// Typecasted size of table
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/// </summary>
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private ulong m_modulo;
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public HashLookup(uint elementsize, ulong memorylimit = MAX_MEMORY)
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{
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//Allocate as a large boolean/bit array
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m_lookup = new T[Math.Max(32, Math.Max(1024, memorylimit * 8) / elementsize)];
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m_modulo = (ulong)m_lookup.Length;
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}
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/// <summary>
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/// Adds a hash to the table
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/// </summary>
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/// <param name="key">The hash key</param>
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/// <param name="value">The actual hash data</param>
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public void AddHash(ulong key, T value)
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{
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//Textbox hashing, the value modulo number of entries
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// works because the input is high quality random data
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var bit = key % m_modulo;
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m_lookup[bit] = value;
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}
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/// <summary>
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/// Queries the table to see if a hash exists.
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/// A true result value is definitive, a false result value should be interpreted as maybe.
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/// </summary>
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/// <param name="key">The hash key</param>
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/// <param name="data">The actual hash data</param>
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/// <returns>True if the hash was found, false otherwise</returns>
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public bool HashExists(ulong key, T value)
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{
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//Textbox hashing, the value modulo number of entries
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// works because the input is high quality random data
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var bit = key % m_modulo;
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return object.Equals(m_lookup[bit], value);
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}
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/// <summary>
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/// Calculates number of used entries in the table
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/// </summary>
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public ulong Entries
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{
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get
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{
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ulong c = 0;
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foreach (var x in m_lookup)
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if (!object.Equals(x, default(T)))
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c++;
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return c;
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}
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}
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/// <summary>
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/// Gets a value between 0 and 1 descring how
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/// many entries are used
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/// </summary>
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public double TableUsageRatio
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{
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get
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{
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return Entries / (double)m_lookup.Length;
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}
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}
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}
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}
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