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A simple Bloom Filter implementation in C#
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| using System; | |
| namespace BloomFilter | |
| { | |
| class Program | |
| { | |
| static void Main(string[] args) | |
| { | |
| AddItem("test"); | |
| AddItem("test2"); | |
| AddItem("test3"); | |
| AddItem("test4"); | |
| AddItem("test5"); | |
| Console.WriteLine(PossiblyExists("whatever")); | |
| Console.WriteLine(PossiblyExists("test")); | |
| Console.WriteLine(PossiblyExists("test2")); | |
| Console.WriteLine(PossiblyExists("test3")); | |
| Console.WriteLine(PossiblyExists("test4")); | |
| Console.WriteLine(PossiblyExists("test5")); | |
| Console.WriteLine(PossiblyExists("test6")); | |
| Console.ReadKey(); | |
| } | |
| private static byte[] _bloomFilter = new byte[1000]; | |
| static void AddItem(string item) | |
| { | |
| int hash = Hash(item) & 0x7FFFFFFF; // strips signed bit | |
| byte bit = (byte)(1 << (hash & 7)); // you have 8 bits | |
| _bloomFilter[hash % _bloomFilter.Length] |= bit; | |
| } | |
| static bool PossiblyExists(string item) | |
| { | |
| int hash = Hash(item) & 0x7FFFFFFF; | |
| byte bit = (byte)(1 << (hash & 7)); // you have 8 bits; | |
| return (_bloomFilter[hash % _bloomFilter.Length] & bit) != 0; | |
| } | |
| private static int Hash(string item) | |
| { | |
| int result = 17; | |
| for (int i = 0; i < item.Length; i++) | |
| { | |
| unchecked | |
| { | |
| result *= item[i]; | |
| } | |
| } | |
| return result; | |
| } | |
| } | |
| } |
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