89 lines
2.4 KiB
C#
89 lines
2.4 KiB
C#
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using System;
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using System.Buffers.Binary;
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using System.Collections.Generic;
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using System.IO;
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using System.Runtime.InteropServices;
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using System.Text;
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using System.Threading;
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using System.Threading.Tasks;
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namespace PCL.Core.Utils.Hash;
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public class MurmurHash2Provider : IHashProvider
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{
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public static MurmurHash2Provider Instance { get; } = new();
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public int Length => 8;
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public byte[] ComputeHash(ReadOnlySpan<byte> data)
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{
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var filtered = new List<byte>(data.Length);
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foreach (var b in data)
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if (b != 9 && b != 10 && b != 13 && b != 32)
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filtered.Add(b);
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return _ComputeHash(CollectionsMarshal.AsSpan(filtered));
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}
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public byte[] ComputeHash(string input, Encoding? encoding = null)
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{
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encoding ??= Encoding.UTF8;
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return ComputeHash(encoding.GetBytes(input));
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}
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public byte[] ComputeHash(Stream input)
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{
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using var ms = new MemoryStream();
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input.CopyTo(ms);
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return ComputeHash(ms.GetBuffer().AsSpan(0, (int)ms.Length));
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}
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public async ValueTask<byte[]> ComputeHashAsync(Stream input, CancellationToken cancellationToken = default)
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{
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using var ms = new MemoryStream();
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await input.CopyToAsync(ms, cancellationToken).ConfigureAwait(false);
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return ComputeHash(ms.GetBuffer().AsSpan(0, (int)ms.Length));
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}
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private static byte[] _ComputeHash(ReadOnlySpan<byte> data)
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{
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var h = (uint)(1 ^ data.Length);
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var i = 0;
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var loopTo = data.Length - 4;
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for (; i <= loopTo; i += 4)
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{
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var k = data[i]
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| ((uint)data[i + 1] << 8)
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| ((uint)data[i + 2] << 16)
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| ((uint)data[i + 3] << 24);
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k *= 0x5BD1E995;
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k ^= k >> 24;
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k *= 0x5BD1E995;
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h *= 0x5BD1E995;
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h ^= k;
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}
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switch (data.Length - i)
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{
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case 3:
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h ^= (uint)(data[i] | ((uint)data[i + 1] << 8));
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h ^= (uint)data[i + 2] << 16;
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h *= 0x5BD1E995;
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break;
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case 2:
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h ^= (uint)(data[i] | ((uint)data[i + 1] << 8));
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h *= 0x5BD1E995;
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break;
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case 1:
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h ^= data[i];
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h *= 0x5BD1E995;
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break;
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}
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h ^= h >> 13;
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h *= 0x5BD1E995;
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h ^= h >> 15;
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return BitConverter.GetBytes(h);
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}
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}
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