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111 行
4.0 KiB
111 行
4.0 KiB
#if NETCOREAPP3_0
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using System;
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using System.Runtime.InteropServices;
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using System.Runtime.Intrinsics.X86;
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#endif
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namespace LiteNetLib.Utils
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{
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//Implementation from Crc32.NET
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public static class CRC32C
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{
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public const int ChecksumSize = 4;
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private const uint Poly = 0x82F63B78u;
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private static readonly uint[] Table;
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static CRC32C()
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{
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#if NETCOREAPP3_0
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if(Sse42.IsSupported)
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return;
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#endif
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Table = new uint[16 * 256];
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for (uint i = 0; i < 256; i++)
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{
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uint res = i;
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for (int t = 0; t < 16; t++)
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{
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for (int k = 0; k < 8; k++)
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res = (res & 1) == 1 ? Poly ^ (res >> 1) : (res >> 1);
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Table[t * 256 + i] = res;
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}
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}
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}
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/// <summary>
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/// Compute CRC32C for data
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/// </summary>
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/// <param name="input">input data</param>
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/// <param name="offset">offset</param>
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/// <param name="length">length</param>
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/// <returns>CRC32C checksum</returns>
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public static uint Compute(byte[] input, int offset, int length)
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{
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uint crcLocal = uint.MaxValue;
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#if NETCOREAPP3_0
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if (Sse42.IsSupported)
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{
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var data = new ReadOnlySpan<byte>(input, offset, length);
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int processed = 0;
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if (Sse42.X64.IsSupported && data.Length > sizeof(ulong))
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{
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processed = data.Length / sizeof(ulong) * sizeof(ulong);
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var ulongs = MemoryMarshal.Cast<byte, ulong>(data.Slice(0, processed));
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ulong crclong = crcLocal;
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for (int i = 0; i < ulongs.Length; i++)
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{
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crclong = Sse42.X64.Crc32(crclong, ulongs[i]);
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}
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crcLocal = (uint)crclong;
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}
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else if (data.Length > sizeof(uint))
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{
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processed = data.Length / sizeof(uint) * sizeof(uint);
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var uints = MemoryMarshal.Cast<byte, uint>(data.Slice(0, processed));
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for (int i = 0; i < uints.Length; i++)
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{
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crcLocal = Sse42.Crc32(crcLocal, uints[i]);
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}
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}
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for (int i = processed; i < data.Length; i++)
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{
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crcLocal = Sse42.Crc32(crcLocal, data[i]);
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}
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return crcLocal ^ uint.MaxValue;
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}
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#endif
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while (length >= 16)
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{
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var a = Table[(3 * 256) + input[offset + 12]]
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^ Table[(2 * 256) + input[offset + 13]]
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^ Table[(1 * 256) + input[offset + 14]]
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^ Table[(0 * 256) + input[offset + 15]];
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var b = Table[(7 * 256) + input[offset + 8]]
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^ Table[(6 * 256) + input[offset + 9]]
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^ Table[(5 * 256) + input[offset + 10]]
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^ Table[(4 * 256) + input[offset + 11]];
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var c = Table[(11 * 256) + input[offset + 4]]
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^ Table[(10 * 256) + input[offset + 5]]
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^ Table[(9 * 256) + input[offset + 6]]
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^ Table[(8 * 256) + input[offset + 7]];
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var d = Table[(15 * 256) + ((byte)crcLocal ^ input[offset])]
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^ Table[(14 * 256) + ((byte)(crcLocal >> 8) ^ input[offset + 1])]
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^ Table[(13 * 256) + ((byte)(crcLocal >> 16) ^ input[offset + 2])]
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^ Table[(12 * 256) + ((crcLocal >> 24) ^ input[offset + 3])];
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crcLocal = d ^ c ^ b ^ a;
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offset += 16;
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length -= 16;
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}
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while (--length >= 0)
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crcLocal = Table[(byte)(crcLocal ^ input[offset++])] ^ crcLocal >> 8;
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return crcLocal ^ uint.MaxValue;
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}
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}
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}
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