110 lines
2.6 KiB
C#
110 lines
2.6 KiB
C#
using System.Security.Cryptography;
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namespace MyNes.Core
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{
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public class Crc32 : HashAlgorithm
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{
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public const uint DefaultPolynomial = 3988292384u;
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public const uint DefaultSeed = uint.MaxValue;
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private uint hash;
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private uint seed;
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private uint[] table;
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private static uint[] defaultTable;
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public override int HashSize => 32;
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public Crc32()
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{
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table = InitializeTable(3988292384u);
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seed = uint.MaxValue;
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Initialize();
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}
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public Crc32(uint polynomial, uint seed)
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{
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table = InitializeTable(polynomial);
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this.seed = seed;
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Initialize();
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}
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public override void Initialize()
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{
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hash = seed;
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}
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protected override void HashCore(byte[] buffer, int start, int length)
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{
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hash = CalculateHash(table, hash, buffer, start, length);
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}
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protected override byte[] HashFinal()
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{
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return HashValue = UInt32ToBigEndianBytes(~hash);
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}
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public static uint Compute(byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(3988292384u), uint.MaxValue, buffer, 0, buffer.Length);
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}
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public static uint Compute(uint seed, byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(3988292384u), seed, buffer, 0, buffer.Length);
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}
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public static uint Compute(uint polynomial, uint seed, byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
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}
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private static uint[] InitializeTable(uint polynomial)
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{
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if (polynomial == 3988292384u && defaultTable != null)
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{
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return defaultTable;
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}
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uint[] array = new uint[256];
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for (int i = 0; i < 256; i++)
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{
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uint num = (uint)i;
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for (int j = 0; j < 8; j++)
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{
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num = (((num & 1) != 1) ? (num >> 1) : ((num >> 1) ^ polynomial));
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}
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array[i] = num;
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}
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if (polynomial == 3988292384u)
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{
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defaultTable = array;
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}
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return array;
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}
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private static uint CalculateHash(uint[] table, uint seed, byte[] buffer, int start, int size)
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{
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uint num = seed;
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for (int i = start; i < size; i++)
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{
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num = (num >> 8) ^ table[buffer[i] ^ (num & 0xFF)];
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}
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return num;
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}
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private byte[] UInt32ToBigEndianBytes(uint x)
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{
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return new byte[4]
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{
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(byte)((x >> 24) & 0xFFu),
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(byte)((x >> 16) & 0xFFu),
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(byte)((x >> 8) & 0xFFu),
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(byte)(x & 0xFFu)
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};
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}
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}
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}
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