AxibugEmuOnline/OtherCore/MyNes.Standard2/MyNes.Core/Crc32.cs

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2024-07-24 15:03:33 +08:00
using System.Security.Cryptography;
namespace MyNes.Core
{
public class Crc32 : HashAlgorithm
{
public const uint DefaultPolynomial = 3988292384u;
public const uint DefaultSeed = uint.MaxValue;
private uint hash;
private uint seed;
private uint[] table;
private static uint[] defaultTable;
public override int HashSize => 32;
public Crc32()
{
table = InitializeTable(3988292384u);
seed = uint.MaxValue;
Initialize();
}
public Crc32(uint polynomial, uint seed)
{
table = InitializeTable(polynomial);
this.seed = seed;
Initialize();
}
public override void Initialize()
{
hash = seed;
}
protected override void HashCore(byte[] buffer, int start, int length)
{
hash = CalculateHash(table, hash, buffer, start, length);
}
protected override byte[] HashFinal()
{
return HashValue = UInt32ToBigEndianBytes(~hash);
}
public static uint Compute(byte[] buffer)
{
return ~CalculateHash(InitializeTable(3988292384u), uint.MaxValue, buffer, 0, buffer.Length);
}
public static uint Compute(uint seed, byte[] buffer)
{
return ~CalculateHash(InitializeTable(3988292384u), seed, buffer, 0, buffer.Length);
}
public static uint Compute(uint polynomial, uint seed, byte[] buffer)
{
return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
}
private static uint[] InitializeTable(uint polynomial)
{
if (polynomial == 3988292384u && defaultTable != null)
{
return defaultTable;
}
uint[] array = new uint[256];
for (int i = 0; i < 256; i++)
{
uint num = (uint)i;
for (int j = 0; j < 8; j++)
{
num = (((num & 1) != 1) ? (num >> 1) : ((num >> 1) ^ polynomial));
}
array[i] = num;
}
if (polynomial == 3988292384u)
{
defaultTable = array;
}
return array;
}
private static uint CalculateHash(uint[] table, uint seed, byte[] buffer, int start, int size)
{
uint num = seed;
for (int i = start; i < size; i++)
{
num = (num >> 8) ^ table[buffer[i] ^ (num & 0xFF)];
}
return num;
}
private byte[] UInt32ToBigEndianBytes(uint x)
{
return new byte[4]
{
(byte)((x >> 24) & 0xFFu),
(byte)((x >> 16) & 0xFFu),
(byte)((x >> 8) & 0xFFu),
(byte)(x & 0xFFu)
};
}
}
}