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

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)
    		};
    	}
    }
}