CRC32.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PDTools.Hashing;

    public static class CRC32
    {
	private const uint _poly1 = 0xedb88320;
	public static uint[] checksum_0x77073096 = new uint[256];
	public static uint[] checksum_0x77073096_rev = new uint[256];
	private const int _poly2 = 0x04c11db7;
	public static uint[] checksum_0x04C11DB7 = new uint[256];
	public static uint[] checksum_0x04C11DB7_rev = new uint[256];

	static CRC32()
	{
		uint fwd, rev;
		for (uint i = 0; i < checksum_0x77073096.Length; i++)
		{
			fwd = i;
			rev = i << 24;
			for (int j = 8; j > 0; j--)
			{
				if ((fwd & 1) == 1)
					fwd = ((fwd >> 1) ^ _poly1);
				else
					fwd >>= 1;

				if ((rev & 0x80000000) != 0)
					rev = ((rev ^ _poly1) << 1) | 1;
				else
					rev <<= 1;
			}
			checksum_0x77073096[i] = fwd;
			checksum_0x77073096_rev[i] = rev;
		}

		for (uint i = 0; i < checksum_0x04C11DB7.Length; i++)
		{
			fwd = i << 24;
			rev = i;

			for (int j = 8; j > 0; j--)
			{
				if ((fwd & 0x80000000) != 0)
					fwd = (fwd << 1) ^ _poly2;
				else
					fwd <<= 1;

				
				if ((rev & 1) == 1)
					rev = ((rev >> 1) ^ _poly2);
				else
					rev >>= 1;
			}
			checksum_0x04C11DB7[i] = fwd;
			checksum_0x04C11DB7_rev[i] = rev;
		}
	}

	public static uint CRC32_0x04C11DB7(string keyMagic, uint initialValue = 0)
	{
		uint crc = initialValue;
		for (int i = 0; i < keyMagic.Length; i++)
		{
			int b = keyMagic[i] & 0xFF;
			crc = (crc << 8) ^ checksum_0x04C11DB7[(crc >> 24) ^ b];
		}

		return crc;
	}

	public static uint CRC32_0x04C11DB7(Span<byte> bytes, uint initialValue = 0)
	{
		uint crc = initialValue;
		for (int i = 0; i < bytes.Length; i++)
		{
			int b = bytes[i] & 0xFF;
			crc = (crc << 8) ^ checksum_0x04C11DB7[(crc >> 24) ^ b];
		}

		return crc;
	}

	/// <summary>
	/// For GT5P JP Demo and others
	/// </summary>
	/// <param name="input"></param>
	/// <returns></returns>
	public static uint CRC32_0x04C11DB7_UIntInverted(uint input)
	{
		uint result = 0x0;
		for (int i = 0; i < 4; i++)
		{
			result = (result << 0x8) ^ CRC32.checksum_0x04C11DB7[(result ^ input) >> 24];
			input <<= 0x8;
		}
		return ~result;
	}

	/*
	public static uint CRC32_0x04C11DB7_UIntInvertedReverse(uint input)
	{
		uint inputNormal = ~input;
		uint result = 0;

		byte[] bytes = BitConverter.GetBytes(inputNormal);

		for (int i = 0; i < 4; i++)
		{
			result = (result << 0x8) ^ CRC32.checksum_0x04C11DB7_rev[(result >> 0x24) ^ bytes[i]];
			
			
		}

		return result;

	}*/

	public static uint crc32_0x77073096(Span<byte> data, int length)
        {
            uint checksum = 0xFFFFFFFF;
           
            for (int i = 0; i < length; i++)
                checksum = checksum_0x77073096[(byte)(checksum ^ data[i])] ^ (checksum >> 8);
            
            return ~checksum;
        }
}