#nullable disable
// Common/CRC.cs

namespace SevenZip
{
	class CRC
	{
		public static readonly uint[] Table;

		static CRC()
		{
			Table = new uint[256];
			const uint kPoly = 0xEDB88320;
			for ( uint i = 0; i < 256; i++ )
			{
				uint r = i;
				for ( int j = 0; j < 8; j++ )
					if ( (r & 1) != 0 )
						r = (r >> 1) ^ kPoly;
					else
						r >>= 1;
				Table[i] = r;
			}
		}

		uint _value = 0xFFFFFFFF;

		public void Init() { _value = 0xFFFFFFFF; }

		public void UpdateByte( byte b )
		{
			_value = Table[(((byte)(_value)) ^ b)] ^ (_value >> 8);
		}

		public void Update( byte[] data, uint offset, uint size )
		{
			for ( uint i = 0; i < size; i++ )
				_value = Table[(((byte)(_value)) ^ data[offset + i])] ^ (_value >> 8);
		}

		public uint GetDigest() { return _value ^ 0xFFFFFFFF; }

		static uint CalculateDigest( byte[] data, uint offset, uint size )
		{
			CRC crc = new CRC();
			// crc.Init();
			crc.Update( data, offset, size );
			return crc.GetDigest();
		}

		static bool VerifyDigest( uint digest, byte[] data, uint offset, uint size )
		{
			return (CalculateDigest( data, offset, size ) == digest);
		}
	}
}