1 // Common/CRC.cs

     2 

     3 namespace SevenZip

     4 {

     5 	class CRC

     6 	{

     7 		public static readonly uint[] Table;

     8 

     9 		static CRC()

    10 		{

    11 			Table = new uint[256];

    12 			const uint kPoly = 0xEDB88320;

    13 			for (uint i = 0; i < 256; i++)

    14 			{

    15 				uint r = i;

    16 				for (int j = 0; j < 8; j++)

    17 					if ((r & 1) != 0)

    18 						r = (r >> 1) ^ kPoly;

    19 					else

    20 						r >>= 1;

    21 				Table[i] = r;

    22 			}

    23 		}

    24 

    25 		uint _value = 0xFFFFFFFF;

    26 

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

    28 

    29 		public void UpdateByte(byte b)

    30 		{

    31 			_value = Table[(((byte)(_value)) ^ b)] ^ (_value >> 8);

    32 		}

    33 

    34 		public void Update(byte[] data, uint offset, uint size)

    35 		{

    36 			for (uint i = 0; i < size; i++)

    37 				_value = Table[(((byte)(_value)) ^ data[offset + i])] ^ (_value >> 8);

    38 		}

    39 

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

    41 

    42 		static uint CalculateDigest(byte[] data, uint offset, uint size)

    43 		{

    44 			CRC crc = new CRC();

    45 			// crc.Init();

    46 			crc.Update(data, offset, size);

    47 			return crc.GetDigest();

    48 		}

    49 

    50 		static bool VerifyDigest(uint digest, byte[] data, uint offset, uint size)

    51 		{

    52 			return (CalculateDigest(data, offset, size) == digest);

    53 		}

    54 	}

    55 }