private void Encode(uint crcInitialValue = 0x0)
{
var bytes = new List <byte>();
var frameControlByte0 = (byte)Type;
if (FramePending)
{
frameControlByte0 |= (0x1 << 4);
}
bytes.Add(frameControlByte0);
bytes.Add(0); // frameControlByte1
bytes.Add(DataSequenceNumber);
if (AddressInformation != null && AddressInformation.Bytes.Count > 0)
{
bytes.AddRange(AddressInformation.Bytes);
}
if (Payload != null && Payload.Count > 0)
{
bytes.AddRange(Payload);
}
var crcLength = CRCPolynomial.GetLength();
var crc = CalculateCRC(bytes, crcInitialValue, CRCPolynomial);
switch (crcLength)
{
case 2:
bytes.Add(crc[0]);
bytes.Add(crc[1]);
break;
case 4:
bytes.Add(crc[0]);
bytes.Add(crc[1]);
bytes.Add(crc[2]);
bytes.Add(crc[3]);
break;
default:
Logger.Log(LogLevel.Error, "Cannot generate CRC of invalid length {0}, the packet will not contain CRC data", crcLength);
break;
}
Bytes = bytes.ToArray();
}
public bool CheckCRC(uint crcInitialValue = 0x0)
{
var crcLength = CRCPolynomial.GetLength();
var crc = CalculateCRC(Bytes.Take(Bytes.Length - crcLength), crcInitialValue, CRCPolynomial);
// Byte little endian order
switch (crcLength)
{
case 2:
return(Bytes[Bytes.Length - 2] == crc[0] && Bytes[Bytes.Length - 1] == crc[1]);
case 4:
return(Bytes[Bytes.Length - 4] == crc[0] && Bytes[Bytes.Length - 3] == crc[1] && Bytes[Bytes.Length - 2] == crc[2] && Bytes[Bytes.Length - 1] == crc[3]);
default:
Logger.Log(LogLevel.Error, "Cannot check CRC of invalid length {0}", crcLength);
return(false);
}
}
/// <summary>
/// Generates a CRC using a common polynomial for the next closest bitlength above that specified.
/// For example, a bit length of 13 through 16 will use the CCITT16 polynomial masking off bits necessary to maintain the specified bitlength.
/// </summary>
/// <param name="data">Data to generate a CRC for</param>
/// <param name="offset">The offset into the source data at which to start the CRC</param>
/// <param name="length">The number of bytes in the source data to analyze</param>
/// <param name="polynomial">Standard polynomial to use for the CRC</param>
/// <param name="seedCRC">CRC seed value</param>
/// <returns>The CRC</returns>
/// <returns></returns>
public static ulong GenerateChecksum(byte[] data, int offset, int length, CRCPolynomial polynomial, ulong seedCRC)
{
int bits = 0;
switch (polynomial)
{
case CRCPolynomial.CRC_8:
bits = 8;
break;
case CRCPolynomial.CRC_10:
bits = 10;
break;
case CRCPolynomial.CRC_12:
bits = 12;
break;
case CRCPolynomial.CRC_16:
case CRCPolynomial.CRC_16ARC:
case CRCPolynomial.CRC_CCITT16:
bits = 16;
break;
case CRCPolynomial.CRC_24:
bits = 24;
break;
case CRCPolynomial.CRC_CCITT32:
case CRCPolynomial.CRC_32:
bits = 32;
break;
case CRCPolynomial.CRC_64:
bits = 64;
break;
}
return(GenerateChecksum(data, offset, length, bits, (ulong)polynomial, seedCRC));
}
public static ulong GenerateChecksum(byte[] data, int crcBitLength, CRCPolynomial polynomial)
{
return(GenerateChecksum(data, crcBitLength, (ulong)polynomial, 0));
}
public static ulong GenerateChecksum(byte[] data, int crcBitLength, CRCPolynomial polynomial)
{
return GenerateChecksum(data, crcBitLength, (ulong)polynomial, 0L);
}
public static ulong GenerateChecksum(byte[] data, int offset, int length, CRCPolynomial polynomial, ulong seedCRC)
{
int crcBitLength = 0;
switch (polynomial)
{
case CRCPolynomial.CRC_10:
crcBitLength = 10;
break;
case CRCPolynomial.CRC_12:
crcBitLength = 12;
break;
case CRCPolynomial.CRC_CCITT16:
case CRCPolynomial.CRC_16ARC:
case CRCPolynomial.CRC_16:
crcBitLength = 0x10;
break;
case CRCPolynomial.CRC_64:
crcBitLength = 0x40;
break;
case CRCPolynomial.CRC_8:
crcBitLength = 8;
break;
case CRCPolynomial.CRC_24:
crcBitLength = 0x18;
break;
case CRCPolynomial.CRC_32:
case CRCPolynomial.CRC_CCITT32:
crcBitLength = 0x20;
break;
}
return GenerateChecksum(data, offset, length, crcBitLength, (ulong)polynomial, seedCRC);
}
