/// <summary>
///
/// </summary>
/// <param name="codingType"></param>
public CRCEntity(CRCCoding codingType)
{
Initialize(codingType);
}
private void Initialize(CRCCoding codingType)
{
switch (codingType)
{
case CRCCoding.CRC16CCITT:
order = 16; direct = 1; polynom = 0x1021; crcinit = 0xFFFF; crcxor = 0; refin = 0; refout = 0;
break;
case CRCCoding.CRC16:
order = 16; direct = 1; polynom = 0x8005; crcinit = 0x0; crcxor = 0x0; refin = 1; refout = 1;
break;
case CRCCoding.CRC32:
order = 32; direct = 1; polynom = 0x4c11db7; crcinit = 0xFFFFFFFF; crcxor = 0xFFFFFFFF; refin = 1; refout = 1;
break;
}
//Initialize all variables for seeding and builing based upon the given coding type
//at first, compute constant bit masks for whole CRC and CRC high bit
crcmask = ((((ulong)1 << (order - 1)) - 1) << 1) | 1;
crchighbit = (ulong)1 << (order - 1);
//generate lookup table
generate_crc_table();
ulong bit, crc;
int i;
if (direct == 0)
{
crcinit_nondirect = crcinit;
crc = crcinit;
for (i = 0; i < order; i++)
{
bit = crc & crchighbit;
crc <<= 1;
if (bit != 0)
{
crc ^= polynom;
}
}
crc &= crcmask;
crcinit_direct = crc;
}
else
{
crcinit_direct = crcinit;
crc = crcinit;
for (i = 0; i < order; i++)
{
bit = crc & 1;
if (bit != 0)
{
crc ^= polynom;
}
crc >>= 1;
if (bit != 0)
{
crc |= crchighbit;
}
}
crcinit_nondirect = crc;
}
}