HashValue is an overridden LongWord function in
TIdHashCRC32 that implements calculation of the 32-bit CRC value for a block of data. HashValue reimplements the inherited method to use the pre-computed table of 32-bit CRC values for all 256 possible character combinations that can be represented by each byte in the input data. HashValue calculates the CRC result by performing an exclusive OR for the current CRC value and the precomputed CRC value in the table for low nibble of the current input data.