[Boost-users] [crc] Easy way to get the "correct checksum" constant?

From: Norbert Unterberg (nunterberg_at_[hidden])
Date: 2007-11-06 04:12:34

Some CRC algorithms (when using 0xFFFF as an initial value and final 
XOR) have a nice property that then checking the consistency of a data 
block that has a CRC checksum appended, the resulting checksum value is 
a constant.

Is there an easy way to extract this constant value from boost::crc 
directly?

Example: We use a CRC like this:

typedef
boost::crc_optimal<16, 0x1021, 0xFFFF, 0xFFFF, true, true>  crc_type;

When sending a block of data, we append the generated CRC. The receiver 
side feeds the complete block incluing the CRC bytes into its generator. 
When the data block has no errors, the crc.checksum() is always exactly 
0x0F47. Currently, I manually calculate that constant by something like 
this:
        crc_type crc;
        crc_type::value_type val(0);
        crc.process_bytes(&val, sizeof(val));
        m_key = crc.checksum();

Is there an easier way to extract this "crc is correct" value?

Norbert