Boost CRC 16 bit

Question

Using an online crc calculator, I know that 32311E333530 (hex) = E558 (hex) for CRC-CCITT (0xFFFF). How can I do this with boost crc?

    std::string crc_str = "32311E333530";
    boost::crc_16_type result;
    result.process_bytes(crc_str.data(), crc_str.length());
    std::cout << "checksum = " << result.checksum();

Checksum yields 59589 (decimal) = E8C5 (hex), when E558 (hex) = 58712 (decimal).

What my user manual for serial device says:

unsigned short calculate_crc16(char *data_ptr, unsigned short data_length)
{
    unsigned short index;
    unsigned short new_crc = 0xFFFF;
    //Loop through the entire buffer array of data
    for (index = 0; index < data_length; index++)
    {
        new_crc = (new_crc << 8) ^ crc_table[(new_crc >> 8) ^ (*data_ptr++)];
    }
    return(new_crc);
}

static const unsigned short crc_table[256] =
{
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
};

You don't reallt want crc_16_type do you? You want crc_ccitt_type because the CRC you are trying to match is CRC-CCITT — Jerry Jeremiah, Apr 20 '16 at 03:25
http://www.boost.org/doc/libs/1_60_0/libs/crc/crc.html#crc_ex — Jerry Jeremiah, Apr 20 '16 at 03:26
@JerryJeremiah thank you; I had the same thought; the checksum comes out to 56822 with that; perhaps I'm missing some step specific to the `0xFFFF` format? — xinthose, Apr 20 '16 at 03:34
I think so, According to http://www.lammertbies.nl/comm/info/crc-calculation.html the string "123456789" results in this: CRC-CCITT (XModem) = 0x31C3, CRC-CCITT (0xFFFF) = 0x29B1, CRC-CCITT (0x1D0F) = 0xE5CC, and CRC-CCITT (Kermit) = 0x8921 so there are quire a few of them. — Jerry Jeremiah, Apr 20 '16 at 03:45
This may help: http://stackoverflow.com/questions/32518157/difference-in-boost-crc-and-linux-lib-crc-ccitt-c — Jerry Jeremiah, Apr 20 '16 at 03:47
@JerryJeremiah I see in crc's documentation that you can build your own variable like so `boost::crc_optimal<16, 0x1021, 0xFFFF, 0, false, false> crc_ccitt2;` I will try to tweak it some; I'll post the code in my user manual — xinthose, Apr 20 '16 at 03:51
Please note that your input string is not 323... in hex, but the ASCII characters for 323... This yields a different CRC than expected. — Jonas Wolf, Apr 20 '16 at 04:24

selbie · Accepted Answer · 2016-04-20T04:44:08.810

UPDATED

You are confusing ascii string with a byte array. Not the same thing.

This will produce the results you expect:

int main()
{
    const unsigned char data[] = {0x32, 0x31, 0x1E, 0x33, 0x35, 0x30};
    boost::crc_ccitt_type result;
    result.process_bytes(data, 6);
    std::cout << "checksum = " << std::hex << result.checksum() << std::endl;
    return 0;
}

Prints: checksum = e558

Old Answer

Because the CRC for that string is definitely xE8C5 or 0xDDF6 for CRC-16 and CRC-CCITT respectively.

Running "32311E333530" through the calculate_crc16 as you have posted from your book's code:

int main()
{
    std::string crc_str = "32311E333530";
    unsigned result = calculate_crc16(crc_str.c_str(), crc_str.length());
    std::cout << "checksum = " << std::hex << result << std::endl;
    return 0;
}

prints:

checksum = ddf6

Running it the same string through Boost using the crc_ccitt_type as follows:

int main()
{
    std::string crc_str = "32311E333530";
    boost::crc_ccitt_type result;
    result.process_bytes(crc_str.data(), crc_str.length());
    std::cout << "checksum = " << std::hex << result.checksum() << std::endl;
    return 0;
}

prints:

checksum = ddf6

So the Boost code matches the output of the code from your serial manual.

Typing 32311E333530 (sans quotes) into this online crc calculator generates the following:

"32311E333530"
1 byte checksum 112
CRC-16  0xE8C5
CRC-16 (Modbus) 0xEAA1
CRC-16 (Sick)   0x9254
CRC-CCITT (XModem)  0x590F
CRC-CCITT (0xFFFF)  0xDDF6
CRC-CCITT (0x1D0F)  0xF065
CRC-CCITT (Kermit)  0xF2EC
CRC-DNP 0x8034
CRC-32  0xFB5DA62C

Notice that CRC-16 is E8C5 - just as your original boost code reports. CRC-CCITT matches as well.

So what's the issue? The boost code for ccitt matches both the manual's code as well as the online tool. The boost results for crc-16 match what my online calculator says as well.

I see. Thank you. If you click Input Type as Hex, you'll see it. So if I'm getting the result from an ASCII string, how do I convert DDF6 or 56822 to my needed E558 as my manual suggests? — xinthose, Apr 20 '16 at 04:30
Why do you expect E558? It's clearly incorrect. What "online calculator" did you use that you referred to in your question? — selbie, Apr 20 '16 at 04:36
Oh, I see your problem. You are confusing ASCII strings with binary. Hold on... I'll update the answer. — selbie, Apr 20 '16 at 04:39
yes, I see now; if I convert `32311E333530` to binary before the crc, then the checksum comes out as `58712` — xinthose, Apr 20 '16 at 04:43

Boost CRC 16 bit

1 Answers1