igor1212 has asked for the wisdom of the Perl Monks concerning the following question:

Hello to all. I need to do a crc 16 calculation in perl. My example data is 6401(hex)and CRC should be: 13BC (hex).

I've tried every combination using digest::crc and string::crc, but I've got no correct crc value.

I've received a c function for crc calculation from my device vendor, but I need this in Perl.

C Function:

unsigned short crc_16_rec (char *pucData, unsigned short ucLen) {

        unsigned int  i;
        unsigned char ucBit, ucCarry;

        unsigned short usPoly = 0x8408;//reversed 0x1021
        unsigned short usCRC  = 0;

        for (i = 0; i < ucLen; i++) {
        usCRC ^= pucData[i];
        for (ucBit = 0; ucBit < 8; ucBit++) {
            ucCarry = usCRC & 1;
            usCRC >>= 1;
            if (ucCarry) {
                usCRC ^= usPoly;
            }
        }
    }
       return usCRC;
}

[download]

Can somebody please help me with this, because I'm stuck here!

Best Regards!

Igor

Replies are listed 'Best First'.
Re: CRC 16
by BrowserUk (Patriarch) on Oct 08, 2012 at 08:21 UTC

    I can't see how 0x8404 is the 'reverse' of 0x1021 by any stretch of my imagination,(*)

    but a simple brute force conversion yields:

    #! perl -slw
use strict;

sub crc16 {
     use constant POLY => 0x8408;
     my $crc = 0;
     for my $c ( unpack 'C*', $_[0] ) {
         $crc ^= $c;
         for my $b ( 0 .. 7 ) {
             my $carry = $crc & 1;
             $crc >>= 1;
             if( $carry ) {
                 $crc ^= POLY;
             }
         }
     }
     return $crc;
}

my $data = "\x64\x01";

printf "crc: %04x\n", crc16( $data );

__END__
C:\test>997760.pl
crc: 13bc

    [download]

    Which works for the (inadequate, single) sample data.

    (* 0x1021 -> 0001_0000_0010_0001 bitwise reversed -> 1000_0100_0000_1000 -> 0x8408 )

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

    RIP Neil Armstrong
[reply]
[d/l]
Re: CRC 16
by moritz (Cardinal) on Oct 08, 2012 at 12:36 UTC
[reply]

      It's not the same algorithm.

      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.

      RIP Neil Armstrong
[reply]
        Hello BrowserUk,

        Your solution did the work perfectly!

        Thanks!

        Igor
[reply]

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