in reply to Re: CRC-16 algorithm
in thread CRC-16 algorithm

Thanks! OK, got it and tried it. The documentation is a bit sparse, but using String::CRC gives rise to a program like so:

use strict;
use warnings;

use String::CRC;

my $message = $ARGV[0];

my $crc16 = crc($message);
print "CRC16 in decimal: $crc16\n";
print "CRC16 in hex:\n  ", unpack('H*', pack('S', $crc16)), "\n";

[download]

Running the program gives this output:

cradcliff% ./crc16-modular.pl foo
CRC16 in decimal: 1736882148
CRC16 in hex:
  b7e4
cradcliff% ./crc16-modular.pl foobar
CRC16 in decimal: 3375757715
CRC16 in hex:
  f993
cradcliff% ./crc16-modular.pl foobaz
CRC16 in decimal: 3375757723
CRC16 in hex:
  f99b

[download]

More simply: 

'foo'    => 0xb7e4
'foobar' => 0xf993
'foobaz' => 0xf99b

Can anyone verify that these are correct values for a CRC-16 checksum, assuming the conditions I specified earlier? Alternately, can anyone supply sample string-checksum pairs I can use to test this program?

Thanks, ~c

Replies are listed 'Best First'.
Re: (String::CRC) Re: CRC-16 algorithm
by PodMaster (Abbot) on May 21, 2003 at 07:02 UTC
    Try crc($message,16); because the default is 32 (like the pod says).

    MJD says you can't just make shit up and expect the computer to know what you mean, retardo!
    I run a Win32 PPM repository for perl 5.6x+5.8x. I take requests.
    ** The Third rule of perl club is a statement of fact: pod is sexy.

[reply]
[d/l]

      Yes, I forgot to add that. Unfortunately, even with the change, the result is:

      cradcliff% ./crc16-modular.pl 123456789
CRC16 in decimal: 4535
CRC16 in hex:
  11b7

      ...which doesn't match the 0xBB3D result provided by the on-line calculator. I'm guessing that String::CRC doesn't use the CRC-16 polynomial or some other CRC-16-specific setting.

      I'll check my other algorithm against the on-line calculator. If anyone has algorithmic hints, please post them.

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        CRC16 crc = new CRC16(); System.out.println("CRC16 = " + crc.getCRC16("050101")); } public String getCRC16(String input) { byte[] bytes = input.getBytes(); int crc = 0x0000; for (byte b : bytes) { crc = (crc >>> 8) ^ table(crc ^ b) & 0xff; } return Integer.toHexString(crc); }
[reply]

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