String::CRC crc function returns incorrect result, why?

Z

`Zidane Tribal

it would appear that using the command 'crc("data")' from the String::CRC
returns incorrect results (although, they are at least consistently
incorrect).

for example, this script.....

#!/usr/bin/perl -w
use strict;
use String::CRC;
print "crc: " . crc($ARGV[0]) . " " . length($ARGV[0]) . "\n";

produces this output:

zidane@bluemist:~/ps2/dev/crccheck$ ./crctest.pl 12345
crc: 3817467633 5
zidane@bluemist:~/ps2/dev/crccheck$

whereas this command:

zidane@bluemist:~/ps2/dev/crccheck$ echo -n "12345" | cksum
3288622155 5
zidane@bluemist:~/ps2/dev/crccheck$

produces a different crc value.

this is also true using String::CRC32, DIGEST::CRC and DIGEST::CRC32 (using
the command line commands cksum and crc32 to create respective crc and
crc32 values to test against)

my query is simple.... why is this? although the values are different,
they are consistently different (i.e. the same result returned with each
call given the same data). can anyone explain what i am doing wrong?

`Zidane.
 
J

Joe Smith

`Zidane Tribal said:
it would appear that using the command 'crc("data")' from the String::CRC
returns incorrect results

No, it's not. crc != cksum; there are many different CRC algorithms.
for example, this script.....

#!/usr/bin/perl -w
use strict;
use String::CRC;
print "crc: " . crc($ARGV[0]) . " " . length($ARGV[0]) . "\n";

produces this output:

zidane@bluemist:~/ps2/dev/crccheck$ ./crctest.pl 12345
crc: 3817467633 5
zidane@bluemist:~/ps2/dev/crccheck$

whereas this command:

zidane@bluemist:~/ps2/dev/crccheck$ echo -n "12345" | cksum
3288622155 5
zidane@bluemist:~/ps2/dev/crccheck$

produces a different crc value.

The String::CRC::Cksum module calculates a 32 bit CRC, generating
the same CRC value as the POSIX cksum program.

linux% cat cksum.pl
#!/usr/bin/perl -w
use strict;
use String::CRC::Cksum qw(cksum);
print "cksum: " . cksum($ARGV[0]) . " " . length($ARGV[0]) . "\n";
linux% perl cksum.pl 12345
cksum: 3288622155 5


-Joe

P.S. The newsgroup comp.lang.perl is defunct; use comp.lang.perl.misc instead.
 

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