Generating a CRC-16/XMODEM checksum in Hex

[Djinni]

Hello,

I am trying to generate a a CRC-16/XMODEM checksum. I have been using: http://reveng.sourceforge.net/crc-catalogue/16.htm#crc.cat.crc-16-xmodem and crccalc.com as a guide. As well as Digest/CRC.pm however I have been unable to get the perl module Digest::CRC to give me the expected result.

 
#!/usr/bin/perl -w
use strict;
use Digest::CRC qw(crc64 crc32 crc16 crcccitt crc crc8 crcopenpgparmor
+);

my @s=( 
    { 's'=>"9848C503738276ADCA02BF5DC1A3ABF2", 'crc16'=>"9F4B" },
    { 's'=>"841374844ADDF4A36CEDB127C82086B9", 'crc16'=>"408E" },
    { 's'=>"8AC1070ACD1659BB4F507191E33F7AD4", 'crc16'=>"E1E3" },
    { 's'=>"34623A01DCDA35BED462953B4E2458DA", 'crc16'=>"7B40" },
    { 's'=>"E29107CB32975E859D76A885BF57BE35", 'crc16'=>"2B92" },
    { 's'=>"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", 'crc16'=>"0041" },
);

# width=16 poly=0x1021 init=0x0000 refin=false refout=false xorout=0x0
+000 check=0x31c3 residue=0x0000 name="CRC-16/XMODEM"

my $width = 16;
my $init = 0x0000;
my $xorout = 0x0000;
my $refout = 0;
my $poly = 0x1021;
my $refin = 0;
my $cont = 0x31c3;

for my $tv (@s) {
    
    my $crc16 = crc($tv->{s},$width,$init,$xorout,$refout,$poly,$refin
+,$cont);
    print qq{
Input was: $tv->{s}
crc: $crc16 -- Should be: $tv->{crc16}
};
}

I have another issue in that I do not understand what "cont" is here.

[Djinni]

As is so often the case with these things. Mearly asking for help (not even getting any) is sometimes sufficient to help one see the solution!

#!/usr/bin/perl -w
use strict;
use Digest::CRC;

my @s=( 
    { 's'=>"9848C503738276ADCA02BF5DC1A3ABF2", 'crc16'=>"9F4B" },
    { 's'=>"841374844ADDF4A36CEDB127C82086B9", 'crc16'=>"408E" },
    { 's'=>"8AC1070ACD1659BB4F507191E33F7AD4", 'crc16'=>"E1E3" },
    { 's'=>"34623A01DCDA35BED462953B4E2458DA", 'crc16'=>"7B40" },
    { 's'=>"E29107CB32975E859D76A885BF57BE35", 'crc16'=>"2B92" },
    { 's'=>"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", 'crc16'=>"0041" },
);

my $ctx = Digest::CRC->new(type=>"crc16");
$ctx = Digest::CRC->new(width=>16, init=>0x0000, xorout=>0x0000, 
                        refout=>0, poly=>0x1021, refin=>0, cont=>0);
 
for my $tv (@s) {
    my $key = $tv->{s};
    my $value = pack "H*", "$key";

    $ctx->add($value);
    my $digest = $ctx->digest;
    my $hexdigest = sprintf("%X", $digest);


    
    print qq{
Input was: $key
crc: $digest as HEX: $hexdigest -- Should be: $tv->{crc16}
};
}

$hexdigest now has the expected data value!

[stevieb]

"As is so often the case with these things. Mearly asking for help (not even getting any) is sometimes sufficient to help one see the solution!"

That's called Rubber Duck Debugging :)