Re: Encoding BCD

[Corion]

This code:

if ($test1 = $test2) {
   $comp = "EQUALS";
}  else  {
   $comp = "Does NOT Equal";
}

does not do what you think it does. Most likely you want to use one of the comparison operators, eq for string comparison or == for numerical comparison. Look at:

my $test1 = 123;
my $test2 = 456;
print "1. Test1: '$test1', test2: '$test2'\n";
if ($test1 = $test2) {
   print "2a. Test1: '$test1', test2: '$test2'\n";
   $comp = "EQUALS";
}  else  {
   print "2b. Test1: '$test1', test2: '$test2'\n";
   $comp = "Does NOT Equal";
}
print "3. Test1: '$test1', test2: '$test2'\n";

I use the following to convert a BCD string to a Perl number/string:

=head2 C<decode_COMP3>

Decodes a COMP3 BCD-number with trailing sign

=cut

sub decode_COMP3 {
    # Cut off the last nibble
    # 0C -> +
    # 0D -> -
    # 0F -> (unsigned number)
    my $digits = unpack "H*", $_[0];
    my $sign = chop $digits;
    #print "$digits\n";
       if ($sign eq 'D' or $sign eq 'd') { $sign = '-' }
    elsif ($sign eq 'C' or $sign eq 'c') { $sign = '+' }
    elsif ($sign eq 'F' or $sign eq 'f') { $sign = ' ' }
    else { $digits .= $sign; $sign = '?' };
    "$sign$digits"
};

In your case, maybe you want to throw away all the sign handling. The code could then be:

sub decode_BCD {
    unpack "H*", $_[0];
};

When debugging string packing/unpacking problems, I often write me a test suite to make sure all my assumptions about the data get documented somewhere. You might want to use something like the following:

use strict;
use Test::More tests => 4;
use_ok 'MyBCDDecodePackage';

is decode_BCD("\x12\x34\x56","123456");
is decode_BCD("\x00\x34\x56","003456");
is decode_BCD("\x12","12");

and then add all cases from your actual input data that you find interesting/problematic.