so

sub encode_BCD {
    return pack 'H*', join '', @_
}
[download]

If you need to ensure < 99 , or dealing with signs properly, you'll have to add that part

Seems to work https://en.wikipedia.org/wiki/Binary_coded_decimal

-1,234,56
0001 0010 0011 0100 0101 0110 0111 1101
1    2    3    4    5    6    7    -

$ perl -le " print join q/ /, split /....\K/, unpack q/B*/, pack q/H*/
+, q/1234567-/ "
0001 0010 0011 0100 0101 0110 0111 1101

$ perl -le " print join q/ /, unpack q/(A4)*/, unpack q/B*/, pack q/H*
+/, q/1234567-/ "
0001 0010 0011 0100 0101 0110 0111 1101
[download]

This format is a bit odd nowadays (more normal would be ASCII decimal which takes 2 8 bit bytes instead of 2 4 bit nibbles, but that extra space is usually not of consequence). Anyway this is how to calculate the "digits". The integer "div" or modulo operation is only one machine instruction and the integer multiply is also only one machine instruction. I don't know how good Perl is at this. See Perl pack() and unpack() for how to cram these into one 8 bit value.

#!usr/bin/perl -w
use strict;

my @tests = (2,11,23,89,99);

foreach my $num (@tests)
{   
   my $units = $num % 10; #modulo is the remainder
   my $tens = ($num - $units)/10;
   printf "decimal=%02d BCD=%04b %04b\n", $num, $tens, $units;
}

__END__
decimal=02 BCD=0000 0010
decimal=11 BCD=0001 0001
decimal=23 BCD=0010 0011
decimal=89 BCD=1000 1001
decimal=99 BCD=1001 1001
[download]

sub bcd
{
    local $_ = shift;
    
    # enforce two digits
    $_ = "0$_" while 2 > length;
    die "too big" unless m{^(\d)(\d)$};
    
    return chr(16*$1 + $2);
}
[download]

I fail to see the connection, and how the linked document is useful in this question. Can you please explain it?

Sure, EBCDIC is historically based on BCD, but I don't see how that is useful with the conversion from numbers to BCD.

Perl 6 - the future is here, just unevenly distributed

I figured the explanations were useful, and the conversion code in the article could serve as a staring-point example, and be modified to deal with BCD. The OP was looking for a starting point. I did not find any direct BCD starting points, so I posted the EBCDIC one.

             I hope life isn't a big joke, because I don't get it.
                   -SNL