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

sub longdiv {
    # take the parameter passed into the sub and store in $in
    my $in = shift;

    ...

    # return the result
    return ($out, $carry);
}


sub longmul {
   my ($div, $mod) = @_;

   my $out = sprintf('%06d', substr($div, -3, 3, '') * 222 + $mod);

   while (length($div)) {
      substr($out, 0, 3, sprintf('%04d',
         substr($out, 0, 3) + substr($div, -1, 1, '') * 222
      ));
   }

   $out =~ s/^0+//;

   return $out;
}


# call the function and print the output
my ($out, $carry) = longdiv("15000000");
print("$out, $carry\n");  # WRONG. Should be 67567 and 126.
print(longmul($out, $carry), "\n");
print(longmul('67567', 126), "\n");