# the original code indicates there can never
        # be more than one charge code associated with
        # any given $src and $dest pair; if there are,
        # we would have to use an array ref here and
        # a foreach loop in the main processing.

        # only one charge code:
        $charge_codes{$src}{$dest} = $code;

        # # for multiple charge codes:
        # push @{ $charge_codes{$src}{$dest} }, $code;