package HexMath;
# add or multiply hexadecimal
my (%times, %sums);

BEGIN {    # create tables
    for my $x ( 0 .. 15 ) {
        my $hx = sprintf '%x', $x;
        for my $y ( 0 .. 15 ) {
            my $hy = sprintf '%x', $y;
            next if exists $times{$hx}{$hy};
            $times{$hx}{$hy} = $times{$hy}{$hx} = sprintf '%x', $x*$y;
            $sums{$hx}{$hy} = $sums{$hy}{$hx} = sprintf '%x', $x+$y;
        }
    }

    printf "\n%4s: ", 'x ';
    printf "%4x ", $_ for 0..15;
    for my $x ( 0 .. 15 ) {
        my $hx = sprintf '%x', $x;

        printf "\n%4.4s: ", $hx;

        for my $y ( 0 .. 15 ) {
            my $hy = sprintf '%x', $y;
            printf '%4.4s ', $times{$hx}{$hy};
        }
    }
    print "\n";

    printf "\n%4s: ", '+ ';
    printf "%4x ", $_ for 0..15;
    for my $x ( 0 .. 15 ) {
        my $hx = sprintf '%x', $x;

        printf "\n%4.4s: ", $hx;

        for my $y ( 0 .. 15 ) {
            my $hy = sprintf '%x', $y;
            printf '%4.4s ', $sums{$hx}{$hy};
        }
    }
    print "\n";

}



sub add {
    my $answer = shift;
    while( defined(my $addend  = shift)) {
        substr($answer,0,0,'0'x(length($addend)-length($answer))) if length($answer) < length($addend);
        substr($addend,0,0,'0'x(length($answer)-length($addend))) if length($addend) < length($answer);
        print "$answer + $addend = ";

        my $c = 0;
        for my $hexit ( 1 .. length($addend) ) {
            my $x = lc substr($answer, -$hexit, 1);
            my $y = lc substr($addend, -$hexit, 1);
            my $s = $sums{$x}{$y};
            #my $u =
            printf "\n\t#%d: %s + %s = %s\n", $hexit, $x, $y, $s;
        }

        print "$answer\n"
    }
}

package main;
HexMath::add('a','b','cqcq','d');