#!/usr/bin/perl

use strict;
use warnings;

{
   use bytes;
   
   my %lookup;
   my @reverse;
   my $scale;

   BEGIN
   {
      my $x = 0;
      my @chars = (' ', 0..9, 'A'..'Z');
      keys %lookup = 65_536; # preallocate hash buckets
      for my $i (@chars)
      {
         for my $j (@chars)
         {
            for my $k (@chars)
            {
               $lookup{ $i.$j.$k } = $x;
               $reverse[$x++] = $i.$j.$k;
            }
         }
      }
      $scale = $x;
   }

   # Functions using multiplication...
   
   sub alphanum_to_bytes_M
   {
      my $head = $lookup{ substr($_[0], 0, 3) };
      my $tail = $lookup{ substr($_[0], 3, 3) };
      my $n    = ($head * $scale) + $tail;
      pack(N => $n)
   }
   
   sub bytes_to_alphanum_M
   {
      my $n = unpack(N => $_[0]);
      my $head = int($n / $scale);
      my $tail = $n - ($head * $scale); 
      $reverse[$head] . $reverse[$tail]
   }
   
   # Functions using bitshifting...
   
   {
      use integer;
      
      sub alphanum_to_bytes_B
      {
         my $head = $lookup{ substr($_[0], 0, 3) };
         my $tail = $lookup{ substr($_[0], 3, 3) };
         pack(nn => $head, $tail)
      }
      
      sub bytes_to_alphanum_B
      {
         join q{}, @reverse[ unpack(nn => $_[0]) ]
      }
   }
   
   # Function to pretty-print byte strings for display purposes...
   
   sub show_bytes
   {
      my ($str) = @_;
      sprintf
         'bytes[%s]',
         join q{ },
            map { sprintf('%02x', ord(substr($str, $_, 1))) }
            0 .. length($str)-1
   }
}

my @lines = <DATA>;

print "MULTIPLICATION:\n";
foreach (@lines)
{
   my $b;
   chomp;
   printf(
      "'%s' => '%s' => '%s'\n",
      $_,
      show_bytes($b = alphanum_to_bytes_M($_)),
      bytes_to_alphanum_M($b),
      );
}

print "BIT SHIFTING:\n";
foreach (@lines)
{
   my $b;
   chomp;
   printf(
      "'%s' => '%s' => '%s'\n",
      $_,
      show_bytes($b = alphanum_to_bytes_B($_)),
      bytes_to_alphanum_B($b),
      );
}

__DATA__
      
     0
     1
     A
     Z
ABCDEF
ABCDEG
ZAAAAA
ZZZZZZ