#!/usr/local/bin/perl5 -w



# From RFC 2045:

#                   Table 1: The Base64 Alphabet

#    Value Encoding  Value Encoding  Value Encoding  Value Encoding
#        0 A            17 R            34 i            51 z
#        1 B            18 S            35 j            52 0
#        2 C            19 T            36 k            53 1
#        3 D            20 U            37 l            54 2
#        4 E            21 V            38 m            55 3
#        5 F            22 W            39 n            56 4
#        6 G            23 X            40 o            57 5
#        7 H            24 Y            41 p            58 6
#        8 I            25 Z            42 q            59 7
#        9 J            26 a            43 r            60 8
#       10 K            27 b            44 s            61 9
#       11 L            28 c            45 t            62 +
#       12 M            29 d            46 u            63 /
#       13 N            30 e            47 v
#       14 O            31 f            48 w         (pad) =
#       15 P            32 g            49 x
#       16 Q            33 h            50 y

$base="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

$start=0;
%basehash=();

foreach $i (split //, $base)
{
  $basehash{$i}=$start;
# print $i, " ", $basehash{$i}, " ", $start, "\n";
  $start=$start + 1;
}

while(<>)
{
  chomp;
  @array = ( split //, $_ );

  $twirl   = 0;
  $outchar = 0;
  $inchar  = 0; # Predefine this so it will persist outside the inner loop.

  while
  (
    ( ( $inchar = shift @array ) or ( defined( $inchar ) ) )
    and
    ( not ( $inchar eq "=" ) ) # Handle base64 pad character.
    and
    ( not ( $inchar eq "-" ) ) # Handle missing blank line after data
                               # and before MIME separator, which latter
                               # seems always to start with "--".  This
                               # isn't really data for this program, but
                               # including it is a frequent and likely
                               # user error, so cope.
  )
  {
#   print STDERR "$inchar", "\n";

    if ($twirl == 0)
    {
      $outchar = $outchar + ( $basehash{$inchar} * 4 );
#     print STDERR $twirl, " ", $outchar, "\n";
      $twirl = 1;
    }
    else
    {
      if ($twirl == 1)
      {
        $outchar = $outchar + int ( $basehash{$inchar} / 16 );
#       print STDERR $twirl, " ", $outchar, "\n";
#        print $outchar;
#        print "  ", chr $outchar , "\n";
         print chr $outchar;

        $outchar = ($basehash{$inchar} % 16) * 16;
#       print STDERR $twirl, " ", $outchar, "\n";
        $twirl = 2;
      }
      else
      {
        if ($twirl == 2)
        {
          $outchar = $outchar + int ( $basehash{$inchar} / 4 );
#         print STDERR $twirl, " ", $outchar, "\n";
#         print $outchar;
#         print "  ", chr $outchar , "\n";
          print chr $outchar;

          $outchar = ( $basehash{$inchar} % 4 ) * 64;
#         print STDERR $twirl, " ", $outchar, "\n";
          $twirl = 3;
        }
        else
        {
          if ($twirl == 3)
          {
            $outchar = $outchar + ( $basehash{$inchar});
#           print STDERR $twirl, " ", $outchar, "\n";
#           print $outchar;
#           print "  ", chr $outchar , "\n";

            print chr $outchar;
            $outchar = 0;
            $twirl = 0;
          }
        }
      }
    }
  }
  # if ( $inchar eq "-" )
  # {
  #   exit(0); # We've overshot the data; stop reading more lines.
  # }
}

# print %basehash;