#!/usr/bin/perl

sub base64_decode( $ );

$chars = '';
while (<>) {
  y/A-Za-z0-9+\/=//cd;
  y/A-Za-z0-9+\/=/\000-\100/;
  $chars .= $_;
  while (length($chars) >= 4) {
    print base64_decode $chars;
    $chars = unpack("x4 a*",$chars);
  }
}

sub base64_decode( $ ) {
  my ($a,$b,$c,$d) = unpack("C4", $_[0]);
  my $stuff = ($a<<18) | ($b<<12) | ($c<<6) | $d;
  if ($c == 64) {
    $stuff = pack("C", ($stuff >> 16) & 255);
  } elsif ($d == 64) {
    $stuff = pack("CC", ($stuff >> 16) & 255, ($stuff >> 8) & 255);
  } else {
    $stuff = pack("CCC", ($stuff >> 16) & 255, ($stuff >> 8) & 255,
                  $stuff & 255);
  }
  $stuff;
}

.