convert very large unsigned numbers to base62?

["D. Dante Lorenso" <dante@xxxxxxxxxxx>]

I'd like to convert very large unsigned numbers (ala bigint) to a text 
string using base62.  I created this PL/PERL function to do the trick:

--------------------
CREATE OR REPLACE FUNCTION "public"."ls_crypt_convert_base" (in_value 
text, in_base integer) RETURNS text AS
$body$
  my ($value, $base) = @_;
  $base = ($base > 62) ? 62 : (($base < 2) ? 2 : $base);
  my @nums = (0..9,'a'..'z','A'..'Z')[0..$base-1];
  my $index = 0;
  my %nums = map {$_, $index++} @nums;

  # short circuit if no value
  $value =~ s/\D//g;
  return if ($value == 0);

  # this will be the end value.
  my $rep = '';
  while ($value > 0) {
      $rep = $nums[$value % $base] . $rep;
      $value = int($value / $base);
  }
  return $rep;
$body$
LANGUAGE 'plperl' IMMUTABLE RETURNS NULL ON NULL INPUT SECURITY INVOKER;
--------------------

  # SELECT ls_crypt_convert_base(999999999999999999::text, 62);
   ls_crypt_convert_base
  -----------------------
   1bS0EMtBbK8
  (1 row)

  # SELECT ls_crypt_convert_base(888888888888888888::text, 62);
   ls_crypt_convert_base
  -----------------------
   13F7tmqjhmu
  (1 row)

  # SELECT ls_crypt_convert_base(7777777777::text, 62);
   ls_crypt_convert_base
  -----------------------
   8umLiF
  (1 row)

  # SELECT ls_crypt_convert_base(123456789::text, 62);
   ls_crypt_convert_base
  -----------------------
   8m0Kx
  (1 row)


Did I just reinvent the wheel?  It seems like something like this is 
should already be built into PostgreSQL and I just don't know where to look.

-- Dante