sub sumdigits {
  my($n,$base) = @_;
  my $sum = 0;
  $base =  2 if !defined $base && $n =~ s/^0b//;
  $base = 16 if !defined $base && $n =~ s/^0x//;
  if (!defined $base || $base == 10) {
    $n =~ tr/0123456789//cd;
    $sum += $_ for (split(//,$n));
  } else {
    croak "sumdigits: invalid base $base" if $base < 2;
    my $cmap = substr("0123456789abcdefghijklmnopqrstuvwxyz",0,$base);
    for my $c (split(//,lc($n))) {
      my $p = index($cmap,$c);
      $sum += $p if $p > 0;
    }
  }
  $sum;
}
[download]

From Math::Prime::Util::PP. List::MoreUtils::PP might be also of interest.