I note two things: you only want the number of elements in the intersection and union, not the actual intersection and union; and your method suggests that there are no duplicates in the sets. So you don't need to find the union, explicitly. It is just the total number in I + J, minus the intersection. 
sub get_int_uni2 {
  my ($in, $jn) = @_;
  my %i;
  @i{@$in} = ();
  my $int = grep exists $i{$_}, @$jn;
  return ($int, @$in + @$jn - $int);
}

[download]
Sadly, I don't see any real improvement in performance (thanks to BrowserUK for the benchmarkery).
Caution: Contents may have been coded under pressure.

In reply to Re: Fast, Efficient Union and Intersection on arrays by Roy Johnson
in thread Fast, Efficient Union and Intersection on arrays by barvin

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