array_intersect: followup: early exit if first empty intersection found

[pve-common.git] / src / PVE / Tools.pm

diff --git a/src/PVE/Tools.pm b/src/PVE/Tools.pm
index c31ebeb9e62421765b96835b2a4b3b04325f22dc..a9addcd7e595cc0737a0f1d3eca9f84da9e18447 100644 (file)
--- a/src/PVE/Tools.pm
+++ b/src/PVE/Tools.pm
@@ -1654,28 +1654,34 @@ sub dev_t_minor($) {
 sub array_intersect {
     my ($arrays) = @_;
 
-    return [] if @$arrays == 0;
-    return $arrays->[0] if @$arrays == 1;
+    return [] if scalar(@$arrays) == 0;
+    return $arrays->[0] if scalar(@$arrays) == 1;
 
-    my $return_arr;
-    @$return_arr = array_unique(@{$arrays->[0]});
+    my $array_unique = sub {
+       my %seen = ();
+       return grep { ! $seen{ $_ }++ } @_;
+    };
+
+    # base idea is to get all unique members from the first array, then
+    # check the common elements with the next (uniquely made) one, only keep
+    # those. Repeat for every array and at the end we only have those left
+    # which exist in all arrays
+    my $return_arr = [ $array_unique->(@{$arrays->[0]}) ];
     for my $i (1 .. $#$arrays) {
        my %count = ();
-       foreach my $element (@$return_arr, array_unique(@{$arrays->[$i]})) {
+       # $return_arr is already unique, explicit at before the loop, implicit below.
+       foreach my $element (@$return_arr, $array_unique->(@{$arrays->[$i]})) {
            $count{$element}++;
        }
        $return_arr = [];
        foreach my $element (keys %count) {
            push @$return_arr, $element if $count{$element} > 1;
        }
+       last if scalar(@$return_arr) == 0; # empty intersection, early exit
     }
 
     return $return_arr;
 }
 
-sub array_unique {
-    my %seen = ();
-    return grep { ! $seen{ $_ }++ } @_;
-}
 
 1;