+
+sub make_corelist_delta {
+ my($version, $lines) = @_;
+ # Trust core perl, if someone does use a weird version number the worst that
+ # can happen is an extra delta entry for a module.
+ my %versions = map { $_ => eval $lines->{$_} } keys %$lines;
+
+ # Ensure we have the corelist data loaded from this perl checkout, not the system one.
+ require $corelist_file;
+
+ my %deltas;
+ # Search for the release with the least amount of changes (this avoids having
+ # to ask for where this perl was branched from).
+ for my $previous(reverse sort keys %Module::CoreList::version) {
+ # Shouldn't happen, but ensure we don't load weird data...
+ next if $previous > $version || $previous == $version && $previous eq $version;
+
+ my $delta = $deltas{$previous} = {};
+ ($delta->{changed}, $delta->{removed}) = calculate_delta(
+ $Module::CoreList::version{$previous}, \%versions);
+ }
+
+ my $smallest = (sort {
+ (keys($deltas{$a}->{changed}) + keys($deltas{$a}->{removed})) <=>
+ (keys($deltas{$b}->{changed})+ keys($deltas{$b}->{removed}))
+ } keys %deltas)[0];
+
+ return {
+ delta_from => $smallest,
+ changed => $deltas{$smallest}{changed},
+ removed => $deltas{$smallest}{removed},
+ }
+}
+
+# Calculate (changed, removed) modules between two versions.
+sub calculate_delta {
+ my($from, $to) = @_;
+ my(%changed, %removed);
+
+ for my $package(keys $from) {
+ if(not exists $to->{$package}) {
+ $removed{$package} = 1;
+ }
+ }
+
+ for my $package(keys $to) {
+ if(!exists $from->{$package}
+ || (defined $from->{$package} && !defined $to->{$package})
+ || (!defined $from->{$package} && defined $to->{$package})
+ || (defined $from->{$package} && defined $to->{$package}
+ && $from->{$package} ne $to->{$package})) {
+ $changed{$package} = $to->{$package};
+ }
+ }
+
+ return \%changed, \%removed;
+}