from  Raja R Harinath  <address@hidden>

	* lib/Automake/Condition.pm (multiply): New.
	* lib/Automake/DisjConditions.pm (_multiply): Use it.
	(sub_conditions): Likewise.

diff -u lib/Automake/Condition.pm lib/Automake/Condition.pm
--- lib/Automake/Condition.pm
+++ lib/Automake/Condition.pm
@@ -495,6 +495,37 @@
   return @res;
 }
 
+=item C<$cond-E<gt>multiply (@conds)>
+
+Assumption: @conds represent a disjunction of conditions
+
+Return the result of multiplying $self with that disjunction.  The
+result will be another list of conditions suitable to construct a
+C<DisjConditions>.
+
+=cut
+
+sub multiply ($@)
+{
+  my ($self, @set) = @_;
+  my %res = ();
+  for my $cond (@set)
+    {
+      my $ans = $self->merge ($cond);
+      $res{$ans} = $ans;
+    }
+
+  # FALSE can always be removed from a disjunction.
+  delete $res{FALSE};
+ 
+  # Now, $self is a common factor of the remaining conditions.
+  # If one of the conditions is $self, we can discard the rest.
+  return ($self,()) 
+    if exists $res{$self};
+
+  return (values %res);
+}
+
 =head2 Other helper functions
 
 =over 4
diff -u lib/Automake/DisjConditions.pm lib/Automake/DisjConditions.pm
--- lib/Automake/DisjConditions.pm
+++ lib/Automake/DisjConditions.pm
@@ -317,14 +317,7 @@
 sub _multiply ($@)
 {
   my ($self, @set) = @_;
-  my @res = ();
-  foreach my $selfcond ($self->conds)
-    {
-      foreach my $setcond (@set)
-	{
-	  push @res, $selfcond->merge ($setcond);
-	}
-    }
+  my @res = map { $_->multiply (@set) } $self->conds;
   return new Automake::DisjConditions (Automake::Condition::reduce_or @res);
 }
 
@@ -630,7 +623,9 @@
 =item C<$self-E<gt>sub_conditions ($cond)>
 
 Return the subconditions of C<$self> that contains C<$cond>, with
-C<$cond> stripped.
+C<$cond> stripped.  More formally, return $res such that 
+$res->_multiply($cond) == $self->_multiply($cond) and $res does not
+mention any of the variables in $cond.
 
 For instance, consider:
 
@@ -656,17 +651,16 @@
   my ($self, $subcond) = @_;
 
   # Make $subcond blindingly apparent in the DisjConditions.
-  # For instance `$a->_multiply($b)' (from the POD example) is:
-  #   new Automake::DisjConditions
+  # For instance `$b->multiply($a->conds)' (from the POD example) is:
   # 	(new Automake::Condition ("FALSE"),
   # 	 new Automake::Condition ("A_TRUE", "B_FALSE", "C_FALSE"),
   # 	 new Automake::Condition ("A_TRUE", "B_FALSE", "C_TRUE"),
-  # 	 new Automake::Condition ("FALSE"));
-  my $prod = $self->_multiply ($subcond);
+  # 	 new Automake::Condition ("FALSE"))
+  my @prodconds = $subcond->multiply($self->conds);
 
   # Now, strip $subcond from the remaining (i.e., non-false) Conditions.
   my @res;
-  foreach my $c ($prod->conds)
+  foreach my $c (@prodconds)
     {
       push @res, $c->strip ($subcond) unless $c->false;
     }